Cozy Builders Mailing List FAQ
Last Updated: September 24th, 2018
Frequently Answered Questions
in the Unofficial Cozy Builders Mailing List
Table of Contents:
This FAQ was created and originally maintained by Bil Kleb who could not
have begun without the magnanimous efforts of Marc Zeitlin, the creator of
the Unofficial Cozy Builders Mailing List, and all its contributing
members. It is currently maintained by Marc Zeitlin, with the
contributions and help of many mailing list members.
If you have any questions regarding this FAQ, send them to Marc
Zeitlin otherwise, please direct questions to the list
itself if you are a member.
1.1 - What mailing list?
cozy_builders e-mail list. It was set-up by Marc
Zeitlin to share and distribute Cozy-related information and
for general communication between Cozy builders. As of November, 2013
there are over 690 members from various countries, including: Australia,
Brazil, Canada, Chile, Denmark, France, Germany, Italy, Japan, Korea,
Mexico, The Netherlands, South Africa, Spain, Sweden, Turkey, U.K.,
U.S.A., and Venezuela. Members range from prospective builders who just
have info paks, to those with 1000 hours or more on flying Cozy aircraft.
Some are building stock Cozy's or other Rutan-style aircraft, while some
are implementing numerous modifications. See
for the complete story, including the criteria and method for becoming a
member of the mailing list.
1.2 - What is a FAQ?
FAQ stands for frequently asked questions or frequently answered
questions, take your pick. So, by definition, a question/answer pair makes
it into the FAQ only because it has been frequently discussed in the
group. There is no "importance" criterion as to which get included in the
FAQ, it is just a matter of frequency. FAQs are very prevalent on the
internet, for instance check out the Internet FAQ Consortium at
for more FAQs then you can probably read in a life time.
FAQs are developed primarily to reduce the volume of traffic on a
given newsgroup or mailing list. Typically, only the questions for which
there is a consensus of answers make it into the FAQ. However, there are
always the controversial questions which have multiple answers/sides
which are never settled, such as the debate over retractable gear or
which epoxy system to use. In this situation, the answer to the
frequently asked question, takes the form of merely providing
information from opposing sides, i.e., really no answer at all; allowing
the reader to educate his/herself. Thus, the general arguments from each
side do not need to be rehashed ad nauseum, and the FAQ provides the
reader a basis from which a more detailed question about a given
argument can be developed.
You can obtain an HTML version of this FAQ on the World Wide Web at
1.4 - How do I contribute to the FAQ?
For starters, POST RESPONSES to questions in the
group TO THE GROUP and not just to the individual who
asked. This FAQ is composed of questions and answers that make it into the
group's archives, so if you do not make your responses to the group as a
whole, others will not benefit from the exchange.
When you approach a chapter or topic that does not have any entries in
the FAQ, or it has been a while since the last update:
To save yourself some work, you might want to consider only the stock,
"to-plans" questions at first, but remember to make a list of
questions/issues that you are leaving in the archives.
- Make sure you have a current version of the FAQ (see Section
1.3 above) and check with the FAQ curator, Marc
Zeitlin, to be sure that someone else is not already
working on the same thing.
- Riffle through the mailing list archives. (See the next Section, 1.5,
for an example of how to get all the archives for a given chapter or
- Use an existing chapter as a guide and pull out the questions that
seem to crop up more than once or have a consensus answer. (Remember,
like Jeopardy, phrase the questions as questions and try to make both
the question and answer as concise as possible without losing
- Stick these into a plain text (ascii) file.
- Include the date you obtained the archive files for distillation.
- Send the results to the FAQ curator, Marc
Zeitlin, for final formatting.
MOST IMPORTANTLY, ALWAYS HAVE SAFETY PARAMOUNT IN YOUR MIND
WHEN DOING THIS SIFTING. If a topic is controversial, and
does not seem to have a consensus of answers, it may be better just to
leave it in the archives. You could merely phrase the question and then
state that "no consensus exists - read the archives for various points
of view". Otherwise, you could give a SHORT summary of
the disagreement, briefly outlining the arguments from each side.
If you take exception to a FAQ question/answer or simply want to
expand its scope, pose such a question to the mailing list.
Note: This service is only available to Mailing List Members
Chapter 4 - Fuselage Bulkheads [as of: 11 feb 07]
[distiller: Wayne Hicks]
Comments and Tips
- A neat trick for applying epoxy or flox without creating a mess is
to use a sandwich bag like a cake icing tool. Pour your flox, 5-minute
epoxy, or whatever into the corner of a sandwich bag, cut the corner,
then gently squeeze the mixture out the opening. This works extremely
well for controlling the flow onto whatever surface.
- When joining foam panels "edge-to-edge", avoid applying too much
5-minute epoxy since it will squeeze out of the joint and, when cured,
it is very difficult to sand flush. So prior to bonding, run a strip
of tape along both edges on the "top" faces. Then flip both pieces
over, butt them together, and run one length of tape over the seam to
form a hinge. Again, flip the pieces over, and, lifting at the hinge,
stand the panels up to from an upside-down "V" (or hang one panel over
the edge of a table) with the now-opened "hinge" facing upward. Apply
epoxy onto/into the seam, and spread it around. Collapse the panels
flat onto the table and allow the excess epoxy to squeeze out of the
"hinge". Quickly wipe off the excess epoxy and pull the top tapes off.
After cure, pull off the bottom tape.
4.1 - What is the best method for creating the other half of the
There are as many solutions as there are builders. The rule of thumb
is to avoid Xerox machines as they can distort the images. Some builders
have had luck with professional printing services, but if you use these be
sure to compare every image against the original plans. Here are some of
the more popular alternatives.
- Trace the reverse image, then cut and tape the two tracings
together. Allow some overlap on the match line for the tape, and tape
both sides to prevent one piece from creeping toward the other.
- Aircraft Spruce is now selling duplicate sets of the drawings for a
small fee. It is still recommended that you avoid cutting up the
master set of drawings as these often contain details used in later
chapters and keeping track of everything once its cut can be
- Blueprint duplication services and machines can often handle this
task, as their machines are designed specifically to keep sizes
identical (contractors often take measurements right from the plans if
they are not dimensioned).
- Some readers have bought or borrowed time on plotters. The CAD
templates section of this site contains AutoCAD drawings of several of
the more annoying drawings to trace, especially the bulkheads for
Chapter 4. These may be used to print a full-size set of templates.
- A few builders have created precise, steel templates of some of the
more critical drawings, such as the canard and wing hot wire guides.
Ask on the list to see where these are; they tend to be circulated
from builder to builder on an as-needed basis.
4.2 - I have noticed that some of the dimensions shown on the
templates do not match exactly to the lines shown. What should I do?
As with any plans-built aircraft, it is always good practice to
verify dimensions when given. In general, panel dimensions should are
usually symmetrical about the vertical match lines. Do not waste too much
time worrying about exact dimensions. Just "stay on the lines" and your
fuselage assembly will go well in Chapter 6.
4.3 - What is the best way to cut the foam panels?
All the foams used in construction of the bulkheads are easily cut
with a utility knife. Do not try to cut through the entire panel in one
stroke. Make several shallow cuts to keep from gouging the foam. Use a
metal straight-edge for straight lines; and carefully free-hand curved
lines. Some people prefer to use razor saws and power tools such as
jigsaws and bandsaws.
4.3.5 - How do I minimize air bubbles in my layups?
Builders have found all of the following tips to be helpful:
- Avoid making layups too dry. You can tell this is the case if they
feel like "shark skin" (they are rough to the touch) or the fabric is
white. The cloth must be saturated and the fibers must be
fully wet before the smaller air bubbles can be removed, especially
- Stipple, stipple, stipple! It gets irritating after a while but it's
the single best thing to do to get and keep air out of your layups.
Start from the center, tapping every bit of the layup, working your
way to the outside. On multiple-layer layups, stipple each layer
before you move on to the next. Be sure not to stipple to hard, or at
an angle, as this could shift the fibers and give bubbles a better
hold. Be careful with the squeegee, too, or the same thing could
- On multiple-layer layups, it's OK to over-saturate the first layer
and let the second soak up the excess (provided you stipple well).
However, some epoxies wet out better than others, and this may leave
you with too much epoxy between layers. This also traps air bubbles in
- Squeegee in several passes. If a "wave" of epoxy builds up in front
of the squeegee this can disrupt several layers of the fiberglass.
Stop frequently and clean the squeegee.
- Use a hair dryer to warm the area you are working on. This helps the
epoxy wet out the fabric better, and also flow more easily when you
squeegee and stipple. Be sure to use only gentle heat to avoid
damaging the foam or causing an epoxy exotherm.
- Use the "poor mans vacuum bag" technique. Buy rolls of 4 mil or
thicker plastic film, and lay this over your completed layups. Stipple
before doing this, but save your squeegee work until after this step.
When you squeegee now, do allow a small wave to build up. Squeegee
gently from the center to the edges, and all of the air bubbles will
"ride the wave" out of the layup. You can get down to bare minimums in
terms of completed weights using this technique, just be sure to avoid
dry layups. It's best to weight down all pieces cured with this method
because if the plastic lifts up it will force an air bubble into the
4.4 - According to Chapter 3, page 4, 5-minute epoxy should be used
for joining foam boards together while the next page specifies the use
of micro slurry only. Which one is used when?
5-minute epoxy is typically used when joining foam panels
"edge-to-edge". Micro is used when joining foam blocks
"surface-to-surface". In general, most of the foam joining work in Chapter
4 is edge-to-edge. You will get the chance to micro foam together in
4.5 - How do I cover the backside of the seat back?
Being 42" wide, you will need to use two pieces of BID cloth.
Remember to overlap the adjoining sides by 1" as stated in Chapter 3.
4.6 - Do you cover the cutout areas (notches) in the seat back with
BID or leave them uncovered?
There is no need to cover the notches or exposed foam. You will apply
flox to the exposed edges and 2-BID tape the entire seat back in place
during fuselage assembly (Chapter 6).
4.7 - Should I cut the electrical duct holes and the torque tube
holes in the bulkheads now, or is it better to wait?
It is definitely easier to cut the holes before the bulkheads are
assembled to the fuselage, but most builders wait to figure out the actual
placement of the holes. The final hole locations will vary depending on
how accurately you have assembled the fuselage and precisely where you run
your control linkage, etc.
4.8 - Is the F22 doubler supposed to be shorter width
Yes. There should be a 3/8" gap between the outside edges of F22
and the F22 doubler. The 3/8" gap is needed to provide room
for the 3/8"-foam sides during fuselage assembly (Chapter 6).
4.9 - For the F22 doubler, do I overlap just below the
sloped edges, or do I overlap the top edge as well?
The overlap in on the bottom edge only. The canard is mounted onto
the top edge and as will become apparent in Chapter 7, the top edge of F22
and F22 doubler are flush with the canard cut-outs. (See
Chapter 6, Figure 8, and Chapter 7, Figures 20 and 23.)
4.10 - What is the purpose of adding an extra inch to the overall
height of the F28 bulkhead?
Rounding F28 or leaving it flat is purely a personal
choice based on aesthetic value. Builders desiring a pointy nose opt for
the flat F28. Those that want a round nose generally opt to
raise F28 the extra inch (or more) as depicted on the
template. It is simply a builder preference!
4.11 - Is the bottom of the instrument panel supposed to be flat?
In general, yes. You might find that when you match up the templates
for the Instrument Panel, the bottom edge at the match line is lower than
the sides. You can elect to redraw the bottom line straight or leave it as
is. If you leave it as is, the curvature will be so slight that it will
not be noticeable after the fuselage bottom is installed in Chapter 6.
During fuselage assembly (Chapter 6) some builders have found that the
bottom of the instrument panel is .2" to .25" too short. This depends
greatly on builder accuracy. You might consider extending the bottom by
1/4" and trimming to fit during fuselage assembly (Chapter 6).
4.12 - For the instrument panel stiffeners, should I flox the
corner where the two layups come together at 90 degrees?
No. In this case, use dry micro to form a radius to help the BID
cloth to bend during the layup. Flox corners are generally used for
structural joints where glass to glass bonding is required. The plans are
pretty good about calling out flox corners when they are needed. If you
need a radius in a corner, use micro unless told otherwise.
4.13 - Can the structural integrity of the airframe be destroyed by
installing too many instruments on the instrument panel?
Most canards have instrument panels that look like swiss cheese. The
panel is very flimsy until the instruments are installed. Many builders do
not experience problems, but others are more comfortable having installed
complete aluminum panels over the foam IP, or having installed aluminum
ribs behind the IP. Regardless, you should not cut instrument holes until
you have nearly completed the bird since new technology might make your
holes obsolete by the time you are ready to fly.
4.14 - Should I Alodine the aluminum engine mount inserts before
The general consensus is to clean and treat any exposed aluminum
pieces. Sand with 220 grit for a good mechanical bond, clean with
something like Alumiprep, then Alodine. You can buy the cleaning and
treating agents from an auto paint store or order the aircraft quality
stuff from Wicks or Aircraft Spruce.
4.15 - On the temporary firewall, do I leave the cosmetic pieces
It does not matter as you use the fake firewall only for fuselage
assembly (Chapter 6). In fact it only really has to be a piece big enough
to accommodate the four longeron holes. On the real upper firewall, the
cosmetic pieces are removed prior to laying up the wraps for the
turtleback/fuselage and firewall/engine mount hard points. The cosmetic
pieces are reinstalled after that.
4.16 - How important is it to use exactly 22 layers for the landing
gear hard points?
The important point is that the hard points be 1/4" thick. The "22
layers" referenced in the plans is a guideline of how many layers it
typically takes. You may use more or less depending on you layup
technique and by how much weight you use to squeeze out the excess
epoxy. Do not worry if your hard points are slightly thicker than 1/4"
(within reason). Add more layers if not thick enough. Note: some
builders have avoided this step altogether by buying a scrap of 1/4" G10
material from their local plastics supplier.
Another option is to cut the landing gear bulkheads from the foam
first, then use the scrap to make spacers to place around this layup.
Make the layup a bit thicker than the plans call for (25-26 layers seems
to work well) then add a sheet of plastic to the top of it, squeegee,
and weight down with VERY heavy weights (60-80lbs works well). Make sure
the weight is riding on the spacers after a few minutes, and the layup
will come out precisely the same thickness as the foam.
4.17 - Should I go ahead and drill the pair of 1/4" holes in the
forward landing gear bulkhead now (as per plans)?
Definitely yes! It is easier than doing it after the bulkhead is
installed. Note: the pair of holes in the AFT LG
bulkhead hard points are not drilled until after installation so that a
drilling jig can be fashioned to assure alignment of the two sets of
4.18 - Which is the correct location for the holes in the hard
points for the forward LG bulkhead -- 1.2" from top per the written
dimensions on the drawing, or 1.45" from top per measuring the
The hardpoint quarter-inch holes shown on the drawing do not match
with the dimensions given. Most builders are drilling the holes at the
stated dimensions (1.2" from the top). Drilling the holes too low will
cause an interference later between the landing gear strut and the landing
gear cover (Chapter 9). You get another chance in Chapter 9 to line up the
holes correctly when the gear is installed (Chapter 9), so do not sweat
4.19 - How does one finish the inside edges of the bulkheads?
Some people route them out slightly and fill with micro, others do
4.20 - I have heard some people have had problems with the pulley
mounting blind screws in the firewall turning after a period of time.
What can I do to prevent this?
Provided you install them per plans, and do not over-torque the nuts
that will be installed on these screws, you should not encounter this
problem. However, there are a few preventive measures you can take if
- Instead of cutting flat sides on each screw head, cut a slot across
it. Then weld in a piece of stiff wire such as piano or safety wire.
- Install them per plans. If they start to turn, cut a slot in the
visible end of the screw, thread the nut on, then use a screwdriver in
the slot to keep the screw from turning while the nut is tightened.
You will need an open-end wrench instead of a socket set to make this
- Cut the heads of the screws into + signs instead to give them more
- Some builders are opting to avoid using the pulleys entirely, and
instead use bicycle cable tubing to route the control wires into the
wing roots. This is not an approved change but some builders have
reported satisfaction with the simplification.
4.21 - Iíve noticed differences between F22 sketches and the
M4 drawing. S hould I be concerned?
When building F22, the sketches (chapter 4 page 2) and the foam
layout (chapter 2 page 5) suggest a foam extension to be installed in the
outer and center web. The full size M4 drawing does not show
these extensions. Trace the full size M4 drawing as shown. The
overall height dimension when assembled is 21.25 inches.
4.22 - I have noticed the NG-30 assembly from chapter 13 is wider
than the vertical web on my F22 bulkhead.
The vertical web on the F-22 bulkhead is 3.5" wide. The NG-30
assembly is 3.8" wide. Making the vertical web .3" wider will allow a
nicer fit, and the extra width can be trimmed off later if not needed in
4.23 - F22 may have a different size on the M-drawings then the ACS
large-drawings. Which one is correct?
When building F22, it appears that the width of F22 on the large
drawings are 22mm (just under one inch) less than on the M-drawing.
Builders have used both variants and there are no reported problems. The
obvious difference is that the nose-section will be almost 1 inch narrower
if you use the large-drawing instead of the M-drawing. Another thing to be
aware of is that if you build from the large-drawing, F28 need to be
trimmed off a bit since F28 is based on the M-drawings width of F22. The
easiest thing to do is to build F22 from the M-drawings, not the
Chapter 5 - Fuselage Sides [as of: 29 sep 97]
[distiller: Darren DeLoach]
Comments and Tips
- Cut and glue the Masonite and 3/8" foam BEFORE
you glue your jigs to the table, so that you have plenty of flat space
available to work on.
- Change the 5.9" dimension to 6.25" (See questions/answers 12.1
Left in the Archives
- Positioning the LWX and LWY stringers.
5.1 - How do I get a smooth curve when cutting the FJA
Although the measurements given in the plans do not fall on a true
monotonically increasing curve, the Masonite effectively "filters" the
curvature anyway, so do not worry about it. To draw a nice curve along the
measured points, use a metal yardstick. Lay the yardstick on edge along
the points to be connected and you will get a nice smooth curve.. You can
use small finishing nails on the points as a reference to steady the
yardstick if necessary.
5.2 - How much should the longerons extend beyond the fuselage
When you glue the longerons together the book says, "let the excess
extend equally at both ends," with the front doubler placed 5" from the
front end (with the excess extending beyond). When you attach the
longerons to the sides the book says "[l]et the longerons overhang
slightly at the forward end and the remaining excess extend aft." If you
take this literally, you will find that when you assemble sides to the
bulkheads, since F28 gets placed 6.25" (was 5.9") back from
the front of F22, your doubler location may be a 1/2" to 1"
short (too far aft) of this point. Instead, when you attach the longerons
to the sides use roughly the same overlap that you had when you glued the
longerons together and the front doubler will be positioned properly.
Measure the 6.25" (was 5.9") back to be sure, and also make sure the the
rear doublers will go all the way through the firewall.
5.3 - I used the wrong longeron overlap and now my doubler does not
reach the 6.25" (was 5.9") location of F28. How can I fix
Basically, you flox on an extension to the doubler, then glass over
it. For a good, strong joint and peace of mind, make a scarf joint
matching the added on piece to the existing longeron. Flox it in place and
glass over the piece. To make a scarf joint you would taper the end of the
longeron back for 4" or 5". You would also taper the add on piece, forming
an angled wedge. You will be placing the two wedges together. This is a
much stronger joint than gluing end-grain to end-grain.
5.4 - The plans appear to show a definite crease in the Masonite
when mounted on the jigs. Is this correct?
No. The Masonite should follow smooth curves, the lines depicted in
the plans are simply to point out that the differences in FJB/C
and FJD/E result in differences from top to bottom.
5.5 - Do I do anything different from the plans' canted indentation
to use Vance Atkinson's fuel gauges?
Various solutions are being used. The simplest is to use a
rectangular indentation (so that you can have the gauges flush with the
sides) which is flat, not canted, since Vance's gauges have a 180 degree
view anyway. Others have installed them in a canted indentation per plans.
Note: be sure to make your indentation long enough so that your top and
bottom fuel holes will go through glass-to-glass and not glass-foam-glass.
The second edition plans (#501, up) point this out.
5.6 - Where is the urethane foam used that is listed in the
The urethane foam was originally included in the Chapter 5 materials
list to make the forms for the electrical conduits. However, the Chapter 5
plans call for using 3/4" Clark foam to shape the conduits instead of
urethane. The bottom line is if you use Clark foam for the conduits, then
you do not need the urethane in this chapter, though you WILL
NEED this foam later when building the NACA scoop (Chapter 7).
On the other hand, urethane is probably a better foam for shaping the
conduits than Clark; but just make sure you will have enough left over for
the NACA scoop. If you use the Clark foam, make sure you purchase the
urethane for Chapter 7 since it is not in the Chapter 7 materials list in
the plans or the Wicks catalog.
5.7 - How should I position the electrical conduit?
If you assume that the conduit is exactly parallel to the upper
longeron, it will intersect the firewall rudder bracket. Instead, match
the temporary firewall up with the fuselage sides before gluing the
electrical conduit in place, you may find that it needs to be installed at
a slight angle to hit its hole in the firewall. You might also choose to
simply cut the channel at about 14.7" down instead of the 14.5" called for
in the plans. For the beveled area, a good choice is from 6" beveled down
to 8" from the firewall, though anywhere between LWX and the
firewall will do; there is nothing magical about the degree of the slope,
you just want to make sure that it is gradual enough to push electrical
5.8 - How do I get the 4 UNI layers to lay down on the double
90-degree turns of the front fuselage doubler on the top longeron?
Do not bother. Look at the photos in Chapter 6, there is a picture
showing the F28 installation which shows the glass not even
reaching the end of the longeron. Chapter 7 has a picture showing this
area with a backsaw plowing through it! The whole front end of the doubler
will be cut off to mount the canard, so do not waste time trying to get
the glass to lay down perfectly.
5.9 - What about the divots I got when I removed the sides from the
jigs and tried to remove the epoxy blobs?
In general, do not worry about them. The simple solution is to fill
them with dry micro. On the PVC foam, you could fill with micro, let cure
and then sand flush. (On softer foam, you would use the dry micro
immediately before glassing without a cure stage, as it is difficult to
sand cured micro without sanding softer foams away first.) If you really
want to go for perfection, route out these spots to half the depth of the
foam (about 3/16") and glue in (dabs of 5-minute epoxy on bottom only)
pieces of the 3/8" PVC to match the hole size, then sand flush.
Chapter 6 - Fuselage Assembly [as of: 22 oct 97]
[distiller: Terry Pierce]
Comments and Tips
- When installing bulkheads, double and triple check the
measurements. Check to see if you are supposed to be measuring from
the front or the back of the bulkhead, especially on the landing gear
- When cutting out the landing brake make sure the brake starts 2"
from the front of the front seat back (not the back as it might appear
in the drawing).
- Some folks are widening the landing brake hinge from the original
10" Long-EZ width to 16" or more inches.
Left in the Archives
- Fuel valves
- NACA Scoops
- Vacuum bagging the bottom
- Speed brake
- Seatback brace / heat duct
- Aileron control tube holes
- Firewall longeron holes
- How to recover from attaching the landing gear bulkheads in the
6.1 - Where should I locate the F28 bulkhead?
Many builders have found that when installing the canard in Chapter
12, there is not enough room between F22 and the F28 cut-out for the
trailing edge. Most builders have moved the F28 to the 6.25 position
instead of the 5.9 inches called out in the plans. (See
Chapter 12 of this FAQ).
6.2 - Do you need to tape the landing gear bulkheads to the sides
of the tub with 2 plies of BID?
Yes. As with the other bulkheads, tape these joints with 2 plies of
6.3 - Should I lap the multiple plies of UNI that are added to the
landing gear bulkheads onto the sides of the tub?
6.4 - How do I bend the 1/16" thick 2024-T3 aluminum sheet for the
fuel valve mounting bracket without cracking it?
First you might consider using a softer type of aluminum (like 5052).
Otherwise you need to make sure that the radius of your bend is 3/16" or
greater. Do this by bending it around something with this radius (e.g.,
sand the radius into a piece of wood, then bend the aluminum around the
wood). Also make sure that you make the bend perpendicular to the grain in
the aluminum (not parallel to the grain).
6.5 - Do I really need to lay-up and attach the bottom of the
fuselage in one, uninterrupted session?
You could do this in one step, but it really takes away from the "fun
factor". Just laying up the BID on the contour of the bottom is a big job
(a lot of time, even with a couple of helpers). People who have done this
in one step say they would never do it this way again. Most suggest:
- Lay up the bottom and peel ply where the the bottom is going to
meet the sides and the bulkheads.
- Let cure.
- Remove peel ply, sand, and flox the bottom to tub
- After flox cures, turn tub on its side or bottom, and tape all the
joints at your leisure.
6.6 - What do the plans mean by "lay one ply of BID at 45 degrees
on the fuselage bottom, then run the second ply the other way"?
Apply the first ply of BID at 45 degrees to the longitudinal axis of
the bottom (the long direction). Now, imagine standing at the front edge
of the bottom and suppose that the selvage is ascending away from you as
you look from left to right. Now, the second ply of BID is also positioned
45 degrees to the longitudinal axis but this time the selvage would be
descending towards you when looking from left to right. This insures that
your 1" BID overlaps in the first and second plies do not lie on top of or
parallel to each other. Your BID overlaps from the first and second plies
will make an "X" pattern if you do things correctly.
6.7 - Where should the 3rd ply of BID on the fuselage bottom be
placed and how large should it be?
The 3rd BID layer is to provide extra strength and scuff protection
in the areas where the rear passengers will stand when entering and
exiting the plane. In general, the 3rd layer can cover from the aft edge
of where the seatback will be to all the way aft. Some builders only apply
the 3rd layer from the seatback brace aft. Orientation does not really
matter, but a 45-degree orientation to the fuselage centerline is probably
6.8 - Remember to check that the aft landing-gear bulkhead is
attached the right way!
The aft landing-gear bulkhead has an 8-ply-buildup on the front side.
Remember to flox the bulkhead in place with the plies facing forward - not
Chapter 7 - Fuselage Exterior [as of: 5 jun 98]
[distiller: Darren DeLoach]
Comments and Tips
- Be sure not to cut into the longeron past the midpoint of the
landing brake, or you will cut away too much foam and will not be able
to match the round part of the LG bulkheads without extra work.
- The antenna toroids are just about the same thickness as the 3/8"
foam, be careful when routing out the foam for the toroids and coax to
avoid cutting into the glass on the opposing side.
- Some coax info from Jim Weir
of RST (
for our purposes, there is no difference between RG-58, RG-58/U and
RG-58A/U. Plenum or PVC covered is fine, PVC is cheaper, plenum is
usually lighter and narrower. Make sure your BNC connectors and
crimper are appropriate for the type you select. Jim prefers the
soldered, screw-on connectors, but says crimped connectors are fine
- See question/answer 8.3 regarding the allowing
for step recess.
- See question/answer 9.12 if you are going to
install an electric landing brake.
Left in the Archives
- NACA inlet versus arm-pit scoops
- Modifications for Wayne Lanza's speed brake
7.1 - What shape should the 1" urethane foam on the outside of the
triangular plywood pieces be?
You could use two oversize triangular pieces, or one big rectangular
piece, it does not matter. One big rectangular piece errs on the safe
side. Most of this foam is sanded off anyway.
7.2 - The NACA template does not match the bulkhead cutouts. Which
There is a some "slop" allowed in the width of the scoop, the
critical part is that the slope of the ramp be smooth, have a 7 deg.
slope, and have sharp edges where the curved sidewalls meet the fuselage
bottom. Most people appear to trust the template over the bulkheads; and,
for example, cut off an extra 0.1" from each side of a bulkhead if needed
to match the template. The cutout in the aft LG bulkhead seems to be the
one most often enlarged.
7.3 - How far do the joggles extend down the sides for the landing
There appears to be no "right answer", but a general consensus seems
to be the middle of the gear strut, or roughly the top of the triangular
plywood gussets. See the photo of Marc Z's landing gear cover at
and notice that you do not need a joggle on the foam covering the plywood
triangles, just the area along the LG bulkheads. Note also that the cover
rounds the curve of the bulkhead only a short distance.
7.4 - My plywood parts C and D do not match
the plans template well. What did I do wrong?
Do not sweat it -- these are basically just support for the foam
filler pieces around the gear legs, as well as tie-ins for the bulkheads
to the sides, everyone's will be a little different. Just sand them to fit
reasonably well, and fill any voids in the joint with flox. The plans are
trying to tell you that your parts will be different when it says to make
a foam version to trial-fit first.
7.5 - When shaping the rear of the fuselage, the plans describe the
horizontal dimensions of the area to be removed, but what about the
Visualize a hot-wire cutter, one side fastened on a pivot 25" forward
of the firewall, right on the edge of the foam at the "top" corner ("top"
because the fuse is upside down). Now visualize how the foam will be cut
if you take your imaginary hot-wire cutter and slide it along the firewall
from the bottom to the small triangle of the lower firewall with the other
end merely pivoting at the front. You will have cut out roughly a triangle
of varying depth, deeper at the firewall and shallower toward the front
(with no foam cut out in front of the wing spar cutout). Stop shaping if
you get down as far as the electrical channel (which most people seem to).
As the plans point out, it is not very important how it looks ahead of the
spar cutout as this area is hidden under the strake.
7.6 - Jim Weir of RST says to put the Marker Beacon antenna on the
bottom, while the plans say put a Nav antenna there. What should I do?
Each has its own set of issues regarding routing. (See following
answers to Questions 7.7 and 7.8.)
Nat prefers the Nav while Jim Weir
of RST (
prefers the Marker Beacon since its ideal length is so long (78") and it
should be oriented horizontally, fore-aft. Recall that you have got enough
room on the wings for just about as many Nav, Glide Slope, and FM antennas
as you could possibly want.
7.7 - If I decide to go with the Nav antenna on the bottom, are
there any special things to watch out for?
- Be sure to layout the cut-out for the nose wheel and route the
cable to avoid this (refer to Chapter 13). Otherwise you may have to
reroute your antenna when you reach Chapter 13.
- Avoid the area where the landing light will be (refer to Chapter
7.8 - If I decide to go with the Marker Beacon antenna on the
bottom, where do I put it?
To avoid the landing brake, you need to run it between the landing
brake and a fuselage side, instead of right down the middle. You can put
the coax joint just ahead of the landing brake, near the bottom of the
front seat back. Run the cable perpendicular to the tape to at least the
middle of the fuselage (or even to the other side), then forward to just
behind the instrument panel, being sure to miss where the front landing
gear cutout will be positioned (refer to Chapter 13) and the landing light
cutout (refer to Chapter 17).
7.9 - When glassing the bottom fuselage, what does, "[t]he overlap
of the bottom layup with the side layup should be at the corners, and
the edges of the plies should be staggered one inch and the overlap of
each ply should be one inch" mean?
Each pair of plies (one from the side and one from the bottom) must
be overlapped 1". Each 1" overlap area made by these pairs of plies should
be offset from the 1" overlap area of the plies below it, to avoid a bulge
in the side area. So, for example, the overlap area of two full sets of
plies would span 2" total, 1" per layer times two layers.
7.10 - How do I get the glass to lay down in the joggles for the LG
This appears to be a nasty problem, judging from the archives.
Several methods have been attempted and documented in the archives. You
are not really going for strength in the glass here, so the sharp turns
are not really a problem, you just need to get a good flat surface for
your LG cover to sit on. In general, there are two kinds of methods
mentioned in the archives:
- The most popular method: put flat, weighted objects over the glass
in the joggles, like weighted blocks of wood (see Marc Z's Chapter 7
or strips of flat steel from your local hardware store. Some weighting
may be required to keep everything in place, and make sure you put
plastic wrap or tape on the objects for release.
- Instead of making a pair of 90 degree angle corners, radius the
corners so that it is easier to make the glass stay put. One problem
mentioned is that this method requires more filler, and using micro
might be prone to chipping, flaking, etc. Instead you might consider a
combination of micro and flox or just flox as the filler. However, you
will probably still need some weighted flat objects just like in the
7.11 - The plans do not indicate what type of wood reinforcement to
use for the step. What type of wood should I use?
You should use birch plywood or some other hardwood. The step will be
under compression once the bolts are tightened (and whenever someone
steps on it).
If you follow the plans when laying out the urethane-foam for the
NACA-scoop, you may determine that the transition between the front edge
of the NACA scoop and the bottom of the fuselage may not be smooth. As
the fuselage-bottom starts to go down aft of the landing brake, the ramp
for the NACA-scoop may go upwards with a small angle relative to the
fuselage bottom (when the fuselage is placed upside down). To avoid this
you may fill the space between the aft side of the landing brake cutout
and the front side of the plans 1 inch thick urethane foam of the NACA
scoop with additional 7.5 inches of 1 inch thick urethane. When sanding
the NACA scoop, almost all of this foam will be removed leaving just
enough to make the transition smoother.
Chapter 8 - Head Rest & Seat Belts [as of: 24 nov 98]
[distiller: Wayne Hicks]
Comments and Tips
Left in the Archives
- Rationale for narrowing shoulder harness spacing
- Retractable step plans and modifications
- Bolt and bushing specifications for seat-belt attachments
8.1 - What if the radius of curvature of my Ken Brock step does not
fit my fuselage corner?
This is quite common. Most builders shape the birch reinforcement
piece to conform to the step, recess the step into the foam, or bend the
step to fit the fuselage curve. See the archives for how-to's on bending
8.3 - Should I recess the step and outer reinforcement piece?
If you want your step to be flush with the fuselage outer surface,
then you will need to recess the wood reinforcement piece into the foam
and make the step curvature match the outside of the tub. You should have
instinctively known to do this in Chapter 7 before the bottom and sides
were glassed. ;-(
8.4 - How long is the interior birch insert for the forward port
seat-belt attachment point?
The forward port insert should be made longer than the others so that
all four bolts go through it. Two bolts go through the step, inserts, and
seat-belt attachment bracket. The remaining two bolts go through the step
only, one on either side of the bracket.
8.5 - Does anybody know if the head rests were designed for
There is a copy of a RAF letter in the Chapter 8 archives (1996) that
thoroughly explains the structural purpose and limitations of the
triangular head rest. The head rests, as originally designed for the
Long-EZ, offer limited roll-over protection in the event that the plane
flips upside-down with little to no forward speed. They were never
intended to protect the passengers at crash speeds. The Cozy offers more
protection because of its turtleback and bulkhead immediately behind the
pilot and passenger.
8.6 - How many layups go on the inner and outer surfaces for the
Per the plans, you glass 1-BID onto what will be the interior pieces
of the headrests, then cut them out to shape. You next assemble the pieces
with 5-minute glue and nails, round off the edges, vacuum the dust, then
glass the outsides with 2-BID. Then you finish up by 2-BID taping the
8.7 - Is there a better way to mount the nut plates under the
Maybe. Most builders install the nut plates before glassing the
shoulder brace in place. The basic method is to rivet the nut plates onto
1"-aluminum squares, flox the squares under the head rest, and use two
small screws to hold the aluminum squares securely to the plywood inserts.
Check the Chapter 8 archives for step-by-step instructions.
Chapter 9 - Main Gear & Landing Brake [as of: 28 dec 98]
[distiller: Wayne Hicks]
Comments and Tips
- To get the tabs straight and parallel with no twist or incline, use
two long boards (one each side) to clamp the tabs. Use gage blocks
between the boards and jig blocks to keep from exerting too much
- For landing gear tab layups, do not over-tighten the clamps;
otherwise, the layers will slide around too much resulting in sharp
bends, creases, and separations.
- Try using 3/8" OD vinyl tubing on the trailing edge for the
nylaflow conduit instead of soda straws. It is easier.
- Try using a 15" width for the 2nd torsional wraps. A 15" width will
allow the edges to extend past the trailing edge. Trimming will be
easier, neater, and the trailing edge will be stronger.
- If you find that aluminum tape is too flimsy for building up the
trailing edge, try aluminum flashing, thick poster-board, or strips of
counter-top laminate material (e.g., Formica).
- Before securing the landing gear strut and jig to your table top,
lay out ample wax paper or plastic first. Otherwise, you might not
catch all the excess epoxy and your jig will permanently attach itself
to your table top.
- Consider ordering bolts and screws of varying lengths - some
shorter, some longer - than those called for in the Chapter 9 parts
list. Your glasswork may have made the bulkheads thicker or thinner
than the prototype airframe.
- An alternative to using the spot-facing tool is to use a bimetal
hole saw adjusted and calibrated for the correct-sized hole. You do
this by bending the outer teeth inward or filing them down.
- According to Nat, if using the Cleveland brakes, make sure the
disks are 3/8" thick and NOT 3/16".
- When installing the tires and tubes, the tube stem should line up
with and on the same side as the red dot or triangle on the tire. This
helps to keep the tire and tube installation balanced.
- Canard Pusher #51, page 5 for a great article about using Teflon
hose assemblies instead of Nyloseal or Nylaflow tubing.
- Matco does not make a left- and right-sided brake. The brakes are
identical except for the location used to install the bleeder valve.
You can see this on Marc Z's web page: http://www.cozybuilders.org/chapters/chap09_6.html
Left in the Archives
- Main Gear Struts: performance, testing, and tradeoffs of approved
and non-approved main gear struts
- Changes to accommodate Wayne Lanza's electric landing brake system.
- Wheels and Brakes: specifications, performance, and tradeoffs
between Cleveland and Matco systems. Highlights:
- The higher the brake's energy absorption specification, the
more energy can be absorbed by the brakes before they start to
fade or begin to boil the brake fluid.
- Formulas used by the FAA for computing the energy absorption
spec needed for a particular plane at gross weight.
- Both Cleveland and Matco offer high-energy absorbing brake
- Choice for wheel sizes vary, with most builders choosing 5"
wheels or the low profile 6" wheels.
- The nose wheel is the limiting factor for soft field
performance, so going with standard 6" wheels (larger diameter)
for soft field performance may not offset the weight and drag
9.1 - When glassing the forward landing gear bulkhead
reinforcements, what is a good technique for getting the BID cloth to
lay down in the corners?
Cut the glass cloth oversize, wet the surface area, work the glass
down in the corners first, then work outward from there. Have patience, do
not become frustrated too quickly -- the cloth becomes more manageable as
you wet it out. Do not be afraid to move the glass around a bit. If it
still will not lay down, cut darts.
9.2 - How do I determine how much material to trim off the "bump"
of the trailing edge of the landing gear?
You need to sand enough material off the "bump" so that the
cross-section dimension is approximately 5.75". Take a look at Drawing M-9.
You want the strut to be 5.75" in cross-section AFTER
the torsional layups because 5.75" is the fore-to-aft dimension of the jig
box glued on top of the strut for laying up the tabs. However, do not take
off more than 1/8". If necessary, adjust the width of your jig box.
9.3 - What do I do with the first 4-UNI torsional wraps when I get
to the leading edge?
Scissor-trim the edges to be either butted together or to within an
eighth-inch or so, but try to avoid overlapping the edges. The gear legs
are airfoils and you want the leading edge to be smooth. Nothing critical
will happen if you do overlap, but you will end up with an unwanted bump
and a cosmetically challenged gear leg. If you do overlap a few fibers,
simply sand the overlap under the leading edge is smooth (which you will
have to do anyway to get rid of the 5-minute glue used to hold the strut
on top of the nail heads).
9.4 - What is the correct angle for trimming the gear ends?
(One page of the plans says 8 degrees while the next page says 13
degrees . . . ) Trim the gear legs at an 8-degree angle. This angle allows
enough incline for the landing gear legs to sit flat on the floor while
jigging. However, it does not really matter as you will trim the leg end
after installing the axles, wheels, and brakes.
9.5 - This jigging process for the landing gear is an exercise in
geometric futility. Why am I doing all this?
Your goal is to ensure that the axles can be installed at the correct
location. To do this, you must ensure that the ends of the landing gear
(mating surfaces for axles) end up in the right place. This involves a
three-step process. First, you jig the landing gear strut against the
backboard to locate the centerline, ensure the gear legs are of nearly
equal length, and locate the sweep at the right place. Second, after
building the jig box on top of the strut and re-jigging onto the table
top, you re-calibrate the length and sweep, with sweep being most
critical. This step ensures that you "take out" any irregularities in the
backboard jig and jig box before committing to locating and drilling the
pilot holes through the tabs. The final step re-calibrates the length and
sweep of the gear strut while mounted in the fuselage. You can make any
final adjustments then, and locate the axles in the right place on the
legs. If you follow the plans anywhere close to what is written, you will
end up with the ends of the gear legs at or very near (within 1/4") the
proper FS location for mounting the axles.
9.6 - After locating the tab attach points (.75" above the strut),
I notice that one is higher than the others. What should I do?
Unless your strut came out of the mold perfect, then it is quite
possible for one attach point to be higher or lower than the other. Simply
use the higher of the two as your reference mark. These marks get
transferred to the jig block built on top the strut and later to the
drilling jig you use when drilling the holes through the tabs. The
important point is that the holes are parallel with the legs. (You made
sure the holes in the bulkheads were straight, right?) With the legs
level, you certainly WOULD NOT want to screw this up by
drilling holes into the tabs just because one side of the gear bump was
slightly thicker/higher/lower than the other side, right? Differences in
attach point measurements can also be attributed to how you did the
torsional wraps and how accurate you were with the jigging, measuring, and
9.7 - After jigging onto the table top, I found that my gear legs
are not the same length and do not have the same sweep. Should I make
the corrections now?
If all measurements are within reason (say 1/4"), NO! You want to
resist all tweaking efforts until you have mounted the strut in the
fuselage and checked the fit. The leg lengths and sweep can be altered by
altering the holes (carefully) in the bulkheads. It is better and easier
to tweak the holes in the bulkheads than the holes in the gear tabs. Once
you have the fuselage leveled, the strut re-jigged, and measured the
station settings of the gear, then make any final cutting and tweaks to
the gear lengths. You can also "dial-in" the gear legs by where you place
the axles. If the axle placement is way off, then go back to the beginning
and try again.
9.8 - Any good techniques for clamping the tabs?
Try and squeegee out as much epoxy as possible before trying to clamp
the tabs. To get the tabs straight and parallel with no twist or incline,
use two long boards to clamp the tabs and use gage (spacer) blocks between
the boards. Do not use too much clamping force. 45 layers of fiberglass is
like walking on greased ball bearings. Too much pressure will cause the
layers to slide around, buckle, and separate, causing the tabs to be
uneven after cure. In the worst case, too much pressure also causes a
crease in the tab that can lead to localized stress areas and potential
9.9 - How critical is it for the tabs to be absolutely straight?
Not very critical but do not get sloppy. During the "spot-facing"
procedure, you end up drilling holes in the tabs straight and true,
negating any variances in the tabs. Warped wood and incorrect clamping
techniques are the major contributors to tabs that come out twisted and
9.91 - What is the correct orientation for mounting the MG-4
bushings? The plans are not very clear on which way the bushing flange
When mounting the MG-4 bushings make sure the flange is on the inside
of both the forward and aft bulkheads or another way to say it is they are
supposed to go from the inside toward the outside.
9.10 - How snug should the landing gear be when installed?
You want a "machined" fit -- not too snug, but not too loose. Too
snug a fit may cause galvanic corrosion (you may not be able to remove the
gear studs). Too loose a fit will allow the gear to "bang around" on
landings, causing undue stress and premature damage to the fuselage
structure. After opening the landing gear tab holes to 3/4", you might
find the fit to be too snug for the bushings. Use a rat-tail file
(careful!) or 100 grit sandpaper to just barely open the holes big enough.
Once the strut is check-fitted in the fuselage and the bushings are floxed
in place, everything should line up perfectly.
9.11 - The plans calls for three .025" shims to be 5-minute epoxied
between the hinge and LB-23. What are they use for?
These shims approximate the thickness of the 3-BID layup that gets
glassed over LB-23 in a later step. The shims are later
removed and discarded after LB-23 is floxed in place and
before permanently drilling/tapping/installing the landing brake to LB-23.
Three small pieces of duct tape stacked together will serve the same
purpose as the shims.
9.12 -What is the spacing of the three 1" shims for placement of LB-23?
The spacing of the shims is not critical. Put one in the center and
the other 2 on either side LB-23.
9.13 - What are the modifications required to implement the
electric brake mechanism?
The slot through the fuselage bottom is longer and wider than plans,
and additional attachment points get added onto the seat-back brace for
the electric mechanism. All modifications are easily accomplished, but it
is best to have the mechanism in your possession before starting the
landing brake construction (or even before glassing the outside of the
fuselage in Chapter 7). Each installation is a custom fit and slot
dimensions vary widely. In general, plan on a slot about 3/4" to 1-1/4"
wide and about as long as the plans slot. Some builders are widening the LB-19
plywood insert by about 1/2" on each side.
9.14 - How do you install the brass fittings for the brake lines?
The pieces include an insert that is slid up into the nylaflow
tubing, a threaded cap, an insert that goes over the tube, and the brass
fitting. Slide the first insert up into the tubing. Slide the threaded cap
onto the end of the tubing. Slide the other insert over the tubing. Feed
the tubing into the brass insert. Screw the threaded cap onto the brass
fitting, ensuring that the outer insert lies on top of the inner insert.
If you did this correctly, the outer brass insert will be squeezed between
the cap and the fitting, thereby firmly crimping the tubing in place. The
inner insert is there to provide wall strength so that the nylaflow tubing
is not crushed.
9.15 - What is the diameter for the two holes that are cut into the
foam piece used to close off the landing gear box?
These are inspection holes and diameter is not critical. Nat
recommends 3- to 4-inch diameter. Since you will be 2-BID taping the piece
to the landing gear bulkheads, it is best to cut the holes to leave about
1.5-2.0 inches at the edge of the piece.
9.16 - Should I apply 2 plies of BID tape the three foam pieces
that close the top of the landing gear box?
Yes. In general you should always tape when joining fiberglass
components. (See Chapter 3 and the Cozy Newsletters.) The plans are very
specific about calling out when not to tape.
Chapter 10 - Canard [as of: 29 mar 2010]
[distiller: Bil Kleb]
Comments and Tips
Left in the Archives
- Dihedral ("bent") canard
- Vacuum bagging the canard
- Using composite parts as opposed to aluminum.
10.1 - Are the A and B canard templates
supposed to be slightly different?
No. According to the Canard Pusher newsletter, template A
seems to have been reproduced more consistently correct, so make B
10.2 - How do you remove the twist of the cores after hot wiring?
The plywood jigs are bonded to the core, so shimming them should
allow you to remove any twist, i.e., the leading and trailing edges are
perfectly straight and both ends are level.
10.3 - How do you use only two 8' 2x4's to support the canard?
You do not. Either splice in some extra pieces or buy 12' lengths.
Absolute straightness is not all that critical since you are just using
them for support.
10.4 - What does spar cap tape look like?
It does not look like standard UNI cloth. It should look like small
bundles of fibers with a VERY loose thread running back
and forth holding it together, and one plastic thread along one edge.
10.5 - What do I do if my spar cap tape is only 2.5 inches wide and
the plans call for 3-inch tape?
Lately, the spar cap tape from Wicks and Aircraft Spruce is supplied
in 2.5 inch rolls instead of 3 inch rolls. Not to worry though as either
width contains the same thread count. Once the spar cap tape is wetted out
and the cross-threads are pulled, the fibers will fill the spar cap trough
as you squeegee them into place.
10.6 - How many layers of spar cap tape did you use?
This question arises from the concern that just filling up the trough
with whatever fits is not very comforting. Based on the amount of spar cap
tape called for in the plans, it looks like a minimum of 6 plies on the
bottom and 8 on the top. People have reported bottom/top layups of: 9/11
and 7/10. According to the Canard Pusher newsletter, the plans for the
Long-EZ were changed from specifying the number of plies to just filling
the trough because some spar cap tape had less glass than others.
10.7 - What do I do about dips below the ideal contour along the
spar cap layups before skinning?
As long as you have a smooth transition from the spar cap to the
foam, you will be able to glass the canard skin. Contour after skinning
with micro. DO NOT PUT MICRO OR FLOX BETWEEN THE CAP AND THE
10.8 - What is gray tape?
Duct tape, for glass release.
10.9 - How do you make the BID fit when glassing the bottom of the
You have to pull them slightly out of 45 degree alignment to stretch
the piece to fit. Just be sure that the fibers are still straight after
10.10 - Does anyone have a good method to get the 1/32" depression
in the foam at the ends of the canard?
Put tape along edge of where the depression is to end and use a long
sanding block. The tape serves to protect the foam outside the depression.
10.11 - When using Canard Contour Checking Template E, why is there
a gap between the template and the foam core at the trailing
edge? (Why does the checking template E not match the hot wire
Cozy Newsletter #53, Builder Tip #7 suggests that template A/B be
modified at the trailing edge to increase elevator up travel. If
this change was made to hot wire templates A/B, then Checking Templates E
and F must also be adjusted accordingly. If they are not, the bottom
Checking Template (E) will show a gap to the foam at the trailing edge,
and the top Checking Template (F) will sit too high on the trailing edge
and show gaping to the rest of the foam surface.
Chapter 11 - Elevators [as of: 11 nov 13]
[distiller: Bil Kleb]
Comments and Tips
- Double check your cores prior to glassing with the appropriate
- You might have to file the corners of the NC-2 hinge
inserts to fit inside the windows in the torque tubes.
- Install the hinge pin when pop riveting the NC-2's to
- Wait to the last second to put vaseline or grease in the hinge pin
holes to block epoxy from getting in, so that they do not become
debris magnets during sanding, filing, etc. Using Clark foam is also
suggested for this purpose for fear of accidentally getting grease on
some yet-to-be-bonded surface.
- The foam might break if you try to slip the foam over the torque
tubes, you might have to slide the tubes in lengthwise (see the 1995
archives for details).
- Pay close attention to the dotted lines in Figure 4, indicating the
orientation of the NC-2's with respect to the foam cores.
- Make sure that you do not have more than 22 degrees of trailing
edge down travel, otherwise you might experience poor "stall"
characteristics and long takeoff rolls when using full aft stick.
Anymore than 22 degrees creates less lift and more drag.
- You might consider putting a joggle on the elevator before skinning
for the UNI that raps the counterbalance weights.
- Some recommend to use the new L template from
Newsletter #50 when mounting the elevator hinges. Use of this template
assures 15 degrees of trailing-edge up travel.
Left in the Archives
- "Sparrow strainer" elevator trim
- A different method to terminate the ends of the canard hinge pins.
- The entire "elevators mounted too low" syndrome.
11.1 - Did people Alodine the aluminum parts before installing?
The general consensus seems to be that the chemicals are relatively
cheap, the extra time required negligible, and it seems it cannot do any
harm but might do considerable good.
11.2 - Where can you get the countersunk pop rivets (BSCQ-44)?
At this writing, neither Aircraft Spruce and Specialty nor
Wicks Aircraft Supply was carrying them. Someone suggested trying Deering
Engineering in Los Angeles, California, at (310) 595-1168 or any aircraft
repair station. Others have just been substituting the non-countersunk
11.3 - When this elevator is in it is full, trailing-edge up
position, is there still a gap between the elevator and the canard?
No clear answer. Some indicate that you will have a cosmetic
paint-chipping problem if there is not a gap, and others say you will
never what to use that much elevator deflection anyway.
11.4 - Did anyone try to temporarily attach the NC-3
hinges with a minimum amount of flox, check the movement/position of
the elevator, and then finish filling with flox?
11.5 - Do you paint the sides of the outboard elevator
counterbalance weights AND the foam spacers?
One mention of smearing wet micro on both sides of the foam and the
lead weight, sanding smooth, and painting.
11.6 - Why and how should I protect the outboard elevator mass
balance weights from shear forces?
A number of flyers have noticed a crack in the foam of the outboard
mass balance on the elevator after they have been flying for a few years.
This can happen from:
The following steps can decrease the chance of issues with the outboard
mass balance weight:
- an impact to to the mass balance
- long-term vibration - possibly flutter
- the mass balance acting as the hard stop for the elevator trailing
edge down and the pilot repeatedly pulling hard on the stick causing
the mass balance to impact the canard.
- Using the incorrect foam for the spacer from the LE of the elevator
to the lead weight - a high density foam is specified in the plans,
although some have used low density foam by mistake
- The plans do not call for any layups on the sides of the mass
balance. However, putting a 1 ply of BID at 45 degrees on either side
of the mass balance over both the lead weight and the high density
foam would increase the shear resistance as well as damage tolerance.
- Ensure the mass balance is NOT the hard stop for
- Ensure that you use the correct high density foam as the weight
Chapter 12 - Canard Installation [as of: 21 dec 07]
[distiller: Wayne Hicks]
Comments and Tips
- You can achieve a perfect fit between the F22 BID
pads and the canard lift tabs by using flox to fill any remaining
gaps. Wrap the tabs with box sealing tape, apply flox onto the BID
pads, press the canard into place, and remove excess flox before
- You can also achieve "perfect fits" by using the same method for
sealing under the canard and around the holes in the fuselage sides
for the MKNC12A's (elevator torque tube offsets).
Left in the Archives
12.1 - Why do I not have enough room to mount the canard?
This is a common problem if you mounted your F22 and F28
bulkheads as specified in Chapter 6 of the plans. F28 should
really be called F28.3. A look at the M-11
drawing will show there is not enough room provided for the canard width
(tabs to trailing edge).
12.2 - How do I accommodate my F28 bulkhead that was
mounted according to 5.9" dimension in Chapter 6?
There are several solutions. Although it sounds like major surgery,
the easiest is to carefully cut out F28 and move it from
5.9" to 6.25". If you cannot bear the thought of doing that, then try
the following minor surgery:
- Trim 0.1" from the canard trailing edge, leaving AT LEAST 3/8" of
- Gradually taper the fuselage sides back below the longeron about
1/8", to leave a small space between the trailing edge of the canard
and the fuselage. You need to leave room for 1 ply of BID, filler,
and paint. Note: you will have to futz with this area anyway when
you get your elevators installed to clear the torque tubes closely
with a seal.
- Add BID pads as required on F22 to level/align the
canard to the fuselage as per plans.
12.3 - How do I properly set the canard incidence angle?
Use the G template. Ensure the top longerons are level. Shim the
canard until the top of the G template is level. DO NOT USE the hot-wire
templates. The "waterline" on the hot-wire templates is NOT THE SAME as
the "reference line" on the G template. The waterlines on the hot-wire
templates are only used to ensure the templates are referenced to each
other to take out core twist prior to cutting. You will end up with NEGATIVE
INCIDENCE if you use the waterlines. DO NOT DO THIS.
NEGATIVE INCIDENCE IS DANGEROUS. It leads to long
take-off rolls and lots of trim at a (slower) cruise speed.
12.4 - How do I fix a canard mounted with a negative incidence
Do the following:
- Ensure the canard is straight with no twist.
- Ensure the G template is correctly made to plans.
- Level the fuselage (top longerons dead level)
- Sand the fuselage sides down a bit (under rear of canard) as
needed to level the G template.
- Remove the alignment tabs and remount at the correct angle, or
make new ones.
- Ensure the lift tabs are mounted as indicated below with the
correct BID/Flox pads.
12.5 - Can a flox pad be used instead of BID pads when fitting
the canard tabs to F22?
It is a split-decision. The BID pads are used to:
It is recommended to use the BID pads first, then take up any remaining
gaps with flox. You can achieve a great custom-fit by wrapping the
mounting tabs with gray tape or Saran wrap, putting a bead of flox on
the F22 bulkhead where the mounting tab will go, positioning
the canard into place, and holding it there until cure.
- Custom-fit the location of the canard to ensure incidence and
- Provide crush pads when bolting the mounting tabs to F22.
- Provide load paths to strengthen F22 at that
- Provide some relief strength to keep from wallowing out the bolt
12.6 - What is the procedure for replacing the alignment pins
with removable bolts?
The alignment pin method is perfectly okay, but the better the
quality of the workmanship, the more difficult it is to remove the
canard. The alignment pin design relies on some slop between the pin,
insert, and the surrounding structure. The following method provides for
better fit, "straight up" canard removal (easier), and better torsional
- Remove the pins.
- Re-drill the longeron doubler with a 3/8" drill all the way along
the length of the doubler. Flox in an aluminum or steel sleeve (3/8"
OD x 3/16" ID). Cut the sleeve slightly longer than the longeron
doubler or else you will have to ream the tapered surface of the
- Make a small 2024-T3 aluminum plate with an AN3 nut
- Flox the nut plate onto the forward surface of the alignment tab.
- Insert a long AN3 bolt (approximately 4") from aft of
the doubler, into the sleeve and screw into the nut plate.
- If all of the alignment is done correctly, tightening the AN3
will cause the main lift tabs to locate flush and correctly
positioned against F22. Removal of the canard now
requires the removal of the two AN3's, from the rear
tabs, and the two AN4's from the main lift tabs,
followed by a simple vertical movement of the canard; i.e., there is
12.7 - Were the M drawings ever revised to include the plans
change from Newsletter #80 which required changes to templates F
& G to increase the canardís angle of incidence?
The standard M drawings provided with the plans were not revised for
this change to the plans. Newsletter #80, which calls out this
change, also includes revised drawings for templates F & G which
supersede those on M-17 and M-18. This newsletter is included when you
purchase the plans.
However, the re-formatted version of the drawings available from
Aircraft Spruce, which connects the various M-drawings along the match
lines, does include this revision to templates F & G on sheet 10.
Chapter 13 - Nose, Nose Gear and Brakes [as of: 10 Aug 08]
Comments and Tips
1 - What if I want to upgrade the brake lines to aluminum hard
lines and stainless steel & teflon flexible lines?
The plans-specified Nylon brake lines leave a lot to be desired
in terms of heat and UV resistance. Installed properly,
there have been cases of them serving decades of trouble-free
service, but there are countless cases of the lines leaking at the
fittings, and becoming brittle due to heat and/or UV exposure.
There is a better way, and that is to install aluminum or
stainless hard lines where they do not have to move, and Teflon
with braided stainless steel where flexibility is required.
The following is a shopping list to change to this better
approach to brake lines.
From Pegasus Auto Racing
#3 Stainless Steel Braided PTFE Hose
25' will cover both lines from master cylinder to hard lines, and
all the way from the bulkhead down the gear leg to the caliper. You
might get by with 20', but 25 works for certain, and allows for
Straight 3AN Hose End for size #3 PTFE Brake Hose
8 are required.
From Aircraft Spruce
AN822-3D Elbow, -3 Flared Tube to 1/8" NPT
2 are required. These go from the master cylinder to the PTFE/SS
line. Order 4 if your calipers need these instead of the straight
AN815-3D Union, -3 Flared Tube to -3 Flared Tube.
AN832-3D Union, Flared tube, Bulkhead & Universal
AN924-3D Aluminum Nut
4 are required. These connect the PTFE/SS line to the 3/16" hard
line at the front, and the 3/16" hard line to the PTFE/SS at the
gear leg. You may prefer to use AN832-3D bulkhead fittings,
especially at the rear bulkhead. If you do, don't forget to buy
AN924-3D nuts to hold those bulkhead fittings in place. Used at
the front it also makes it so you can create a small flange to
mount the fittings so it doesn't rely on the hard line to hold it
5052-0 3/16" Aluminum Tubing
Buy two 12' sections. It is OK to have them roll it for you. It
unrolls just fine. If Aircraft Spruce won't roll it for you, I
know Wicks will. If you really want stainless, it is 03-16020 at
$4.97/ft. If you're going to do that, you could just as well use
the PTFE/SS all the way and save some money on fittings.
AN816 Nipple, -3 Flared tube to 1/8" NPT
2 are required. These go from the PTFE/SS line to your caliper.
Depending on your caliper positioning, you might prefer an
AN818-3D Nut, and Coupling Sleeve
4 are required.
I strongly suggest that you consider purchasing Matco dual parking
brake PVPV-D for $125.65. It will change your fitting requirement
just a bit. You'll need 4 more AN816-3D fittings, but you can
eliminate two of the AN815-3D (or AN832-3D if you so choose)
unions. The parking brake is best placed just forward of the
instrument panel so that you can either reach through the leg
opening and turn it by hand, or use a short control cable to the
Left in the Archives
13.1 - What is a Nose Gear Ratchet and is it necessary?
A Nose Gear Ratchet is designed to keep the nose gear up when it is
up and down when it is down. During flight it is possible for the nose
gear to jiggle it is way down, increasing drag. While taxiing, despite
the fact that the nose gear "locks" over center, it is remotely possible
for it to jiggle and vibrate itself into an "unlocked" position,
resulting in possible damage to the gear mechanism. Therefore, some
method of locking the nose-gear mechanism in place is highly
recommended. The most commonly used method is with a nose gear ratchet
which is nothing more than a modified Craftsman socket wrench. This unit
was originally designed by Curt Smith, and is still available from Bill
Another option is described in the archives and can be easily fabricated
using part of a ring type ratchet and hexagonal aluminum tubing.
13.2 - Is the orientation of the nose gear handle important?
It is important that the nose gear handle be vertical when the nose
gear is fully retracted (the position it will remain in for hours and
hours while flying cross country to visit the in-laws). If it is
installed in any other orientation it will poke either the pilot or
co-pilot in the thigh and become quite uncomfortable.
13.3 - What is a Nose Lift, and is it necessary?
A nose lift is a unit that lets you and your passengers board the
Cozy with the nose wheel retracted (it is normal parking position), flip
a switch and the nose gear will extend, raising the nose to normal taxi
and take off position. Vance Atkinson designed a unit which was
published in the April 1995 Central
States Association Newsletter. (See
or contact Terry Schubert
for more information about the Central
States Association.) There is also a ready-to-install unit
available from Steve Wright
Remember a nose lift is purely optional, and it does add 8 or 10 pounds
to the weight of your airplane.
13.4 - Can I install landing lights in the nose instead of the
per plans location under the fuselage?
Absolutely. One method of doing this is shown by Marc Zeitlin in
his online builders log book at
Several builders have done this, with the general consensus being that
it looks "snarky". One brand of driving light that will fit this
installation is available from J C Whitney, part #13BD2224R.
Another is sold at Wal Mart (the egg shaped driving lights with THICK
If you choose to put landing lights in the nose, it will be
necessary to use a molded nose cone. You can use either Lexan or
Plexiglas for the lenses, with Plexiglas being somewhat easier to work
with (Lexan absorbs water and will need to be dried at about 150 deg F
for a day or else it will bubble). 1/16" to 1/8" material is
acceptable, it is heated to about 300 to 350 deg F and pressed over
the area on the nose cone where the lens will go to mold it to shape
(using material from an old T-shirt between the lens and nose cone to
keep the soft lens material from being scratched). For a more detailed
description see this topic discussed in the archives.
It is important to make sure that the pitot tube is plumbed such that
there is a continuous uphill slope back to the instrument panel. This is
important so as to avoid any tendency for water to collect in low spots.
13.6 - What is the proper layup schedule and geometry for NG30?
In newsletter number 86, Nat Puffer suggests a modification to the
geometry and layup schedule for NG30 in order to help prevent breaking
these pieces during a hard landing. This design change may be easy to
miss since it is located on the last page of the newsletter. The
modifications consist of both increasing the height of the low spot on
NG30 by 2 inches and augmenting the original layup schedule with two
additional plies of UNI (the verbiage says BID, but the drawing clearly
shows UNI, and the words in the image say "two ply UNI") two inches wide
on each side of each NG30. Radii of 1 inch should be applied as
indicated in the newsletter to reduce stress concentrations.
Chapter 14 - Center Section Spar [as of: 10 may 99]
[distiller: Wayne Hicks]
Comments and Tips
- When mounting and aligning the main spar, it helps to have the
canard installed as a reference. By closing one eye and sighting
with the other, you can visually sight over the canard, then lower
your head until each side of the spar just disappears behind the
canard. Even minor variations over the 12' distance are clearly
- When built to proper dimensions, the spar top and bottom will be
flush to the strake skins (Chapter 21) and will match to the wings.
If the spar is built too thick, you will have to use micro filler to
get the wings to match up. Some builders are suggesting that
reducing the height of the bump marked by Layup 6 in section C-C
(page 14-9) helps to keep the spar within dimensions.
- The aluminum inserts tend to slide around when you put weight on
them. They can be held in place with brads, which are removed from
the front side after cure.
Left in the Archives
14.1 - Is there a reason why Layup #1 goes after Layup #2?
There seems to be NO specific reason for the swap. Chapter 14, page
2, step 4 has layup #1 going after layup #2. You then do the remaining
layups in numerical sequence.
14.2 - What dimension should I use for CS1 and CS4
(Section A-A), 8.41" or 8.51"?
Most builders say to use 8.51" and Nat issued a newsletter change
14.3 - Is it okay to drill wire-routing holes into the CS5
and CS6 bulkheads?
The Cozy Classic plans call for up to a 1.5" hole for wiring. It is
better to make the holes prior to installation since access afterwards
is very limited.
14.4 - At what waterline (WL) should the spar be mounted?
Although not specifically called out in the chapter text, the
M-drawings show the top of the spar located at WL22, exactly 1" lower
than the top of the longerons (WL23).
14.5 - Is there a better technique for glassing the inside
- Make a "corner" pattern from cardboard.
- Wet out the plies that go around the corners onto plastic or
- Fold the plies around the cardboard as if you were gift-wrapping
the corners of a box.
- Position the cardboard into the spar so that the outward-facing
wetted cloth is against the bottom and in the correct orientation.
- Unfold the plies and press against the sides.
- You may have to cut some darts. If so, make the darts so that the
end faces and sides overlap at least 1" on the top.
14.6 - Why donít the thickness values given in Figure 11 agree
with the results obtained when multiplying the number of plies at
each of those locations by the 0.025Ē theoretical thickness per ply
of UND tape?
The number of plies given in Figure 11 is likely derived from the
design calculations, and based on the specifications of the UND tape
used at that time. However, the ďAPPROXĒ thickness values were
probably obtained from direct measurements of the prototype's actual
layup, and correspond to the checking templates on drawing M20.
Both the layup schedule and the thicknesses in Figure 11 should be
considered approximations. Since the specifications of the UND tape may
vary, the most important consideration is for the dimensions of the spar
cap trough to be correct (based on the spar cap checking templates), and
for the layup to completely fill the trough using good laminating
Chapter 18 - Canopy & Turtleback [as of: 10 may 99]
[distiller: Wayne Hicks]
Comments and Tips
- Do not cut the window holes in the turtleback until you have the
window panes in hand. That way you can just trace them and avoid
making the holes too big.
- When masking off the canopy, make sure to use tape with backing
adhesive compatible with the canopy. Do not use duct tape or masking
tape on the canopy. They leave a residue that is hard to remove.
- At altitude, the canopy may have a tendency to shrink, causing it
to lift up at the front and distort at the turtleback. Some builders
raise the instrument cover to ensure that the flexure does not allow
cold drafts in.
- Step 11 and Figure 45: Nat has issued a newsletter change to the
canopy cut line dimensions. The cut line between the removable
forward deck and the actual hinged part of the canopy should be at
4.5 inches aft of the instrument panel instead of the 5.5 inches as
shown in Figure 45. If you use 5.5 inches, the canopy latch wil not
match up to the hardpoint and catch on the canopy.
- Step 12: It is easy to overlook the fit of the canopy interior
frame related to the top of instrument panel. The frame will fit
fine until you glass frame interior. You will likely have to remove
additional foam from canopy frame to blend this area.
- Step 13:
- Do step 14 before step 13. Reduces probability of canopy
- Remember to do the 15-ply layups for the two handle pads.
- Buy three sheets of foam for turtleback fabrication. The two 24"
x 48" sheets of Clark foam are not enough. The Mark IV turtleback is
46" x 57" (max.). Each 6" x 48" strip has to be extended. As you
move to the narrow end the extensions become shorter. Bottom line:
buy three sheets.
- You will need .016" aluminum or shim stock to build the
turtleback jig. This is not in the parts list.
- To mark the match line for the glass in the turtleback form,
clamp a straight edge across the diagonal at the top of the form.
Use a level to mark the foam directly under the straight edge every
6" or so. Connect the dots to get your match line.
- The plans say to peel ply where the rib and drip trough go. You
are not told to mark the turtleback for these until the next step.
At least put a few marks in to give you an idea where to put the
peel ply before you glass. You can do the final (accurate) placement
Left in the Archives
- Canopy latch systems. (Al Wick has developed a new system based
on auto parts.)
- Forward opening canopies. (Uli Woelter (email address anyone?)
has forward-hinging canopy plans for sale.)
- Opinions on clear, green, and smoke-tinted canopies.
- Adapting non-approved or custom-built canopy bubbles.
- Buffing out scratches in canopies.
18.1 - What is a good method for installing the foam into the
In order make the foam conform to the compound curve, you need to
taper the forward side of each end of the 6" wide strips while leaving
the center at 6". Here is a neat way for doing that:
- Lay the foam strip in the form and place a weight over the center
to hold it steady.
- Overlap the foam onto the previous piece at the ends.
- Mark the overlap with a pencil.
- Take the foam out of the form and trim the overlap with a utility
- Place the foam back in the form, weight the center and use coarse
sandpaper to fit it against the previous piece.
- Once the foam is fitted, mark the wooden slats for the aluminum
- Take the foam out and install the aluminum strips.
- Replace the foam and continue with the next piece.
18.2 - How do I raise the canopy and what are the issues?
Many builders are raising the canopy to provide more head and
shoulder room. In general, there are two options. The first is to raise
the front end of the turtleback while maintaining the height of the
turtleback at the firewall. The second choice is to raise the turtleback
the same height at the front and the back. Obviously there are
combinations in between these two options. The key issue to resolve is
maintaining the clean lines from the nose, up over the canopy bubble,
across the turtleback and onto the cowl to the spinner. The Mark IV
turtleback was designed so that there is a slight break in the curvature
where it meets the engine cowling. Also, the is a slight break in
curvature where the bubble canopy meets the turtle back. The net result
is that if a 6'6" builder wants to have more head room, he just raises
the front end of the turtle back. This actually smooths out the
curvature where the bubble meets the turtleback and where the turtleback
meets the cowling. No reason for average size people to do this however.
18.3 - What kind of tape do I use on the canopy?
3M black electrical tape is likely your best bet. It will stick to
the acrylic canopy and leave no residue upon removal, even after a
couple of years. Do not use masking tape, duct tape, box sealing tape,
or risk the use of "off-brand" electrical tape. The residues from these
tapes actually bond to the acrylic and are very difficult to remove.
18.4 - What is the best tool for trimming the canopy bubble?
You want to use something that abrades the material quickly without
chipping or removing material too fast. One builder recommends a 2",
circular, composite trim-saw blade called a "TUF-GRIND". Also mentioned
is a Dremel tool with an abrasive ball or cutting wheel and a belt
sander. Avoid using a jigsaw as this may cause cracks to develop later.
DO NOT USE A DRILL BIT. Whatever tool you use, BE
CAREFUL, GO SLOW, AND USE LOTS OF PATIENCE
18.5 - What is the best way to remove Spraylat coating or tape
residue from the canopy?
There are commercial products
that are compatible with acrylics that can be used for removing tape
residue. Ensure that any product which touches the acrylic canopy is
compatible with acrylic. Kerosene or avgas can be used in a pinch. Do
not use alcohols, ammonia or glass cleaners as these will cause damage
to the canopy over time. Spraylat can be softened and removed easily by
applying one or two new coats, then peeling it off as directed.
18.6 - Can a Lancair 320 canopy bubble be used on the Cozy?
A few builders have opted for the Lancair 320 bubble because it is
rounder and wider in almost all dimensions when compared to the Cozy IV
bubble. You will need to make some modifications to the turtleback and
canopy frame, however. Other builders have had custom canopies made to
suit their requirements. Note: these are not an approved Cozy
modification. Check the archives for more details.
18.7 - Can I make my own side windows?
Yes. Once you have got the turtleback made, you can cut your
windows from 1/8" acrylic material, heat the windows on a cookie sheet
in the oven, and then drape-mold them over the turtleback or mold. Wear
gloves! We do not recommend performing this heating in a gas oven as the
acrylic may catch fire if it gets too close to the flames.
- Cover the turtleback with plastic tape for release and then make
a mold over it using cheese cloth and plaster of paris. Messy, but
it works. Mold should be at least 1/4" thick (6 layers of cheese
cloth minimum) 1/2" would not hurt.
- After the plaster dries, drill two small holes at opposite
diagonal corners through the turtleback and through the plaster for
- Remove the mold and cut out the window opening in the turtle
back. Do a nice neat job finishing the inside edges.
- Take the mold, the portion of the turtleback you cut out, and get
a piece of aluminum sheet to lay the plexiglass on while it is in
- Once the oven reaches 275 deg F, lay your plexiglass on the
aluminum sheet and insert into the oven for about 5 minutes. It will
curl up slightly and then lay back down. Remove it just before it
completely flattens again.
- Put on a pair of oven mittens and remove the plexiglass and
aluminum from the oven. Gently slide the plexiglass onto the mold
and then place the foam portion you removed from the window cut-out
over the plexiglass to hold in place while it cools. You will have a
glass/foam, plexiglass, plaster mold sandwich.
- After it cools, use the foam cutout and mark around it with a
magic marker. Use the holes in the plaster mold as a guide for
- Mark it again 1/2" wider than the foam cutout, trim to this line,
and voila', you have got a window!
- Trim the inside of the turtleback and remove the 1" strip of
fiberglass and foam where the window will go.
- Lay the plexiglass in the opening and mark it with a fine felt
tip marker. Use this as a final guide for placing the acrylic tape.
- Rough up the edges and place weights on the backside of the
window to hold it in place while the flox cures.
- Install the 1" strip and bid tape after the window has cured in
18.8 - Any advice for locating the window placement?
The following will give you the basic outline of the windows--you
will still need to check accuracy by laying the windows over the outline
to make sure that they are about 3/4" larger then the marked outline. If
things still look good, radius the corners of the outline and recheck to
make sure that the windows will fit properly. Do not cut anything unless
you already have the windows in hand.
- Measure up along the front curve of the turtleback and place
marks at 2-3/8" and 16-1/16".
- Measure up along the back curve of the turtleback and place marks
at 5-1/4" and 12-5/8".
- Run a piece of masking tape between the two upper marks and the
two lower marks. (This just makes it easier to draw the lines.)
- Remark the above dimensions and clamp a flexible straight edge (a
6' aluminum ruler works real well) between the bottom front and
bottom rear marks using spring clamps (or whatever). Draw a line
between the two points.
- Do the same thing for the top marks. These delineate the top and
bottom of the windows.
- Hook your tape measure to the leading edge of the turtleback at
the lower mark. Measure back and place marks at 5-3/16", 18-1/4",
24-13/16" and 38-7/16".
- Move to the top mark and measure back 5-3/16", 24-15/16", 31-1/4"
and 39-1/8". (Again, run a piece of masking tape between the marks
to aide in drawing the line.)
- Use a straight edge to connect the top and bottom sets of marks.
18.9 - Is there an alternative method to hold the rear windows in
contact with the turtleback outer skin during cure?
If you cannot manage the Cleco's, another solution is to clamp a 2"
x 4" the full length of the turtleback, then insert soft foam wedges
between the 2" x 4" and windows. Be aware that the windows do not always
have the same curvature as the turtleback, so you can expect some minor
flox filling. If this is unacceptable, you can shape the windows to the
exact curvature by heating them in your kitchen oven to about 150-270
deg F until soft. (See question/answer 18.7.)
18.10 - How can I make the canopy hardware accessible and
As called for in the plans, most of the nuts and bolts holding the
canopy hardware in place becomes inaccessible once buried under with
micro. You can provide accessibility for removal later by enlarging the
recesses in the glass and foam to install nut plates. Use long rivets
(not driven, just floxed into the holes) to secure the nut plates.
18.11 - Any good ideas on how to make the canopy water/wind
Most builders are using some form of weather stripping or pliable
gasket, while others are applying a bead of silicone. For the
turtleback, some builders have built up the drip rail with micro and
have closed off the ends of the drip rails with BID to direct the water
onto the side longerons.
18.12 - What is the best way to secure the canopy hinge pins in
There are three general methods:
The last idea has additional merit as a rescue feature: if the loops are
made big enough, a rescue squad could pull the pins out to release the
canopy -- although, so could thieves for that matter . . .
- Drill a hole in each end of the hinges (or hinge pins) and secure
with a small cotter pin or safety wire.
- Apply silicone into each end of the hinges
- Make a small loop in one end of the hinge pin and secure in place
with safety wire or a screw.
18.13 - What should I do if my canopy latch hardware does not
Because of the curvature in the longerons, the aluminum rods will
need to be bent slightly to align the rod ends with the threaded
fittings. Fit the straight tubing first, then determine where to place
the bends, and finally, gently bend the rod in increments over something
rounded (like the handle of a hammer) until you get the desired fit.
Remember: this is an iterative process and it requires patience to get
all the latch fingers to catch and secure the canopy equally.
18.14 - Is there an emergency egress system to unlatch the canopy
from the rear seats?
Many years ago a supplement was issued to the Long-EZ plans which
showed details of an alternate latching system with an emergency release
cable running to the rear seat. The supplements may still available from
Debbie Iwatate. Alternatively, consider that the turtleback bulkhead and
the head rests are wide enough for a small-to-average-sized adult to
wiggle through to access the canopy latch.
18.15 - What canopy gas strut do I need?
The archives mention lots of struts that will work and as many
methods and locations for mounting. Here is one set of part available
from NAPA (an automotive parts store):
|| Manu. P/N
|| NAPA P/N
| Gas spring
| Ball stud
|| Manu. P/N
|| NAPA P/N
| Gas spring
| Ball stud
18.16 - What is the preferred geometry for mounting the canopy
Again, beyond the plans dimensions, it is a builder's prerogative.
Keep these guidelines in mind:
- The gas strut puts pressure on the structure. So do not select a
strut that applies so much force that it breaks the structure.
Conversely, beef up the structure so that the strut will not cause a
- In the closed position, the strut should be pushing the bulkhead
away from the shell of the turtleback and away from the hinge.
- Lowering the head-rest pivot point reduces the force needed to
open the canopy, but lowering it too much means moving the canopy
mounting point further outboard to maintain the opening angle on the
18.17 - How do I make a one-piece cover for the instrument panel?
A lot of the builders are making the fuselage top as one piece
between F28 and the instrument panel. This allows complete
access to the instrument without removing the canard. Here is the
- Chapter 18, step 15:
- Do not use the 1/8" spacer as shown in Figure 63. Just place a
piece of tape instead.
- Chapter 18, step 16:
- Do not apply box sealing tape to F28. Apply it to
fuselage top instead. This makes the 4-ply angle piece permanently
attached to F28. You then have the option of installing
the 5 screws through the fuselage top instead of through F28.
Some people have chosen to eliminate most or all of the 5 fasteners.
- Chapter 18, step 17:
- Forget all the tabs on instrument cover. Just permanently attach
cover to fuse top.
Chapter 19 - Wings, Ailerons, & Wing Attach [as of: 10
[distiller: John Slade]
Comments and Tips
- Use a laser pointer to align the wing jigs. One builder offers
the following procedure: Use a 12 ft long straight board. Put lag
screws through each two feet along both edges and use them as
leveling screws. Bondo the screws to the floor. By adjusting the
height of the nuts you will be able to get the board exactly level.
Bondo the forms to this board and align with the laser pointer.
- Use a long tube with color water (a water level) for leveling
things. A hose pipe with fittings and a clear tube at each end works
- A piece of shower curtain rod cover tubing from Walmart or K-mart
works nicely for electrical conduit in the wing.
- If you want flush rudder belhorns, get plans for the Cozy MKIV
from AeroCad or for the Long-EZ by
sending $10 to:
Rutan Aircraft Factory
Mojave, California 93501
(THESE ARE NO LONGER AVAILABLE - RAF HAS SHUT DOWN!!!)
- Read the chapter 20 section of the FAQ
before starting this chapter.
- Sand a joggle in the wing foam to avoid a bump when adding the
Left in the Archives
- Drilling holes in completed wings
- Wing washout history
- What to do with a melted wing
- How to remove and install your wings by yourself (see message from
Bill Theeringer dated Tuesday, 23 June 1998)
- Lots of different tips and tricks for aligning and attaching
- Aileron end ribs
- Oxidation of A13
- Wing root shield
19.1 - Are the wing airfoils standard Eppler 1230?
No. They are modified.
19.2 - Is there a difference between the Cozy IV and Cozy III
Yes. The buttline locations are different and the Cozy IV wings are
19.3 - What material should I use to build the wing jigs?
Build the wing forms out of 5/8" or larger plywood. Anything less
is too weak.
19.4 - Why is there a kink in my trailing edge at BL 67.5?
Do not worry. It is supposed to be there. Simplest thing to do is
leave it there. Some say it is cosmetic only, is a carry over from the
Long-EZ cowling shape and is not necessary on the MkIV. AeroCad
have removed this kink in their prefab cores and wings. It would be
quite hard to remove it manually by redesigning the jigs. If you do
remove this kink and make a straight trailing edge, then your cowling
wont fit properly unless you get it from AeroCad. AeroCad cowlings fit
either wing type.
19.5 - What shape should my wingtips be?
The area where the strobe and position lights attach obviously has
to be flat because the base of the light fixture is flat. The area of
the wing tip forward of the light fixture is aesthetic. Any shape
(within reason) will do. It is up to individual taste.
19.6 - Is the sheer web cut supposed to be 90 degrees to the
19.7 - What is the technique for cutting out the spar caps?
Yes. When cutting the wing cores, use mixing sticks (with 2 nail
holes) to temporarily continue straight over the spar cap troughs. Then
remove the sticks and cut out the troughs as a separate operation.
Presto no wire lag problems, nice neat corners.
19.8 - Is my chord length going to be wrong when I glue the
leading edges back on?
No. Plans dimensions allow for this.
19.9 - What about covers for the wing attach bolt access holes?
Before glassing the wings, sand a slight depression around the
attach holes to accommodate a 5 BID cap with a shoulder. Make two caps
for each wing and cure in place. Drill [not through the spar cap] a hole
between the two holes and use a soda straw to allow moisture to drain.
Drill a small drain hole in the lower cover. Glass a small aluminum
plate with a nut plate attached to the top cover. Connect the two covers
and hold them in place with a long bolt from the lower cap to the upper
cap. An alternative to the bolt is a spring in a tube which attaches to
hooks on inside face of each cover. Use micro to form a smooth
transition from the wing surface to the cover.
19.10 - How do I ensure a straight trailing edge when adding the
Use a long aluminum extrusion to keep the trailing edge straight.
Home Depot sell these for screen enclosures. AeroCad
supplies an aluminum T-bar with their wing cores for this purpose. Mask
most of the extrusion with plastic shipping tape and leave a strip of
aluminum exposed. Glue this strip to the bottom skin trailing edge. Use
weights and clamps to get the trailing edge straight against the
extrusion. Once the top skin is cured, use a very thin putty knife to
pop the extrusion from the bottom of the wing.
19.11 - Is there an easy way to get the 1-inch wide peel ply
Use a razor knife to score the foam at the forward edge of the peel
ply. This way, when you pull up the peel ply, the foam will break off
evenly. Use pliers to pull up the peel ply. Do not leave it on for more
than a few weeks.
19.12 - Why is the aileron cut-out parallel to the center line?
KISS. It is much simpler to make it that way and it looks fine when
finished. Some builders have changed this, and the cuts end up being
canted. However, if you do not get it just right, you will restrict and
/ or bind the ailerons.
19.13 - How do I ensure straight cuts when cutting the ailerons
Bondo a straight edge to guide the cut, then use a strong razor
knife or hacksaw blade held almost level with the surface.
19.14 - Should I make my Ailerons longer than plans?
Apparently Dick Rutan and the Berkut both extended the standard
ailerons as well as AeroCad whose
ailerons are 6 inches longer than the Cozy. Jeff Russell says that this
results in a noticeably faster roll rate. Longer ailerons are NOT
recommended by Co-Z Development. It is your choice. If you do extend the
ailerons, and also plan to install hidden belhorns, be aware that the
rudder conduit goes very close to the tip of the aileron.
19.15 - How can I remove epoxy that snuck into my hinges?
Try using a soldering iron on the offending hinge. You should get
enough heat to burn the epoxy around the pin without damaging the
19.16 - Does it matter that my cores are not completely straight
along the aileron and rudder hinge lines?
Yes. If the hinge line is bent the hinges will bind. Fix this
before skinning the core.
19.17 - Do the plans hinges wear too much?
Some think they do, especially if your hinge lines are not
perfectly straight. Get the teflon hinge kit by sending $27 ($32
851 S.W. 63rd. Ave
North Lauderdale, FL 33068
or Email email@example.com.
19.18 - Should I worry about the clearance on the ailerons?
Absolutely. Be very careful about this. The October 1999 Central
States Newsletter carries a story about an EZ driver who had his
ailerons lock up with full deflection during high speed maneuvers. G
forces cleared the problem. On landing, marks were seen which indicated
that the aileron had caught on under the bottom wing skin. The aileron
clearance is critical full span.
19.19 - Does anyone have a neat way to attach the aileron hinges?
Yes. Everyone does. The plans do not tell you how to make the
aileron side of the hinge come into contact with the aileron while the
bondo cures. Everyone seems to have a different trick for this. The
favorite seems to be wedging something under the hinge. Stiff earplugs
or foam are suggested. One builder said that he used bondo on the
visible / accessible edge of the aileron side of the hinge and it held
19.20 - Does it matter if the clearances between the aileron and
the wing are different for the left and right sides?
Yes. This can produce a roll tendency. Builders have used gap
sealing tape to demonstrate this.
19.21 - What should I do about the wing root area?
Carve out the root area a little deeper then you think necessary in
the area around the aileron torque tube (the plans call for depressions
but it is unclear how deep to make them). Test the hardware in the area
before laying up the glass.
19.22 - Is there a better alternative to the plans phenolic
bearing in the wing root?
Yes. Many builders are using a spherical teflon, UHMW (ultra-high
molecular weight polyethylene) or Delrin bearing here. Typical solutions
include a kit from Infinity
Aerospace, and another from AeroCad.
Numerous bearing manufacturers are suggested by builders in the archives
including a Spherical Bearing part no. COM-10 made by
FK Bearings Inc.
11 DePaola Dr.
Southington CT 06489
phone: (800) 662-06489. One builder got his from a local distributor:
Allied Bearings & Supply at (615) 255-1204. Cost was ~$10 each.
19.23 - How important is the weight of the aileron?
Very! Stay within plans guidelines for weight and balance of
ailerons. Do not increase the weight of the mass balance rod to
compensate. If your ailerons will not balance per plans, scrap them and
build new ones. Use minimal filler and primer on the ailerons during
19.24 - How should I fill my spar caps to match the contour?
Use additional roving threads as needed. Use strips of UNI to fill
any dips. Do NOT fill with micro because you need a glass to glass bond
between the spar cap and the skin.
19.25 - What if I cannot get the last layer of material in the
This is typically ok, as long as you double checked your spar cap
depths before starting. Use the tolerances given in the plans.
19.26 - Can I use micro to bring the spar cap up to contour?
Absolutely not, NO. The cap to skin bond is fundamental to the wing
19.27 - Why does my spar cap dip at BL 67.5?
It is supposed to be there. (See FAQ 19.3.)
19.28 - What is the best method for drilling the wing attach
The archives are full of discussion on this issue. Consensus is
that the plans recommended spot face tool is not adequate for the job.
It takes a Loooong time, gets very hot, and dulls quickly. In addition,
the excess heat can damage the structure. Various cooling methods are
offered including water. One builder even went through a couple of
spotfacers before trying a different method. Many suggest using a hole
boring tool such as the Morse #TAIO-5/8" high speed hole saw. Use a 1/4"
pilot hole and a long 1/4" pilot bit. Be careful to ensure the hole is
concentric with the pilot hole. If the holes come out a little large (as
much as 0.007" over) RAF say its ok to fill them with flox and cure
while the wing is bolted to the spar. Nat does not like this approach. A
popular method is to grind or use light taps with a hammer to make the
hole cutting tool bore the correct (smaller) size. Another option is to
manufacture LWA9 bushings which will fit the hole resulting
from your boring tool. Others bore undersize and ream the hole to fit
the bushings. One solution was to drill a pilot hole, then expand the
hole with a drill bit on slow speed, then finish off with the spotface
tool just before the drill bit breaks through.
19.29 - What if I drilled my pilot hole in the wrong place?
Plug the hole with flox and drill a new pilot hole. If the final
5/8" hole encompasses the plug then you are fine. If it does not you are
talking with Nat.
19.30 - Does the spacing between the wing incidence bolts matter?
Yes. DO NOT DECREASE this spacing from that specified in the plans.
19.31 - What is the most critical part of wing attachment?
Getting the relative incidence between wings and canard correct.
19.32 - Can I avoid routing the antenna coax along the foam
Yes. One builder describes how to drill the winglet about 1 inch
from the leading edge, then feed the coax through the hole. A second
hole is drilled from the balun area to intersect the first hole and the
coax is snagged with stiff steel wire. In the case of a NAV antenna in
the wing a hole is drilled from the balun to the electrical conduit.
19.33 - Should I add a fourth attachment bolt to eliminate wing
Wing float (movement of the wing relative to the strake during
flight) occurs. It is part of Burt's (and Nat's) design. Do not worry
about it and do not add an additional bolt. (See 21.3
for more discussion.)
19.34 - Can I make rudder belhorns which do not stick out?
Yes. This is the "internal rudder belhorn" modification. See comments
and tips section of this chapter.
19.35 - What are the "V"-shaped layups over the wing attach
The "V"-shaped layup over the wing attach points are reinforcements
to help collect the load and transfer it to the center spar. In Chap.
19, p.6, Fig. 32 the 2" wide layup across the corner is at a point of
stress concentration, and your paint might crack there if you leave it
out. The 12" layup in the valley is where the maximum bending and drag
(pushing backwards) loads are. The drag loads are compressive loads
which tend to buckle the skin. A little extra skin thickness at this
point provides an extra safety factor when exceeding Vne.
19.36 - Can I make my position lights flush?
Yes, provided you do not cut into the UNI and BID cloth that
attaches the winglet to the wing. JD at Infinity
Aerospace may be able to put you in touch with a builder who makes
airfoil shaped lens that covers the entire nav-strobe-tail light
19.37 - How can I construct wing tiedowns?
One builder used small hole/tubes behind the wing spar about 16"
inboard of the winglets. He inserts I-bolts, washers and nuts that go
through the tube and then reach a standard width tiedown. Also carry
rope and "twist-in" tiedowns. Robin du Bois produced some drawings for a
simple tiedown which are available from http://www.cozybuilders.org/.
19.38 - What is the best way to store my wings so they will not
Out of the sun and away from heat. Support them leading edge down
with pads or straps. Others make an airfoil shaped jig lined with carpet
and store the wings vertically, leading edge down. Keep them away from
high temperatures and temperature fluctuations. You will need less space
if you do not attach the winglets. Webbing used to repair lawn chairs
seems to be a popular material for supporting the leading edges.
Chapter 20 - Winglets and Rudders [as of: 29 mar 2010]
[distiller: John Slade]
Comments and Tips
- When positioning the lower winglet: attach the lower winglet to
the upper winglet prior to mounting. Notch-out the lower piece and,
after the upper winglet is mounted, reattached the lower piece that
was cut out. This creates a perfect alignment of the upper and lower
- In order to make the winglet tips, some builders cut the winglet
cores overlength, then sand the styrofoam rather than adding the
urethane tip later.
Left in the Archives
- 1/8 inch rudder cables
- Rudder cables of Canadian Cozy's Eppler 1230 Airfoil
20.1 - Can I leave the lower winglets off?
No, absolutely not. In the aft CG / deep stall testing that Nat
performed, it was discovered that the lower winglets add considerably to
stability; and he strongly cautioned builders to retain them.
20.2 - Can I do the rudder cutouts before attaching the winglets?
No. The rudder includes part of the lower winglet. You need the
winglets attached to get the correct cut.
20.3 - Why is there not a mass balance on the rudder?
No. Rudder mass balance is not needed if your return springs and
stops are properly installed.
20.4 - How long should I make my COM antenna cable from the
Most builders run the cable to be a few more feet longer than the
wing. Then they use a BNC splice within the fuselage and add cable as
necessary to reach the radio stack.
20.5 - Could someone explain how the 8.5" by 3.5" cutout applies
in Chapter 20?
The upper right hand corner of chapter 20, page 1 shows the foam
block cores for both the "Upper" and "Lower" winglets. The lower part of
the pictures is showing the "Lower" winglet. The 8.5" dimension is the
height of the lower winglet. The 3.5" dimensions is showing you how to
cut the blocks so that you get the "aft" sweep of the lower winglet as
you go from WL 18.4 downward, i.e., the lower winglet sweeps back as it
goes down. Remember the upper and lower winglets are cut out separately
and microed together later.
20.6 - Is there an error in the plans winglet templates?
Yes. The labeling of left and right is reversed. Just make sure the
camber is correct and the fishtails line up and you will be fine.
20.7 - Should I make my rudders wider or full span?
One builder says yes, the rest say no--definitely not.
20.8 - Where should I put the drain holes in my winglets?
Drill a small (1/16" to 1/8") hole on the inside bottom winglet at
the lowest point when the airplane is parked nose down. This is to keep
water out of the pocket you made for the belhorn. Also drill similar
holes in the nose on each side of NG-30 so if water gets in
the nose it will also drain.
20.9 - What if my rudder has a kink in it?
This is expected. Nat says,
because of the airfoils and the different chord lengths, you
cannot have both the outside surfaces in the same plane and the
trailing edge straight.
When asked which way is preferred, a bent TE or a canted winglet, the
answer given was, "bent trailing edge."
20.10 - Is there an error on the trailing edge dimensions on Page
1, Figure 1?
Yes. The foam block layout diagram shows 47" for the trailing edge,
but the larger detailed drawing on the same page gives 48" for the same
dimension (40" rudder, plus 9" above rudder, minus 1" urethane foam
cap). To correct it, one can change the 47" to 48" on the foam block
layout, or change 40" to 39" on the rudder. According to the mailing
list archives, Nat Puffer felt that the 1" error made no practical
Chapter 21 - Strakes [as of: 15 sep 01]
[distiller: Wayne Hicks]
Comments and Tips
- If at all possible, attach the wings when building the strakes to
assure a perfect match. If space will not allow it, cut out a
quarter-inch plywood panel in the shape of the wing's profile and
bondo or glue it onto the outboard end of the spar.
- The top and bottom strake skins are identical except that the top
is 0.2 inches longer along the R33 and R57
ribs. Use one to make the other.
- Make sure the landing gear and jig tables are blocked off to give
the strakes a solid foundation.
- Install release tape along the aft edge and fuselage side of the
table before bondoing the table in place.
- Reference lines drawn onto the jig table are a tremendous help
when installing the R33 and R57 ribs. The BL33
and BL55 stations can best be determined by extending a
straight-edge across the longerons at the instrument panel and
measuring outward 33 and 57 inches respectively.
- At a minimum, peel-ply all inside skins for 2 inches on either
side (4 inches total) of where the ribs and bulkheads will contact
the skins. This will significantly reduce the amount of prep sanding
required for subsequent BID taping. It is a very good idea to
judiciously peel ply the entire inner strake surfaces with each
epoxy coating. This will eliminate pin holes and significantly
reduce chances of leaks.
- The BL dimensions are to the Inside face of the
bulkhead. Carve the outside (farthest from the fuselage) to get the
contours of the bulkheads to match the sweep of the strake. Do not
carve the inside edges.
- Run a string from the 17.4-inch water mark on the wing (or spar
template) to the 17.4-inch mark at the FS60 location on
the fuselage side. Use as a guide to set the leading edge bulkheads
straight and level.
- The 1-inch spacing is fine for scoring the bottom foam to bend
around the bulkheads. One-half inch cuts are better for scoring the
top foam. The smaller spacing minimizes the flat spots that occur on
the top of the curved part of the strake between the two bulkheads.
- Small, 5-inch kitchen colander strainers make ideal screens for
the holes to the fuel sumps. Buy these colanders from any kitchen
store. Simply cut off the handle and flox the rim into place.
- Fully trim the fuselage strake openings before putting the top on
permanently so that you can repeatedly match up the top skin to the
same place on the fuselage.
- The rib flange or "T-hat" method of attaching the top strake skin
to the ribs is highly recommended. (Description of process is
- It is a ton of work to tape all inside edges after floxing the top
skin to the bulkheads. But try to do all taping in the same session
to save yourself from having to prep sand while upside down in the
back of your airplane.
- Process for Constructing Rib Flanges (a.k.a, the "T-Hat Method")
This process involves installing BID flanges onto the top of the
ribs and bulkheads. Although there are no reported issues with the
plans method, builders feel this process increases the surface
contact area for adhering the top strake skins to the ribs, and it
also reduces the chances for leaks. Be forewarned, this method
does add several cure cycles and several days to the strake
- Make sure all ribs and bulkheads are trimmed to closely match
the inside strake skins.
- Place the top skin on the strake. Use a felt marker to draw a
line where the ribs and bulkheads contact the upper skin.
- Apply 2 pieces of 2-inch wide duct tape along each side of the
mark on the inside skin.
- Make up some 2-inch wide, 2-ply BID tapes and peel-ply one
side of the BID tapes. (Some builders prefer 1-ply BID tapes.)
Apply the tapes onto the top inside strake skin, centered on the
line with the peel-plied side touching the inside strake skin.
You only need to do this for the interior fuel tank edges. Do
not extend the flanges into the storage area since you will be
taping these areas like normal.
- Do not put any peel ply between the BID tapes
and where those tapes will contact the ribs and bulkheads!
- Apply micro to the top of each rib. (Yes, the plans say
"flox", but that comes later. In this step, the micro is used
like foam to merely fill in any gaps between the top strake skin
and the ribs/bulkheads.)
- Install the upper strake skin in place, weight it down, and
let it cure. The BID tapes will permanently bond to the ribs and
bulkheads in an exact fit to the strake skins.
- After cure, pop the top strake skin off. Remove the excess
micro from under the "T-Hats"(flanges) tape at the top of the
rib. Radius the micro and prep sand the underside of the tape
and the top of the rib sides.
- Tape the flanges to the ribs and bulkheads by applying a 1-ply
BID tape (2 inches wide) on the underside of the flange onto the
top sides of each rib and bulkhead. Let cure.
- Remove any peel-ply from the tops of the flanges and prep
sand. Remove all duct tape from the inside strake skin and
prep-sand. Apply a heavy coat of epoxy to the inside strake skin
and wait for the epoxy to reach the slightly tacky state.
- Apply wet flox to the tops of the flanges, put the upper skin
in place, and weight it down heavily to ensure a good flox
squeeze. Scrape away excess flox from accessible areas.
Left in the Archives
21.1 - Do I need to treat the exposed foam in the cut-outs
through the bulkheads?
Technically, no. The bulkhead foam is impervious to aviation fuel
and does not allow the fuel to permeate through the foam. Some builders
suggest smearing a thin layer of micro or flox to keep any foam flecks
for getting into your fuel strainer and system.
21.2 - Why can I not use the area between the TTE bulkhead and
the spar for fuel instead of pour-foam?
At 6 lbs/gallon, the fuel weight in that area would greatly limit
the aft CG envelope for the plane, possibly resulting in main wing
stall. A Velocity pilot did not follow this advise and ended his flying
career in with an inverted flat spin. If you think you ever need more
fuel for longer range, install an auxiliary tank in the back seat.
21.3 - Do I need a 4th Wing Attachment point between the strake
and wing leading edge?
No! There is no technical or structural reason for doing this. The
center spar/strake combination results in a structure so stiff that the
wings do not twist at flight loads. As for the history of this question,
some German aviation authorities made a political decision to require
Long EZ builders to put a 4th attachment point where the wing leading
edge meets the strake. Burt Rutan adamantly objected to the change. Cozy
Classics built in Germany had to adopt the 4th attachment point too.
(See 19.33 for more discussion.)
21.4 - What will I need to do differently if I am using the
Featherlite Leading Edge Kit?
The kit's leading edges eliminate the need for the leading edge
baffles (TLE and BLE). They also wrap several
inches back onto the R33 and R57 ribs, so you
will need to modify the noses of your ribs slightly and shorten the top
and bottom strake skins per the kit's installation instructions. If you
plan to use the leading edge kit, order them and have them delivered
before starting on the strakes.
21.5 - What epoxy is best for sealing the fuel strakes?
Safe-T-Poxy is generally considered the best to use, but in
general, all of the approved laminating epoxies are okay to use too. Do
not use commercially-available sealing agents as some are not compatible
with some epoxies and can flake off and clog your fuel system with
21.6 - How do I get a good seal inside the strakes and ensure
coverage of pin holes?
Follow the plans and use generous amounts of epoxy. What you are
shooting for is a tank with a nice, clear, pure epoxy lining. Work the
epoxy with a squeegee or brush focusing on getting good coverage along
all joints, fuselage sides, center section spar, end rib, vents drains,
and caps. Some builders wait for the epoxy to become tacky before
applying the next coat. Cover with peel ply or plastic, and verify no
air bubbles exist.
21.7 - What are the pros and cons of installing strake windows?
Opinions vary. General consensus is strake windows are nice for
backseat passengers, but useless for frontseaters. The windows tend to
get scratched up too over time from items stored in the strakes. If you
choose to use strake windows, do not make then too large. You must
maintain the structural integrity of the bottom strake skin. See
archives for suggested window dimensions.
21.8 - How does one get remarkably straight and narrow seams
between the wings and strake junctions?
The general procedure is the glass over the existing joint with a
2-BID tape. After cure, bondo a straight-edge lined up with the center
of the joint, then use a razor saw or hacksaw blade to cut the joint
21.9 - Why is the fuel valve on the seatback?
The Cozy's seatback location eliminates some of the fuel lines
running through the cabin but retains the ability for the pilot to place
the hand directly on the valve, see the position, and feel the detents.
Earlier Vari-EZ's and Long-EZ's have reported problems with
remotely-located valves operated by cables or torque tubes. Rutan
Aircraft Factory eventually issued a change order to instruct builders
to place the valve within eyeball's reach.
21.10 - Which fuel valve should I buy?
There are many choices, but whatever you buy stay away from an
Imperial valve!! The Imperial valve has a brass body and a tapered plug
that eventually sticks and jams. Not good! The Cozy plans recommend the
Weatherhead valve, which has a delrin spool inside a brass body that
eliminated the sticking problems.
21.11 - If I am installing a fuel injected engine, do I need a
fuel return line and a two-channel fuel valve?
Most Lycoming IO-360's and converted O-360's do not require a
return line for returning high pressure fuel back to the fuel tanks.
Check with your authorized Lycoming representative to be sure. Some
builders are installing fuel recirculation systems to avoid problems
with hot-starting. These systems consist of a fuel relief valve and
return line. Prior to starting, the pilot opens the relief valve
upstream of the fuel distribution spider, turns on the electric fuel
pump, and pushes cool fuel through the fuel system and back to the tank,
thereby purging any hot or vaporized fuel.
21.12 - Do I really need to run the fuel vent lines to the top of
the firewall and then back down underneath the strakes?
Yes! This greatly reduces the risk of fuel draining out if the
plane tips over in a crash. It also reduces the risk of the lines
picking up rain and freezing in flight.
21.13 - Why do I hear double vent lines mentioned occasionally
and why should I install them in my strakes?
Although there has never been an official change to the plans, most
builders are installing two vent lines per strake. The purpose of the
second vent line is to provide venting at the highest strake position
when the plane in parked on its nose, and for redundancy should the
other vent become clogged. The first is installed as per plans and the
second is installed against the fuselage just forward of the spar. Both
lines exit the strakes in the plans location and are run to the top of
the firewall and back below the strakes.
21.14 - Do I really need fuel probes and gages in addition to the
It is builder preference. Some pilots do not like having to look
over their shoulders at the site glasses. Also, the site glasses can be
obscured when luggage is piled into the rear seats. Some pilots find
that fuel gages on the panel help remind them to stay vigilant about
21.15 - What fuel caps should I buy?
Aircraft Spruce and Wicks both stock good fuel caps, including some
very fine lockable fuel caps made by Newton (an English company). The
Brock caps have a reputation of leaking fuel while flying and leaking
water when parked.
21.16 - Do I need to secure my fuel caps so that they never go
through the propeller?
The fuel cap location of the Cozy IV is outside of the prop arc, so
no changes are necessary. Still, it is a good idea to use an anchor
chain to keep from losing the cap if it inadvertently opens in flight.
21.17 - Any tricks for installing the fuel caps?
The easiest way is to install the filler spouts before putting the
top strake skins on. This is out of sequence with the plans and it might
complicate leak checking, but it certainly minimizes debris into the
tank. Alternately, some builders flip the plane over (top side down),
carefully cut away the outside skin and scrape away the foam on the top
strake, pressurize the tanks slightly, then drill the hole for the
filler spouts. Some builders avoid creating debris by cutting through
the top skin with a heated knife.
21.18 - What is the best way to vacuum debris out of the strakes?
Most tank contamination occurs when drilling the holes in the top
strake skins for the filler caps. If you just poke your shop vacuum hose
in the tank, the air that gets sucked out gets replaced by air rushing
into the tank. The air rushing into the tank will disperse the debris
away from the vacuum hose and deposit it throughout the tank, leaving
you with the mistaken impression that the debris has been vacuumed up.
This is why the plans say to duct tape a small diameter hose (vinyl
tubing) to the end of the shop vac to reduce the quantity of air and the
resultant small tornado inside the tank. Do not put a
rag around the vacuum hose to seal off the tank opening---implosion is
just as lethal to your tank as explosion.
21.19 - How do I troubleshoot leaks?
The first and foremost trouble-shooting step is to check that your
testing equipment, hoses, and connections are not leaking! After trying
the plans methods, try spraying soapy water on the joins. Leaks will
make bubbles. Next try filling the tanks with water. If you still cannot
find the leaks, get your friendly neighborhood air conditioning repair
man to fill the tanks with freon or halogen, then use his sniff detector
to pin-point the leaks (no pun intended). When s/he finds the leaks for
you, mark the spots, attach an altimeter to the tank, pull 1500' of
vacuum on the tank, and dab on drops of pure epoxy on the spots
identified as leakers. You can actually see the epoxy get sucked into
the holes. Whatever you do, do not inflate the tanks
more than a few psi as recommended in the plans. A ruptured tank will
ruin your whole day. It is also a good idea to leak check your tanks
again after 40&NBSP;hours, certainly by 100&NBSP;hours, and
during annuals to see if anything has changed.
21.20 - What are the pros and cons of connecting tanks and sumps?
Folks loyal to separate fuel tanks proclaim advantages in isolating
one tank from the other in case of a lost fuel cap, tank rupture, or
contamination. Folks loyal to common fuel systems proclaim ease of fuel
management. Common sumps do introduce more fuel into the cockpit and can
complicate fuel plumbing. Of course, the separate fuel system is the
only approach recommended by the Designer. If you are partial to common
fuel systems, Vance Atkinson's common fuel sump plans are presented in
the January 1993 edition of the Central States Association newsletter.
or contact Terry Schubert
for more information about the Central
21.21 - What are the issues with fueling, static electricity, and
grounding the airframe?
The issue is with build-up of static electricity on the strake skin
surfaces which subsequently discharges and ignites fuel vapors. Static
charge is generated at the filler neck by the movement of the fuel
through the nozzle into the tank, just like rubbing your shoes on a
carpet in low humidity. On a metal airplane this charge is dissipated by
the frame to the grounding clamp. Our plastic planes are non-conductive,
so the charge has nowhere to go. Fuel is non-conductive too, so dangling
a chain or wire into the fuel will not help. Best procedures seem to be
to wipe the strakes with a damp towel to dissipate static build-up,
touch the fueling nozzle to the fuel cap before removing the cap,
provide some method of grounding the fueling receptacle, and never
refuel from a plastic container. Sport Aviation addresses this subject
in the December 1998 issue, page 55. Reference NFPA 407, Standard for
Aircraft Fuel Servicing, for more detailed discussions.
21.22 - Should I seal the AN fittings?
The late, great Tony Bingelis, author of such notable homebuilder
bibles as "Firewall Forward" and "Engines", cautions against
using Teflon tape. Teflon tape has the chance of flaking off into small
pieces, which is not good for the fuel system. Wicks and others sell a
product call Fuelube for this purpose. The stuff is expensive and comes
in very large quantities. You might check with your local EAA chapter or
FBO to get the small quantity actually needed.
Topic - Hotwiring [as of: 10 oct 99]
[distiller: John Slade]
Comments and Tips
Left in the Archives
- [only material from chapters 19 and 20 were used]
HW.1 - Can / should I borrow someone else's templates?
Some builders have cut metal templates using great precision and
are prepared to lend them out for the cost of shipping. Ask in the mail
list. Beware when borrowing other people's templates. Before using them,
compare them to the plans looking for shrinkage and correct alignment of
HW.2 - What material should I use to make the templates?
Formica or Aluminum. Aluminum is best but Formica is easier to
shape and smooth. Be sure to remove all irregularities along the
template edge. Even the smallest bump can hang the wire and give you a
nasty jiggle in the foam. Cut all the templates at once. It is boring
work, but in the long run it will minimize effort.
HW.3 - Can I photocopy the templates?
Yes. But be very careful to ensure that you get accurate copies.
Many copies will give you significant error over the width of a large
template. Use tick marks in the corners to verify overall dimensions
before using copies.
HW.4 - Why are my templates a different size to someone else's?
Paper shrinks and expands according to moisture content. Thus you
can cause distortion if you use the wrong adhesive such as a water-based
contact adhesive. Most people use 3M spray-on contact adhesive (#77).
HW.5 - How accurate do I need to be when cutting my templates?
Some builders ask whether to trim to the OUTSIDE or INSIDE of the
line. Others complain about the lines not meeting correctly when joining
parts of the template. The answer is to be as accurate as you can be.
Try to leave some of the line showing to confirm your accuracy. If the
lines do not match, average the error. Be sure the level lines are
straight. If you consider all the various lay-ups and filler that will
later be applied then the thickness of the line is negligible. Just be
HW.6 - Should I make or use a set of oversize templates?
The consensus seems to be about 50 - 50. Many builders swear by
this method, especially for the winglets where the template sizes are so
different. They hot wire anywhere from 1/16" to 3/16" oversize, then
spline sand to contour using the plans-size templates to guide a long
sanding block. This gets rid of any wire burn caused when the wire has
to go fast at one end and slow at the other. Spline sanding alone is
difficult. Use two people and use the talking numbers on the templates
while sanding. Those preferring the plans method argue that the oversize
method is less accurate, especially when "sanding to the numbers". If
the part moves or bends while you are sanding you will have valleys. Nay
sayers also claim that the majority of planes are built using the plans
method, they all fly fine and perfect cores, even if attainable, are not
going to change flying characteristics.
HW.7 - Can I plot the airfoil shapes digitally and produce a
perfect set of templates.
You probably can, but provided your work is reasonably accurate
using the plans methods will not create an airplane which "corkscrews
through the air". The majority of airplanes built with care fly
straight. It depends on how much of a perfectionist you are and how much
you want to get finished. You may be able to find CAD drawings on the
unofficial Cozy web site.
HW.8 - Should I cut my cores myself, or buy precut cores?
There are pages of discussion on this issue in the archives, much
of which predated formal approval of many AeroCad
prefab parts by Co-Z Development. Some builders say that hot wiring is
easy and fun, others are concerned that the results by a first time
builder are often less than perfect. Consensus seems to be that expertly
prefabricated parts are well worth the cost and will save you a lot of
time. Options such as molded spars and pre-skinned parts are available
and are highly recommended by those who have used them.
HW.9 - How do I get perfect cores?
It is not possible, and you do not have to. Just be as accurate as
you can and gently spline sand the wings before glassing. Small errors
will be hidden by the micro and glass added later. Most seem to manage
fine, but you CAN buy professionally precut cores from Featherlite or AeroCad
if you are really concerned about you are hot wiring abilities.
HW.10 - Does it matter how I pile the blocks?
Follow the plans. Be extra careful about the dimensions used to set
the planform angles. Try to keep any seams as far away from the edges as
possible and at right angles to the cut.
HW.11 - Should I sand the cores?
Yes. Gently sand the wing smooth before laying up the glass. This
will save significant time in finishing.
HW.12 - How much should I worry about the accuracy of my cores?
Do not stop "fussing" with them until they appear perfect. Most of
the bumps and dips can be avoided by not rushing this step. After all
the cores are assembled and out of the forms, sight down the span with a
flashlight (turn out the lights in the shop). You will see the shadows
(low spots) and you can gently sand the bare foam down with a 5 ft.
sanding block 4 inches wide to get near perfect contours before you
lay-up the glass. If the bare foam is straight and true so that the
entire part, when glassed, will be straight. The extra time on the front
end will save a lot of time during the finishing process.
Topic - Epoxy / Solvent Safety Issues [as of: 02 jan 09]
[distiller: Rob Nachtreib]
Comments and Tips
Left in the Archives
- [many discussions of gloves, respirators, allergy sensitivities]
CS.1 - Are epoxies and solvents dangerous?
In general, yes. Each material has a Material Safety Data Sheet
(MSDS) which rates the Health hazard, flamability hazard, and reactivity
hazard. Many MSDS have been collected at:
Hazard ratings are summarized here, on a scale of 0-4, defined as
Severe (4), Serious (3), moderate (2), slight (1), minimal (0).
Hazard Hardner Resin MEK Denatured Alcohol
------------ ------- ----- --- -----------------
Health 3-4 1 2 1
Flamability 1-2 1 3 3
Reactivity 0 0 1 0
You should read the MSDS for your particular hardener, resin, and
Maybe. Allergic reactions are unique to each individual. For a given
person, development of an allergic reaction seems to be a function of
cumulative exposure (critical dose). There's no way to predict the
critical dose to become sensitized But, once you sensitized, you are
Two people can have very different critical dose, up to and
including practically unlimited exposure (i.e. - bare skin touching
Your reaction to one allergen has little value in predicting your
reaction (if any) to another.
To be sure, limit your exposure to <particular>.
Severely limit your exposure to <particular>. That means gloves
and respiratory protection. If an alternative to <particular>
exists, you might try that, but you should probably limit your exposure
to the alternative, too.
It depends on what material you're working with. Check the MSDS.
The MSDS usually say something to the effect "wear gloves impervious
to this material." Some MSDS actually say what glove material is
impervious. The MSDS for MGS 335 Hardener says Butyl or Nitrile. The
MSDS for Aeropoxy Hardener says neoprene or "rubber". An MSDS for MEK
(there are several) says butyl gloves.
You might need multiple kinds of gloves.
Don't just buy any old gloves from the paint department at Home
Depot and think you'll be safe. MEK can dissolve some disposable vinyl
It depends on what material you're working with, and the concentration.
Check the MSDS.
The MSDS usually say something to the effect, "use only with
adequate ventilation, avoid breathing of vapor or spray mist." Many
MSDS will give air concentration limits.
The MSDS for EZ-Poxy hardener says "if airborne concentrations of
MDA is less than or equal to 10 times the [personal exposure limit],
wear a half-mask respirator with a combination organic vapor/HEPA
An MSDS for MEK (there are several) says that "for occasional use,
where engineered air control is not feasible, use properly maintained
and properly fitted NIOSH approved respirator for organic solvent
vapors. A dust mask does not provide protection against vapors."
%% end of cozy-faq %%
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