Cozy Builders Mailing List FAQ 
Version: 1.19
Last Updated: May 3rd, 2023

Frequently Answered Questions
in the Unofficial Cozy Builders Mailing List

Table of Contents:

Credits:
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.

Preliminaries

1.1 - What mailing list?

The 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 http://www.cozybuilders.org/ 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 http://www.faqs.org/faqs/ 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.

1.3 - Where can I get the latest version of this FAQ?

You can obtain an HTML version of this FAQ on the World Wide Web at http://www.cozybuilders.org/mail_list/cozy-faq.html.

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:

  1. 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.
  2. 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 topic.)
  3. 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 information.)
  4. Stick these into a plain text (ascii) file.
  5. Include the date you obtained the archive files for distillation.
  6. Send the results to the FAQ curator, Marc Zeitlin, for final formatting.
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.

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.

1.5 - How do I get files from the list server, Googlegroups?

Note: This service is only available to Mailing List Members

See:

https://groups.google.com/forum/#!forum/cozy_builders

Chapter 4 - Fuselage Bulkheads [as of: 11 feb 07]

 [distiller: Wayne Hicks]

Comments and Tips

4.1 - What is the best method for creating the other half of the templates?

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.
  1. 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.

  2. 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 difficult.

  3. 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).

  4. 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.

  5. 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:

  1. 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 with BID.
  2. 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 happen.
  3. 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 those spaces.
  4. 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.
  5. 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.
  6. 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 layup.

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 Chapter 5.

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 than F22?

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 glassing?

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 in?

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 holes.

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 full-size drawing?

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 it!

4.19 - How does one finish the inside edges of the bulkheads?

Some people route them out slightly and fill with micro, others do not.

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 you like:

  1. 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.
  2. 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 work.
  3. Cut the heads of the screws into + signs instead to give them more holding power.
  4. 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 - I’ve 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 chapter 13.

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 large-drawings.

Chapter 5 - Fuselage Sides [as of: 29 sep 97]

 [distiller: Darren DeLoach]

Comments and Tips

Left in the Archives

5.1 - How do I get a smooth curve when cutting the FJA jig?

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 sides?

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 this?

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 materials list?

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 lines through.

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

Left in the Archives

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 BID tape.

6.3 - Should I lap the multiple plies of UNI that are added to the landing gear bulkheads onto the sides of the tub?

No.

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:
  1. Lay up the bottom and peel ply where the the bottom is going to meet the sides and the bulkheads.
  2. Let cure.
  3. Remove peel ply, sand, and flox the bottom to tub
  4. 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 best.

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 backwards!

Chapter 7 - Fuselage Exterior [as of: 5 jun 98]

 [distiller: Darren DeLoach]

Comments and Tips

Left in the Archives

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 is correct?

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 gear cover?

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 http://www.cozybuilders.org/chapters/chap09_3.html 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 vertical extent?

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 <jim@rst-engr.com> of RST (http://www.rst-engr.com/) 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?

  1. 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.
  2. Avoid the area where the landing light will be (refer to Chapter 17).

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 cover?

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:
  1. 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 photos at http://www.cozybuilders.org/chapters/chap07.html) 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.
  2. 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 method above.

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).

7.12 - I don't think I'll get a smooth transition on the bottom of the fuselage in Step 1, using the plans sizing of the urethane foam. What should I do?

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

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 the step.

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 roll-over protection?

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 headrests?

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 joints.

8.7 - Is there a better way to mount the nut plates under the shoulder brace?

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

Left in the Archives

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 marking.

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 delamination.

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 not flat.

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 should be.

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

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 conform.

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 SKIN!

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 canard?

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 doing so.

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 templates A/B)?

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

Left in the Archives

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 equivalents (BSPQ-44).

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?

No.

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:

Chapter 12 - Canard Installation [as of: 21 dec 07]

 [distiller: Wayne Hicks]

Comments and Tips

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:
  1. Trim 0.1" from the canard trailing edge, leaving AT LEAST 3/8" of glass-to-glass bond.
  2. 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.
  3. 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 angle?

Do the following:
  1. Ensure the canard is straight with no twist.
  2. Ensure the G template is correctly made to plans.
  3. Level the fuselage (top longerons dead level)
  4. Sand the fuselage sides down a bit (under rear of canard) as needed to level the G template.
  5. Remove the alignment tabs and remount at the correct angle, or make new ones.
  6. 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:
  1. Custom-fit the location of the canard to ensure incidence and alignment.
  2. Provide crush pads when bolting the mounting tabs to F22.
  3. Provide load paths to strengthen F22 at that location.
  4. Provide some relief strength to keep from wallowing out the bolt holes.
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.

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 load control.
  1. Remove the pins.
  2. 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 doubler.
  3. Make a small 2024-T3 aluminum plate with an AN3 nut plate attached.
  4. Flox the nut plate onto the forward surface of the alignment tab.
  5. Insert a long AN3 bolt (approximately 4") from aft of the doubler, into the sleeve and screw into the nut plate.
  6. 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 no juggling.

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 canard’s 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

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 Theeringer <Composite_Aircraft_Accessories@Compuserve.com>. 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 http://www.ez.org/csa/csa_newsletter.php or contact Terry Schubert <jschuber@juno.com> for more information about the Central States Association.) There is also a ready-to-install unit available from Steve Wright <staggerez@comcast.net>. 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 http://www.cozybuilders.org/my_cozy.html. 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 lenses).

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.

13.5 - How should the pitot tube pipe be routed?

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.

13.7 - Is the BID and flox attachment between the brackets (MKNG-3/MKNG-4) and the strut (NG-1) strong enough to withstand repeated landing loads?

While most installations have no problems, there have been instances of NKNG-3/MKNG-4 brackets disbanding from the strut, becoming loose and sliding along the strut. The joint can be strengthened by adding a flox fillet on each end of NG3/NG4 up to the thickness of the steel, so that the fillet/ramp provides support by helping to hold the metal pieces in place. Such a fillet/ramp can also be built up from UND with the fibers parallel with the strut. An additional measure to ensure that the brackets cannot move is to add a bolt laterally (left-to-right or right-to-left) through middle of the assembly, at/near the center line between the fwd/bottom surface and the aft/top surface of the strut (i.e the strut’s bending neutral axis).

Chapter 14 - Center Section Spar [as of: 10 may 99]

 [distiller: Wayne Hicks]

Comments and Tips

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 specifying 8.51".

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 layups?

One alternative:
  1. Make a "corner" pattern from cardboard.
  2. Wet out the plies that go around the corners onto plastic or aluminum foil.
  3. Fold the plies around the cardboard as if you were gift-wrapping the corners of a box.
  4. Position the cardboard into the spar so that the outward-facing wetted cloth is against the bottom and in the correct orientation.
  5. Unfold the plies and press against the sides.
  6. 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 don’t 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 0.025” 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 “APPROX” 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 technique. .

Chapter 18 - Canopy & Turtleback [as of: 10 may 99]

 [distiller: Wayne Hicks]

Comments and Tips

Left in the Archives

18.1 - What is a good method for installing the foam into the turtleback jigs?

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:

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.
  1. 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.
  2. After the plaster dries, drill two small holes at opposite diagonal corners through the turtleback and through the plaster for future reference.
  3. Remove the mold and cut out the window opening in the turtle back. Do a nice neat job finishing the inside edges.
  4. 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 the oven.
  5. 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.
  6. 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.
  7. 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 positioning it.
  8. Mark it again 1/2" wider than the foam cutout, trim to this line, and voila', you have got a window!
  9. Trim the inside of the turtleback and remove the 1" strip of fiberglass and foam where the window will go.
  10. 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.
  11. Rough up the edges and place weights on the backside of the window to hold it in place while the flox cures.
  12. Install the 1" strip and bid tape after the window has cured in place.

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.
  1. Measure up along the front curve of the turtleback and place marks at 2-3/8" and 16-1/16".
  2. Measure up along the back curve of the turtleback and place marks at 5-1/4" and 12-5/8".
  3. 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.)
  4. 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.
  5. Do the same thing for the top marks. These delineate the top and bottom of the windows.
  6. 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".
  7. 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.)
  8. 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 removable?

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 tight?

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 place?

There are three general methods:
  1. Drill a hole in each end of the hinges (or hinge pins) and secure with a small cotter pin or safety wire.
  2. Apply silicone into each end of the hinges
  3. Make a small loop in one end of the hinge pin and secure in place with safety wire or a screw.
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 . . .

18.13 - What should I do if my canopy latch hardware does not line up?

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):
OLD:
Description Manu. P/N NAPA P/N
Gas spring SPD-5150-40 819-5587
Ball stud SPD-1005 735-1591
Bracket SPD-1010 735-1592

NEW:
Description Manu. P/N NAPA P/N
Gas spring SPD-5150-40 819-5587
Ball stud SPD-1005 735-1896
Bracket SPD-1010 735-1897

18.16 - What is the preferred geometry for mounting the canopy gas strut?

Again, beyond the plans dimensions, it is a builder's prerogative. Keep these guidelines in mind:

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 process:
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 oct 99]

 [distiller: John Slade]

Comments and Tips

Left in the Archives

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 wings?

Yes. The buttline locations are different and the Cozy IV wings are 4" longer.

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 waterline?

Yes.

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 top skin?

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 strip off?

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 out?

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 surrounding structure.

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 overseas) to 
  Gary Hall
  851 S.W. 63rd. Ave
  North Lauderdale, FL 33068
or Email gary.chris@comcast.net.

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 just fine.

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 finishing.

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 spar cap?

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 design.

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 holes?

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 surface?

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 float?

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 points for?

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 combination.

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 warp?

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

Left in the Archives

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?

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 winglet?

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?

On the Winglet BOTTOM Tip Template (shown on drawing M-20), the label has left and right reversed. The note should be changed to “This side for RT. Transfer numbers to other side for LT”.

All other notes are correct. Nevertheless, the templates can be confusing. The following is an alternate description of the correct winglet template orientation:

* In the correct orientation, all “INBOARD” label arrows will point toward the wing, and all fishtails will be on the same side (also toward the wing).

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 difference.

Chapter 21 - Strakes [as of: 15 sep 01]

 [distiller: Wayne Hicks]

Comments and Tips

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 disastrous results.

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 back open.

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 site glasses?

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 fuel management.

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. (See http://www.ez.org/csa/csa_newsletter.php or contact Terry Schubert <jschuber@juno.com> for more information about the Central States Association.)

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

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 level lines.

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 consistent.

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

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:

   http://www.cozybuilders.org/ref_info/

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 solvent.

CS.2 - Will I develop an allergy to <particular> epoxy/hardener/resin/solvent?

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 forever.

Two people can have very different critical dose, up to and including practically unlimited exposure (i.e. - bare skin touching EZ-Poxy).

Your reaction to one allergen has little value in predicting your reaction (if any) to another.

To be sure, limit your exposure to <particular>.

CS.3 - I've developed an allergy to <particular> epoxy/hardener/resin/solvent. What can I do?

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.

CS.4 - What sort of gloves should I use?

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 gloves.

CS.5 - What sort of respiratory protection should I use?

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 cartridge."

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."

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