Date: Tue, 03 Feb 1998 19:44:05 -0500 From: Rob Cherney Subject: RE: COZY: Landing Light At 08:59 AM 2/3/98 -0800, Jim Hocut wrote: > >BTW, who was it that said they had a source for pitot heaters a while >ago? I've got my per plans pitot tube installed but not plumbed yet >and I need to start thinking about a heater for it. > I ordered a Cessna heater element (80w, 12v) from Preferred Airparts (330-698-0280). It cost me $23 plus shipping. The part number is 0721105-5. Rob- +------------------------------------------------------------------+ |Robert Cherney Home Phone: (410)465-5598 | |Ellicott City, Maryland e-mail: cherney@home.com | +------------------------------------------------------------------+ Date: Tue, 03 Feb 1998 12:44:26 +0000 From: David Domeier Subject: COZY: pitot/pitot heat Jim, re "BTW, who was it that said they had a source for pitot heaters a while ago? I've got my per plans pitot tube installed but not plumbed yet and I need to start thinking about a heater for it." I have not figured out one can heat the plans pitot tube, so I bought a heated pitot tube from Wicks which will be mounted somewhere on the fuselage below the canard. I did not like the nose pitot source on my LEZ because the airspeed indicator was always jumping up and down a bit. I think there may be a pressure build up on the nose causing this to occur. Do you know of any other airplane with the pitot source in this location flat off the nose? I don't. All the jets use some sort of extended tube. dd Date: Wed, 04 Feb 1998 21:29:59 -0500 From: Rob Cherney Subject: Re: COZY: pitot/pitot heat At 12:44 PM 2/3/98 +0000, David Domeier wrote: >Jim, > > re "BTW, who was it that said they had a source for pitot heaters a >while ago? I've got my per plans pitot tube installed but not plumbed >yet and I need to start thinking about a heater for it." David: Nat recently sent me this in response to my post about a Cessna part: "Re Pitot tube heaters. Jack Wilhelmson invented a pitot tube heater that was quite simple and inexpensive. Regards, Nat" Rob- +------------------------------------------------------------------+ |Robert Cherney Home Phone: (410)465-5598 | |Ellicott City, Maryland e-mail: cherney@home.com | +------------------------------------------------------------------+ From: Epplin John A Subject: RE: COZY: pitot/pitot heat Date: Thu, 5 Feb 1998 07:51:27 -0600 I purchased a kit from someone last spring. I can look it up somewhere if noone else can remember who it was. Someone on the Cozy mailing list I am sure. I changed mailers since and my records are hard to get to. It consisted of two small flexible heating strips about 1/4 by 2 in that have an adhesive applied to one side. The plan was to stick these to the aluminum tube and a small bi-metal thermostat along with them. Wrap the assembly in an insulating sleeve and then shrink tubing. The strips were about 50 watts at 13 or 14 volts as I remember. I did not exactly follow the plan he outlined. I made a block of aluminum about 3/4 thick 1 high and 2 wide. I screwed the thermostat on the back side, the heater strips on the top and bottom sides. I drilled and tapped 1/8 pipe thread into one end into the center of the block. >From the front, I drilled, tapped and chamfered to fit standard SAE O-ring straight thread fittings. I believe it would be 1/8 in hydraulic fittings. I then made the pitot tube from 1/2 in al. round about 3 in long. Threaded and O-ring grove on one end and beveled to a 3/16 through hole on the forward end. The block is mounted to a piece of phenolic that I embedded in the nose about as far forward in the nose center as I could get it. two plate nuts are riveted to the phenolic to attach the block to. I made a phenolic bushing 3/4 od 1/2 id with a thin flange that is flush with the nose skin and buts against the aluminum block. I milled a wrench flat on the pitot tube just outside the skin and turned the outer part down to the wrench size. As of now I have no idea how this is going to work but it does look neat. With two heaters one should have some sort of current monitor to let the pilot know if the system is working OK. The cost here is reasonable and weight is very little more than un-heated tube. With two heaters it should be somewhat reliable. John epplin Mk4 #467 -- Starting canopy experience! From: "Rick Roberts" Subject: Re: COZY: pitot/pitot heat Date: Thu, 5 Feb 1998 06:22:09 -0800 It was Nick Ugolini! He put together a nice little set up! Rick Roberts Date: Thu, 05 Feb 1998 09:41:24 -0600 From: Robert and Carla Kittler Subject: COZY: pitot heaters I've been watching the discussion regarding pitot heaters and would like to share a thought or two. Regardless of whether or not you're planning on flying IFR, pitot heat, I think most would agree, is a pretty good idea. For all those who are considering or who have made homemade, non certified masts, are you insuring that they are effective under all flight conditions. That is, if for example, you're doing 190KIAS and the OAT is -15C (ISA at top of a decent) is your mast effective. Or on approach at 100KIAS up here in the winter with the temp still at -15 or 20C. My point is, be sure to consider the fact that there is significant heat loss in flight and if the system isn't effective under severe temperature conditions then it's not really worth very much. If you're planning on IFR on a regular basis, perhaps a certified mast is worth the investment. my 2 cents Rob Date: Thu, 05 Feb 1998 10:08:19 +0000 From: atlasyts@idt.net Subject: Re: COZY: pitot/pitot heat Jeff Russel uses pitot tube flush with the nose and told me that is happy with it. Bulent From: Epplin John A Subject: RE: COZY: pitot heaters Date: Thu, 5 Feb 1998 09:09:37 -0600 > -----Original Message----- > From: Robert and Carla Kittler [SMTP:rkck@mindspring.com] > Sent: Thursday, February 05, 1998 9:41 AM > To: cozy_builders@hpwarhw.an.hp.com > Subject: COZY: pitot heaters > > I've been watching the discussion regarding pitot heaters and would > like to > share a thought or two. > > Regardless of whether or not you're planning on flying IFR, pitot > heat, I > think most would agree, is a pretty good idea. For all those who are > considering or who have made homemade, non certified masts, are you > insuring that they are effective under all flight conditions. > > That is, if for example, you're doing 190KIAS and the OAT is -15C (ISA > at > top of a decent) is your mast effective. Or on approach at 100KIAS up > here > in the winter with the temp still at -15 or 20C. My point is, be sure > to > consider the fact that there is significant heat loss in flight and if > the > system isn't effective under severe temperature conditions then it's > not > really worth very much. > > If you're planning on IFR on a regular basis, perhaps a certified mast > is > worth the investment. > > my 2 cents > > Rob [Epplin John A] Excellent discussion. I intend to imbed a small thermocouple as close as I can to the tip of the tube sometime during my test program. I don't know just what to expect for temp drop from the heater to the tip but I will find out. John epplin Mk4 #467 Date: Thu, 05 Feb 1998 09:47 -0600 (CST) From: Michael Pollock Subject: Re: COZY: pitot/pitot heat >David Domeier Wrote: >I have not figured out one can heat the plans pitot tube, so I bought a >heated pitot tube from Wicks which will be mounted somewhere on the >fuselage below the canard. On our Velocity 173RG, we installed the Cessna type heated pitot tube 8 inches under the right canard on the fuselage side, such that the tube was parallel to the fuselage skin - not pointing straight ahead. The accuracy is great from 75mph up to full throttle cruise of 205mph TAS. We were off by a max of 2mph at the lower end. --- Michael.Pollock@mci.com Flying Velocity N173DT Building Cozy4 #643 From: cdenk@ix.netcom.com Date: Thu, 5 Feb 1998 20:09:42 -0600 (CST) Subject: Re: COZY: pitot/pitot heat On 02/05/98 10:08:19 you wrote: > >Jeff Russel uses pitot tube flush with the nose and told me that is >happy with it. >Bulent > > Suprised, since there is a boundary layer of still air at the skin. I wonder what his calibration numbers are? Date: Thu, 05 Feb 1998 22:28:27 -0500 From: "Jeff S. Russell http://www.AeroCad.com" Subject: Re: COZY: pitot/pitot heat cdenk@ix.netcom.com wrote: > > On 02/05/98 10:08:19 you wrote: > > > >Jeff Russel uses pitot tube flush with the nose and told me that is > >happy with it. > >Bulent > > > > > > Suprised, since there is a boundary layer of still air at the skin. > I wonder what his calibration > numbers are? I saw no differance in using a 2 inch flow tube or just a hole at the start of the nose. Go figure? Airspeeds from 70 knots to 160 were flown with a Cozy and Cherokee six to check this both ways. I also rapped the airspeed tube around a 180 - 200 degree oil line about 8" from the tip of the nose. Pitot heat is free on this one. -- Jeff Russell/AeroCad Inc. E-mail: Jeff@aerocad.com P.O. Box 7307 Port St. Lucie FL. 34985 Shop# 561-460-8020 Home# 561-343-7366 Composite workshop info: http://www.Sportair.com From: SWrightFLY@aol.com Date: Fri, 6 Feb 1998 08:30:58 EST Subject: Re: COZY: pitot/pitot heat In a message dated 98-02-05 22:39:08 EST, jraero@gte.net writes: << I saw no differance in using a 2 inch flow tube or just a hole at the start of the nose. Go figure? Airspeeds from 70 knots to 160 were flown with a Cozy and Cherokee six to check this both ways. >> Same here- My vaieze had a 1 1/2 inch tube which after being "crunched" by a big foot at a fly-in was cut flush....... No difference in the air speed. Steve Wright Wright Aircraft Works From: lschuler@cellular.uscc.com Date: Fri, 06 Feb 98 10:06:49 -0600 Subject: Re: COZY: pitot/pitot heat Steve Wright wrote: >In a message dated 98-02-05 22:39:08 EST, jraero@gte.net writes: << I saw no differance in using a 2 inch flow tube or just a hole at the start of the nose. Go figure? Airspeeds from 70 knots to 160 were flown with a Cozy and Cherokee six to check this both ways. >> >Same here- My vaieze had a 1 1/2 inch tube which after being "crunched" by a >big foot at a fly-in was cut flush....... No difference in the air speed. Somone wrote about the fighter planes having long stingers to be more accurate. Not wholly true. Most of the reasoning is to break the sound barrier ahead of the plane, which moves the shock cone beyond the wing tips. At least that's my understanding of it. We don't have that problem. (I wish!) The flush-mounted pitot in the nose should work 'fairly' well, especially at higher speeds as long as it is dead center on the most forward part of nose. The sharper the nose point the better (for the flush pitot anyway). This is because this point on the nose is 'generally' the stagnation point of the airflow (zero flow, max pressure). Moving the stagnation point out a couple inches via a long pitot tube, won't change this. The difference on a flush-mount will likely arrise at lower speeds due to the angle of attack of the nose. Slower flight generally requires a higher angle of attack. This higher angle causes the stagnation point to move down the nose and thus some of the pressure at the pitot is now converted to flow up and over the front of the pitot. Small, maybe; but very real and measurable. Same thing happens to a pitot stuck three feet in front of the nose; it's just that the size of the pitot (relative to the nose of the plane) is so much smaller that there is effectively less cross flow as the stagnation point moves. Thus greater accuracy at all speeds. Sticking the pitot a quarter inch, half inch, or 2 inches in front of the nose would be better than being flush. It's a trade in accuracy over the range of the aircraft. Just remember that with a flush-mount dead on the stagnation point at cruise, the plane will be flying a bit faster than indicated when flying lower speeds. Moving the pitot off stagnation center in any direction, or moving the stagnation point by changing angle of attack/airflow would cause an inacuracy in one or all speed ranges; depending on how far off from center and in what direction. This is why the CAFE folks use a wing mounted boom for their test flights. Take a look at the boom; you will see a gimbaled arrow near the tip of the boom. The arrow is the pitot; not the boom. It automatically adjusts the stagnation point regardless of which way the plane (or boom) is pointed. More 'n ya ever cared to know. Larry Schuler MK-IV #500 lschuler@cellular.uscc.com Date: Fri, 06 Feb 1998 19:53:24 +0200 From: Chris van Hoof Subject: COZY: Pitot Greetings to all, Got the question from a friend, and thought i'd put this to the panel... The pitot being placed as per plans, seems to be prone to damage, filling with dirt etc...since my plane is not flying yet, all these points are speculation....why then can this not be placed in one of the winglets? say, High up? Would there be any disadvantage (except the plumbing?) Any thoughts here? Thanks in advance. Chris #219 From: "Vance, John M." Subject: RE: COZY: Pitot Date: Fri, 6 Feb 1998 13:20:07 -0500 Chris van Hoof wrote: =The pitot being placed as per plans, seems to be prone to damage, =filling with dirt etc...since my plane is not flying yet, all these =points are speculation....why then can this not be placed in one of the =winglets? say, High up? Would there be any disadvantage (except the =plumbing?) Been done by Vance Atkinson. I have a photo somewhere at home, can scan and email to individuals if interested. He was happy with the set up when I talked to him at Sun-n-Fun two years ago. John M. Vance Cozy 3, chapter 13 From: SWrightFLY@aol.com Date: Fri, 6 Feb 1998 14:59:28 EST Subject: Re: COZY: pitot/pitot heat In a message dated 98-02-06 12:13:41 EST, lschuler@cellular.uscc.com writes: << Moving the pitot off stagnation center in any direction, or moving the stagnation point by changing angle of attack/airflow would cause an inacuracy in one or all speed ranges; depending on how far off from center and in what direction. This is why the CAFE folks use a wing mounted boom for their test flights. Take a look at the boom; you will see a gimbaled arrow near the tip of the boom. The arrow is the pitot; not the boom. It automatically adjusts the stagnation point regardless of which way the plane (or boom) is pointed.>> I'm giving serious consideration to monting my pitot tube at the tip of the winglet. If I mounted the tube 3 or 4 inches in front of the top of the winglet no one can step on it. Any thoughts. Steve Wright Wright Aircraft Works From: lschuler@cellular.uscc.com Date: Fri, 06 Feb 98 13:59:32 -0600 Subject: Re: COZY: Pitot Chris van Hoof wrote: >Got the question from a friend, and thought i'd put this to the panel... >The pitot being placed as per plans, seems to be prone to damage, >filling with dirt etc...since my plane is not flying yet, all these >points are speculation....why then can this not be placed in one of >the winglets? say, High up? Would there be any disadvantage (except >the plumbing?) >Any thoughts here? You can really put a pitot just about anywhere on the plane as long as it's pointed corrctly and has zero turbulent interference. The winglet could work 'technically'. Problems become practical application issues, such as the tubing run as you mention. Be careful of creating a low point where water can collect. For that reason, the winglet is not real good; low point may end up being your airspeed indicator. Check out Nat's idea of a removable pitot. Larry Schuler #500 lschuler@cellular.uscc.com From: lschuler@cellular.uscc.com Date: Fri, 06 Feb 98 13:48:57 -0600 Subject: Re[2]: COZY: pitot/pitot heat Forward per Nat's request. Removable pitot called out in the plans has it's merits. No decission on my end yet... I'm still futzing with the elevators. :-) Larry Schuler Cozy-IV plans#500 lschuler@cellular.uscc.com ______________________________ Reply Separator _________________________________ Subject: Re: COZY: pitot/pitot heat Author: "Nat Puffer" at Internet Date: 2/6/98 9:52 AM Dear Larry, The Cozy Mark IV plans show a removeable pitot in the nose. There are many advantages to this. You can remove the pitot and install a pipe plug so that when you are working on the airplane in your shop, you won't keep jabbing yourself. When you park your airplane nose down, you can put a pipe plug in so people don't step on the pitot and so insects don't crawl in. You can weld an eye-bolt to the pipe plug so it can also serve as a nose tie-down. A friend locally mounted his pitot on the leading edge of the canard. He kept bumping into it and it was a pain to have to disconnect when removing the canard. The nose is the one place you can be sure of undisturbed air. One time I forgot to remove the pipe plug and went flying. There was enough leakage through the threads that I had the same (as near as I could tell) airspeed indication as with the pitot. When installing the pitot in the nose, one should make sure that the 1/4" tubing is a straight and inclined run up to the panel so that any water will not be trapped in the line. If the line has a dip in it, water could be trapped, and cause the airspeed indication to be unsteady. By the way, there is no boundry layer at the point air impinges on a surface. Best regards, Nat (please post to cozy builders) Date: Fri, 06 Feb 1998 15:29:25 +0000 From: David Domeier Subject: Re: COZY: Pitot Chris, Larry Schuler was probably right on when he wrote: "The difference on a flush-mount will likely arrise at lower speeds due to the angle of attack of the nose. Slower flight generally requires a higher angle of attack. This higher angle causes the stagnation point to move down the nose and thus some of the pressure at the pitot is now converted to flow up and over the front of the pitot. Small, maybe; but very real and measurable." My experience in this area was that the IAS was never steady and it may well have been caused by the pitot hole not being centered vertically on the stagnation point of the nose of the airplane. I had changed the up slope of the nose slightly to resemble a Piper Seneca profile and that could have caused the pressure point to be lower, expecially at lower speeds. Now that being said, and all the comments on this subject by other guys, I must conclude that a plan pitot hole in a plan nose job is most satisfactory. However, since I bought an electric pitot tube, I will install it somewhere on the left fuselage below the canard. I wouldn't install a pitot tube in a winglet because of all the plumbing and wire required to get there. It's trouble enought running wires out there for lights and cable for anntennas. dd Date: Tue, 10 Feb 1998 08:16 -0600 (CST) From: "Michael Pollock" Subject: COZY: Re:pitot heat >Ian Douglas wrote: >I am looking at pitot installation on my Cozy and was wondering if you >could be more specific in the placement of your pitot. If you installed >it per the Velocity plans, I can go look at a friends down the street. >If not how far back from the canard LE is the tip of the pitot. You say >it is 8" below the (assuming the bottom of) the canard. Is the tube >parallel to a water line 8" below canard, or is there an angle off of >the water line? Ian, I made several comments that were wrong about the pitot. Our heated pitot tube on our Velocity 173RG is the Piper, Mooney, etc. type. It is mounted 6" below the bottom of the canard level with the waterline and parallel to the fuselage side. The nose of the pitot is 4" aft of the canard leading edge. Velocity aircraft is using the same position on several of their demos. The only inaccuracy that I have noticed is during a slip right wing down because my pitot is mounted on the right side of the plane. I like the location because it does not hit me when I do my walk around, also the overall accuracy is great. --- Michael.Pollock@mci.com Flying Velocity N173DT Building Cozy MKIV #643 From: "Brown, Michael" Subject: COZY: Pitot Heat Date: Thu, 25 Jun 1998 17:14:00 -0700 I'm presently receiving instrument training in my cozy and, although I don't plan on using the plane for "hard" IFR, I do anticipate needing to fly into the occasional stratus layer or cloud. My CFII strongly recommends the addition of a pitot heat system to prevent pitot tube icing, as well as an alternate static source before any real IFR flight is attempted. I can rig up the alternate static source easily, but does anyone have suggestions on a pitot heat system for the EZ-types? My current pitot is a machined brass tube extending from a boss on the nose bowl, connected to the airspeed indicator by 1/4 inch aluminum tubing. What kind of heat system might do the job with minimum penalty (weight, cost, electrical power drain, etc.)? Any and all suggestions would be appreciated. Michael Brown N97PZ michael.brown@alliedsignal.com From: cdenk@ix.netcom.com Date: Thu, 25 Jun 1998 20:10:37 -0500 (CDT) Subject: Re: COZY: Pitot Heat I use a ordinary heated pitot, (not the piper blade type) mounted several inches below the canard, with the tip of the tube ahead of the canard, in a horizontal position. The mast is about 2" below and 2" forward of the canard 1/4" bolt heads.The mast is a piece of streamline aluminum tubing well floxed into the fuselage side. Although tubes come for side mount, they are hard to find. Instead drill a new drain hole and solder up the old one, just lightly drill the hole out to expose the brass. The heater draws 6 amps. I use a 72 amp alternator, which is just right for mine. It charges with 1200 rpm with everything on. This important on long taxi or waiting clearance. Don't like distraction of having to turn off and on just before launching, got enough other thinks that are critical. My alternate is a bayonet type fuel quick drain mounted under the instrument panel. To open I just push in and turn. Remember anytime the static system is opened (a tubing connection broken) the system must be checked and a logbook entry made by an approved A & E (a special certificate). The static and altimeters (visual and encoding) and transponder must be checked every 2 years at a cost of $120 + altimeter repairs etc. An 1/8" of ice on the leading edges requires 10 knots more on final to get the nose up for flare, otherwise at 5 knots a carrier landing. From: Jim Hocut Subject: RE: COZY: Pitot Heat Date: Thu, 25 Jun 1998 22:57:40 -0400 > does anyone > have > suggestions on a pitot heat system for the EZ-types? As luck would have it, I've been working on a pitot heater that works with the per plans pitot (per Cozy IV plans anyway, I haven't seen the Long EZ plans - I'm assuming the pitot is the same). I've been through two iterations with pretty good results, should be able to do my third and final attempt at it within a few weeks (i.e. when I feel like messing with it). It fits over the pitot, and on the ground is able to get the pitot too hot to touch in less than a minute, and draws less than 1 Amp. Before I go making any great claims about how it works though it needs to be flight tested. Seeing as how I don't have a flying Cozy yet, and the per plans pitot won't fit on an Aeronca or C-172, I wonder if anybody near Atlanta with a flying plane would be willing to gamble a bit of fuel and flight time in exchange for a free pitot heater. Assuming it works OK I'll try to get some photos scanned and at least enough verbage on-line so that anywone who's interested can copy it. Jim Hocut jhocut@mindspring.com From: SWrightFLY@aol.com Date: Fri, 26 Jun 1998 08:48:50 EDT Subject: Re: COZY: Pitot Heat In a message dated 98-06-25 23:00:22 EDT, you write: << I wonder if anybody near Atlanta with a flying plane would be willing to gamble a bit of fuel and flight time in exchange for a free pitot heater. >> Steve Wright here in Nashville TN. We would love to put it on our Cozy Mk-3 which is IFR, and flown IFR quite often. This is the Cozy that tested the prototype Noze-Lift. Its a great test bed. Please call me at 615-373-8964.....Thanks From: "Brown, Michael" Subject: Re: COZY: Pitot Heat Date: Fri, 26 Jun 1998 08:32:00 -0700 Thanks for both suggestions (pitot heat and alternate static). Do you have any problem with the pitot not getting a good signal during turns or sideslips, since it is now mounted to the side of the fuselage? Does the heater come with a thermostat, or is it just on/off via the switch? Mike Brown N97PZ michael.brown@alliedsignal.com ---------- Original reply from: cdenk@ix.netcom.com "I use a ordinary heated pitot, (not the piper blade type) mounted several inches below the canard," "The heater draws 6 amps. I use a 72 amp alternator, which is just right for mine. It charges with 1200 rpm with everything on. " "My alternate is a bayonet type fuel quick drain mounted under the instrument panel. To open I just push in and turn." From: "Brown, Michael" Subject: RE: COZY: Pitot Heat Date: Fri, 26 Jun 1998 08:28:00 -0700 Thanks, Jim. Yes, my Cozy (III) system is the same as the Cozy IV - I even use the molded nose bowl from Featherlite. So, did you just strap an electrical heating element to the tube, or what? Is there a thermostat included to prevent overheating? Please do post the pic's when you get a chance - it's something I would like to see. Mike Brown N97PZ michael.brown@alliedsignal.com ---------- Original reply from: Jim Hocut: "It fits over the pitot, and on the ground is able to get the pitot too hot to touch in less than a minute, and draws less than 1 Amp." From: lschuler@cellular.uscc.com Date: Fri, 26 Jun 98 10:33:01 -0600 Subject: Re: COZY: Pitot Heat Michael Brown wrote: >snip >...does anyone have suggestions on a pitot heat system for the EZ-types? Michael, Check the archives. I believe there is a nifty, non-electric pitot design available. Used mostly by sail plane folks (no electrical system). Larry Schuler lschuler@cellular.uscc.com Date: Fri, 26 Jun 1998 12:03:59 -0500 From: Tom Brusehaver Subject: Re: COZY: Pitot Heat I was thinking, that 1A version sounds great. But, it sounded a little too good, and so I am presenting my thoughts, and would enjoy other comments, including someone telling me this is too weird to think about :-). I assume, the goal of pitot heat is to raise the temprature of the air entering the pitot system somewhere above freezing. In order to do this at all tempratures, is must be able to maintain at least some difference to the ambiant air temprature, vs the freezing (or amount above) temprature (lets call it deltaT). I don't know what flight levels folks fly at, so coming up with a minimum temprature that the deltaT would have to be would be a guess, lets say -40 is the minimum temprature this system would have to work at (-40 is same for C and F), that gives a deltaT of 72F or 40C. The 1A heating element would be producing 12watts of heat. At 200MPH, there would be lots of cooling (probably greater than 12W? I don't know how to calculate that, I guess it would matter about the exposed surface, or maybe the sq.in of the opening of the tube, and velocity). Even if say you never flew at tempratures below say 10F (-11C?) the deltaT would still be 11C and 22F. I am not sure a 12watt heater could cover that. From: cdenk@ix.netcom.com Date: Fri, 26 Jun 1998 15:54:51 -0500 (CDT) Subject: Re: COZY: Pitot Heat If I leave the pitot heat on after landing, and shut it off as part of the shutdown checklist, and then try moving the plane ( I use the pitot tube as a handle) it too hot to touch with the bare hand even for 5 seconds. I would guess its temperature is over 150 F. These pitot tubes are used on certified aircraft at speeds and altitude well beyond the COSY limits, i.e. Beech Kingair, etc. I don't think the ability of these tubes to do their job is any concern. From: cdenk@ix.netcom.com Date: Fri, 26 Jun 1998 16:34:24 -0500 (CDT) Subject: Re: COZY: Pitot Heat The tube is far enough forward that the nose is sloping inward at a good rate. I haven't noticed any effects during slips, I'll try to check it on next flight and if there is something, I'll post it. The heater is on always, it might be self limiting. Some heating elements will increase in resistance (less heat and power) when the temperature goes up. From: cdenk@ix.netcom.com Date: Fri, 26 Jun 1998 16:42:08 -0500 (CDT) Subject: RE: COZY: Pitot Heat Use the certified pitot tube, and don't worry when your icing. I once had a pitot tube freeze on a C-172 on an ILS approach. Airspeed went to ZERO, which I knew was in error. The airliners in front and back of us "missed" when snow squalls moved through. It wasn't bad ceiling visibility when we got inside the outer marker. The heating element went bad. Now that I think of it a warning light that comes on if current ceases would be nice. How about some electronic guru working on that. From: lschuler@cellular.uscc.com Date: Fri, 26 Jun 98 16:20:45 -0600 Subject: Re[2]: COZY: Pitot Heat Tom Brusehaver wrote: >snip >I assume, the goal of pitot heat is to raise the temperature of the >air entering the pitot system somewhere above freezing. >snip Well, not exactly (at least the way I think of it). Air doesn't really enter the Pitot per se'. The pitot is supposed to be in stagnant air so that all you get is pressure; zero movement. In any case, the little air that is in the line to the ASI just gets smashed (pressure) against a rubber diaphragm with nowhere to go beyond that wall. The other side of the diaphragm is the static line which basically just allows the diaphragm to move (if the side opposite the pitot entry were closed off/sealed, the diaphragm wouldn't move). At any rate, I think the idea of heat here is to melt/prevent ice from plugging the hole in the end of pitot rather than heating the air. Gotta admit that heating the stagnant air inside the tube can't hurt, since it just kinda sits there. Larry Schuler lschuler@cellular.uscc.com From: Jim Hocut Subject: RE: COZY: Pitot Heat Date: Fri, 26 Jun 1998 20:27:16 -0400 > > The 1A heating element would be producing 12watts of heat. At > 200MPH, > there would be lots of cooling (probably greater than 12W? I don't > know how to calculate that, I guess it would matter about the > exposed > surface, or maybe the sq.in of the opening of the tube, and > velocity). > > Even if say you never flew at tempratures below say 10F (-11C?) the > deltaT would still be 11C and 22F. I am not sure a 12watt heater > could cover that. OK, I have to admit something. I'm actually using about an 8 Watt heating element. I started out with about 12 Watts but decided it was too hot (got hot enough to burn my hand in about 15 seconds), then tried 10 Watts (still too much), then settled on 8. As Larry pointed out there's no air flow through the pitot, so we're not really losing any heat there. All we have to do is keep that little AN840 hose nipple warm, and it has so little mass that it doesn't take much power to make it hot. The only other heat energy lost (and this is the big question mark) is to the slipstream. The heated pitot on Cessna's, Piper's, etc. are bare metal, and are big, so they lose lots of heat to the slipstream and consequently require lots of power (plus they're anchored to a big metal heat sink (wing) so more heat is lost there). What I've got is little, and is insulated with several layers of fiberglass, so it's not going to lose anywhere near the magnitude of heat energy to the slipstream as those big bare aluminum ones. Yes, some heat gets out the sides through the fiberglass, but not near as much as what is directed inward to the pitot. Look at it this way, my 8 watt unit uses somewhere about 1/10 the power of the big ones, yet has less that 1/10 the mass and 1/10 the surface area, and in addition is insulated with fiberglass instead of being bare metal. I suspect that it's going to work OK. However, like I said, I sure don't want to make any claims of success until I get a chance to test it in flight with a thermocouple stuck up it's backside. Once I get a chance to try it out I'll post some photos etc. Jim Hocut jhocut@mindspring.com From: cdenk@ix.netcom.com Date: Fri, 26 Jun 1998 20:25:20 -0500 (CDT) Subject: Re: Re[2]: COZY: Pitot Heat On 06/26/98 16:20:45 you wrote: > > >Tom Brusehaver wrote: >>snip >>I assume, the goal of pitot heat is to raise the temperature of the >>air entering the pitot system somewhere above freezing. >>snip > >Well, not exactly (at least the way I think of it). Air doesn't >really enter the Pitot per se'. The pitot is supposed to be in >stagnant air so that all you get is pressure; zero movement. In any >case, the little air that is in the line to the ASI just gets smashed >(pressure) against a rubber diaphragm with nowhere to go beyond that >wall. The other side of the diaphragm is the static line which >basically just allows the diaphragm to move (if the side opposite the >pitot entry were closed off/sealed, the diaphragm wouldn't move). > >At any rate, I think the idea of heat here is to melt/prevent ice from >plugging the hole in the end of pitot rather than heating the air. >Gotta admit that heating the stagnant air inside the tube can't hurt, >since it just kinda sits there. > >Larry Schuler >lschuler@cellular.uscc.com > > > > The certified does just that, its a heated shroud tube with a drain hole, and incidently the tube itself is also heated, maybe enough to boil any water thats in there. From: cdenk@ix.netcom.com Date: Sat, 27 Jun 1998 14:48:49 -0500 (CDT) Subject: COZY: Heated Pitot Tube location I checked the location of my pitot tube. The forward edge of the streamline aluminum tubing mast is 1" forward and 6.25" below the canard leading edge. I think 7" or 7.5" below might be better and give more clearance to canard bolts. All dimensions are to the forward most point of the leading edges. From: cdenk@ix.netcom.com Date: Tue, 7 Jul 1998 16:05:45 -0500 (CDT) Subject: COZY: Re: pitot tubes - Source Certified heated pitot tubes are made by: Aero Instrument Co., Inc. 14901 Emery Avenue Cleveland, Ohio 44135 ph. 216-671-3133 THe part # PH506L for left side the fuselage level mount. price $111.50 + $3.00 shipping for UPS ground. The have the drain hole location for all angles of mount. If you drill your own, new location be careful of the heating element. The suggest mounting leading edge down 2 degrees for better drainage.