Date: Sun, 04 Aug 1996 22:52:31 -0700 From: Paul Comte Subject: COZY: "destabilizing in pitch" In the builders forum at Oshkosh 96, both Nat and Jim Patton addressed issues about the stability of the cozy design. The common thread is expressed in the phrase "destabilizing in pitch". (I hope someone can attribute that quote so credit will be given where it is due.) I've brought this up because of the recent discussions here about design changes especially in fuselage width. The sobering comments by Jim Patton about his experiences in a wildly pitching aircraft that looses over 3300' in 22 seconds SHOULD make you think through how much longer it will take to complete your project if you test it thoroughly. He described the transition between the slow hard-banked turn and being pitched through 90 degrees and pointing straight down "violent". Central to this issue is that the fuselage generates lift and will also present a larger surface during nose high attitudes. Those that want a bigger fuselage should plan for a longer building and testing their new design version. I don't think I'd have written this post if not for the thoughts by Bill Fox's presentation at the Cozy builders dinner. Bill is a retired director from Lockheed's Skunk works. He continued this thread without cues. According to Bill even Lockheed had problems with the YF-12 variant's nose cone causing a "destabilizing in pitch" problem. Their yaw was induced by the supersonic shockwave missing the lip of the engine inlet causing an instant loss of thrust. (I suppose the loss of 30,000 LB of thrust 20 feet off the centerline while up supersonic at 80,000' can cause complications) A bunch of injuries and deaths later (the plane pitches up and breaks in half) they started adding stabilizing features to the aircraft. The writers of the recent posts mentioning ad hoc fuselage expansions may want to pursue independent design analysis prior to construction. Paul From: "Steve Campbell" Subject: RE: COZY: "destabilizing in pitch" Date: Mon, 5 Aug 1996 09:02:10 Jim is a test pilot (retired) who flew the tests that Nat commissioned on the effects of CG loading, canard size, and lower winglet effects. Nat has written this up in several locations including the newsletters. The incident being referred to here is when the plane was being flown with the long canard and a very aft CG. It was interesting to hear the details from Jim first hand. I would refer you to Nat's writeups for the details. Steve On Mon, 05 Aug 96 08:50:51 est, lschuler@cellular.uscc.com wrote... > Paul, > > Waht was Jim Patton flying? > > If it was a Cozy MKIV, what was different from plans? > > If Cozy MKIV, what was determined to be the cause? > > More detail here would be very beneficial to all..... (especially for > those of us who didn't get to Oshkosh). > > Anyone else have info on this "Incident"? **************************************** Stephen A. Campbell Associate Professor, EE University of Minnesota ***************************************** Date: Mon, 05 Aug 1996 15:04:33 From: RSiebert1@gnn.com (Reid Siebert) Subject: Re: COZY: "destabilizing in pitch" Jim Patton was flying Nat's airplane. This flight, as well as many others, was part of the deep stall flight testing Nat did, and reported in Sport Pilot, a few years ago. The result of the flight testing was that the Cozy could stall AND SPIN when flying with the original length Roncz canard. Finally shortening the canard tips by three inches made the problem go away. This is why Nat is so adamant about everyone shortening their canard. I attended Jim Patton's forum on stall testing aircraft, and he also talked at the Cozy Builder's forum, as Nat's guest. He did deep stall & spin testing on many small aircraft, including the Velocity and Cozy. He even showed an inflight video of the Cozy stall/spin flight, which proved to be quite a wild ride that even Jim had never experienced. What I learned from all of this was enough to convince me to follow Nat's plans when it comes to the canard construction. It is one part of the airplane that can't be compromised! My four days at Oshkosh was well worth the time and money. Reid Siebert - Mk.IV #221 Date: Mon, 5 Aug 1996 14:03:16 -0400 From: CheckPilot@aol.com Subject: Re: COZY: "destabilizing in pitch" In a message dated 96-08-05 11:15:03 EDT, you write: << Jim is a test pilot (retired) who flew the tests that Nat commissioned on the effects of CG loading, canard size, and lower winglet effects. Nat has written this up in several locations including the newsletters. The incident being referred to here is when the plane was being flown with the long canard and a very aft CG. It was interesting to hear the details from Jim first hand. I would refer you to Nat's writeups for the details. Steve >> This was also without the lower winglets. Jim Subject: Re: Re[2]: COZY: "destabilizing in pitch" Date: Mon, 5 Aug 1996 16:24:24 -0400 (EDT) From: "Randy Smith" While I think that flight testing is necessary, I don't see the connection between widening the fuselage and pitch instability. The examples given (from what I can remember) were the flight tests with the long canard and extreme aft CG, and then the transonic flight testing of a fighter plane with jet engine inlets not seeing the desired shock pattern. Neither condition should exist on the Cozy and only one is connected to a wider fuselage but at trans/supersonic speeds. Please tell me where the connection to my flight envelope will be as I did not get to hear the speaker. Tell me how the change in lift from the fuselage will effect the pitch stability and to what magnitude. (My guess is that wider fuselage = more "lifting body" effect (or more drag) which will throw off the pitch stability.) Tell me if this is a problem I should worry about greatly or "just keep it in mind." Why did Nat stop his fuselage widening of the Long EZ to Cozy3 and Cozy 3 to Cozy 4 where he did? What did he do to restore the stability? --* --- -* **-* *-** -*-- -* Crash Rescue Team 7 - Don't PANIC! |Cozy MkIV| NCR General Purpose Computing Randy.Smith@ColumbiaSC.NCR.COM |---( )---| Global Support Center Voice 803-939-7648, V+ 633-7648 ___o/o\o___ West Columbia, SC 29170 "I am the way, the truth, and the life..." -JC Date: Tue, 6 Aug 1996 14:30:05 -0400 From: SMilesCozy@aol.com Subject: Re: Re[2]: COZY: "destabilizing in pitch" Larry Schuler wrote: >I thought this was about something different. It sounded like it >might have to do with the fuselage width. It does, at the forum they discussed how fuselage ahead of the cg tends to be de-stabilizing since it acts as a lifting body. Any additional width ahead of cg helps to lift nose at high aoa. This is what is theorized happend to MkIV, widened fuselage from 3 place, used same canard area, (increased span to compensate for wider fuselage), It caused too much lift up front, stalled main wing. The fix, shorten canard. > I am one of "THOSE" people attempting to achieve a bit more comfort. Therefore, I > am always very keen on what others may experience with the "wider fuselage". >Beacuse of my mods, I intend to go through an extensive test period; probably >the first 75 to 100 hours or so. Sounds like a good idea :^) Keep us informed on your progress, anything we can learn from each other helps all. Steve Miles Cozy MkIV 272 starting soon Date: Fri, 23 Aug 96 13:06:49 est From: "Larry Schuler" Subject: COZY: Cozy width Randy, Hope you don't mind; I'm going to share this with the group. There are others also working on wider fuselage (much further along than I); they might get something out of it. >I talked with Nat last week (in person, sat in his plane as well to >validate my suspicion that the fusalage needs to be wider). He said When I sat in it, was morning after a rain storm..... got my feet very "soaked"; Nat might be an engineer, but his workmanship is a bit short (my opinion). I certainly give him credit for constantly "fideling" with ideas on his plane though; we all benefit. >rather offhand and non-commital that the plans built model was about >2 inches wider than the prototype and that "it could probably go a >little more." I pretended like I didn't hear it. I was also rather >vague as to my plans but tried to convince him that we would be >doing >extensive testing on the plane after completion. I figure I won't tell >him unless he asks. Maybe 6" wider? I figure it's a basic trade-off between speed (drag), comfort, and structure (stress). More comfort costs a bit in speed, the structure weighs a bit more and usefull load will be a few pounds less unless structure can handle the added gross. I like the trade. It's a personal choice. Remember, the first VE was designed by Burt for a VW engine and great economical performance (relative to the then current factory stuff). The VE absolutly achieved that goal and more. The LE was nicer, roomier, but had a bigger engine, wing etc. MK-III and IV are roomier still; each has a bigger engine and other trade-offs. Look at the cabin area of Burts round the world plane.... Absolutly superb performance per design goal; but I am not as small as Ms Yeager or as skinny as Dick; and I don't intend to set any records (except maybe my own personal one.... to build it).... It's all about choices.... I try not to underestimate Nat's legal liability in fostering mods...... He has bitten off a lot and we are benefiting from his risk. If we modify it, he doesn't even want it called a Cozy; I can't blame him a bit. >I asked him what was his criteria for stopping when he decided to widen >the long-EZ in order to make the Cozy-3 and then the MK IV. He didn't >give me a hard answer but rather something like, "until it looked >right" and then he rattled off the things he made bigger for the MK IV. > Not why he stopped where he did. My hunch is that he is a small guy >with >a small wife and stopped when they could both fit. Funny how that works isn't it.... I'm bigger, sooooo....... What "things" did he rattle off? Your conversation would be interesting to the entire group I am sure. >Let me know what you find in this area. I suspect that I will have to >have a cu$tom canopy made. Last time I talked to Aero Plastics was a year ago when I was thinking about this; said a special would cost about $300 for special set-up plus regular Cozy charge. That was before the recent increases. Not sure what I will do at the moment.... I am quite a way from needing it and I still don't know what shape it will be, or wheather it will be front-hinged like Phillip's..... (he has some neat ideas). >Nat said that the main spar was overdesigned. I don't think this will >be a problem for either spar. I'm not surprized; Infinity and others say the same. >The thing that got me wondering is what % of lift/drag is generated by >the fuselage? There was a "you'll all die if you do this" mood on the >mailing list a few weeks ago and after I asked some specific >questions, no one seemed to want to talk about it. The examples given >were from Nat's reduced canard span/aft CG testing and from a test >pilot's story of a jet fighter turbine inlet at transsonic speeds. >Have you seen any data as to how much "lifting body" lift/drag we get >from the fueslage? >I know the wetted area will increase and result in more drag, but by how >much? If I build it will I die?..... beats me. I certainly don't intend it that way. I am indeed "EXPERIMENTING", no doubt about it; that's the name of this hobby. I keep remembering Mr Whitman; he knew what he was doing (he thought so) and had built many planes in his long life.... One of them finally got him; but I'll bet twenty years wages that he didn't intend it that way. The idea is to try to do this in an educated, informed manner; that's the hard part when we don't do this for a living; but, I'm trying. As for additional lift from the fuselage: Some, I expect, but should only be significant at higher angles of attack. Yup, this implies that it might be a concern at main wing stall angles of attack. However, thinking this through a bit, the main wing stall problem is generally only a "problem" with aft CG loading. It could be a problem during aerobatics too (if the angle of attack can get that high). My only concern (without rambling too much) is: Will the "front" of the fuselage add sufficient lift to the already present canard lift to allow sufficient angle of attack to stall the main wing during "normal category" flight manuvers while operating within the "normal" CG range? My immediate answer is: I doubt it. Primarily because I will be getting additional fuselage lift (like a lifting body) from the entire fuselage, not just the front, near the canard. My longer answer is: "I won't know for sure until it's tested." {Gee, now Nat has me saying it.} If I happen to put a hole in the ground testing it, you will hear about it. If it works, I will try to see that everyone has a chance to hear about that too..... all ya gotta do is wait five or so years before I can test it. In the meantime, the best I can give you is my opinion..... FWW. As for the "you'll die' stuff.... I might be wrong, but my guess is the Wright brothers heard the same comment. That is not a bad thing; in fact it helps me make sure I think things through (I hope). Multiple perspectives are always good, and that is what this list is all about. The lifting body comments made me stop and think....... That's a good thing. I havn't calculated the additional drag or tried to find the additional Cl. I'm not sure why I should, since I have nothing of any value to compare it to. If anyone has the curves and calculations of the stock Cozy fuselage design from wind tunnel tests and completed measurements, perhaps they would be willing to share it. If that info is available, then tracking what I have might be meaningful. I could try to predict the speed reduction to within one or two mph, but why? I already know it's going to be slower. I'll have a precise answer in five years; but the difference might be due to the way I build the belly scoop, or the engine carburation, or canopy gap, or something totally separate {since my fuselage will have absolutly no ripples -:)}. At the moment, it may sound rather crude, but I am happy wth a good old fashiond SWAG [Scientific, Wild-A** Guess] on the percent drag/lift change. Based on prior knowledge: I "guess" they will both be more since it's a bigger fuselage {I just can't prove it; and won't be able to when I fly it}. Now look who's rambling......... Larry Schuler MKIV-#500 >Thanks, (its late and I'm rambling) >-Randy >Cozy MKIV - #485 Date: Mon, 26 Aug 1996 14:26:23 -0400 From: CheckPilot@aol.com Subject: Re: COZY: Cozy width In a message dated 96-08-23 14:18:11 EDT, you write: << >I asked him what was his criteria for stopping when he decided to widen >the long-EZ in order to make the Cozy-3 and then the MK IV. He didn't >give me a hard answer but rather something like, "until it looked >right" and then he rattled off the things he made bigger for the MK IV. > Not why he stopped where he did. My hunch is that he is a small guy >with >a small wife and stopped when they could both fit. >> Either in Downie's book about Rutan acft or in the early newsletters Nat talked about designing 22CZ and that Burt told him it would be 15mph slower than the Long and not to do it. He just bought Long-Ez plans and kept to himself (interesting how history repeats itself). I think the reason he made it just big enough (I believe he said 38" across at the shoulders, the same as a 150/152) was to minimize the flat plate drag. He tried to recoup the losses through the NACA scoop and other cleanups, resulting (according to one newsletter) in an approximate 1.8 mph loss compared to a hypothetical Long-Ez based on CAFE 400 results. Just a little rambling. Jim Cozy III #455 Date: Mon, 26 Aug 96 14:23:53 est From: "Larry Schuler" Subject: Re[2]: COZY: Cozy width Hi Roy, Finished the final layup on the instrument panel yesterday; I will not make the firewall bulkhead unitl I must (engine mount concerns). I am presently fixing the 5-minute epoxy "dings" in the fuselage sides; that will probably take the remainder of this week. Will then be mating and trimming the bulkheads to the fuselage sides for the next week or so. Nifty thoughts on comparisons. I wish I had a copy of all the plans in hand; I'd REALLY like to know what the dimentinal and structural differences are..... THAT would show the linear progression of the shape and structure. Alas, I am strapped for funds to do such plans collecting. As for a wind tunnel: if I could afford the use of one, I would be building a Lancair IV-P, not a Cozy. -:) In any case, I think that knowing the exact, measurable, differences in drag, air speed etc. due to a wider fuselage is one of those scientific things that I am not compelled to know prior to flight. Knowing that I will go slower is important (I already have that information); knowing how much slower is Not (for this application). Stress differences, however, are of great concern (to me). Believing that it will stay together at any speed up to VNE + Margin is imperative! Larry ______________________________ Reply Separator _________________________________ Subject: Re: COZY: Cozy width Author: Roy Grossinger at INTERNET Date: 8/23/96 4:49 PM Hey Larry. Haven't talked to you in a while. How has it been going? I've been interested in your design change, not that I am going to remake my bulkheads and widen the fusealage, but for the interesting engineering questions it brings up. Since many things can be compared lineraly, why don't you see if you can get data from a VE, a LE, a Cozy III, a Cozy IV, and finnaly and AroeCannard. They are basical the same, with the biggest change from the VE to the LE (I guess). See if you can come up with a correlation to changes in the cannard length, wing surface area, and frontal surface area. This could give you clues as to the responce a six inch change in width may have on the speed/drag and the extra lift you may notice with a wider belly. You could go to a wind tunnel, but who has that kind of change? Anyhow, with all the planes flying you should be able to get data from many sources. ============================================================================= Roy H. Grossinger- ME grossinr@rastro.colorado.edu Cozy Mk IV #503; Chapter 4 ROY_GROSSINGER@Radon-hq.ccmail.compuserve.com CU's Go - 4; Hull Layup "A man's destiny is his character" | ___ | |---------(>-<)---------| http://www.abwam.com/grossing / ~~~ \ o/ \o Date: Tue, 27 Aug 1996 10:17:50 -0400 From: DFinn7971@aol.com Subject: Re: Re[2]: COZY: Cozy width In a message dated 96-08-26 17:54:05 EDT, lschuler@cellular.uscc.com (Larry Schuler) writes: << Finished the final layup on the instrument panel yesterday; I will not make the firewall bulkhead unitl I must (engine mount concerns) >> As another thought on the firewall, I raised the height of my canopy by two inches. This results in the need to add 2" to the height of the firewall. IIf you are tall (I'm 6' 3") you might want to consider doing the same to your canopy. You can save yourself some effort by building the firewall to the corrected shape rather then modifying it later. Dick Finn Cozy Mark IV #46 DFINN7971@AOL.COM Date: Wed, 28 Aug 96 18:01:42 est From: "Larry Schuler" Subject: Re: Re[2]: COZY: Cozy width Hey! I'm 6'3" also..... That was the other part I didn't mention for delaying. Anyway, was 2" added fairly straight back or was that how it ended up at the firewall? Is it enough? Thanks, Larry Schuler MKIV-#500 Date: Thu, 29 Aug 1996 16:55:53 From: JRaerocad@gnn.com (Jeff Russell) Subject: Re[3]: COZY: Cozy width "Larry Schuler"wrote: >Hey! I'm 6'3" also..... > >That was the other part I didn't mention for delaying. >Anyway, was 2" added fairly straight back or was that how it ended > To add commentary to the first question, it probably wouldn't hurt too much to make the fuselage out of the thicker foam and contour the inside to make it roomier. (This is just an off-the-top-of-the-head guesstimation and I wouldn't think of doing this without a prototype tested and structural analysis performed on the new structure. This commentary is purely philosophical.) The loading around the curve probably wouldn't change much if the fuselage was curved out slightly. However, chages would have to be made to the instrument panel and front seatback. The instrument panel could, I suppose be made oversized and sanded down to match the new shape, but since the seatback is made sealed(fiberglassed) on the edges and is at a 45=B0 angle, multiple seatbacks may have to be fabricated before an acceptable fit with the fuselage sides is obtained. Also, the jigs for the fuselage sides would have to be modified to make the longerons end up in the same location. As far as drag goes, this probably wouldn't be affected too much as long as there is a gradual transition from the nose to the tail of the aircraft. I don't want to discourage your ideas because: 1. A rounder Cozy would probably look cool. 2. Extra space in any airplane is a luxury. 3. If new ideas were shunned, we wouldn't be building Cozys. Oh, and I forgot. I am in the process of doing the fuselage sides and the foam used (forgive me I can't remember which) is not all that easy to 'carve'. When I was done sanding the control stick depressions, I was glad that that's all there was to do. If you try this let me know and send pictures, I just thought that I'd give you something to think about. It sounds to me like a lot of planning ahead would be needed though. Jon Graf #506 Jonathan Graf graf@ectss2.jsc.nasa.gov