Date: Tue, 26 Mar 1996 19:31:29 From: JRaerocad@gnn.com (Jeff Russell) Subject: Short Canard? There are now at least 2 flying AeroCanards/MkIV's with the cutoff Ronce canard. Both people have complained about the long distance of runway it takes with 2 people (360 lbs) and a 85 to 90 mph rotation speed to lift the canard. I can tell you that both of these airplanes have about the same empty CG as our AeroCanard, but empty weight on the 2 airplanes are 1225 lbs and 1385 lbs. The 1385 lbs plane is using an Infinity RG with Full leather and heavy IFR pannel. The lighter plane flew last week for its first time with duel people on its taxi test with the same result as above. Dave Ronnenberg was one of the pilots in this test so this Info should be correct. The CG was 97.5 when the rotation speed was 90 mph. Our airplane with the 147" canard at the 96.25 CG (400 lbs) in the front seat rotates at 78 mph with about 2000 feet of runway at 1880 flying weight with 95 deg. giving an 3600' density altitude. Our AeroCanard has flown at 96 - 102.1 CG and a Gross weight of 2160 lbs. With these weights and CG's tested, I have never felt I was going to run out of elevator on my take off's or landings. Worse case was landing speeds about 80 knots and take off's at 70 knots with 2500' of runway used. My min. front seat weight is 195 lbs. I weigh 155 lbs. so I carry 30 lbs. in the nose when solo, but I can safely carry 400 in the front seat. If you are a big pilot and want to carry the same size beside you, the manditory cutoff of the canard might make you crash and burn if the runway is not 10,000 feet long. I am not telling builders to change what they have, have built, or are building, but you need to plan on how flying your airplane will affect the needs of you and of the canard. The heaver airplane took off with 370 lbs in the front seat on a 3800' runway with water on the other end. He almost ended up into the drink becouse of his short canard. I don't want to see this kind of things and I know neither do you. Hope this helps. AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com Date: Tue, 26 Mar 1996 20:23:53 -0500 From: JHocut@aol.com Subject: Re: Short Canard? Could the incidence angle have anything at all to do with this? Quite a while ago there was a discussion on the homebuilding newsgroup about some Cozy's have a negative incidence, and really eating up runway. Someone on the newsgroup said (incorrectly) that the answer was to lengthen the nosegear by an inch or two. At the Cozy forum, Nat said the the proper solution would be to shorten the main gear a little bit, in order to get the incidence in the range of 0 to 1-1/2 degrees. Jim Date: Wed, 27 Mar 1996 08:20:02 From: JRaerocad@gnn.com (Jeff Russell) Subject: Re(2): Short Canard? >Could the incidence angle have anything at all to do with this? I can tell you that our incidence on the AeroCanard is 1-1/2 + on the nose. The others are also about the same. The airplane with the Infinity gear seams to change angle when the main wings get light at rotation speed. So he has to bounce the nose to get the canard flying. The angle of incidence was also checked on the wing/canard and both showed (OK). AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com Date: Wed, 27 Mar 1996 10:35:43 From: JRaerocad@gnn.com (Jeff Russell) Subject: RE: (3)short canard? On both the airplanes plus mine, the wings were set using the Root hotwire templete to set the angle and the canard was also checked by a template also. On the RG airplane, the canard was check by me, making sure shape an angle of incidence were correct. On the other one, the canard was made from AeroCad. Dave Ronnenberg checked all of the above before taxi test. Don't forget the elevator is also shorter when cutting the canard off. I don't mind sturring the pot if good answers come from it. Also on my 3 place Cozy, Nat told me becouse I did not like the front seat max weight that changing the canard to a longer style could help this. I went from a GU to a Ronce 150" canard and loved it. My front seat mim. weight went from 175 to 220 lbs and max front seat went from 365 to 410 lbs. The 2nd owner flew the a max front seat of 435 lbs. for over 100 hours before he purchased a new airplane. more to think on. AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com From: Marc J. Zeitlin Subject: Re(2): Short Canard? Date: Wed, 27 Mar 96 9:00:23 EST Jeff Russell Writes: >There are now at least 2 flying AeroCanards/MkIV's with the cutoff Ronce >canard......... >The CG was 97.5 when the rotation speed was 90 mph. Our airplane with >the 147" canard at the 96.25 CG (400 lbs) in the front seat rotates at 78 >mph with about 2000 feet of runway at 1880 flying weight with 95 deg. >giving an 3600' density altitude. Our AeroCanard has flown at 96 - 102.1 >CG and a Gross weight of 2160 lbs. Jim Hocut Asked: >>Could the incidence angle have anything at all to do with this? Jeff Replied: >I can tell you that our incidence on the AeroCanard is 1-1/2 + on the >nose. The others are also about the same. The airplane with the >Infinity gear seams to change angle when the main wings get light at >rotation speed. So he has to bounce the nose to get the canard flying. >The angle of incidence was also checked on the wing/canard and both >showed (OK). I know we've hashed over this "short canard" issue a lot (6 - 9 months ago; it should be in the 1995 archives) but I feel the need for enlightenment once again. Jeff gives as examples two aircraft which apparently have trouble rotating on takeoff. Both planes have a correlating factor of the short canard. Before we can assume causality, we need to take a look at ALL the factors that can affect rotation, and not ASSUME that one factor causes the behavior. 1) Canard Shorter - Jeff gives as an example his own plane, which rotates at 78 mph under the conditions given. If we take Jeff's canard of 147", cut it back to 141", and apply the lift equation, we end up with 95.9% of the canard area, and a rotation velocity of 104.2% of the previous velocity, or 81 mph. So, this would seem to indicate that for the short canard to produce EXACTLY the same amount of lift at EXACTLY the same angle of attack, Jeff's canard would only have to go 3 mph faster - this is almost within the error bands of airspeed indicators - it would be hard to notice (and Nat claims he hasn't noticed any difference in HIS plane's rotation speed). 2) Relative incidence of canard/wing - the relative angles of the canard and wing have a large effect on the speed at which rotation will occur. Since we don't have a specification for this angle, and since it's very difficult to measure, many people may not even know what the angle is, or should be. I know I don't. (I believe that this is a large problem with the plans - there are no tolerances given for some VERY important specifications). 3) Absolute incidence of canard and wing with respect to ground - As we know, many V.E., L.E., and COZY aircraft have had trouble rotating. In many cases, people have traced the problem to the absolute incidence angle (supposed to be between 0 and 1-1/2 degrees for the MKIV). While Jeff states that his is dead nuts on the high end (leading to low rotation speeds) and that the other two are "about the same", we don't know exactly what they are, and Jeff states that one of the aircraft changes the angle as the gear unloads, causing the pilot to have to bounce the nose to rotate! 4) Canard Airfoil - The shape of the laminar flow canard airfoil can have a large effect on the lift produced by the canard. Any aircraft having trouble producing canard lift may have an airfoil shape problem. Now, I won't claim that the canard length didn't cause the reported problems with these two aircraft. I merely state that OTHER FACTORS exist which MAY have as much or more effect on the rotation of these aircraft, and that we CANNOT assume that a correlation = causality. Until someone does more research into the existing geometry of these aircraft (or adds 3" to each wingtip and sees what happens), we just can't be sure. Nat's plane flies fine with the short canard, Jeff's plane would have a marginal speed difference with the short canard; it's very difficult for me to believe that the short canard causes a 7 - 12 mph rotation speed difference. With all the other confounding factors, all the tolerance buildups that can occur to cause these to be other than what is required, and with all the evidence from previous aircraft showing that these other factors DO cause higher (and sometimes VERY much higher) rotation speeds, I don't think we should blame the short canard just yet. Now, as someone who has already hacked their canard to the shorter length, I am of course concerned, but not worried............. -- Marc J. Zeitlin Email: marcz@an.hp.com From: Marc J. Zeitlin Subject: RE: (3)short canard? (fwd) Date: Wed, 27 Mar 96 10:53:35 EST Jeff Russell wrote: Glad to hear that qualified people have gone over both of these aircraft. Eliminating some known possibilities does not imply that one other known possibility is the culprit, however. There's still the issue of the retracts unloading, and other unknown factors, which are, er, unknown :-). >........... Don't forget the elevator is also >shorter when cutting the canard off. Area is area - the C is determined by elevator angle, not size. L > >I don't mind sturring the pot if good answers come from it. Excellent. Nothing like a good argument (whoops, sorry - DISCUSSION) to make people think :-). >....... I went from a GU to a Ronce 150" >canard and loved it. My front seat mim. weight went from >175 to 220 lbs and max front seat went from 365 to 410 lbs. Did adding the length to the canard substantially change your rotation speed? Like by 7 - 12 mph? Or did it only substantially change the weight capacities? >The 2nd owner flew the a max front seat of 435 lbs. for over >100 hours before he purchased a new airplane. I don't doubt at all that having the longer canard can change the maximum front seat weight a great deal, and for those who need that, keeping the canard long may be the right answer. Personally, at 150 lbs, I don't think I'll EVER have 400 lbs in the front seat, but that's just me. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Wed, 27 Mar 1996 11:20:15 -0500 From: JHocut@aol.com Subject: ReReReRe: short canard? In a message dated 96-03-27 10:54:27 EST, you write: >I don't doubt at all that having the longer canard can change the maximum >front seat weight a great deal, and for those who need that, keeping the >canard long may be the right answer. Personally, at 150 lbs, I don't >think I'll EVER have 400 lbs in the front seat, but that's just me. You scrawny little guys make me sick. At 210 (more if it's right after the holidays), I won't have any problem with staying over the min. front seat weight. I'd like to be able to carry a passenger who's at least close to my size, so am seriously thinking about not shortening the canard. One little point also, when we talk about a MIN or MAX front seat weight, what we're really talking about is the CG location. The wings and canard don't know how much weight is in the front seat (but they'll sure let you know about it if you're over gross weight or out of the CG range). Jim Date: Wed, 27 Mar 1996 17:14:07 From: JRaerocad@gnn.com (Jeff Russell) Subject: RE: (3)short canard? (fwd) Marc writes: >Did adding the length to the canard substantially change your >rotation speed? Like by 7 - 12 mph? Or did it only substantially >change the weight capacities? With the canard change (GU to Ronce) this is not apples to apples. My rotation speed at the same CG was about 5-8 knots slower. From many EZ drivers that switched from the GU to the Ronce, the complaint of longer takeoff rolls and higher landing speeds were normal. The Ronce canard would also stop flying sooner on landing than the GU. >canard long may be the right answer. Personally, at 150 lbs, I > don't think I'll EVER have 400 lbs in the front seat, but that's >just me. I am only 5-10 lbs heaver then you. I seem to get more calls from people that are a bit heaver then me (200-240+) that want demo rides and I could not do this if my dingy was to short. Enough on that. AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com Date: Wed, 27 Mar 1996 12:48:52 -0500 From: Phillip.Johnson@Lockheed.on.ca (Phillip Johnson) Subject: Short Canard? This whole business of the canard length is indeed complex. Nat's tests, described in news letter #44, indicate that the lift associated with the canard is not directly proportional to the canard area. There is a complex relationship of interaction between the main wing and the canard that is not understood. One of the things that is clear from the experimental data put forward by Nat is that the lift is affected by some higher order function than simple proportionality with wing area. The new data regarding take off role would also tend to support Nat's findings. With respect to Marc Z's comment saying that: > (and Nat claims he hasn't noticed any difference in HIS plane's rotation speed). I had correspondence with Nat prior to Oshkosh last year with respect to the canard length and rotation speed. It appears that Nat, on take off, accelerates to a given speed and then rotates. When he shortened the canard he did not change his take off procedure and the same rotation speed was maintained. He therefore concluded that rotation speed was unchanged. (Not very scientific). It appears that he never actually tested the minimum rotation speed for both cases. Phillip Johnson From: Lee Devlin Subject: Short Canard Date: Wed, 27 Mar 96 10:51:12 MST Jeff wrote: > The airplane with the Infinity gear seams to change > angle when the main wings get light at rotation speed. So he has to bounce the nose > to get the canard flying. The angle of incidence was also checked on the wing/canard > and both showed (OK). The fact that bouncing the nose causes the canard to fly is the 'smoking gun' in this case. It tells you that the canard incidence is the more likely cause of the problem and not the lack of lift caused from reducing the canard's length. The bouncing causes the canard to transition through a range of negative, neutral, and positive lift. The comment about the main gear unloading is also very important. This would indicate the main wing begins flying first, which can be expected, and can exacerbate the rotation problem by lowering the incidence angle of canard and wing as the plane accelerates. A main landing gear with a softer spring constant would tend to make this effect worse. Loading the front seat also causes the nose gear, spring, and front tire to compress which further lowers canard incidence. We are not talking about a lot of distance here. A one inch change in the vertical position of the canard or wing will result in around .7 degrees change in incidence which is nearly half the tolerance window! Measurement of the incidence therefore is only meaninful if you have the plane loaded while you do the measurement. Add to that the unknown effect of the plane's speed and the way it loads the airfoils and you can conceivably get the plane in a state so that it cannot take off at any reasonable speed or distance. Lee Devlin Date: Wed, 27 Mar 1996 18:46:22 From: JRaerocad@gnn.com (Jeff Russell) Subject: Re: (3)short canard? From: Dick.Finn@FNB.sprint.com >Dick noted the attached: > >Jeff, > >I shortened my canard as advised by Nat in his newsletter. >It came at a good time as I was in the process of building it then. >Nat set the requirement to cut 3" (I think) from both ends. This >does not cut into the elevators. My elevators are the same length >as a standard length canard. I wish that was true, but the long canard/elevators are 147" from end to end. The short would be 141" from end to end. Unless your tips are longer, I think this is what you should have. AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com Date: Wed, 27 Mar 1996 17:59:00 -0500 From: Dick.Finn@FNB.sprint.com Subject: Re[2]: (3)short canard? Jeff Russell noted the attached: Jeff, I shortened my canard as advised by Nat in his newsletter. It came at a good time as I was in the process of building it then. Nat set the requirement to cut 3" (I think) from both ends. This does not cut into the elevators. My elevators are the same length as a standard length canard. Dick Finn Cozy Mark IV #46 ______________________________ Reply Separator _________________________________ Subject: RE: (3)short canard? Author: owner-cozy_builders@hpwarhw.an.hp.com at INTERNET Date: 3/27/96 10:40 AM Don't forget the elevator is also shorter when cutting the canard off. From: Lee Devlin Subject: Re: (3)short canard? Date: Wed, 27 Mar 96 18:05:48 MST Bill wrote: > A brief note to all =FB=FB.........I talked to Nat about shortining the=20 > canard when the newsletter came out. I also was concerned that it would=20 > cut into the elevator. He knows my size and to=F4=A8ld me that if I took 2= > =FB=FB" > off each end it would be acceptable and it would eliminate the elevator=20 > problem. 2 bits Bill W [Sorry, this is how Bill's text appears in my email system.] Yes, it seems as if shortening the canard by 4" was all Nat had intended to do. It was Jim Patton who convinced him to cut off another 2" for good measure. Nat wrote in Newsletter 45: ------------------------------------------------------------------------ My educated guess (based upon experience with the Varieze) was that the canard would have to be shortened by 8 inches to move the c.g. range 1 inch farther aft. I decided to do this in two steps, to get an intermediated reference point. It is hard to describe my surprise when, after just shortening the span by 4 inches, I could no longer get the main wing to stall, even with the c.g. as far aft as 103.2. Jim Patton persuaded me to shorten the canard span another 2 inches (making a total of 6 inches) for added insurance to cover variations between builders. With 6 inches less span than shown on the plans I was still able to take off and land at a c.g. 1 inch forward of the design forward limit, which is equivalent to more then 400 lbs. in the front of our plans model Mark IV. ------------------------------------------------------------------------ So, it would be hard to for Nat to argue with you if you only wanted to take off 4" total instead of all 6" since that is also a tested configuration. Lee Devlin Date: Wed, 27 Mar 1996 23:54:57 -0500 From: Nigel Field Subject: Short Canard continued Folks, Have been keenly following the discussions on the short canard, now and 6 months ago, and am trying to make sense of it all. Am especially interested since i am soon to start on another Cozy canard again, since i built one way too short. There is dumb and dumber, and i fully qualified for both by reversing the block dimensions when i cut the cores. I put the longer block in the middle and the short on the ends. Didnt pick it up until it was almost done. Having built two previous canards I just got too complacent. Have wrestled with just what length to make it. Two builders at osh said make it long due to the high rotation speed and move the engine back a couple of inches. I am very reluctant to do that without knowing why. I went through a similar experiment with my VE now 5 years ago when i built a short roncz canard to replace the GU. A lot of folks said I would kill myself so i designed a weight and balance spread sheet which also calculates wing and canard loading in lbs/ft sq for any weight condition. I have found it a very valuable tool for playing "what if". I played with the length thus area, to give me a loading 10% higher than i had with the GU since the A/C was extremely pitch sensitive and was mildly divergent stick free in pitch axis. It was worse the higher i flew and at 10k would reach + -45 deg in three cycles. I arrived at 118 inch span 13 ft sq area and built it. I also reasoned that if it would rotate at a respectable speed say 70 kts then it would fly. Fly it did, much better than the 144 inch GU, fully stable in pitch, much better feel, 4 kts faster, and NO pitch down in the rain. I mention all this because i am convinced the answer is in canard wing loading. For example my VE canard is 13 ft sq and lifts 229 lbs for a loading of 21.9. It roatates nicely at 60 kts. I took Jefs data and loaded it into the spread sheet appropriately modified for the MKIV and got a canard loading of 41.3. Using square law this works out to a rotation speed of 80 Kts about what guys are getting. Does this make sense?? I have made a few assumptions since i dont have anyones exact W/B data and the S sheet needs the main wing center of lift to give accurate loadings. I have calculated it at FS 128 but this may off a bit since i dont know the exact lift distribution of the wing and strakes. Does anyone have this data and can provide it? Also can anyone can send me actual W/B data for a MKIV and/or MkIII so i can load and run it. Can provide the Spread sheet in lotus 4 as an Email attachment if anyone wants it just ask. I think its a nice tool to help make sense of this and I want to solve it for my Cozy project. Sorry so long, Nigel Date: Thu, 28 Mar 1996 11:05:30 From: JRaerocad@gnn.com (Jeff Russell) Subject: Re: Short Canard? Phillip Johnson writes: >I had correspondence with Nat prior to Oshkosh last year with >respect to the canard length and rotation speed. It appears that Nat, >on take off, accelerates to a given speed and then rotates. When he >shortened the canard he did not change his take off procedure and the >same rotation speed was maintained. He therefore concluded that >rotation speed was unchanged. (Not very scientific). It appears that >he never actually tested the minimum rotation speed for both cases. This is why I would still like to know if there are any MkIV's flying with the short canard. I understand there are at least 9 total in the air. I can also tell you that moving a weight to change CG insted of adding real weight can be misleading on testing this bird. I think it was a good idea for using a moving weight to (get out of trouble) if testing aft CG went wrong (main wing stall). For testing runway lengths, rotation, real weights are needed. Has Nat ever tested 400 lbs in the plans model? Has Nat ever tested to gross yet? Has nat ever tested to gross at fwd CG? I have been told (No) on all of the above from him. I have done all three on the AeroCanard and it gets pretty hairy at high alt. plus high heat. Short canard for me? what do you think. AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com Date: Thu, 28 Mar 1996 15:46:56 From: JRaerocad@gnn.com (Jeff Russell) Subject: RE: (3)short canard? (fwd) >........... Don't forget the elevator is also >shorter when cutting the canard off. > >Area is area - the C is determined by elevator angle, not size. Greg Russell writes: Rockwell Engineer (Rocket Scientist) True, but the size of the elevator does determine how much air flow is deflected - giving either possitive or neg. lift. A longer elevator would also give a much faster response. AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com Date: Thu, 28 Mar 1996 11:10:53 -0500 From: Phillip.Johnson@Lockheed.on.ca (Phillip Johnson) Subject: Short Canard After a day punctuated with short canard postings my mind could not put it to rest. The archives show that I have been at issue with the topic since the outset of this group. Lee Devlin's smoking gun theory had considerable merit so I channelled my thoughts in this direction. Lee's comment stating that by bouncing the main gear of the RG version there would be a change in angle of attack seemed reasonable although it suggested that we are looking for about a worst case +/-1.2 degree change in incidence assuming the Infinity gear oscillates with the maximum unlimited excursion of +/- 1 inch. If Lee is correct, then increasing the static pitch by 1.2 degrees should achieve the same goal without needing to excite a pitching motion for take off. Now since the change in Cl (Lift Coefficient) for a change in angle of attack is typically of the order 0.067 per degree, a delta Cl of 0.08 may be expected from the Canard. For ICAO conditions this yields a change in lift of 21.1 lbs at 90 mph (90 mph is Jeff Russel's data). Interestingly enough, Nigel Field says that the canard wing loading is approximately 40 lbs / sq ft when heavily loaded (my calculations agree with Nigel in this matter). Now if we take the difference between the long canard wing area and the short canard wing area and multiply by the wing loading we get a figure of 21.7 lbs. i.e. the short canard provides 21.7 lbs less lift than the long canard. The oscillation mode adopted by the RG pilot would yield a maximum of 21.1 lbs of extra lift. By Chance the numbers are almost identical, I expected to see similar values not this level of correlation so this equality should not be used to express the validity of the analysis simply as a guide. So having established that the pitch of 1.2 degrees has a similar effect on rotation as increased canard area, what can one do about it. I found two solutions: 1) Increase the canard to the original length. This is not very practical to someone who has built the short canard. 2) Increase the elevator travel. In my text book searching last night it appears that most aerofoils, operating with slotted flaps like our elevator, will work with an elevator travel up to about 40 degrees whereafter the improvement in lift is small for a large elevator displacement. The problem with increasing the travel lies in that the stall occurs at a lower angle of attack than at low elevator angles. This is noticeable in Newsletter #44 when Nat recants the story of the canard stalling at full elevator with the short canard but not the long canard. In that situation he needed more elevator the keep the same angle of attack than with the long canard thus a stall occurs with a heavily loaded front end whereas one simply runs out of lift when it is lightly loaded (and in the approved CofG range). Nigel field recants his story of his Vary eze where he reduced his canard length to improve his stability. In his situation the aircraft was tail heavy thus most of his flying was in the aft CofG regime. In these conditions the CofG was close to the location of the neutral stability as he indicated. By reducing the canard length he moved the location of neutral stability rearwards thereby improving stability. Heavy pilots, like myself, would have been operating well forward of the point of neutral stability and so the aeroplane would have been less responsive than when Nigel flies. Nigel is an FAA standard pilot.) Nigel neglected to write that to overcome the loss of elevator authority he increased the elevator travel but one needs to be cautious when operating with a side by side configuration (Cozy) where the front seat load range is significant, because with the increased elevator travel IT IS POSSIBLE TO GET INTO A DEEP STALL SITUATION EVEN WITHIN THE APPROVED CofG RANGE. I can't remember the tolerances for the elevator travel, but some of the problems, encountered by the two aircraft, may have been exacerbated if the elevator travel was on the short side of the acceptance window. A small change here would appear to make a big difference, at least according to the text books. Nat likes the short canard because he is a light weight and so is Shirley. He has set the canard length to give a lively but not unstable flight regime for himself. Heavier pilots will find that with the short canard, they will be operating in the forward part of the envelope and thus a more stable, less exciting plane will be evident. The long canard will reduce the stability bringing the heavy pilot into the same regime as the light pilot with the short canard, BUT CAUTION IS NECESSARY, EVEN FOR A HEAVY PILOT, WHEN FLYING IN THE AFT CofG REGIME. To Conclude: Increase the elevator travel and you will get of the runway but risk deep stall. Keep the stock elevator travel, prevent deep stall but kill yourself trying to get of the runway. There is no free lunch. Phillip Johnson Date: Thu, 28 Mar 1996 20:00:51 From: JRaerocad@gnn.com (Jeff Russell) Subject: RE: (5)Short Canard Phillip Johnson writes: >Doesn't the fixed gear version compress the landing gear the >same as the RG. I know it is a different mechanism, but as the load >is taken onto the main wing the load to the main gear is reduced >thereby causing the tail end to be raised in a similar fashion to >that of the RG. The RG compresses the Oleo strut 2 inches, does not >the standard gear spring deflect a similar amount? If it does then the >same argument applies to both aircraft. The RG that Infinity makes has a 8" Oleo strut that normaly sits with about 4" compressed. If the airplane is lifting up 4" higher in the rear at about rotation speed, I wonder what kind of angle this produces on the canard. The main fixed gear seems to spread about 3" giving a 2" lower squat at 2000 lbs. At best you would only see a 2" rise when unloading that weight. The 1 1/2 deg. angle that I measure on the longeron is with about 1300-1400 lbs of airplane + fuel. The angle of the longeron only changes about 1/2 deg. with 380 lbs in the front seat with the electric lift I use on the nose strut. The spring acts stiffer in this configuration than the standard Brock stuff. I have had both systems in the AeroCanard. The RG airplane also has this same nose lift, 200 hp and CS MT Prop. More to chew on. AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com Date: Thu, 28 Mar 1996 20:01:41 From: JRaerocad@gnn.com (Jeff Russell) Subject: RE: (6)short canard? > Jeff said that the heavier plane (with the retract bouncing > problem) weighed 1385 lbs empty, and took off with 370 lbs > in the front seat. That adds up to 1755 lbs, and with 20 gallons > of fuel, we're up to ~1875 lbs. That puts us at about 83-84 mph > by Nat's calcs (obviously the C.G. position will have an effect, > not just weight) But the point is that the takeoff speeds are NOT > that far off the published ones for that weight (Jeff said 85 - 90 mph) > in an airplane that has an admitted angle of attack problem as the > gear unloads. What I have not told you is the RG with a worse CG then the 97.5 saw 100+ MPH without canard rotation. Scarry huh!!!!! The main wing is flying at this speed. Also, longer and deeper ailerons on the wing not changing the area of the wing will also produce (more lift, more responsiveness) then the standard one in the plans. Also this has been tested on the AeroCanard. More to come. AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com From: Marc J. Zeitlin Subject: RE: (3)short canard? Date: Thu, 28 Mar 96 16:35:39 EST I wrote: >>........... Don't forget the elevator is also >>shorter when cutting the canard off. >> >>Area is area - the C is determined by elevator angle, not size. Jeff Russell writes: >Greg Russell writes: Rockwell Engineer (Rocket Scientist) > >True, but the size of the elevator does determine how much air >flow is deflected - giving either possitive or neg. lift. >A longer elevator would also give a much faster response. No question. On the other hand, the elevator already goes from tip to root - it couldn't be any longer. When cutting the length, you're not changing the percentage of the canard that has elevator (and therefore a higher maximum lift coefficient). Now, if you could cut the canard length, and keep the original elevator length........ :-). Anyway, Chuck Wolcott has been trying to post info regarding his rotation speeds, but has been having trouble with his mailer. Given that Jeff was going to get some more information on geometry of the two aircraft, Chuck's information, Nigel Field and Philip Johnson's calculations, Lee Devlin's indication of canard angle with landing gear extension/retraction, I'd say that we've got a lot of possible culprits here, of which the length is certainly one. I also went back and looked at the performance graphs published in the owner's manual (and on the web at): http://www-msy-me.wal.hp.com/~marcz/cozy_mkIV/performance/ and noticed that Nat says that the minimum takeoff speeds are: WEIGHT SPEED 1600 lbs. 66 KTS (76 mph) 1800 lbs. 71 KTS (82 mph) 2000 lbs. 76 KTS (87 mph) Jeff said that the heavier plane (with the retract bouncing problem) weighed 1385 lbs empty, and took off with 370 lbs in the front seat. That adds up to 1755 lbs, and with 20 gallons of fuel, we're up to ~1875 lbs. That puts us at about 83-84 mph by Nat's calcs (obviously the C.G. position will have an effect, not just weight) But the point is that the takeoff speeds are NOT that far off the published ones for that weight (Jeff said 85 - 90 mph) in an airplane that has an admitted angle of attack problem as the gear unloads. The other plane is somewhat more problematic - with a 1225 lbs empty weight, two people and 20 gallons aboard, we're up to 1705 lbs. This puts it in the 80 mph rotation range (by Nat's predictions), although 360 lbs in the front seat and medium fuel will put the C.G. pretty near the front, I think. The rotation speed seems high, at 85 - 90 mph, but George Grahams comments about the possible position of the main gear (Jeff will check on this) lead us to question what parameters we HAVEN'T considered yet that may affect rotation speed. I find this a fascinating subject (as if you couldn't tell) :-). -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Thu, 28 Mar 1996 18:10:47 -0500 From: Phillip.Johnson@Lockheed.on.ca (Phillip Johnson) Subject: RE: Short Canard Marc Z writes: > The other plane is somewhat more problematic - with a 1225 lbs > empty weight, two people and 20 gallons aboard, we're up to 1705 > lbs. This puts it in the 80 mph rotation range (by Nat's > predictions), although 360 lbs in the front seat and medium fuel > will put the C.G. pretty near the front, I think. The rotation > speed seems high, at 85 - 90 mph, but George Grahams comments about > the possible position of the main gear (Jeff will check on this) > lead us to question what parameters we HAVEN'T considered yet that > may affect rotation speed. Doesn't the fixed gear version compress the landing gear the same as the RG. I know it is a different mechanism, but as the load is taken onto the main wing the load to the main gear is reduced thereby causing the tail end to be raised in a similar fashion to that of the RG. The RG compresses the Oleo strut 2 inches, does not the standard gear spring deflect a similar amount? If it does then the same argument applies to both aircraft. Phillip Johnson From: Marc J. Zeitlin Subject: RE: Short Canard Date: Thu, 28 Mar 96 18:34:47 EST Phillip Johnson writes; > Doesn't the fixed gear version compress the landing gear the same as > the RG. Who knows? > ..... I know it is a different mechanism, but as the load is taken > onto the main wing the load to the main gear is reduced thereby > causing the tail end to be raised in a similar fashion to that of the > RG. We would need to know the vertical component of the spring constant of the standard gear. If it's really stiff, then the load may transfer to the wing, but the motion might be very small. > .... The RG compresses the Oleo strut 2 inches, does not the standard > gear spring deflect a similar amount? Good question - does anyone have an answer? For you guys with flying planes, how far do you have to jack up the plane in order to change a tire? While the oleo may comress 2 inches, the tire compresses as well. This tire compression # would be the about the same for both planes. We would need to jack up a retract plane and a std plane and subtract 2" from the retract # to get the tire compression, and then subtract that # from the std # to get the std strut motion. Then we could compare the strut stiffness to the oleo stiffness. > ................... If it does then the same > argument applies to both aircraft. If it does then the retracts fall out of the argument, but the landing gear position may still be an issue. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Fri, 29 Mar 1996 08:26:02 -0500 From: Phillip.Johnson@Lockheed.on.ca (Phillip Johnson) Subject: RE: (5)Short Canard Jeff Russell Writes > The RG that Infinity makes has a 8" Oleo strut that normally sits > with about 4" compressed. Infinity tell me that they should compress 2 inches and that seems to agree with what I have seen on Bill Threeringer's Long eze loaded to 2200 lbs. The 4 inches mentioned above suggests under inflation of the Oleo, but this may be necessary to achieve adequate incidence angle. I have the Infinity RG for my MKIV they are installed but no engine is attached so I can't give real measured data. I made my own hydraulic nose gear and strut, and set the position based on the 2 inch compression. If the 4 inch figures are correct I guess I will have about 2.5 degrees additional nose up attitude. Infinity Recommend 100 psi in the strut, what was being used in the RG you tested? Regards Phillip Johnson Date: Fri, 29 Mar 1996 08:34:11 -0500 From: wilhelmson@scra.org Subject: Re[2]: Short Canard I will add my experience to this debate, since it seems to be a subject of interest. I will make it short. I have found that the major factor for takeoff is the "absolute incidence" angle. If this angle is low or negative the takeoff run will be long regardless of all other factors. My easy tested solution to this is to adjust the nose wheel to give a loaded positive angle.(I will send a drawing of a device that allows this to be done and still retract the gear fully). I have also found that the other problems associated with the canard loading (deep stall, running out of trim on flair, etc.) must be controlled by the PIC by keeping the CG within the range that the airplane has been tested for. Date: Sat, 30 Mar 1996 12:21:46 From: JRaerocad@gnn.com (Jeff Russell) Subject: Short Canard? The AeroCanard converted Cozy that has an empty weight of 1225 lbs. Here's his empty CG. NO oil with everything in that he will normaly carry on board. R Main 601 lbs L Main 602 lbs nose +22 lbs when he added oil (16 lbs.)his nose weight went to +3 to 5 lbs. same as ours. The main gear was at FS.109 instead of FS. 109.5 The canard was also found to be set almost 1 degree off (neg.) We were told that Dave Ronnenberg did check this on preflight but it was not right. The canard has been adjusted and we will here what that change makes ASAP. Keep you guys up to date AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com Date: Sat, 30 Mar 1996 14:18:57 From: JRaerocad@gnn.com (Jeff Russell) Subject: Re: Short Canard? Phillip Johnson writes: >Thus the nose weight should be 22 - 5.7 = 16.3 lbs. Is there >something going on that I am missing? It must be that the +22 is at level and also the 16.3 lbs. with the oil added. This did not add up to me, but this is what I was told. The weight of 3 to 5 lbs would take place if the nose was lifted to 1-1/2 degrees plus with the nose strut fully out?? Its hard to get good info sometimes. The book says to lower the nose to level the longeron. Then see what the weight is. What about the change in Flight station of the nose wheel?? Do you use the nose wheel FS at level or at the nose high stops to get your empty CG.?? The wheel can move by a couple of inches back from 0 to 1.5 deg. AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com Date: Sat, 30 Mar 1996 12:39:41 -0500 From: Phillip.Johnson@Lockheed.on.ca (Phillip Johnson) Subject: Short Canard? Jeff Russell writes > R Main 601 lbs > L Main 602 lbs > nose +22 lbs > when he added oil (16 lbs.)his nose weight went to +3 to 5 lbs. > same as ours. How can this happen? The oil lives at FS 142 so the moment about the main gear is 142 - 109 = 33 in x 16 lbs =528 lbs in. Now since the nose wheel is at FS 16, as I remember it, this would cause a lightening of the front end of: 528 / (109 - 16) = 5.67 lbs. Thus the nose weight should be 22 - 5.7 = 16.3 lbs. Is there something going on that I am missing? Phillip Johnson Date: Sat, 30 Mar 96 14:52:43 est From: "Larry Schuler" Subject: RE: (3)short canard? Marc wrote: >George Grahams comments about the possible position of the main gear (Jeff >will check on this) lead us to question what parameters we HAVEN'T >considered yet that may affect rotation speed. >I find this a fascinating subject (as if you couldn't tell) :-). Me too!!!!!! Here's a few more variables to ponder: Toe-in/out; main wheel bearing tightness; break pre-set; slightly higher drag of extended retracts (vs cleaner fixed gear).... all causing a nose-down torque. Just a few more differences between airplanes of same general style. If the rotation speed is raised due to mains unloading, doesn't that imply that the main wing is beginning to lift "before" the canard? Isn't that a no-no and leads to main wing stall sooner? It was my understanding that the canard design is such that the canard lifts before the main and gives out (stalls) before as well?????? Also, If the main wing unloads the main gear; doesn't the canard unload the nose gear about the same time to keep canard incidence in line with the main, or is the pilot holding the nose down deliberately for too long?????? Is the fixed gear so stiff that they don't "unload" also????????? Perhaps Phillip Johnson is right: need a bit more elevator travel to get canard lifting sooner to compensate for main gear unloading (regardless of gear type), but risk main wing stall if not flown properly. Phillip, maybe we need to design a variable elevator limit tied to airspeed using a tap off the pitot to a simple diaphram, spring, and cam to go with the increased travel. Maybe I'm nuts too. Larry Schuler MKIV #500 From: "Kevin Russert Walsh" Organization: Intelligent Automation Systems Date: Mon, 1 Apr 1996 19:24:44 +0000 Subject: (Fwd) Re: BOUNCE >Look at it this way: >Everyone assumes that the canard will stall before the main wing. >If you take this as a given then you must also accept that on a >takeoff run the main wing will lift before the canard. >Examine what would happen if the canard were to fly before the main >wing. With elevator power it would be possible to pull the canard >into a flying mode, while the main wing stayed nicely stalled. >Adding power and more angle to the equation you would have a Cozy >plowing down the runway nose high, but never really getting the main >wing unstalled. Not a pretty way of alighting, I would say. > >So the nature of the beast is such that the main wing will start >working first and quit working last. Because of this you would have >to find that the main gear may unload and bring the canard to a >slightly lower angle of attack. > >I think that people are going about this the wrong way by trying to >increase elevator travel, changing incidence, etc. If the plane flys >great in the air, at all CG positions and weights, and the only >problem is that it unsticks at a high speed, (Althought coming to >the first conclusion may be hampered by the second) then the problem >is that the plane is not seated right on the ground. > >No offense to the current designers or people who have modified their >planes with retracts, etc. but the original Rutan planes sat on the >ground at a noticable positive angle of attack. Did something get >lost along the way in search of a plane that looked right when it was >parked? Sorry for everyone to get this twice. My mail is screwing up and really making me pull my hair out!! (Wait, I don't have any hair) When Mark told me it bounced I forwarded it back to the list, but failed to modify it. A combination of a bad computer and an inoperative operator can really lead to problems!!! Kevin R. Walsh Mechanical Engineer Intelligent Automation Systems 149 Sidney Street Cambridge, MA 02139 TEL 617.354.3830 FAX 617.547.9727 Date: Mon, 01 Apr 96 18:59:08 est From: "Larry Schuler" Subject: RE: short canard? Phillip might have a better idea. I like the momentary push button as long as the darn thing won't slip from under a finger on rough pavement or rough air; could put you in the trees. After I wrote the last note about tying a limit to the airspeed, I remembered that it ain't just air speed that stalls a wing (ie. Canard); it's angle of attack and Renolds Number. E-Mail sure is easy to respond to without thinking stuff through......... Larry Schuler MKIV-#500 ______________________________ Forward Header __________________________________ Subject: RE: short canard? Author: Phillip.Johnson@Lockheed.on.ca (Phillip Johnson) at INTERNET Date: 4/1/96 12:58 PM Larry Schuler Writes. > Phillip, maybe we need to design a variable elevator limit tied to > airspeed I'm ahead of you on that one. My thoughts were to include a two position stop that could be electrically or manually implemented. On take off the stop was withdrawn and the system defaulted to higher elevator angles. After take off the shallow stop was reinstated thereby giving the normal flight conditions that keeps Nat happy. If the two position stop were implemented electrically, (solenoid,) then a control stick mounted button like the PTT switch could activate this mechanism. Press the button during rotation thereby giving more elevator travel. after rotation the button is released and normal flight conditions prevail. The thought also crossed my mind that this might be a good way to reduce landing speeds for forward CofG conditions if the landing under these conditions is elevator limited. Of you guys out there who are flying, do you find that you are elevator limited on landing? Phillip Johnson From: Lee Devlin Subject: BOUNCE (short canard) Date: Tue, 2 Apr 96 15:50:19 MST Kevin wrote: > >So the nature of the beast is such that the main wing will start > >working first and quit working last. Because of this you would have > >to find that the main gear may unload and bring the canard to a > >slightly lower angle of attack. The Cozy front seat load is highly variable. A heavy load tends to compress the front strut, spring, and tire to a lower position which lowers the angle of attack of the canard. If the canard AOA becomes negative and produces negative lift, it can cause the nose to compress further as the plane accelerates making it even more difficult to rotate. It's a sort of 'toggling over center' condition. The main gear also contributes to it since it unloads as the main wing begins to produce lift. And Kevin are correct, the main wing begins lifting earlier and stops later, not vice versa as an earlier posting suggested. The RG may have another issue. An oleo strut supports a force that is proportional to the ratio of uncompressed-to-compressed volume. If there is 100 psi of air in an 8" strut at no-load condition, then compressing it 4" will double the pressure to 200 psi. If the strut piston is 2" in diameter, each strut would support ~600 lbs. at 4" of deflection which sounds about right for an empty Cozy. As the plane accelerates, the main wing begins lifting the rear of the plane. Here is how the gear would unload in an RG configuration that employs oleo struts: compression % of weight carried by: distance (in.) gear wing 4 100% 0% 3 60 40 2 33 66 1 14 86 0 0 100 If, like mentioned in one of Jeff's postings, the fixed gear deflects 2" with a similar load, then the corresponding numbers for the load distribution would be as follows: compression % of weight carried by: distance (in.) gear wing 2 100% 0% 1 50 50 0 0 100 All of these numbers are assumptions, so please don't take this information literally. Also, I did not show the numbers for a fully loaded plane which would further compress the oleo struts by about 1.5" and the fixed gear by 1.3". The main wing on the RG gets 'help' from the gear for a longer range of distances which would tend to reduce the plane's AOA more than the fixed gear as it accelerated down the runway. So, at equivalent speeds, the RG is likely to raise its main wing higher than the fixed gear using the numbers here, which, like I mentioned, are based on my assumptions. The point is that a plane attempting take off is not really flying and must transition into flight through some regimes that may be working to prevent the transition. Lee Devlin From: Marc J. Zeitlin Subject: short canard, etc. Date: Tue, 2 Apr 96 23:35:06 EST Larry Schuler wrote: >> If the rotation speed is raised due to mains unloading, doesn't >>that imply that the main wing is beginning to lift "before" the canard? Kevin Walsh replied: >Yes, the main wing should always lift before the canard. This is an ambiguous statement. As air flows over the wings and canard, both will begin producing lift. The question is (or should be) "will the canard produce enough lift to raise the nose of the aircraft before the wing produces enough lift to raise the tail of the aircraft?" So, "before" in the lift context doesn't mean much - the issue is how much, and how does that change incidence angles BEFORE rotation. Larry Schuler wrote: >>Isn't that a no-no and leads to main wing stall sooner? It was my >>understanding that the canard design is such that the canard lifts >>before the main and gives out (stalls) before as well?????? Also, If >>the main wing unloads the main Kevin Walsh replied: >Without a serious hysteresis (sp?) in the system, this is not >possible. Most wings exhibit some hysteresis, but it is on the order >of a few tenths of a degree. I'm sorry - maybe I'm dense, but I have no clue to what this is referring, and I understand the concept of hysteresis in wings. >Look at it this way: >Everyone assumes that the canard will stall before the main wing. >If you take this as a given then you must also accept that on a >takeoff run the main wing will lift before the canard. See my first paragraph for a response. The main wing AND the canard begin producing lift as soon as the plane starts moving forward. There is no "before". The amount of camber in both wings ensures that at the possible attitudes (as long as the nose gear hasn't collapsed) they will both be generating lift - not down force. >Examine what would happen if the canard were to fly before the main >wing. With elevator power it would be possible to pull the canard >into a flying mode, while the main wing stayed nicely stalled. >Adding power and more angle to the equation you would have a Cozy >plowing down the runway nose high, but never really getting the main >wing unstalled. Not a pretty way of alighting, I would say. O.K. Kevin, I know I've been out of school for a long time, but I seriously doubt that M.I.T. has changed the definition of "stall" in the meantime. The main wing is not "stalled" when the plane is traveling down the runway. Stall occurs at HIGH angles of attack, not low ones as during the takeoff run. If you lift the canard (and nose) too early, the main wing will NOT stall, since it stalls at an aircraft angle of attack HIGHER than that of the canard (one of the whole points of the configuration). Since the canard is flying (by definition) the main wing CANNOT be stalled. It may not be producing enough lift to get off the ground, (dependent on velocity) but it's NOT stalled. (BTW, "alight" means to land). >So the nature of the beast is such that the main wing will start >working first and quit working last. Because of this you would have >to find that the main gear may unload and bring the canard to a >slightly lower angle of attack. The first sentence is absolutely incorrect. As stated, both lifting surfaces begin producing lift as soon as the aircraft starts moving forward. The ground angle of attack of each of the surfaces will determing how much lift at what speed, and the compliance of the landing gear will determing how much that ground angle of attack will change with an increase in velocity. If the nose gear is softer than the mains, and the canard produces lift faster than the wing in relation, you may actually see an INCREASING angle of attack before rotation. So, the second sentence MAY be correct, but is not necessarily so. >I think that people are going about this the wrong way by trying to >increase elevator travel, changing incidence, etc. If the plane flys >great in the air, at all CG positions and weights, and the only >problem is that it unsticks at a high speed, (Althought coming to >the first conclusion may be hampered by the second) then the problem >is that the plane is not seated right on the ground. Not necessarily. You need to ask how the plane stalls (or bobs) and at what speed. It may FLY just fine with the canard a couple of degrees off one way or the other, since in cruise you can correct for this with changing elevator angles. At low speeds, if you run out of elevator, you're done. You don't want TOO MUCH elevator either, however, because then you WILL stall the canard. There was some speculation a while ago that this was what caused long ground runs on certain individual's V.E.'s, L.E.'s and COZYs. If the pilot pulled the stick back all the way, the canard would stall and not produce enough lift for rotation. Sorry if I sound pissy, Kevin. I've got a pounding headache and the thought of people getting the completely wrong impression of how planes fly rubbed me the wrong way. We've beat this short canard thing to death (again). Of the two planes with high rotation speeds that began this discussion, we've got: 1) Infinity retracts with WAY too much compliance, causing a HUGE decrease in ground angle of attack during takeoff run. Lee Devlin has given excellent explanation of how this works. Solution - pump up the struts and reset the ground AOA. 2) Canard set at an angle at least 1 degree and possibly 2 1/2 degrees below that specified in the plans. Solution - re-mount the canard at the right AOA. Neither plane has a rotation problem caused by a shorter canard. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Wed, 03 Apr 1996 14:59:57 From: JRaerocad@gnn.com (Jeff Russell) Subject: Re: short canard, etc. Marc writes: >1) Infinity retracts with WAY too much compliance, causing a HUGE > decrease in ground angle of attack during takeoff run. Lee > Solution - pump up the struts and reset the ground AOA. >2) Canard set at an angle at least 1 degree below that specified in > the plans. > > Solution - re-mount the canard at the right AOA. The airplane with the 1 degree problem has now been adjusted corectly. It still flew with elevator trailing down about 1/8". The wings were also checked OK, but were adjusted with one washer on the bottom hardpoint to change the angle down (a 1/4" at the strake L.E. down mis-match) This produced a level trailing edge on the elevator. The airplane STILL takes 90 mph to rotate the canard with 360 lbs up front. He also told me that the canard does not pitch buck with this CG on it. We also see about the same but ours bobs up and down about 3 to 4 inches. All I know for now. I should hear more ASAP......... >Neither plane has a rotation problem caused by a shorter canard. AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 910-961-2238 E-mail: JRaerocad@gnn.com Date: Sat, 6 Apr 1996 03:01:57 -0500 From: KSPREUER@aol.com Subject: Re: short canard, etc. I read all the Short Canard notes with great interest. Having lost an airplane from lack of rotationgets your interest up. While, I intend to keep my canard full length until I test it, I do think the canard length should be set by in flight perameter rather than ground rotation. I say this because there are far more variables involved in the ground case than the flight case. The following list are those that effect rotation speed, those with an asterisk effect rotation speed to a larger degree than min flight speed. *Canard performance at full elevator *Gross Weight *C.G. *Canard aerofoil shape Canard incidence Aircraft ground incidence Wing incidence MLG wheel position MLG spring constant It seems to me that it is most desirable to improve the rotation speed without changing the relative speed that the canard stalls compared to the wing. (assuming it was where it belonged in the first place). So, using the variables that don't effect the flight condition seem to be the place to start to correct the rotation problem. Someone noted that there is a common condition, at least with the GU canard, as follows: you actually get less lift at larger elevator angles (15 to 20 degrees) than at lower angles (around 15), due to elevator stall. I don't know if this effect applies to the Ronzc aerofoil but I would be skeptical of the extended elevator angle cure until that was determined. I'm thinking that I will set a combination of C.G. limits and canard length that results in an adequate margin from main wing stall in my flight test period. I will then minimize the rotation speed using variables that don't effect the canard/wing stall relationship. I would start with the easiest to change. That is probably ground incidence first, wing incidence sencond, canard incidence third ... Of course if one of these was clearly off spec to start with that would move up the list. That was a very interesting fact pointed out in one of the notes. That was that lowering the wing incidence reduced the amount of downward elevator deflection required for a given flight condition. Date: Tue, 6 Aug 96 21:53 WET DST From: jvasher@mail.ic.net (test) Subject: COZY: New canard Why the change.. Why not a placard I have was disappointed with nat's attitude about the new canard. I'm a heavier pilot then what nat wants to fly in his cozy, and when I tried talking with him about the modification to the canard, (mainly keeping the original design (which I think Rutan design?)) he stated it was not safe.. No I'm an a&p and deal with deadly weight and balance limits everyday, Namely the use of a placard to inform pilots not to over load such and such. Now my thoughts were that if these cg ranges could be aft loaded to such an extend that you would stall the cozy simply inform the pilot and leave the options of using the original size canard. I was really suprised to hear nat say he didn't want the front seat loaded beyond 300 pounds. Now I know a ton of pilots and very few could fit two people in the front seat with them... I guess I ran long but I would love to hear others oppinions on the original canard over the newer one. Also, if someone has a better grasp On the difficulties of the loading pleas share.. Here is what I'm after, I way 250, my wife is 160 now that 410 in the front seat and we may fly this plane like this, Wouldn't it be better for us with the original ( 6" longer ) canard? Also, at times we may max the weight limits out with passangers. Thanks jvasher@ic.net Date: Wed, 7 Aug 1996 09:07:34 -0400 From: wilhelmson@scra.org Subject: Re: COZY: New canard Why the change.. Why not a placard I have been flying a Cozy Three place for three years with a 4" longer RONZ conard. My normal front seat weight is 300. I add balast to the nose when I fly solo. If I ever sell the aircraft, I will shorten the canard. As the builder/flyer of the aircraft you have only a liability to yourself and your passengers. As a designer Nat has liabilty far greater. By asking him to approve or agree with your design changes you put him in a no win position. From: Marc J. Zeitlin Subject: COZY: New canard Why the change.. Why not a placard (fwd) Date: Wed, 7 Aug 96 10:11:29 EDT Joe Vasher wrote: > I guess I ran long but I would love to hear others oppinions on the >original canard over the newer one. Also, if someone has a better grasp On >the difficulties of the loading pleas share.. Here is what I'm after, I way >250, my wife is 160 now that 410 in the front seat and we may fly this plane >like this, Wouldn't it be better for us with the original ( 6" longer ) >canard? Also, at times we may max the weight limits out with passangers. I would recommend reading the 1995 archives on the "short_canard", as well as the 1996 archives on "short_canard" and "cg_position". We have hashed out this issue ad-nauseum, and have varying opinions on the subject. Some are leaving their canards long, others are shortening them. Once you've read all the archived info, we can try to address any unanswered questions. I don't think there's a definitive answer to this one - it depends on what you want the plane to do. -- Marc J. Zeitlin Email: marcz@an.hp.com