Canard Aerodynamics: Why You Might Not Want a Canard Airplane

hi I'm Scott welcome back to Canard Boulevard today we're going to be talking about some aerodynamics of the Canard aircraft and then we're going to talk about some reasons why you do not want to buy one of these airplanes coming up if you saw a video I did oh a few months ago it was why did I buy this weird airplane and I talked about all the reasons why uh well why I bought the airplane but what some of the advantages are about these Canard aircraft and what some of those things are that made me want to buy one um a lot of those are correct that I mentioned but there were some misconceptions that I mentioned in there that I got Flack from from uh Mark zeitlin who is the guru of these airplanes nice guy very opinionated but very very smart we had a discussion he said you really need to make a clarification video to address some of the misconceptions that in his opinion are are propagated about canards in general so this video is going to be that and in doing so I'm going to reveal some things about these airplanes that may mean you don't want to buy or build one but then maybe you do so I have written down all this stuff that I've gotten from Mark uh I actually sat through a couple of his hourlong online lectures describing a lot of the details of the aerodynamics of these airplanes to make sure that I had everything correct I'm not going to go into anywhere near the detail that he does I would highly recommend you look at his videos if if you're really interested in the nitty-gritty of the Canard aerodynamics but I'll try to boil it down to something I could fit in just a few minutes here all right I mentioned that Mark zeitlin was uh the one who commented on my original video and what I did is I created this video and put it together sent it to him and said hey what do you think he wrote back and said yeah better you got a few things wrong so what I've done as soon as I'm backed at the airport anyway I'm getting airplane ready for a trip that I'm taking tomorrow I thought I will go over just a few of the things that he mentioned so that when I re-edit this video together I can take out stuff that was wrong and put it in Stu that was right and that is why you're going to see my clothes switching back and forth before it was uh a lot warmer it was I was wearing a t-shirt today it's about 40° and it's uh quite cold in here okay first thing I do want to mention is that I'm going to put links to Mark's videos in the description below so if you do want to see Mark's original presentations where he goes way way way more in depth about the aerodynamics of the Canard than I am here uh then you can do so and check out those links and I really recommend you do if you're interested in these airplanes because he's really the expert when it comes to cozies people asked about the vorlons which are these here and what these do is prevent spanwise flow when the aircraft is at a higher angle of attack and the reason why you want to do that is to prevent separation to prevent stalling of the main Wing these bordons are actually in the stagnation area of the wing there's no actual air flow over these during normal flight in the attitude the wing is at in normal flight it's only when the wing actually goes into a higher angle of attack where these come into play and prevent the spanwise flow which you would normally get from this uh swept wing and in the first of what is probably going to be many clarifications that I record as I'm editing this video uh not only do they prevent spanwise flow but as the wind spanwise flow hits that at a higher angle of attack it creates a a vorticy which then moves across the top of the wing and helps prevent separation which is how then it prevents the wing from stalling at lower air speeds and a higher angle of attack so why do we have this swept wing and it's the same reason airliners have a swept Wing because it has the same effect on lift that a longer aspect ratio does okay that was wrong sweeping the wing decreases the aspect ratio not increase so it actually causes the wing to become a little bit less efficient uh the main reason for the Cozy to have its swept Wings is to get the the vertical stabilizers back far enough that they have some kind of yaw control effect over the airplane so aspect ratio is the ratio of the length of the wing compared to the cord length of the wing and if you look at something like a glider that has very very high aspect ratio Wings they're long and skinny means they generate a ton of lift not quite it increases the coefficient of lift so it makes it more efficient at creating lift basically steepens the lift curve slope if you had an infinitely long Wing then you almost get a two-dimensional flat uh ratio which in theory would be zero drag so the longer the wing the steeper the lift curve slope the higher the coefficient lift and the lower induced drag so it's it's all a good thing and what the higher aspect ratio gives you is more lift for a given angle of attack the other thing that's good about a swept Wing is that it is dynamically or structurally stable any twist in the wing that's caused by stress on the aircraft in Flight causes it to reduce lift which then reduces stress so it's self-correcting uh which is a and that's a benefit of having the swept Wing that was a really piss poor explanation so I'm going to try and do it again showing you on this model what I was trying to say here I'm going to take the propeller off so it doesn't fall out so here we have our cozy so if we look at the wing here if we generate lift here it's going to try and twist the wing this way it's going to try and go this way but of course if you twist it that way that means it's going to nose down it's going to reduce the angle of attack on the main Wing which means it's going to create less lift so if you encounter wind or a control movements or whatever that causes a a increase in lift here which is an increase of stress on the wing what it naturally wants to do then is actually reduce that so it's dynamically stable so we're going to talk about lift curve slope which is the amount of lift given over a certain angle of attack and how it changes as the angle of attack changes and how that is used in the Canard aircraft to make it stable so if we look at a conventional aircraft like this one here we have the main Wing in front and then we have a tail in the back that provides displacement correction so if if we hit turbulence and it goes down like this it's going to correct it and bring it back up kind of like when you're towing a trailer it's it it goes out to one side if if you hit a bump and then it's going to return back if we were to be flying this way in this airplane we'd have the opposite we'd have negative Dynamic stability and if it got displaced it would do this so the way we do this is by creating the air foil on the tail with a higher lift cor lift curve slope which makes it more efficient than the main Wing so that the same angle of attack this Wing at the back creates more lift which then brings it back quickly if it was the opposite and we displaced it this Wing would generate more lift than this one and and the airplane would do this and and rip off its wings so the idea is that as it flies along it gets displaced this one lifts quicker than this one so then it it pushes it back and and restores stability so that is lift curve slope and how it's used in Dynamic stability in the aircraft to do that the front Wing must be more heavily loaded than the rear wing which is fine we have you know cockpit engine uh fuel passengers and we have almost nothing back here so you can see it's it's heav more heavily loaded at the front and the back and also we must have the center of gravity ahead of the center of lift so in a Canard what we have to do is have the lift curve slope of the rear wing be more efficient than the front Wing we want the front Wing to stall first if you recall the front Wing must also be more heavily loaded again it needs to be stalling first before the main Wing the CG in a Canard aircraft has to be ahead of the Cent Center of lift so if the center of lift is here we need to make sure that our CG is ahead of that in a Canard aircraft because otherwise we would have no load on the Canard Wing at all it would never stall and this Wing would stall that's bad and another way we do that is that the Canard has only 15% approximately of the total Wing area of the aircraft however it's carrying between 25 and 35% of the load of the aircraft so it's much more heavily loaded all of this is to make sure that the Canard stalls first before the main Wing stalling the main wing on the Canard very bad not recoverable uh yaw and roll stability in the Canard are interconnected if you roll it it's going to yaw basically and vice versa we have swept Wings to get our vertical stabilizers back behind the airplane and that gives us our directional stability just like our vertical stabilizer here here is back behind our center of gravity our pivot point that gives us our directional stability and in order to do that we need to have swept Wings to get those vertical stabilizers that far back what about winglets cuz these act somewhat like winglets what does that do for us a traditional winglet adds to the lift curve slope because it it extends the length of the wing but without adding bending moment because it's actually up at an angle so we aren't bending it from here it's bending it from here so we get free lift without add the added weight and structure of the wing that would be required to have that extra uh length if they're designed correctly it can produce a little bit of extra thrust simply because you have a air rolling out from underneath the wing and if it hits the the winglet correctly and it's shaped correctly it can then direct that that wind backwards and give you just a little bit of thrust it adds a little bit of efficiency to the wing reduces drag at the best lift drag speed so winglets help you how about on the Cozy though there's not much in the way of drag reduction on a cozy um the best lift drag speed in the Cozy is 85 knots you don't spend a whole lot of time flying around at 85 knots in a cozy so for the speeds that we fly at not really that much of a benefit so I've made a lot of comparisons about efficiency and speed and U capability between the Cozy and other airplanes now if you compare the Cozy to uh CES 172 the Cozy is going to blow it out of the water you can't compare an airplane that that flies at 8 or N9 gallons per hour at 110 knots to a cozy that is flying at 165 knots at 7 and 12 gallons per hour it's far more efficient but there are many many differences much higher Wing loading no flaps so you have much higher uh takeoff and Landing speeds a smaller narrower cabin there's a lot of differences and so we need to do a like more like like comparison so fusels uh size and shape are they side by side are you sitting straight up like an acessa are you reclined in like one of these or like a lan a or glass air that makes a difference because that changes the height of the of the fuselage if you're reclined which means more or rather less frontal surface area which means less drag uh what about the wing size and area highly loaded Wings a lot less drag means higher takeoff and Landing speeds uh higher install speeds but uh a lot less drag less forgiving for for instance a student pilot however is it fixed is it retractable well let's compare fixed and retractable airplanes we have to talk about the engine power are we talking about an IO 360 are we talking about something with an IO 540 and also is it fix fixed pitch or constant speed so airplanes that compare similarly with a lot of those things to the Cozy or like the rv10 the lanir 4 um same similar sizes similar engines similar weights they essentially the same terms of wing loading so those are good comparisons the advantage the Cozy has uh essentially over those aircraft is stall spin resistance but all said and done they're very similar in terms of speeds capability efficiency uh Landing speeds stall speeds so so they're very similar in capabilities okay so if you watched my previous video I talked talked a lot about how the main Wing generates lift and the Canard generates lift so you have all the wings generating lift all the time whereas on a conventional airplane you have lift and downwards lift which means now this Wing has to generate lift to overcome the downward lift of the uh the horizontal stabilizer and that's true that is absolutely true so it's less efficient because you do have to generate extra lift however a Canard up front is generating lift and how's it do that by displacing air mass by creating a a pressure Zone underneath and in doing so creates down wash that then hits the rear wing here which means that this section the streak and this part of the wing is not as efficient as it could be because it's being blanketed by down wash from the Canard so if that were not the case if the Canard was not there and we were magically getting lift from the Canard without having a yard there then yes we would have a far more efficient lifting force on this Wing because we would have nice clean air coming across here and generating lots of lift but we don't have that we have a Canard up front generating down wash if we had the Canard that was stuck you know maybe 15 ft in the air um then it wouldn't be generating down wash that's affecting this Wing we get that efficiency but then you have all this structure and whatever it would take to get the Canard sticking way up in the air and it with would look ridiculous and because we now have less efficient lift on the main Wing because of that Canard down wash that means we need a larger main Wing to generate the sufficient lift for the airplane which makes it a little bit less efficient because we more lift more Wing means more drag because the lift profile then is not equal we have less lift here more lift here and then of course you want less less lift out at the at the edge the ideal lift profile is a purely elliptical where it tapers at the edge Lots in the middle and then tapers at the other Edge instead we have a decrease here which is not optimal so again we need more surface area more Wing in order to compensate for that another reason we need a bigger mean Wing is because we need that stall resistance we need to have extra Wing to make sure that we never reach critical angle of attack on this Wing because it's not recoverable if we didn't have to do that if we could build this wing just to the size that is required in order for the plane to fly efficiently it would be much smaller and the plane would fly faster and less drag but we can't do that because we need to make sure that this Wing never stalls so we need to make sure that it has enough Wing that the critical angle of attack we never get anywhere close to it that the Canard always stalls first so the downwash effect of the Canard plus the additional size to prevent the main Wing from stalling first first essentially nullifies the gift we get for having two lifting surfaces and in the wash the efficiency between this and a conventional airplane of similar size similar wingloading similar power similar everything is essentially the same basically there's no free lunch so what's bad why don't we want to buy this plane High landing speed it lands and takes off fast because we don't have flaps we can't have flaps in this design so we have a very high takeoff and landing speed 70 plus knots people are astounded at this the landing speed you do get used to it but that means it's it's fast you need some Runway and it has to be a hard surface Runway we also have small wheels and particularly on front where we are actually retracting and if you're landing at 75 knots with small wheels they are spinning up fast you are wearing out tires you are wearing out brakes again it's a compromise you have to live with the nose gear the nose strut on the Canard on the Cozy and the Long Easy is not a good design Bert Routan admits it's not a good design he wishes he never did a free castering nose wheel he in fact has wow it's pouring rain outside in fact he's challenged somebody to come up with a different nose gear design for these airplanes with a steerable nose wheel and uh that is a more robust solution because the uh nose gear in these airplanes is not robust it suits the purpose but it it definitely could be better so what and because the nose gear is small it reduces the angle of incidence of the main Wing not to mention the Canard which means that you need more speed in order to rotate it off plus if you hit a bump the angle of the nose gear actually will rotate up which means the nose dips down so you need even more air speed in order to get that up on a conventional airplane you have your propeller on the front and you're doing your takeoff run you've got all this prop wash blowing over your horizontal stabilizer so that when you want to rotate you can pull the the stick back and it pulls the nose up because you've got this prop wash over the tail surfaces you can force the airplane to rotate the main Wing into an angle attack that it will fly at uh simply because you have that extra air from the prop airplane does not you do not have prop wash over your Canard surfaces you have only the Clean Air that the Canard is encountering on your takeoff run which means you have to get up to a higher speed to get the Canard to generate enough lift to lift it that will then rotate the main Wing to its angle of attack that it will start generating lift and then take the plane off the ground if you had prop wash over the Canard you could probably rotate this airplane at 60 knots instead of 70 plus so you need more Runway and but to be fair all high performance airplanes need a lot of Runway a lands or you know lsay 4 it rotates at 70ish knots a lance air 4 rotation speed is not too different from the from the Cozy it needs a lot of air speed to rotate Off The Runway so six of one half doesn't on the other and last thing I'll talk about rotation is if you think about an airplane that that rotates a has the the main gear here so that's the rotation point it's going to rotate on the gear right there so all you need to do is generate a little bit of lift that will offset the difference between the the main gear and the front of the airplane and off it goes whereas on the Cozy the main gear is back here almost at the the fcg and you have to lift the whole front of the plane so the the the pivot is instead of here the pivot is back here so you have a lot more pivot a lot more lifting that you have to actually do in order to get the airplane off the ground okay talking about that rotation pivot the main issue is that the airplane when it's on the ground is not sitting close to or at the angle of incidence that it would be in order to rotate whereas most airplanes it's really close there you only have to rotate it just a little bit to get that the wing up into an angle of incidence into a point where it starts making lift and the airplane starts to fly whereas a Canard you have to get the the Canard up and then continue lifting in order to get the mean Wing into its angle of incidence enough that it starts generating lift and then the airplane starts to fly the problem is pilot over controlling or Pio pilot induced oscillation what happens is you're pulling back on the stick to get the Canard up and you're pulling and pulling and pulling and then it comes up and then the the main Wing starts to to fly and up up it comes and you still got all this back pressure in and the airplane wants to point to the sky and so you let down but now the plane the canard's going down and you pull back up and now you got some Pio happening so that's really just transition training um some people seem to be really afraid of that I think I got that within the first two takeoffs and it was really not an issue for me it's just a question of feel you feel when the canard's coming up you feel when the main Wing starts to fly and you just ease off a little bit on the back pressure on the stick to make make sure that you are not over controlling and just just basically listen to the airplane and feel what it's doing and just respond appropriately so that's basically what I think Mark wanted me to convey uh in terms of the aerodynamics of the of the Canard and the coing in particular if you have any questions comments suggestions and Corrections especially corrections I really appreciate especially on technical videos like this one please leave them in the comment section below if you do like videos like please click like And subscribe I really appreciate that it really helps me out all right I hope this rain isn't too loud and hasn't destroyed this video it's really loud in here thanks for watching

Channel: Canard Boulevard

Views: 58,993

Keywords: Canard, Cozy, Cozy MKIV, Long-EZ, Airplane, EAA, Experimental, Flying, Aviation, Takeoff, landing, aerodynamics, stall, spin, class

Id: LCmaUveNifQ

Length: 22min 39sec (1359 seconds)

Published: Sun Dec 17 2023