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Full Flying Canard


Twin EZ

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So, back to the origin of this thread....

 

"In the process of designing my "perfect" Long ez, I was considering building a full flying canard (vs fixed with elevator). Has anyone ever tried it? Are there specific reasons not to do it on a canard? On Convention AC, they work great. I had stabilators on both of my planes."

 

I suppose I would start with some simple questions: What problem have you identified with the plans canard that you are trying to address? How does a full flying stabilator solve those issues? What issues does it create that you did not have before?

 

I think, as with most modifications, you should start at the problem, and then see how other approaches solve those problems. Often it appears that some people start with a "solution" and then see what problems it solves for them.

 

I know of not one canard structural failure, with the exception of Steve's canard departure that was due to leaving out the lift tab bolts. So, structural failure cannot be the problem you are trying to solve. Additional slow speed capability might be possible, but I have a hard time believing that a fixed geometry stabilator could achieve a better Cl than a slotted flap for a given airfoil. If you're willing to also change the airfoil you have entered very serious test-pilot territory.

Kevin R. Walsh & Michael Antares

Cozy Mk-IV #413

N753CZ

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To the best of my knowledge, there are no problems with the existing canard design. (especiall the Ronzc design). My point wasnt to "solve" a problem, but rather to explore other possibilities. On conventional aircraft, you can get away with a small surface area on a stabilator vs convetntional stabilizer/elevator combination. (albiet, the forces are in the opposite direction). If indeed, the same reduction could be possible in the canard confiuration, we could achieve the same required lift, with the appropriate stall characteristics, while reducing the surface area, which in turn could reduce the induced drag. That was my thought anyways.

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The only advantage that might exist for a canard that has, for the sake of argument, an adjustable angle of incidence would be to keep the airplane from climbing when traveling at very high speeds (which is outside the scope of the builders working out of a basement/hangar.)

 

Fun to "blue sky" but not practical at all.

T Mann - Loooong-EZ/20B Infinity R/G Chpts 18

Velocity/RG N951TM

Mann's Airplane Factory

We add rocket's to everything!

4, 5, 6, 7, 8. 9, 10, 14, 19, 20 Done

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Twin you may want to look around on this site (or in the CSA newsletters)... I beleive there was a LE that was built with 2 80hp Jabiru engines. The owner decided to convert back to one because of the observation made previously (not enough power to maintain altitude on one engine)...

 

If you were to have red this thread from the beginning, you would have noticed that I have commented on Bowden's LE a couple of times.

 

OK... so how would your design be different then? Don't want to rain on your parade but looks like you will have to do some things different... Unless you are happy with the results Mr. Bowden had.

 

But if you can improve the design to your liking... why not...

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I think that Bowden started out with a good idea, and I would love to chat with the guy to get some specific details since I was not able to see his plane in person. His engine choice was pretty good, although I plan on using something else (I'm keeping that part a secret forthe time being). But I do agree with keeping the engines in the 80-90 hp range. I feel that his aero-dynamics for the cowlings were terriblly wrong. We cant afford to put to engines in the breeze and use a boxy cowling that he did with what appears to be holes drilled in the top (cooling issues maybe????). It is imperitive that the cowling and ducting shapes be done in such a way so as to reduce the parasitic as much as possible, otherwise forget it. I have no plans on flying a plane with a top speed of130 kts burning 6-7 gph. What would be the point in that?? Also, looking at his pro choice limited his performance. If we look at the amount of pitch the prop needs to get the kind of cruise speeds in a LE, how in the world can 80 hp spin it on take off. I would imagine that either he had relatively fine picthed props or he would never get of the ground. On a singlke engine, there is more horsepower to push a course pitch prop. I think that it will be necessary to run adjustable props to make this work. Unfortunately that does add complexity, but a necessary evil to the design. Bowdens engine placement seems to be pretty good (approx 5' apart). I can not tell the distance from the prop to the trailing edge. If was to close, there are some efficiency losses occuring there as well.

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I'm no aerodynamist but with such a canard... would you need to increase the lenght of the fuselage to reduce the plane sensativity to pitch change?

 

And does a full flying canard means that the entire airfoil rotates around a pivit point "a la" Eurofighter Typhoon...

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full flying is just that, the whole surface will move. I have not run the numbers yet. But I see no reason to have to extend the nose. the sensitivity is controlled by the amount the control surface moves in relation to the stick movment, and the amount of force applied by the anti-servo tab on the trailing edge. This is only a theoretical idea here...nothing concrete.

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Working on this mod for a long time, you need to consider :

-canard arn't like horizontal tail on conventional aircraft, they participate to the total lift of the aircraft, so you can't reduce them just because this is what they do on conventionnal aircraft, concidere your canard as a wing. if you reduce the size of it, you reduce the amount of lift it produce, unbalancing the aircraft. A small canard like the one you designed is good as a control aircraft more than a lifting canard. In a control canard (EF2000, rafale, and other fighters) are stable without the canard, canard ads only controllability. On EZs, the canards are lifting canards, meaning that the plane can't fly without them. And these lifting canards are more like a wing than an horizontal tail surface.

-to add a sweep canard, you must be careful to consider the total surface of the canard as well as the flow around a swept wing which reduce the efficiency of the airfoil compared to strait wings (at low Mach numbers) (because of the taper and the aspect ratio, the surface needed, and the structure to hold all this in place). More over you must select an airfoil that can cover the range of deflection required during operation without stalling (at high speed, it can be serious)

-talking structure, you must carefully position your hinge point, to make the canard movable without helping actuators, and stable enough to avoid flutter and too much effectiveness and sensitivity. also your hinges must withstand the loads applicable on the canard (ratio of lift compared to the wing times the weight of the aircraft time the G loading times a security factors) and on the interface point with the fuselage.

-Using a flying canard, you loose you stall proof feature, the canard can stall after the wing (depending on the position of the canard at wing stall and the CG position) even more you are much more prone to deep stall, so you need a way to come out from that quite easily.

 

that's to my knowledge, but I'm sure there is more to this...

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I have to agree with everything that you have said. And these are issues that I have been going through. That being said, I could build a fixed canard, keeping the center of lift in the same place, but if indeed we are looking at a decrease in efficiency, for a tappered look, then forget it. The end result needs to work better, not worse.

Im still going foward with the twin idea though:D

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Building experimental aircraft is a little like evolution. The trial and error method is often better then careful calculation and design. Just make sure the you the testing phase doesn't compromise your safety. If someone wants to take a risk for the cause of progressing knowledge then I say more power to them. Without this attitude we would still be riding bicycles off of ramps with feathers stuck to our arms.

Crazy Canuck

Toronto, Ontario, Canada

Cozy MKIV #MK1536

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Pretty dang funny Tmann! [tip of the hat].;) However there are the breeders and the bleeders and there's at least one Cozybuilder who thinks and builds scary stuff and touts it as worthy of flight. Everybody do their own homework, so as to be a breeder, not a ....

Self confessed Wingnut.

Now think about it...wouldn't you rather LIVE your life, rather than watch someone else's, on Reality T.V.?

Get up off that couch!!! =)

 

Progress; Fuselage on all three, with outside and inside nearly complete. 8 inch extended nose. FHC done. Canard finished. ERacer wings done with blended winglets. IO540 starting rebuild. Mounting Spar. Starting strake ribs.

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However there are the breeders and the bleeders and there's at least one Cozybuilder who thinks and builds scary stuff and touts it as worthy of flight.

Although I'm still a bit scared of slapping a big six in the back, that's no way to talk about me just because I'm installing cup holders and wheel spinners! :D
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  • 2 weeks later...

Just a thought. If you want a twin that's not a Defiant derivative would it not make since to clutch two engines to one prop? The only reason I would put the engines on the wings is to make room in the fuselage for a little more seating. Like a Cozy 6/Starship. ( Death trap?) Then I'm guessing you just opened a can of worms with wing area, weights and balance,.....

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I have gotten that same response several times, "what happnens if one quits on take off"? Well, I ask this, on a single engine LE, ....same question. Gues what? same answer: fly the plane as best you can and hope there aint a tree or house in your way.

It isn't the same situation at all - if a single engine quits, your decision is made for you. If you have a twin you need to decide for yourself what to do. And it's very difficult to decide to crash.

 

If you decide to continue under power, a conventional twin leaves you with problems such as asymmetric thrust and yaw. You can easily get yourself into situations such as flipping inverted whilst still above the stall speed.

 

but if indeed we are looking at a decrease in efficiency, for a tappered look, then forget it. The end result needs to work better, not worse. Im still going foward with the twin idea though:D

As a general subsonic rule, narrow wings (high-aspect ratio) produce lift more efficiently than delta wings, so a traditional long-ez canard will almost certainly be more efficient than one with a delta-canard like the one you showed. That much is basic aerodynamics. But designing a new canard is the sort of thing I wouldn't personally mess with unless I had a degree in the subject - and I don't and I gather you don't. Look at the history of the GU / Roncz canards and how long it took to get it right.

 

I've nothing against innovation (quite the opposite - we're all reading this forum because we're willing to accept the unconventional), but I've learned through experience that true innovation is very hard and takes a long time. As a scientist, whenever I start a new experiment, something I never considered emerges to make my life complicated. Whenever I program a computer, bugs appear when the program is asked to do something I didn't consider.

 

Both these spheres of life are relatively safe, but you seem to have decided to risk your life with a design that is really very different from anything that has gone before. Twin engines. A delta canard. A larger wing. Other innovations that you're keeping secret. You say you believe in progressive 'baby steps', but this certainly doesn't seem to be the approach you're taking.

 

Are you working alone? If I were you, at the very least I would pay a qualified competent person to check over my design. There's currently a thread just as long as this one about the design of blended winglets. The changes you're proposing really aren't trivial.

 

Seeing as we like to be radical, my 2c would be that within 15 years, electric - or at least hybrid - aircraft will become quite feasible. My radio controlled helicopter uses batteries that give 4 horsepower / kg in a tiny motor that weighs a few hundred grams and is over 80% efficient. So 25kg of batteries and 25kg of motor and electronics could very feasibly give you the same power output as a 125kg Lycoming 0-235, albeit only for a few minutes.

 

I figure that an electric Long-EZ might save 100kg over an O-235 engine, so you could carry a quarter-ton of batteries instead of the usual fuel load. With today's technology that would give you a flight time of an hour or so. But if some of the rumours I've heard about Lithium-air batteries are true, then we might reasonably expect this to increase by a factor of up to 10 over the coming years. This would put an electric and a IC long-ez nearly on a par in terms of range, except I'd wager the electric aircraft will remain more expensive for some time.

 

What does this have to do with twins? Electric motors are so much smaller and lighter than IC engines that it would be far easier to integrate them into a wing or strake. They also require far less cooling, which would be good for aerodynamics. But the real experience from radio-control modelling is that it's now far simpler to build twin/multi-engined aircraft than it ever was with the internal-combustion variety.

 

With a hybrid approach you could carry 25kg of today's batteries at a cost of about $3000. If your main engine failed, you might get half an hour at 80 knots before they ran flat. You could have five 4-kg motors spread along the wing, each producing 25hp flat out. Loss of any single motor would be a relative non-event. Loss of 2 or more motors would only be significant if they were on the same wing. Lose the generator... And unless you are over the Pacific you will very probably have time to find a suitable airport and set up a good approach.

 

I admit I'm being more than a little speculative here, but at the same time I don't think that this is pure fantasy. In your position I would be significantly worried that by the time I'd got my complex new design worked out and built, it would be nearly obsolete because buying a few electric motors off the shelf was so clearly the right way to go.

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Building experimental aircraft is a little like evolution. The trial and error method is often better then careful calculation and design.

To this end, you would probably be better off buying a functional Veri-EZ or Long-EZ, and then build modifications, testing each modification incrementally until you had explored the performance parameters of your new concept.

 

Then you could execute the concept on a new aircraft. The risk you run with building a new aircraft implimenting new aerodynamic concepts is that you spend 5 years and $70k, and it doesn't work or it sucks.

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