Canard as Elevator

[marbleturtle]

I was thinking about the design of the canard and the problem of elevator flutter... has anyone or any design used a solid rotating canard as the elevator?

 

I'm certainly not going to try it, but it seems like it could be done similar to military aircraft where the entire horizontal stabilizer is an elevator. This is also done on the kit aircraft that was featured on Discovery Wings (forgot the brand). Just a thought...

[JakeC]

Hey Marbleturtle,

 

Someone posed a similar question on my site the other day about the effectiveness of full flying control surfaces and why they usually need to be designed larger than a stabilizer with a hinged flap type control surface to produce the same effect. Here is the link:

 

http://www.homebuiltairplanes.com/forums/showthread.php?s=&threadid=614

 

The response he received is probably applicable to your question as well.

 

Jake

[Jim Sower]

<...has anyone or any design used a solid rotating canard as the elevator...>

 

Just off the top of my head I think of several potential problems:

 

You would pretty much lose the "stall proof" feature of your canard airplane - one of its more important attributes. The reason the main wing doesn't stall is that the canard stalls first. The reason the canard stalls first is that the canard airfoil stalls at a lower AoA (for the most part) than the main wing, and locking them both at the same incidence is the source of your assurance that the canard will reach its stall AoA before the main wing. Unlock the canard incidence from main wing and you have no such assurances.

 

You'd have the structural engineering problem from hell figuring out how to pivot the spar without resorting to a fairly massive structure.

 

Making the canard pivot would require a flutter solution for the whole canard which, I would hazard a guess, would be rather more elaborate than just balancing elevarors by the hinge.

 

Just a theory .... Jim S.

[chuckthedog]

Some guys from Dayton did it about 100 years ago. PS The canard as it applys to a Pickle fork is not realy an elevator. It is a flapavator. Acording to Rutan.

[marbleturtle]

Hey Chuck... I was thinking more along the line of composite canards!

 

I knew the structure would be difficult to design, but I guess the aoa of the canard preventing main wing stall is the prevailing issue. You could limit the pivot, but that would reduce manuverability. Okay, that idea's out, but I'm still thinking about my twin duct fans!

[Jim Sower]

<...guys from Dayton did it about 100 years ago...>

As I recall they had real problems with overcontrol. Didn't the recent "flights" of the replicas exhibit severe pitch sensitivity?

 

What I forgot to mention earlier was "... why would you want to? My EZ elevators were flush or very slightly TE down when flat out (maybe 150-160 kts) and maybe 3/4" TE down on final approach. My Velocity lands with 3/4" TE down elevator with over 450# in the front seat, and cruises 150kts elevator flush with just me (260#) in the front seat. I've never seen more than 3/4" of elevator trim from cruise to landing on any canard I've flown. Marc - what is the most difference in deflection in cruise/landing that you've seen?

 

Years ago I thought about it for a while as a way to get enough pitch authority to overcome / trim out the nose-down pitch from deploying flaps. Also thought about putting the canard on rails and sliding it forward when flaps were lowered. After thinking it through for a while, I decided that since I landed at 125 kts for most of the flying I ever did, why am I straining my brain to get from 70 down to 65 on my EZ/Cozy. It was nuts. Brain fart, pure and simple.

[marbleturtle]

I was thinking about reducing the flutter issue while attempting to push to higher speeds.

[LargePrime]

Is there a flutter issue?

I have never heard of a case of flutter on a canard elevator. If someone know of one please post a referance or something.

[bmacon]

Last month's FLYING mag had a reference to a VariEze accident outside of Palm Springs in which the canard appears to have departed the aircraft in flight --I poked around and found this mandatory ground notice on EZSquadron:

 

http://www.ez.org/raf_elevator_inspection.htm

 

Looks like elevator flutter due to overweight/mis-balanced elevators.

 

If this is old info I apologize - new to the forum and still getting up to speed on what's common knowledge in the collective consciousness.....

 

-Bob Macon

[LargePrime]

Thank you bmacon

 

But if the elevators are made right is there a flutter issue?

 

Again post a ref blah blah blah

[Jim Sower]

<... But if the elevators are made right is there a flutter issue ...>

 

Above 220 mph (or whatever Nat has designated as Vne), Nat and many others would argue that nobody knows. Airspeed (both True and Indicated) is a very important factor in flutter. You'd have to analyze it or have it analyzed or do your own flight test and pray for rain ....

[Tyson]

Originally posted by marbleturtle

I was thinking about the design of the canard and the problem of elevator flutter... has anyone or any design used a solid rotating canard as the elevator?

 

Just to clarify, there is no problem of elevator flutter.

 

There have been problems with people not following instructions (plans and/or operating manual) which have resulted in problems of flutter. This is not a design problem.

[marbleturtle]

No... there is no problem with elevator flutter when one sticks to the design parameters. What I am thinking about is how some of us are looking at higher powered engines for our Cozys (and one jet powered Cozy ). The largest single problem with exceeding Vne up to... say 250mph or 300mph is the potential for catastrophic elevator flutter.

[No4]

Trying to exceed Vne by 50 or 100 mph , imho, is NOT a good idea.

The Cozy is not designed for that dynamic pressure. The aerofoil is completely the wrong shape for starters.

 

Flutter however is my biggest fear, as it is a function of true airspeed as well as indicated airspeed. I'm led to believe it is to do with frequency, oscilation, and resonance. A critical vibration frequency causes massive structural damage.

 

Here's an article on the Lancair 360 regarding flutter, looks like even the "experts" can't agree sometimes.

 

http://www.lancair.net/flutter.html

http://www.aircraftdesigns.com/flutter_analysis.html

http://www.sti.nasa.gov/tto/spinoff1997/t8.html

http://www.google.co.nz/search?q=cache:kacSyld5pDUJ:www.ae.utexas.edu/courses/ase463q/design_pages/spring03/polen/flutter.doc+aircraft++flutter&hl=en&ie=UTF-8

 

 

If anyone has anymore knowledge on flutter, I'd be glad to hear it.

 

[Jim Sower]

My very limited understanding of flutter is that:

A) The math and structural analysis is hideous

B) The condition is significantly altered by relatively small changes in structure.

 

Since Cozys are only very marginally standard, small (and not so small) departures from "design" parameters like stiffness, etc. will abound. That being the case, even if one actually knew all the "design parameters" that affect flutter, and was able to do the math, I suspect that a proper analysis would still be extremely elusive. I believe that it is doubtful that a homebuilder could build two canards sufficiently alike for results to be accurately predictive of performance. I believe it would be very doubtful if a group of diverse homebuilders could build a group of canards to any acceptable standard at all as far as flutter analysis is concerned.

 

Burt tested the elevators to about 200 kts. He is reasonably certain that within the construction parameters he has put forth, they will not flutter below maybe 220 kts. Beyond that, you are on your own. You could test to higher speeds and accept the anecdotal data as valid, but that's about it.

 

That's my shot with what I know ....

 

Now that said, I'm looking for something on the order of 1000 mile range. That's 5 hrs at 200 kts (if I am clever enough and lucky enough to get 200 kts cruise out of a NA rotary). That's also right at 10 gal/hr with hardly any reserve at all. I'd have to be really REALLY clever to get 10 gph at 200 kts. If you could cruise at over 250 kts, with your turbocharged whatever, you would certainly get less mpg than me, so you would get closer to 800 - 850 miles on the same load of fuel. Any destination between your range and mine, I'd get there before you. Any destination short of your range, you'd get there at most 40 min earlier. If that's worth all the extra trouble and expense, go for it. To me, another half hour doesn't matter that much. Particularly since I'm arriving as far ahead of the Lyc Cozys as you are arriving ahead of me.

 

The more I do the math, the more attractive simple and inexpensive gets ... Jim S.

[Tyson]

Originally posted by marbleturtle

What I am thinking about is how some of us are looking at higher powered engines for our Cozys (and one jet powered Cozy ). The largest single problem with exceeding Vne up to... say 250mph or 300mph is the potential for catastrophic elevator flutter.

 

Why build a Cozy if you want to go 250-300mph? Canards are great for efficiency couple with a stall proof design. The only logical reason to keep the Cozy planform at 275mph is because you want a stall-proof design (because you've thrown efficiency out the window).

 

1) The plane was not designed or tested for these speeds.

2) Other designs are available in that speed range.

3) Max efficiency is well below 200 knots in the Cozy.

4) Any engine used to get 250mph will go even farther from max efficiency.

5) The average GA cross-country trip is short enough that the 30 knot difference in top speed gets you there minutes earlier, not hours. At a higher cost.

6) For long-distance traveling, efficiency usually means less stops and an earlier arrival. On a long cross-country you will be fueling your overweight gas guzzler while your efficiency minded hangar partner cruises overhead. Good thing you had a stall-proof design safety factor, because you had to make use of it twice when low and slow landing and taking off again.

 

Jim has it dead-on correct: "The more I do the math, the more attractive simple and inexpensive gets." Change the word "I" to "you" and write the sentence in big letters on the wall in your building area.

[No4]

Thanks for that Tyson,

1) We've gone way off thread, and are back into something discussed by us non builders almost ad infinitum; but we are in the coffee house, you're new here, and so we may still get away with it yet.

2) I agree exceeding Vne in the Cozy is un wise.

3) Plenty of Jet fighters, the Starship, the Tupolev "concordski" are all canards. The Berkut makes 300 mph indicated. We are building experimental aircraft, marble can do whatever suits his fancy.

4) climbing to 25,000 feet 200 CAS = 300 TAS. Miles per gallon will be the same, you will get to your destination faster for the same fuel burn, you will sit thousands of feet above the worst of the weather, you may even catch a 100 mph tailwind, and, God forbid, it might even be jolly good fun.

eg If I was to decide to fly across the Tasman Sea from here in NZ, to Sydney, Australia; I could spend six hours dodging cumulus at 10,000 feet, or three hours watching it all slip past below me. Easy decision for me. I'll be eating Steak and Chips, drinking cold beer whilst you are looking at an inch of ice on your leading edge, hoping the liferaft doesn't leak, and the water isn't too cold (by the way it is very cold).

 

If marble can pull off his 300 mph ducted fan beast, good luck to him, I'd love to see it, you never know he might sell plans for it one day and retire a millionaire.

If you want to build your Defiant to the letter of the plans, best of luck to you too, you'll be building a winner.

I think actualy if you do the math, you are much better off buying a ticket on an airliner.

 

I'm sorry but Jim's profound statement isn't going up as grafiti anywhere round here.

Cheers

[shender1]

Just out of curiosity,

 

What does it cost to have and maintain an ox system? Wouldn't that also have to included in to the cost and time factor?

[No4]

quoting Mountain High's site,

A four place complete kit costs US$ 725

The largest kevlar tank holds 200 man hours of ox.

My friend sucks ox when riding his turbo Cessna 182, and refils are I think $10.

 

http://www.mhoxygen.com/index.phtml

 

Aircraft Spruce, the Cozy's new master, have a wide range here..

 

http://www.aircraft-spruce.com/ntoc.php?sec=ps&cat=oxygensystems

[Jim Sower]

I thought a regulator and canula(sp?) were a lot more affordable than that, and that you could get refils at any welding supply place for chump change.

 

Guess I'll have to revisit my references ....

[dust]

i think to get systems that monitor the breathing, 750 is about right. they have also come out with a carbon fiber tanks that weighs next to nothing, that is what we sized our baggage area for, it was going to be for eithor fuel or ox.

 

enjoy the build

 

Mike

[Tyson]

Originally posted by No4

climbing to 25,000 feet 200 CAS = 300 TAS.

 

I basically agree with all of your sentiments, particularly about the airline ticket.

 

It should be noted that flutter is not simply related to IAS (ie you can't take a Cozy to 48,000 feet with a turbine and safely cruise at 390 knots with an IAS of 200). This mach .67 cruise would indeed be experimental. It is a common misunderstanding that flutter speed (presumed VNE limiting variable) does not change with altitude. It is true that other canards do fly at higher than 200 indicated. The Berkut has a carbon canard (and wings), though I believe the E-racer has essentially a LongEz canard (not sure about this). Regarding flutter, I would Assume that the carbon structure would be less flutter-prone.

 

I mentioned the idea of building another, faster design as it seems a bit if a compromise to build a Cozy into something it isn't. If you look at the KR community, you see people spending thousands of hours and tens of thousands of dollars trying to make a KR-2 into a Glasair (without coming close, except in terms of expenses).

[No4]

Hallo Tyson

How is the Defiant going? I heard they have a very long build time, 6000 hrs is that correct? Can I ask which engines are you using?

I think my ultimate plane would be a Defiant with twin 300 hp Thielert V8's, and retracts. Maybe someday..

 

I agree the Cozy may run into terrible trouble at 390 knots at 48,000 feet. But I am rather hoping to remain at around 18,000 to 23,000 with 250 to 300 knots on the GPS, and 180 Indicated. It is commonly done by light pressurised twins, so I would be dissapointed with myself I can't get it out of a Cozy.

 

It seems flutter is not only the strength of the aircraft, but should the rudder, ailerons, and elevator all clash in rythmn, then somehow the fuselage suffers. From what I can understand making the part as strong as possible is greatly beneficial, and would imagine that mass balancing becomes very important.

 

Would it be worth my while to build a carbon fibre canard, or ailerons?

 

 

 

I think you can get a nose piece and a nice bottle to fit in your handbag for $300, but if you want the U beauty kevlar bottles and electronic breathing management system, for four people is well over $2000. I think you are right though that it's peanuts to refill.

[dust]

there is ONE size of carbon fiber bottle and it is really light and on the large size and relatively inexpensive, it is about 5" * 20", what a coincedence, thats what we left in ourt baggage/storage area.

 

enjoy the build

 

mike

[marbleturtle]

300 mph Cozy is nuts? Well... the Berkut is basically an improved LongEZ. What's nuts about taking a 4 seater to that level?

 

At this point I'm not saying that I will try it. But C'mon people! Where's the fire of enginuity that burns in us to never be satisfied whith the status quo? Where's the spark that defies conventional wisdom and says "yes... man CAN fly!" Aren't lost causes the only ones worth fighting for?!?!?! Isn't defying the incredible odds against us what made this country great?!?!?! Did George Washington ever say "I'm not going to cross the English Channel because its cold and there are too many Brits with guns on the other side"?!?!?! WELL I FOR ONE AM NOT GOING TO STAND IDLE WHILE YOU PEOPLE DENEGRATE OUR GREAT COUNTRY! YOU CAN ALL JUST...

 

wait... $50 a square yard? This carbon fiber stuff is expensive! Uh, 200mph? I'm good with that.