V-TAIL OR CANARD LSA/BURT RUTAN.

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tl-3000pilot
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V-TAIL OR CANARD LSA/BURT RUTAN.

Post by tl-3000pilot »

Just wondering if anyone other than myself thinks it would be nice to see an LSA aircraft with either a V-TAIL design or CANARD design? Not sure how beneficial such a design would be to LSA, but it would be interesting to see one for me. Would be interesting to see what Burt Rutan might come up with if given the task to design an all new LSA. Your thoughts?

Thanks!

tl-3000pilot.
Merlinspop
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by Merlinspop »

tl-3000pilot wrote:Just wondering if anyone other than myself thinks it would be nice to see an LSA aircraft with either a V-TAIL design or CANARD design? Not sure how beneficial such a design would be to LSA, but it would be interesting to see one for me. Would be interesting to see what Burt Rutan might come up with if given the task to design an all new LSA. Your thoughts?

Thanks!

tl-3000pilot.
You can build a Sonex with a V-tail and certify it as an E-AB inside the LSA parameters.

Bruce
- Bruce
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CharlieTango
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by CharlieTango »

The canard designs seem like a compromise to me. Additional speed at the expense of limited pitch attitudes and unrecoverable stall/spin issues.

Slow down to LSA speeds and I see the down side but not the upside.
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by tl-3000pilot »

Merlinspop wrote:
tl-3000pilot wrote:Just wondering if anyone other than myself thinks it would be nice to see an LSA aircraft with either a V-TAIL design or CANARD design? Not sure how beneficial such a design would be to LSA, but it would be interesting to see one for me. Would be interesting to see what Burt Rutan might come up with if given the task to design an all new LSA. Your thoughts?

Thanks!

tl-3000pilot.
You can build a Sonex with a V-tail and certify it as an E-AB inside the LSA parameters.

Bruce
Interesting airplane, just watched a video of that with a very small jet engine on it.

Thanks!

tl-3000pilot.
rsteele
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by rsteele »

CharlieTango wrote:The canard designs seem like a compromise to me. Additional speed at the expense of limited pitch attitudes and unrecoverable stall/spin issues.

Slow down to LSA speeds and I see the down side but not the upside.
I can see stall speed issues, so an LSA may not be possible. I've never heard any stall spin issues, at least not in anything approaching normal flight. You can't stall/spin a Long EZ without serious cross control, not uncoordinated, but true cross control, beyond even a serious slip in a conventional configuration. And these are recoverable. I know someone who did it. On purpose.

Of course, the overall efficiency is also still a question. I think it's been pretty well proven that a convention design is more efficient for a similar mission

Ron
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CharlieTango
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by CharlieTango »

EZs are not favored at high altitude because limited elevators require longer runways and the elevators in canard designs are limited due to unrecoverable stall tendencies across the various canard designs.

http://en.wikipedia.org/wiki/Stall_(flight)#Deep_stall

Canard-configured aircraft are also at risk of getting into a deep stall. Two Velocity aircraft crashed due to locked-in deep stalls.[37] Testing revealed that the addition of leading edge cuffs to the outboard wing prevented the aircraft from getting into a deep stall. The Piper Advanced Technologies PAT-1, N15PT, another canard-configured aircraft, also crashed in an accident attributed to a deep stall.[38] Wind tunnel testing of the design at the NASA Langley Research Center showed that it was vulnerable to a deep stall.[39]
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tu16
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by tu16 »

tl-3000pilot wrote:Just wondering if anyone other than myself thinks it would be nice to see an LSA aircraft with either a V-TAIL design or CANARD design? Not sure how beneficial such a design would be to LSA, but it would be interesting to see one for me. Would be interesting to see what Burt Rutan might come up with if given the task to design an all new LSA. Your thoughts?

Thanks!

tl-3000pilot.
Yes, one can dream :) Design challenge byChief Aerodynamicist, Cirrus Aircraft Company.

http://www.youtube.com/watch?v=TLUpnS7nyUE

Obviously the LSA has a lifting rather than control canard.

The challenge of highly loaded canard by downward pitching moment of powerful main wing flaps may be not as a big issue with LSA where partial/no-flaps landing can be quite common due to slower flight profiile overall.

The danger of insufficiently-loaded canard when main wing may stall before canard (deep stall, unrecoverable spins tail first) I think can be easier addressed in LSA where main CG-contributing components are few and this probably can be designed out (as illustrated in a powerful on-linear simulator above)

Whether this would bring any advantages except wow factor - remains to be seen.
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by tl-3000pilot »

Thank you all for your in-put. Please forgive me, as I'm a bit slow in understanding much of what you are saying in reference to the canard design. I was always under the impression that there was a good safety reason for the canard design, as in helping to prevent stalls from happening in some way. I can see now that I was wrong.

So, there is possibly a "lifting" type of canard as seen in the video link and a canard that enhances maneuvering? Seems to me that if a canard were to be incorporated into an LSA, the "lifting" canard would be the way to go, if it does not make stalls more un-recoverable that is or cause "deep stalls".

Again, I'm blown away by what I read about the Velocity aircraft stall accidents, as I was seriously under the impression that canards added a true sense of safety. Why would Velocity, Rutan and others incorporate the canard, only because their aircraft are built for faster than 120-kts speeds? I thought that somehow a canard stalled first, before the main wings, or something like that?

My desire in seeing a canard in an LSA is for safety and better over-all performance first, styling/looks second, but if it takes away from its over-all safety and creates a worse stall situation, forget it!

tl-3000pilot.
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CharlieTango
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by CharlieTango »

Everything in aviation and aerodynamics is a compromise. This includes the safety aspects of a canard where it will stall and recover before the main wing. The compromise is that in a more extreme maneuver it may backfire.
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by tl-3000pilot »

CharlieTango wrote:Everything in aviation and aerodynamics is a compromise. This includes the safety aspects of a canard where it will stall and recover before the main wing. The compromise is that in a more extreme maneuver it may backfire.
Understood, thanks! :D
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tu16
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by tu16 »

tl-3000pilot wrote: I was always under the impression that there was a good safety reason for the canard design, as in helping to prevent stalls from happening in some way. I can see now that I was wrong....
You're not necessarily wrong. Liftings canards are indeed designed specifically to *normally* stall before main wing so they'd drop the nose before the main wing stalls. But stall speeds are function of wing loading - in a dynamic maneuver and/or with CG aft one can "unload" canard, hence lowering its stall speed while simultaneously loading main wing and increasing its stall speed, reversing the design relationship with possible "deep" stall with both wings stalled.

But this is true that aircraft aerodynamic design is a complex compromise. I'd guess it's double hard to make a "good" LSA in canard configuration.

To maintain stall speed relationship the main wing is designed to operate at lesser lift coefficient than canard, and the root of the main wing is in downwash from canard decreasing its lift even more. Result - you need a bigger wing. Flaps are a problem in canard configurations because of canard loading design limitations - so to meet LSA landing speed limits you need a slower - hence, yet even bigger, that is HEAVIER and more complex - wing.

So I personally do not expect to see much of canard configurations in LSA category - aerodynamics and economics imho are not in favor of it.

However, if "no-stall" behavior would become a design goal for LSA - this can be easily done in traditional configuration, suitable for LSA, method used since 30-s - with spring-loaded forward slats :) (http://www.armchairgeneral.com/forums/s ... hp?t=44394 )
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by tl-3000pilot »

tu16 wrote:
tl-3000pilot wrote: I was always under the impression that there was a good safety reason for the canard design, as in helping to prevent stalls from happening in some way. I can see now that I was wrong....
You're not necessarily wrong. Liftings canards are indeed designed specifically to *normally* stall before main wing so they'd drop the nose before the main wing stalls. But stall speeds are function of wing loading - in a dynamic maneuver and/or with CG aft one can "unload" canard, hence lowering its stall speed while simultaneously loading main wing and increasing its stall speed, reversing the design relationship with possible "deep" stall with both wings stalled.

But this is true that aircraft aerodynamic design is a complex compromise. I'd guess it's double hard to make a "good" LSA in canard configuration.

To maintain stall speed relationship the main wing is designed to operate at lesser lift coefficient than canard, and the root of the main wing is in downwash from canard decreasing its lift even more. Result - you need a bigger wing. Flaps are a problem in canard configurations because of canard loading design limitations - so to meet LSA landing speed limits you need a slower - hence, yet even bigger, that is HEAVIER and more complex - wing.

So I personally do not expect to see much of canard configurations in LSA category - aerodynamics and economics imho are not in favor of it.

However, if "no-stall" behavior would become a design goal for LSA - this can be easily done in traditional configuration, suitable for LSA, method used since 30-s - with spring-loaded forward slats :) (http://www.armchairgeneral.com/forums/s ... hp?t=44394 )
Really good explanation, thanks! :D
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CharlieTango
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by CharlieTango »

I live at, and fly at high altitude so my take is a little biased, nevertheless I see advancement in LSA by adopting turbo normalized or boosted engines, flexible props that flatten under load and room for an O2 bottle.

I cross the sierra in my CT and sometimes in a friends 914 powered Europa. The speed, economy and safety from crossing at 16,000' vs 10,000' are really appealing. A 25kt advantage would make it worth climbing even without mountains to cross.
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tu16
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by tu16 »

CharlieTango wrote:I live at, and fly at high altitude so my take is a little biased, nevertheless I see advancement in LSA by adopting turbo normalized or boosted engines, flexible props that flatten under load and room for an O2 bottle.

I cross the sierra in my CT and sometimes in a friends 914 powered Europa. The speed, economy and safety from crossing at 16,000' vs 10,000' are really appealing. A 25kt advantage would make it worth climbing even without mountains to cross.
Hear, hear... Even flights across Cascades brought up for me the interest in 914 with a flexible prop :) When I looked into it even with fixed pitch prop you still retain some power advantage...
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CharlieTango
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by CharlieTango »

tu16 wrote:...even with fixed pitch prop you still retain some power advantage...
The advantage even with fixed pitch can still be huge. It is LS so lets pick 10,000'. you can optimize for 1 altitude with your fixed prop so make it your typical cruise altitude and use that altitude.

You couldn't pitch too coarse, you still have to have a pitch that works for climbing. My guess is that I could cruise at 135kts+ with a fixed pitch 914 CTSW because I can already get 125+ and that's less than 70hp vs 115hp.

If you could effectively adjust the prop faster yet in cruise and climb.
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