Canard aerodynamics: negative G stall?

gismo

gismo

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After reading about all the virtues of the new canard twin I started wondering what happens when a canard design stalls with a negative G load. The oft touted safety advantage of a typical canard design is based on having the angle of incidence a few degrees higher on the canard than the main wing. Seems to me that in inverted or other negative g flight, that advantage would become a serious disadvantage. Of course it's unlikely any sane pilot is going to attempt inverted flight in a standard category twin but upsets do happen and it's pretty easy to generate a negative g stall while upright as well.

I suspect that as usual the devil is in the details but from a simplistic perspective I'd expect that if you were climbing in slow flight and pushed abruptly you'd stall the main wing causing a rapid nose downward pitch movement much like a tailplane stall in a conventional airplane. I'm having trouble figuring out what would happen next given that the main wing is generally much larger and has a higher aspect ratio than the canard (although that's not always the case).

If you were inverted and stalled the main wing first by pushing too hard, I'd expect the plane to experience a deep and potentially unrecoverable stall but again the relative areas and apect ratios of the two surfaces might be confusing me.

Any aerodynamicists wanna take a stab at this?
 
This is a really interesting question that I hadn't considered.

But the advantages of the canard twin probably would prevent more people from killing themselves than this disadvantage would add.
 
Either way the aircraft will be able to recover. If somehow the main wing stalled before the canard, whether that's upside down or right side up, the aircraft's nose will drop through the horizon and recover. You'd have to do some pretty violent maneuvers for that to happen. The only canard that I know of that stalled the main wing were some of the early Velocitys. That was because of a severe aft CG which caused on two occasions a deep stall. Vortilons, a redesigned wing and adherence to proper loading fixed those problems. Also, while the higher angle of incidence is the primary reason for the canard stalling first, it's also has higher wing loading as well thus giving it a higher stalling speed. If your CG is correct and the canard stalls, the nose is going to go down or up if you're inverted.

Just so happens that this month's PILOTMAG has a brief canard story in it. Dick Rutan describes Mike Melvill crossing the equator inverted in his Longeze.
 
Velocity173 said:
Either way the aircraft will be able to recover. If somehow the main wing stalled before the canard, whether that's upside down or right side up, the aircraft's nose will drop through the horizon and recover. You'd have to do some pretty violent maneuvers for that to happen. The only canard that I know of that stalled the main wing were some of the early Velocitys. That was because of a severe aft CG which caused on two occasions a deep stall. Vortilons, a redesigned wing and adherence to proper loading fixed those problems. Also, while the higher angle of incidence is the primary reason for the canard stalling first, it's also has higher wing loading as well thus giving it a higher stalling speed. If your CG is correct and the canard stalls, the nose is going to go down or up if you're inverted.

Just so happens that this month's PILOTMAG has a brief canard story in it. Dick Rutan describes Mike Melvill crossing the equator inverted in his Longeze.
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One of the magazines has a Velocity Twin on it. Very pretty bird.
 
Velocity173 said:
Dick Rutan describes Mike Melvill crossing the equator inverted in his Longeze.
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We are having lunch with him Saturday. Will ask about his unconventional equator crossing. And will ask the OP question.
 
aviatingfool said:
We are having lunch with him Saturday. Will ask about his unconventional equator crossing. And will ask the OP question.
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Man he's my hero. Wish I could meet him. Tested some of the coolest homebuilts around and the first civilian astronaut. All that without a college degree. A real pilot and adventurer.
 
Seanaldinho said:
One of the magazines has a Velocity Twin on it. Very pretty bird.
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Yeah got the mag. I saw it at the factory last year when I was getting my condition done. It was upside down getting it's engines put in. I actually didn't think they'd ever get that project going. I'm soo glad they did though. Good company that needs to get jump started again.
 
Velocity173 said:
Either way the aircraft will be able to recover. If somehow the main wing stalled before the canard, whether that's upside down or right side up, the aircraft's nose will drop through the horizon and recover. You'd have to do some pretty violent maneuvers for that to happen. The only canard that I know of that stalled the main wing were some of the early Velocitys. That was because of a severe aft CG which caused on two occasions a deep stall. Vortilons, a redesigned wing and adherence to proper loading fixed those problems. Also, while the higher angle of incidence is the primary reason for the canard stalling first, it's also has higher wing loading as well thus giving it a higher stalling speed. If your CG is correct and the canard stalls, the nose is going to go down or up if you're inverted.

Just so happens that this month's PILOTMAG has a brief canard story in it. Dick Rutan describes Mike Melvill crossing the equator inverted in his Longeze.
Click to expand...

Are you saying that if you're inverted and you pull the nose up, the canard will stall first because it has a higher wing loading? If so the nose would go down, not up. But if the wing stalls first the airplane would indeed pitch up and while it might eventually reach an attitude that stalls the canard as well, it seems like the main wing would remain stalled.
 
gismo said:
Are you saying that if you're inverted and you pull the nose up, the canard will stall first because it has a higher wing loading? If so the nose would go down, not up. But if the wing stalls first the airplane would indeed pitch up and while it might eventually reach an attitude that stalls the canard as well, it seems like the main wing would remain stalled.
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I think there are too many variables to tell if the canard will stall first or the main wing. Each canard aircraft has different airfoils, wing loading, angle of incidence, VGs, etc. If the main wing should stall while inverted, I would think it would be a matter of just pulling back on the stick (Split S) to get back flying speed. The canard would still be producing lift in that scenario. Like I said the only way you're not going to get the nose down back to flying speed would be if you had a severe aft CG. Then you'd be in a flat deep stall. Even then most canards have a healthy safety buffer when it comes to CG. I've stalled mine countless times and I operate slightly behind the aft limit. It always recovers even with holding the stick against the stop for 10 secs. Even stalled at a nose high 60 kt push over. Nose took awhile but it bobbed up and down and slowly pitched down to flying speed. The thrust line is actually slightly above CG so it assists in getting the nose down. Only canards I've ever heard of main wing stalling are some Vari/Longezes and there owners did some aggressive maneuvers to do it. Still never heard of any of them not being able to recover.
 
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I'd go try it and find out for you but my engine stops when inverted and I don't have a starter.
 
pericynthion said:
I'd go try it and find out for you but my engine stops when inverted and I don't have a starter.
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Air restarts are no problem. You just need airspeed.

Been there, done that intentionally. With my wood prop, it took ~140 knots to get it to spin/restart.
 
kyleb said:
Air restarts are no problem. You just need airspeed.

Been there, done that intentionally. With my wood prop, it took ~140 knots to get it to spin/restart.
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Yep. I have a cruise prop and it takes about 170-180 mph IAS to get it going from a stopped prop.

Does that mean you volunteer? :)
 
Let's say, for sake of argument, that for whatever reason the main wing does stall first, inverted or not. In theory, if you have enough altitude, you should go in to a tailslide and be able to use the elevator to level you out and put the plane in a nose down altitude before it stops, if you have sufficient momentum.

Or better yet the rudder, in a hammerhead which should result in pointing you straight down.

No, I'm not going to volunteer to test that theory.
 
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