The reason

canard type aircraft claim to be stall proof is that
the mechanism they use for pitch control has
insufficient authority to put the wing at a high
enough angle of attack to cause the wing to stall
during normal (whatever that means) operations.

David Doshay wrote:

Not really quite true. This is exactly the situation with an
Ercoupe, though.

In a canard aircraft the front wing (the canard) should be set
so that it stalls a few degrees before the rear wing. Different
designers have different rules about how many degrees of
'stall margin' is best. Because the wings are on either side
of the c.g., when the front wing stalls first there is a natural
nose down pitching moment, which results in automatic recovery
even when the elevator is held full back. If the pilot persists
in holding the elevator full back the nose pitches right back up
again and the cycle repeats, resulting in what is usually called
a "pitch buck." In the factory Velocity I flew, with the engine at
1500 rpm the pitch buck happened at an indicated 60kts. The
frequency of the buck was roughly 2 Hz and I estimated the
amplitude at the nose to be almost 2 feet. Bucking really is a
good term for what it feels like. At that power setting in the full
pitch buck the nose of the plane remained slightly nose up and
the plane went down at about 100 ft per min. I did this test to
see what would happen if I overcontrolled on landing and ended
up in a pitch buck near the runway ... would the buck result in
tearing the nose gear off? It seems not. But I digress.

So, the reason they state that canard planes don't stall is that
the plane as a whole does not suddenly loose lift, even though
the front wing does stall. Elevator effectiveness is not the cause
of the effect.

But the Atlantis, which started this thread, does not look to be
a canard.

David

It all depends on the energy you use to enter the stall.
If you are talking about straight and level that is one thing. 
That is the key assumption with most stall proof or stall resistant
airplanes. If you are in the soup and you are diving without realizing 
it and you suddenly realize it and pull up you could stall because you are 
entering a potential stall with much more momentum. Of course
you could also pull the wings off. Most PP instructors either do not
understand this or they don't explain it.

Paul Lamar
 
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