It always amuses me when someone says an airplane is stall proof.
If you dive and pull up into a vertical climb what happens when the
airplane
stops climbing and just plain stops. Does the nose only drop 3 or 5
degrees
and start flying again or does it fall completely through to a vertical
dive or does it fall over backwards? What about the torque reaction from
the prop when the airplane is vertical and is not moving?
Paul Lamar
This situation is not a stall since the wing is not supporting the weight of
the aircraft at any speed in the vertical. A stall occurs when flow
separation at a particular angle of attack destroys sufficient lift to cause
the weight of the aircraft to exceed the lift being generated. The stall is
the same and meets the same rule for a Mig-29 and a Piper Cub. The wings
follow the same rules as conventional aircraft. Pitch authority is a
function
of the distance between the center of pressure of the elevators (elevons)and
the average center of pressure on the wing. Pitch sensitivity is a function
of the distance between the average center of pressure of the wing and the
center of gravity. The greater the distance, the less sensitive. There are
some very pitch sensitive aircraft (BD-5) and there are some pitch
insensitive wings (Dyke Delta) As old as the Dyke Delta is it remains a very
efficient design. Lynn E. Hanover
That is an interesting definition for a stall Lynn.
My copy of the New World Dictionary says "Aeron. any condition in which there
is such
a loss of lift and increase of drag that the aircraft tends to drop or go
out of control."
Your dictionary definition is accurate but brief in the extreme. I hope mine
was more visual. Both are the same, except for the out of control part. I can
full stall a Stinson and fly it down final (like a steerable stone)unstall it
and land without a problem. (full stall no loss of control).
I am at a loss to understand how aspect ratio controls pitch sensitivty. I
can load a Grobe sail plane up so that it is so pitch sensitive that Duane
Cole couldn't fly it. at the other end of the scale I can load up a Dyke
Delta so that it couldn't land or take off under 100 MPH. (very low pitch
sensitivity).
Thats no design change, just altering the distance between the avarege center
of pressure and the CG.
Lynn E. Hanover
It also has to do with the rate of change of the lift coef with angle of
attack. That is shown in the chart I uploaded. The term pitch sensitivity is imprecise
and ill defined and not a term you see in the stability and control text books.
Pitching moment coef is the more precise term. There is elevator authority
as well and perhaps that is what you are referring to.
Paul Lamar
I agree with Lynn. The chart you entered does not really deal with , It
just shows that for the same lift coeff thr lower aspect ratio wing has to operate at a
higher angle of attack (and with increased induced drag) Pitch sensitivity is a very
strong function of Cg, and can be some what mitigated by tail volume coeff. A higher
aspect ratio wing has a narrower allowable Cg range than a low aspect ratio wing, and thus
could be accused of greater pitch sensitivity. The lift slope data can be used in aircraft
design for stability enhancement, and is why most canards have a higher aspect ratio for
the canard than the main wing, and the obverse is true for most conventional planes (ie
the horizontal has a low aspect ratio.
I believe that the military is training stall avoidance, rather than recovery, and
demonstrating that the wing can lift at nearly zero airspeed if you unload it by
trajectory.
Vance
Come on Vance the term "pitch sensitivity" is not to be found anywhere in Von Doenhoff,
Perkins & Hage, Von Mises, Hoerner or any other book I have read on the subject for the
last 55 years. Look in the index. No such term. I have heard of stick force per G.
Are you talking about stick angle verses pitch angle or stick angle verses angle of attack?
We need to use standard nomenclature or we will not be able to communicate
on this subject.
Paul Lamar
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