Yoke deflection, load factor & stall

[RichPa]

A small airplane always stalls when you pull back on the yoke and your airspeed is below Va?

Or is it possible that at some speeds to not have enough elevator authority to reach the G for the accelerated stall? Basically, can you pull back on the stick (especially the case you pull full back) without having an accelerated stall?

Please pay attention to my assumption here: for example, a Cessna stalls at 2G at 66 kts. A full back yoke will produce 2G at 66 kts? As an example, always a 80% yoke aft deflection produces 80% of the stall load factor?

I figured out that in some Cessnas at some speeds below Va you can pull back on the stick, you feel the G, but the aircraft doesn’t stall immediately but just seconds after that when the airspeed decreases enough. Is this right or I noticed it wrong?

Also, at some speeds I think you can deflect let’s say 80% aft yoke without accelerated stall, but I figured out not at all.

What I know is that an aircraft can be stalled at any speed and attitude. All it matters is angle of attack, however, this doesn’t help me too much to figure out my problem.

Thank you very much!

[deefer dog]

In still air, for the same aircraft flying in the same conditions and at the same Gof G, the stall will occur at the same elevator stick position - irrespective of the G loading.

This is an age old argument that some will disagree with, but after years of (unscientific) testing in a variety of aerobatic types (and even three different jet types) I am convinced the argument has merit...........but I'm ready for flack!

[RichPa]

What about the same situation considering an inverted stall?

[LAI]

I'm guessing that this would probably be better placed in "Tech Log" where all the boffins live ;)

Anyway, As far as I remember, the speed Va is the point at which the aircraft will reach the stall at its limiting 'g' load (Can't remember if this is the design limit or ultimate load etc...will leave that to the experts!). i.e. in very simple terms: at any speed below Va, it will stall before it falls apart, regardless of how hard you pull.

However, I'm not sure that control authority has anything to do with the definition of Va, so there is no guarantee that you would have enough authority to actually reach an accelerated stall at any particular point. Whether you can or not in any actual aircraft is, I would suggest, a separate design issue.

deefer: I don't know enough to agree or disagree with you definitively! However, my instinct would tell me that CG etc. must have an effect on your theory, as it affects stability and by extension, the control authority available (regardless of how much control deflection is being employed at the time)...?

Standing by to be corrected by someone who knows what they're talking about! :}

[BizJetJock]

It's more likely that you can't do a true 1G stall due to lack of low speed effectiveness. There are types where the certification stall speed is defined as the lowest speed reached when you decelerate at 1kt/sec until you run out of elevator. You can high speed stall these aircraft. PA28's with a very forward CofG come into this category.

[deefer dog]

What about the same situation considering an inverted stall?

Well obviously we would be talking about forward stick position.

I don't know enough to agree or disagree with you definitively! However, my instinct would tell me that CG etc. must have an effect on your theory, as it affects stability and by extension, the control authority available (regardless of how much control deflection is being employed at the time)...?

And your instructor would be correct when referring to the CofG. If you read what I stated I covered that point.

It's more likely that you can't do a true 1G stall due to lack of low speed effectiveness.

There may be one or two types, but in the main that statement is not correct. Care to name any types you know of?

There are types where the certification stall speed is defined as the lowest speed reached when you decelerate at 1kt/sec until you run out of elevator.


A speed reduction of 1kt/sec is used to determine the 1G stall speed simply to avoid distortion of the data as a result of increased G that would emanate as a result of using an increased rate of speed reduction. "Running out of elevator" is not a phrase that forms any part of the definition of STALL.

[LAI]

deefer, my apologies. *Note to self: Improve skim reading technique!

Given the conditions you state, that makes sense!

[PLovett]

Stop thinking "speed" and start thinking "angle of attack".

You may not be able to deflect the control column far enough to cause the aircraft to stall but in reality it will cause the aircraft to lose speed to the point that it is unable to maintain a nose high/level attitude and will begin to descend causing the angle of attack to increase to the point that the wing stalls.

[RichPa]

Well obviously we would be talking about forward stick position.
Of course, but in terms of forward stick autority to induce the inverted stall?

[BizJetJock]

"Running out of elevator" is not a phrase that forms any part of the definition of STALL.

You are quite correct. The phrase used is "the control reaching the stop", as seen in b3 below:

CS 23.201 Wings level stall
(a) It must be possible to produce and to
correct roll by unreversed use of the rolling
control and to produce and to correct yaw by
unreversed use of the directional control, up to the
time the aeroplane stalls.
(b) The wings level stall characteristics must
be demonstrated in flight as follows. Starting
from a speed at least 18.5 km/h (10 knots) above
the stall speed, the elevator control must be pulled
back so that the rate of speed reduction will not
exceed 1.9 km/h (one knot) per second until a stall
is produced, as shown by either –
(1) An uncontrollable downward
pitching motion of the aeroplane; or
(2) A downward pitching motion of the
aeroplane which results from the activation of a
device (e.g. stick pusher); or
(3) The control reaching the stop.

As I said, PA28s with a forward CofG are a good example.