Stall and Stick Position.

[deefer dog]

I happen to be one of the converts - stick position is related to angle of attack.

So, given the following: Same Type, Same WAT, Still Air Conditions, Same Configuration, and irrespective of the accelaration (G)....

Why would the stall NOT occur at exactly the same Elevator Position, every time, irrespective of everything else?

[Pugilistic Animus]

Absolutely correct Deefer Dog

Any time the stick, yoke or wheel is aft of neutral or forward of neutral [inverted stall] you are on your way to the stall

[Dan Winterland]

Any time?

How about at zero g?

[PBL]

Originally Posted by deefer dog

So, given the following: Same Type, Same WAT, Still Air Conditions, Same Configuration, and irrespective of the accelaration (G)....

Why would the stall NOT occur at exactly the same Elevator Position, every time, irrespective of everything else?

It's hard to know where to start with this.

Let's try this. First, you give your preferred definition of what "the stall" is. Is it buffet? Is it holding the stick full aft for two seconds without further increase in pitch attitude? Is it a nose-down pitch which cannot be easily arrested? (See CS 25 201 (d) .) Or do you mean, as many others do, the point at which C_L_Max is reached.?

Then, let us try this. Suppose you are flying an airplane in level flight, with fixed engine power, and decelerating slowly, as if you were performing a Vs1g stall test, until the aircraft stalls. Let us assume the elevator position is measured on a scale [-FullDown, +FullUp], where FullDown and FullUp are in whatever units you prefer. Suppose you are performing your Vs1g test at elevator position X < FullUp. So with this engine power, in level flight, the aircraft will stall with elevator position X held (hypothesis). Then the aircraft will obviously stall in wings-level, vertically-accelerated flight at the same engine power for any fixed elevator position Y where X < Y <= FullUp, and there are (mathematically) infinitely many such positions.

PBL

[Wizofoz]

PA,

So, trimming an aircraft slightly nose up (lets assume it has trim-tabs, and therefore it DOIES move the elevator up from neutral) will lead to it stalling?

Sorry, don't think that is correct.

[AerocatS2A]

Any time the stick, yoke or wheel is aft of neutral or forward of neutral [inverted stall] you are on your way to the stall

Define "neutral". Is it when the elevator is faired with the tail-plane? Is it when there are no forces on the stick? If the former then you can easily fly at a certain power setting that requires up elevator to maintain speed and altitude, that's not "on your way to a stall." If the latter then you can easily fly with a certain trim setting that requires you to hold back (or forward) stick to maintain speed and altitude that is also not "on your way to a stall."

[Pugilistic Animus]

Oh, Y'all oughtta stop

I think you all know what I meant













edit: when trimmed for steady level or steady turning coordinated flight

[Kerling-Approsh KG]

It's astonishing how often people present 'the symptoms of approaching stall' without mentioning stick position or force applied... A fundamental and potentially deadly failing, in my opinion, as both are crucial elements directly in the pilot's control, and of which the pilot should be immediately aware...


The blame has to lie at the feet of the flying instructor community...

...which is why I started the following thread to test my hypothesis:

http://www.pprune.org/flying-instruc...ing-stall.html

QED.

Peter, what proportion of undesired stalls occur without the stick being aft of 'neutral' (define as you prefer but be practical) and/or aft pressure on the stick?

[Pugilistic Animus]

Kerling-Approsh KG

[AerocatS2A]

edit: when trimmed for steady level or steady turning coordinated flight

That doesn't quite work. Fly an aeroplane at 250 knots trimmed for level flight then apply some back pressure, you might find yourself in a stable climb at 200 knots. Still not heading for a stall. As a blanket statement it doesn't work for me.

[Kerling-Approsh KG]

Pugilistic Animus,

Expressive as your emoticons appear to be, I'm afraid I've no idea what you meant!!!

[Pugilistic Animus]

That doesn't quite work. Fly an aeroplane at 250 knots trimmed for level flight then apply some back pressure, you might find yourself in a stable climb at 200 knots. Still not heading for a stall. As a blanket statement it doesn't work for me. Yesterday 17:13

every time you climb you are on the way to a stall

Pugilistic Animus,

Expressive as your emoticons appear to be, I'm afraid I've no idea what you meant!!!

I run into that problem all the time...shall I say ---you are quite correct


I should add that in a stabilized descent with no gusts or other perturbations to the flight path...then you are just fine, with no real danger of a stall...but don't forget to slow down or flare

[Genghis the Engineer]

Stick position is a useful clue as to approaching stall.

Stick position at stall will however vary at the very least with CG, deceleration rate, flap position, and in many aeroplanes - trim setting.

So, whilst I've heard various people expound that an aeroplane will always stall at the same stick position, personally I think that's cobblers. All four of these factors will vary during any given flight.

Stick position can be no more than a guide.

G

[Pugilistic Animus]

at once the stick is moved even ever so slightly aft-from a trim condition [either centered control column or no residual force] or aft of a steady coordinated level or turning flight manuever and even if you begin a 'stabilized climb'---you will stall ---not necessarily at that instant---but you will stall if you have you hands on the controls and you move the stick back you must say in your head "Gee-I'd better watch my power and attitude as I'm on my way to a stall"

[Pugilistic Animus]

pedantic Correction

if you have you hands on the controls and you move the stick back you must say in your head "Gee-I'd better watch my power and attitude as I'm on my way to a stall"

The correct way:

If you have you hands on the controls and you are applying back pressure or forward pressure -for inverted flight- you must say in your head "Gee-I'd better watch my power and attitude as I'm on my way to a stall"