Stalling in a turn

[It flies]

I find this a very interesting subject. But after reading through the thread I can't find a clear answer. A quick Google search turned up this text:

An airplane will stall during a coordinated steep turn
exactly as it does from straight flight, except that the
pitching and rolling actions tend to be more sudden. If
the airplane is slipping toward the inside of the turn at
the time the stall occurs, it tends to roll rapidly toward
the outside of the turn as the nose pitches down
because the outside wing stalls before the inside wing.
If the airplane is skidding toward the outside of the
turn, it will have a tendency to roll to the inside of the
turn because the inside wing stalls first.

If the coordination of the turn at the time of the stall is
accurate, the airplane's nose will pitch away from the
pilot just as it does in a straight flight stall, since both
wings stall simultaneously.

So according to this text it seems that Jeremy Pratt is incorrect? In a perfectly balanced turn the nose will drop (with the wings at an angle to the horizon) but neither wing will fall away.

I think in essence this is what SNS3Guppy is saying. Has someone actually tried this? Anyone who has tried all three variants should be able to give a us clear answer.

[Crash one]

Yes, I have stalled a glider in a very steep turn at 80 knots. The nose dropped out of the turn whilst still maintaining the bank angle, just the same as a level stall, neither wing stalled first because the turn was balanced. All it required was to pull too hard trying to tighten the turn. Recovery was the same, nose "down" maintaining most of the bank until unstalled then continue the turn, not so aggressively.

[BasicService]

Please explain this then guys.

Wings stall at an angle of attack, not a particular speed.

An aircraft in a steady balanced level turn is developing the same amount of lift from both wings, otherwise it would be rolling.

The outer wing is travelling further than the inner wing (in the same time, of course,) therefore it is going faster.

Since the amount of lift developed by a wing varies according to speed and angle of attack (and a constant) , if both wings are developing the same lift and one is going slower than the other the slower wing must have a greater angle of attack.

If speed is decreased the angles of attack must increase to maintain level flight The wing with the greater angle of attack, the slower one, must stall first.

In a level balanced turn both wings will have the same angle of attack, but the outer wing is moving slightly faster so will generate more lift. The outer wing aileron will need to be deflected upward slightly to counteract the rolling moment. The effective angle of attack of this wing tip will be reduced, but the AoA of the rest of the wing will be unaffected. In principle the inner wing tip will stall before the outer wing tip as you suggested, but in practice this will probably be impossible to observe because the wing will be designed so that the wing roots stall first.

Both this and the separate 'spiral staircase effect' (only occurs in a climb or descent) will be most noticeable at low TAS, where the radius of turn is smallest. In a level turn I do doubt whether it's a large enough effect to be noticeable at all.

The statement:

An aircraft in a steady balanced level turn is developing the same amount of lift from both wings

is not correct because it is the sum of the rolling moments around of the C of M that determines whether or not the aircraft is rolling, not the sum of the forces on each side.

[Mark1234]

Originally Posted by basic service

"An aircraft in a steady balanced level turn is developing the same amount of lift from both wings"

is not correct because it is the sum of the rolling moments around of the C of M that determines whether or not the aircraft is rolling, not the sum of the forces on each side.

And a moment is:
a) an instant in time.
b) a force acting at a distance from some axis of rotation.

Answers on a postcard please....

Now you could perhaps make a case that there's an additional moment to offset the prop torque, unless it's a glider, in which case, the rolling moments come from?

[ChrisVJ]

Basic Service.

" . . . designed so the wing roots stall first."

Maybe in a spam can. Have a look at the stall characteristics of different plan forms, elliptical and tapered stall across the wing evenly unless washed out. Various shapes various characteristics. (That's what the 50s designers were working on.)

Not all aircraft need control column deflection to maintain a turn. So many variables there are an almost infinite number of compromises. That's the fun part.

[Mechta]

It sounds to me that most power fliers would benefit from a trip to a gliding club and a few high aerotows in something like a K13, which is often used to demonstrate spinning.

Discuss the purpose of your visit with the club CFI beforehand and most would oblige with some spin demonstrations. As previous posters have mentioned, the lack of torque effect from the engine, plus the ability to listen to the air, as opposed to the engine, will make spin demonstrations in a glider all the more useful.

[John Farley]

Chaps

There has been a lot of emphasis here on ball in the middle so lateral stability does not affect the trim condition of the ailerons.

I fear that is a rather simplistic view of lateral stability. Other aircraft design factors beyond dihedral affect lateral stability. One that will affect many light aircraft is the height of the cg (not just its fore/aft position). If the wing is above the cg then that will produce a rolling moment when there is bank on. (think pendulum effect).

However, all this talk of tiny effects one way or the other is swamped by the swirling airflow that the airframe is immersed in with a traditional prop on the front.

It is my experience that a lot of SEP aircraft do roll out of the turn if stalled in the turn. But there are no golden rules re stalling and spinning and much is type and power dependant. THAT IS THE IMPORTANT THING FOR A PILOT TO REMEMBER. Not why it is so.

JF

[It flies]

Thanks Crash and BasicService. So this seems to be correct:

the airplane's nose will pitch away from the
pilot just as it does in a straight flight stall, since both
wings stall simultaneously.

There are of course a lot of other factors that have an influence. I hope to try accelerated stalls soon myself and see what really happens.*

Mechta, I think that your suggestion is a good one. I'll try this if I get the chance.


* Yes, in a suitable aeroplane with a qualified instructor.

[It flies]

O.k., John. I get your point that to try to establish some general principles from behind a computer isn't all that useful.

Part of the fun of flying for me though, is to try to understand some of the fysics (what is happening when I stall my aeroplane) as well. Would your book 'A view from the hover', help me with this?

[John Farley]

as it happens at A View from the Hover there is an extract from the chapter on stalling........

JF

[Piper.Classique]

However, all this talk of tiny effects one way or the other is swamped by the swirling airflow that the airframe is immersed in with a traditional prop on the front.

Quite. And gusts too.
I spin the supercub from time to time, solo only because of CG limitations, and I can only make it go with the prop. On a straight stall it won't drop a wing at all in calm air, even leaving some power on, and to get it in to a spin takes a hefty bootfull of rudder. I'd be interested to know if the 90 and 135 hp versions are the same (mine is a 150, I haven't tried with the 180)

[It flies]

there is an extract from the chapter on stalling........

I read the extract and it looked promising so I ordered the book. Reading it might raise new questions though...

Thanks for the link.

[HarryP]

FLYER AirPortal

John,
having read your comments, re: stalling, I decided to buy the book. I clicked on the link and got 'FLYER Air Portal', a crappy web site that doesn't work!

The 'Buy' button has no effect. They don't seem to want to sell your book for you. I thought that you should know. Can you tell me how else I can get the book? If you are of a mind to reply, can you e-mail me?

[email protected]

Harry Page

[Fly-by-Wife]

Harry,

I suspect that the problem may lie in your computer configuration rather than the website.

I had no problem accessing the website and buying the book, this morning.

FBW

[ft]

John,
while simplification is often a Good Thing, the particular one of looking at high wing aircraft as pendulums IMHO is a bad one which has caused lots of confusion.

Looking at the force diagram, the lack of a moment arm between the lifting force and the resultant of the weight and acceleration reaction force is obvious - so where would such a righting moment stem from? And that's where we lost the readers with a grasp on physics.



I don't think the explanation of the righting moment due to interference in high wing aircraft is too much to throw at people when discussing lateral stability.

Cheers,
Fred