Author Topic: Stalling  (Read 11800 times)

Offline FlyingBlind

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Stalling
« on: February 26, 2006, 08:54:41 PM »
First of all, why does this happen and how ? What happens with the aircraft etc. ? ???

Offline Ted_Stryker

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Re: Stalling
« Reply #1 on: February 26, 2006, 10:46:33 PM »
Air is a fluid.  Fluids, as they accelerate, lose pressure.  If you notice the top surface of a wing, in cross section, is more rounded than the underside (in most designs).  This curvature causes air to accelerate over the top of the wing, which causes a low-pressure zone to form over it along the wing's contour line (and other parts of the airframe too, as those surfaces are similarly curved and contoured).  This low pressure acts like a suction, pulling the aircraft up into the air against gravity.  This is what we call "lift".  If the airflow over the wings is sufficiently interrupted by, for instance, a very nose-high angle, the air flow over the top of the wings gets interrupted.  In other words, it doesn't flow against the surface of the wing as much, or even at all, depending on how high an angle difference there is between the direction of the flow of the air, and the angle of the plane.  Since more air is hitting the bottom of the wing in a nose-high angle, and very little, if any over the top of the wing, this "lift" force goes away, and the weight of the plane is acted upon by gravity.  The plane then drops, usually with a nose-down angle, in a free-fall basically towards the ground.

This loss of aerodynamic lift is called a "stall".  Unlike a stall in a car, the airplane engine keeps running (unless it's a jet where one can actually have a compressor "stall" in addition to a wing stall, but that's another explanation).

The way one breaks out of a stall is by reducing power, pointing the nose down even further (yes, this sounds counter-intuitive and nuts... but it's how you do it), and then you bring the nose back up carefully, and gradually, while putting power (throttle) back in.  It can actually be fun to practice these, as it's almost like a roller coaster ride.  With practice, one can actually lose very little altitude before a recovery is fully realized.  At the beginning though, one tends to lose quite a bit of altitude during initial training.

The reason we do training for stalls is for the sake of recognition of the stall condition during takeoffs and landings, when the plane is low, and slow, and loss of altitude is the most dangerous.  Quick recovery from such a condition is essential to continued survival.

Not all planes stall out "violently" with the nose heading to the ground either, so it's important to practice in each model you fly.  A Cessna 152, or 172, etc., stall nose down.  A Piper Warrior, or Archer though, tend to stall "flat" and all you may feel is some vibration while the stall warning horn goes off.

A way you can experiment with stalls without being a pilot is to drive with your arm out the window (carefully), and with your arm held straight, and your palm parallel to the ground, you'll feel your arm want to rise.  This is caused by lift being generated.  Turn your palm so it is at more and more of an angle to the ground, until it is almost perpendicular.  You'll notice that as you do so, your arm wants to drop or is pushed backwards.  This is due to the loss of lift.  Same thing that is happening to the airplane's wing.

This lifting action, by the way, works on the same principal as carburetors, and vacuum cleaners.  Air accelerated into the vacuum cleaner's hose loses pressure due to the acceleration, and therefore causes a "suction".  Pretty neat huh?  This is also known as the Bernoulli principal (fluids losing pressure as acceleration increases).

Hope this is of help, and hasn't completely confused things.
We're going to have to come in pretty low! It's just one of those things you have to do... when you land! -- Ted Striker - Airplane!

Offline FlyingBlind

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Re: Stalling
« Reply #2 on: February 27, 2006, 12:27:21 PM »
Oh yes it helped ! :) thanks a lot...now im smarter when i fly a IL-2 in my Sturmovik game :P

Offline Ted_Stryker

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Re: Stalling
« Reply #3 on: February 27, 2006, 03:20:49 PM »
Oh yes it helped ! :) thanks a lot...now im smarter when i fly a IL-2 in my Sturmovik game :P

My pleasure! :)  Glad I was able to shed some light on the topic :)
We're going to have to come in pretty low! It's just one of those things you have to do... when you land! -- Ted Striker - Airplane!

SkyKing

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Re: Stalling
« Reply #4 on: April 07, 2006, 09:26:28 AM »
The easy way to explain WHAT it is that the airflow under the wings is not strong enough to hold them up. 

The WHY can be that the air is moving too slowly, the angle of the wing (in a bank) is so steep that the air moves the wrong direction, or the air is too thin at altitude.

The U-2, which is essentially a jet-powered glider, flies very high, where the air is thin.  At that altitude, the difference between the U-2's redline (maximum) speed and stall speed is less than 10 knots.  If the pilot banks the plane more than a few degrees, the plane stalls.

It is possible to stall with the engine at full power -- in fact, every takeoff starts as with the wings stalled and the engine spooled all the way up.  And, of course, landing is the act of stalling the wings (hopefully at 0 AGL). 

When I first started flying, I hated stalls, especially power-on stalls, with the engine at full power and the nose pointed up.  I hated feeling that I was falling backward.  Nowdays, in my plane, if I find myself getting a little bored flying somewhere I'll do a stall series or two.  And it's fun, on a long runway, to have the main gear light on the ground, just at the stall speed, struts working in and out but not reaching either limit.  If you can go a mile like that, there is nobody in the world who can teach you anything more about airspeed control at the stall break.

Something which is even more fun is to jump the bumps on a rough field landing when you're at about 2/3 of stall speed.  You hit one and get airborne again, then float back to the ground.  It freaks out the passengers, though . . . 

. . .well, maybe it's not the bump, maybe it's the way I scream "We don't have the airspeed!!!" when it happens . . . 

;)




Offline Gulfstream Driver

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Re: Stalling
« Reply #5 on: April 07, 2006, 05:37:55 PM »
The U-2, which is essentially a jet-powered glider, flies very high, where the air is thin. At that altitude, the difference between the U-2's redline (maximum) speed and stall speed is less than 10 knots. If the pilot banks the plane more than a few degrees, the plane stalls.

For the morbid folks out there, this is known as the coffin corner.  Too fast, you come apart.  Too slow, you stall.  And the airplanes that fly at these altitudes and airspeeds aren't exactly docile when they stall.
Behind every great man, there is a woman rolling her eyes. --Bruce Almighty

Offline Frank N. O.

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Re: Stalling
« Reply #6 on: April 14, 2006, 06:23:57 PM »
I was wondering, what exactly is a Super-Stall? It was discovered with the swedish SAAB 35 Draken (The Dragon).

Frank
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."
Leonardo da Vinci

Offline Gulfstream Driver

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Re: Stalling
« Reply #7 on: April 17, 2006, 06:13:19 PM »
Never heard of it...
Behind every great man, there is a woman rolling her eyes. --Bruce Almighty

Offline Ted_Stryker

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Re: Stalling
« Reply #8 on: April 17, 2006, 06:24:43 PM »
I was wondering, what exactly is a Super-Stall? It was discovered with the swedish SAAB 35 Draken (The Dragon).

Frank

I had not heard of this term either, but I did manage to find a reference about it via a Google search.  The information I found is accessible via the link below.  Apparently a "Super-stall" is another name for a "deep stall". 

http://72.14.203.104/search?q=cache:N4zJDTvcR-QJ:www.aviationshop.com.au/avfacts/editorial/tipstall/+Super-Stall&hl=en&gl=us&ct=clnk&cd=1

« Last Edit: April 17, 2006, 06:26:43 PM by Ted_Stryker »
We're going to have to come in pretty low! It's just one of those things you have to do... when you land! -- Ted Striker - Airplane!

Offline Gulfstream Driver

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Re: Stalling
« Reply #9 on: April 17, 2006, 07:29:44 PM »
That makes sense, I guess.
Behind every great man, there is a woman rolling her eyes. --Bruce Almighty

Offline Frank N. O.

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Re: Stalling
« Reply #10 on: April 17, 2006, 08:25:51 PM »
Ah now that explains it, and to my mind also shows a great reason why I never want to fly an airplane with the cg behind the lift point.

Thank you very much :)
Frank
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."
Leonardo da Vinci

Offline Ted_Stryker

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Re: Stalling
« Reply #11 on: April 17, 2006, 08:48:50 PM »
Ah now that explains it, and to my mind also shows a great reason why I never want to fly an airplane with the cg behind the lift point.

Thank you very much :)
Frank

Glad to be of service :)  By the way, pilot's can get a bit lazy when they always fly the same plane and it's only them or them plus one passenger in the plane, in terms of doing a proper weight and balance check.  It is, however, critical that one do so, especially if the passenger has thier own "cg" issues :)   Two factors go into a proper weight and balance check... 1) is the plane's gross weight within the limits for the aircraft, and 2) is the CG point within the fore, and aft limits.  It doesn't take long to check, and it can save lives by knowing ahead of time if there is an issue with either of those two factors.  An over-gross aircraft may be technically in balance on the CG point, but if you may have a lot of trouble getting off the ground and clearing obstacles such as trees, and buildings, and cumulous granitus even if the wheels have left the runway.  Even if able to climb, if there is an emergency and you have to abort takeoff, or return to land, and you are over-gross, you run the real risk of  a collapsed landing gear and high sink rates.  Either the over-gross or out of cg conditions can be dangerous... and it's easy to have BOTH conditions exist simultaenously too.  Flying with either of the two conditions is also not technically legal, and if an accident does occur, you'll likely not get much sympathy from the FAA, nor your insurance company.... if one survives to even have such concerns, that is.

We're going to have to come in pretty low! It's just one of those things you have to do... when you land! -- Ted Striker - Airplane!

Offline Frank N. O.

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Re: Stalling
« Reply #12 on: April 17, 2006, 11:09:05 PM »
Good points! Come to think of it I think my suggestion for the caption of the Chicken Wings thread was regarding take-off weight and cg as well :D

Frank
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Leonardo da Vinci

Offline SkyKing

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Re: Stalling
« Reply #13 on: May 02, 2006, 07:40:38 PM »
I was wondering, what exactly is a Super-Stall?

Attention-focusing.


Offline Frank N. O.

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Re: Stalling
« Reply #14 on: May 03, 2006, 01:01:24 PM »
I was wondering, what exactly is a Super-Stall?

Attention-focusing.


LOL another good one, and true!  :D |:)\

Frank
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."
Leonardo da Vinci