Roost Air Lounge => The Classroom => Topic started by: FlyingBlind on February 26, 2006, 08:54:41 PM
Title: Stalling
Post by: FlyingBlind on February 26, 2006, 08:54:41 PM
First of all, why does this happen and how ? What happens with the aircraft etc. ? ???
Title: Re: Stalling
Post by: Ted_Stryker 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.
Title: Re: Stalling
Post by: FlyingBlind 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
Title: Re: Stalling
Post by: Ted_Stryker 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 :)
Title: Re: Stalling
Post by: SkyKing 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 . . .
;)
Title: Re: Stalling
Post by: Gulfstream Driver 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.
Title: Re: Stalling
Post by: Frank N. O. 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
Title: Re: Stalling
Post by: Gulfstream Driver on April 17, 2006, 06:13:19 PM
Never heard of it...
Title: Re: Stalling
Post by: Ted_Stryker 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".
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.
Title: Re: Stalling
Post by: Frank N. O. 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
Title: Re: Stalling
Post by: SkyKing on May 02, 2006, 07:40:38 PM
Title: Re: Stalling
Post by: fliboye on June 20, 2006, 11:11:37 PM
a stall which makes the nether regions of your seat cringe and the scene go from blue to green rather quickly other wise known as a whip stall, for instance be in level cruise pull the power back to idle and pull the yoke/ stick full aft and hold it maintaining coordination with the rudder as you fall to the earth. kinda cool after the first time. hehehe :o
Title: Re: Stalling
Post by: fireflyr on June 21, 2006, 02:21:49 AM
a stall which makes the nether regions of your seat cringe and the scene go from blue to green rather quickly other wise known as a whip stall, for instance be in level cruise pull the power back to idle and pull the yoke/ stick full aft and hold it maintaining coordination with the rudder as you fall to the earth. kinda cool after the first time. hehehe :o
COOL--but if the boss is taking a nap? ???
Title: Re: Stalling
Post by: fliboye on June 24, 2006, 01:09:21 AM
be very very quiet. ;D ;D ;D ;D
Title: Re: Stalling
Post by: Frank N. O. on July 08, 2006, 01:38:03 PM
a stall which makes the nether regions of your seat cringe and the scene go from blue to green rather quickly other wise known as a whip stall, for instance be in level cruise pull the power back to idle and pull the yoke/ stick full aft and hold it maintaining coordination with the rudder as you fall to the earth. kinda cool after the first time. hehehe :o
` That's also a aerobatics maneuver (when done intentionally) isn't it?
Btw, it reminds me of the joke: To go up, pull the stick back. To go down, pull the stick back harder. :D
Frank
Title: Re: Stalling
Post by: Gulfstream Driver on July 08, 2006, 05:25:55 PM
Frank,
It's not really an aerobatic maneuver, since you're not rolling or pitching more than a certain number of degrees. I forget how much roll or pitch makes it aerobatic, though.
A spin is an aerobatic maneuver, and can only be performed intentionally in certain aircraft (utility or aerobatic category).
Title: Re: Stalling
Post by: fliboye on July 09, 2006, 09:17:38 AM
30 deg pitch 60 deg bank and if done right you are not performing an aerobatic manuver but an extreme parabolic curve or weightless ness off to work hehe 8)
Title: Re: Stalling
Post by: happylanding on July 11, 2006, 05:51:18 PM
30 deg pitch 60 deg bank and if done right you are not performing an aerobatic manuver but an extreme parabolic curve or weightless ness off to work hehe 8)
On this argument....I once tried the 0 gravity with my former boyfriend, who performed it to let me see what happens. is this an aerobatic maneuver or it's just felt alike inside the plane?!?
Title: Re: Stalling
Post by: Stef on July 12, 2006, 02:55:50 PM
The only time I experienced 0g was on a ride with my brother. It's always too short though when you're in a small plane... I would really love to do a ballistic flight, like the NASA does it, just once to see what it's like for two minutes or so! Does anyone know if you can book such a flight? I probably can't afford it anyway, but it's still a more realistic goal than a space trip! ;) (which I'd love to do too!)
Title: Re: Stalling
Post by: Frank N. O. on July 12, 2006, 04:51:47 PM
Ah, I didn't know there was a g definition of what a aerobatics manouver, thanks for the info :)
Stef: I too would love a ride on the vomic comet since I'm very interested in real wolrd space and space-travel as well as science fiction and in real life there's no such thing as artificial gravity like on Star Trek, Star Wars, Firefly etc. and I'd like to know just how weird it feels with the blood going to the head etc. from the 0 g you experience. It's fun to think about too, it's not 0 g since you're effected by earth's gravity but effectively the plane's carefully planned decent effectively gives you the same feel as 0 g, so in reality you're both experiencing 0 g and earth gravity at the same time, physics is actually pretty cool I think. However I don't think it lasts 2 minutes, to my knowledge it's only 30-60 seconds at the most it can do that.
Frank
Title: Re: Stalling
Post by: Turbomallard on July 12, 2006, 04:55:08 PM
If you have lots of extra money, you can try it out here:
www.gozerog.com
First you cough of the money... then maybe something else. :D
TM
Title: Re: Stalling
Post by: happylanding on July 12, 2006, 05:00:21 PM
The only time I experienced 0g was on a ride with my brother. It's always too short though when you're in a small plane... I would really love to do a ballistic flight, like the NASA does it, just once to see what it's like for two minutes or so! Does anyone know if you can book such a flight? I probably can't afford it anyway, but it's still a more realistic goal than a space trip! ;) (which I'd love to do too!)
I believe that link for ZeroG is the same one I was aware of from the St. Louis Science Center. Seems to be the same place. I believe a trip runs close to $4,000 USD... not including the cost of getting up and back to the place, of course.
Title: Re: Stalling
Post by: Frank N. O. on July 13, 2006, 03:19:33 PM
a stall which makes the nether regions of your seat cringe and the scene go from blue to green rather quickly other wise known as a whip stall, for instance be in level cruise pull the power back to idle and pull the yoke/ stick full aft and hold it maintaining coordination with the rudder as you fall to the earth. kinda cool after the first time. hehehe :o
` That's also a aerobatics maneuver (when done intentionally) isn't it?
Btw, it reminds me of the joke: To go up, pull the stick back. To go down, pull the stick back harder. :D
Frank
Happy it was this post I made before you where I myself raised the question about the definition of what aerobatics was, I guess I should've used quotes or at least mention the name of the person I was replying specifically too, sorry for the misunderstanding.
Frank
Title: Re: Stalling
Post by: happylanding on July 13, 2006, 04:28:15 PM
Happy it was this post I made before you where I myself raised the question about the definition of what aerobatics was, I guess I should've used quotes or at least mention the name of the person I was replying specifically too, sorry for the misunderstanding. Frank
Oh, no worries! I was thinking that maybe you got what I was asking as being a reply and then you would have had false info! And well, I actually could have understood that you were talking about another message, since there there is in fact the definition of aerobatics given by flyboye! I sometimes read through the forum too fast!
