OT: Airplane Stall Question

If forward motion can be restored to facilitate airflow over the wing the aircraft will dive to increase speed and the wing incur lift. If an aircraft drops with no forward motion, at an attitude (pitch) which prevents air flow over the wings to induce lift, the aircraft will drop 'flat' towards the earth like a home sick brick. This situation is recoverable if ample altitude is available. The old saying...always fly the airplane. If you fail to fly the plane and altitude to low, the results tend to be fatal.

Not necessarily. As the aircraft stalls, it can fall out of the sky with the wing at great angle to the direction of movement. What little airflow there is over the wing will be turbulent and no lift will be generated. As there is no airflow over the control surfaces, there will also be no control authority. Hopefully the aircraft design will be such that it will pitch down if all the controls are centralised, which is the traditional way of recovering from a stall. Once that happens the aircraft *does* go into a dive and once the airspeed builds up, control authority is restored. The problem is that you have to have enough altitude for this to happen...

Strange you should mention that as I just saw the King Cobra at Biggin Hill that my mate filmed and I saw from a bit closer.

Richard.

That isn't at all correct. A wing stalls when it exceeds its critical angle of attack. That's approximately 18 degrees from the relative wind give or take a few degrees depending on the wing design. This can occur at any speed or any attitude relative to the ground, even inverted or in a dive. The "Cobra" maneuver performed by some high-perfomance fighters is nothing more than a high-speed stall, accomplished by pulling back on the stick so quickly that the wing exceeds the critical angle of attack before the aircraft starts to climb. A stall is caused by flow separation from the top of the wing. What makes most people think a stall is related to airspeed is that as speed decreases, the angle of attack must be increased to keep the same lift, to keep the aircraft from descending. Lift increases until the critical angle of attack is reached, at which point the wing stalls and lift drops off precipitously. There is usually still enough airflow over the control surfaces to control the aircraft. Reducing the angle of attack will break the stall. Aircraft with positive stability will tend to do this on their own if you relase the controls, but neutral or negative stability aircraft like many modern fighters need flight control inputs to break the stall. If you want a pretty in-depth look at stalls and other aspects of flying, check out this website:

I once read that for an early model U-2 at operational altitude, the speed difference between stalling speed and maximum speed was 5 knots.

The "coffin corner" of the flight envelope. As you go higher the air gets thinner so stall speed increases. As you go higher the air temperature reduces so the speed of sound decreases. The U-2 is decidedly subsonic and operates at altitudes where the Mach limit and stall speed approach one another.

The SR-71 escapes this by being decidedly supersonic at operational altitudes.

The Boeing 707 had that same problem. This is one reason why turns at speed and altitude must be made gently if they are to be made at all. You could potentially overspeed the outside wing while stalling the inside wing at the same time. Pilots are allergic to doing that.

A real problem with the 104 was upon landing. In order to reduce landing speeds....bleed air from the engine is used for ' boundary layer ' control. Basically ' blown ' air is forced over the rear flap on the rear of the wing. ( This is also why the F-4 made strange sounds on takeoff and landing ) If the boundary layer air is not working properly ( such as an improper working valve )....landing speeds for the 104 can be excessive....we are talking above 200 knots ! Also....the pilot has to be careful not to reduce the throttle upon landing....or on approach because lower engine RPM's also mean less ' blown ' air over the flaps. So if a pilot suddenly ' chops ' the throttle while landing in a F-104 he is probably going to smack the runway pretty hard. The F-104 was not a forgiving airplane. But in the hands of a skilled pilot it was a wonder.

Chris

wasn't there a nickname for the 104 IIRC Missle with a man in it ? seems appropriate

I remember there being a joke about them.

Q. How does a German get himself an F-104?

A. He buys a field. And waits...

lol I can remember when I was stationed over at Haun AB in Ger when we had war games the German 104s would fly simulated attacks on our airfield geeze tree top level you wouldn'y hear them till it was to late

The airflow is not reduced, it is disrupted. The air breaks away from following the camber or surface of the airflow, and becomes turbulent. The result is that the pressure reverts to free stream pressure and most lift is lost. Not ALL lift, but at least half or more. Losing half of the lift is certainly detrimental to performance. Plus, the turbulence means the tail is flying in very disturbed air and thus control tends to be lost because of that also, except in canards and planes with extreme T-tail. If the elevator is in the region of max disturbed flow from wing, stall becomes unrecoverable, a so-called "deep stall." Fortunately most planes do not get into this condition, but the loss of lift on the wing upsets the position of the net lift vector vs the CG location, and the nose drops violently on many planes.

The airflow is not reduced, it is disrupted. The air breaks away from following the camber or surface of the airflow, and becomes turbulent. The result is that the pressure reverts to free stream pressure and most lift is lost. Not ALL lift, but at least half or more. Losing half of the lift is certainly detrimental to performance. Plus, the turbulence means the tail is flying in very disturbed air and thus control tends to be lost because of that also, except in canards and planes with extreme T-tail. If the elevator is in the region of max disturbed flow from wing, stall becomes unrecoverable, a so-called "deep stall." Fortunately most planes do not get into this condition, but the loss of lift on the wing upsets the position of the net lift vector vs the CG location, and the nose drops violently on many planes.

FWIW In their hurry to get the "new" Luftwaffe up to speed they were putting kids straight from T-33s onto the 104. That was a formula for disasters. The first Belgian pilot to fly the 104 was their chief flying instructor. He went home and wrote the regs for 104 training selection. First requirement was that a pilot had to have at least one previous tour on some other jet fighter (F-84, Hunter, etc.) and the result was a stellar safety record. The Belgian pilots were sorry to see the 104s withdrawn. Like they say at Nellis: "Spam, no matter what kind of can you put it in, is still Spam"!

Bill Shuey

I think that was Lockheed's PR man who invented that. I like 'bullet and blades' myself.

Bill Banaszak, MFE Sr.

alright you buttheads, what's the best 1/48th kit? goddam powers of suggestion!

Hasegawa

thanks ron. i see the manchester conversion sold. i was sure tempted....