3
$\begingroup$

In the crash of Atlantic Southeast Airlines Flight 2311, a worn propeller quill caused the propeller blades to go flat, which created enough drag on that side of the airplane to make the aircraft uncontrollable.

If this were to happen in flight, and the bad engine were completely shut down, would that reduce the drag enough to recover control?

Perhaps in the case of 2311, they might have been too low and too late, but in general, can this type of failure be recovered from? It seems that if the propeller were not being driven at high RPM by the engine that the drag might be less severe.

$\endgroup$
2
$\begingroup$

With the blade angle fixed at 3 deg, even with the engine torque at zero, it wouldn't help them. Think of it as a very small gyrocopter's free spinning rotor descending in autorotation straight down (they can do that); it's making enough lift to slow the descent quite a bit (some autogyros with special landing gear can do vertical landings). An engine with a prop fixed at 3 deg blade angle that is free to spin will spin madly in autorotation like a gyro going straight down, generating massive lift aft (instead of up, as in the case of the gyrocopter).

Having the blades stuck at that position, the only hope would be to have the blades forced to stop spinning and stay stationary, making the blades just act as speed brakes with an AOA, in our case, of 87 deg. But they have to be prevented from turning. As soon as they start turning they will start making negative lift.

So, theoretically, if the airplane had a propeller brake (which some airplanes do; it allows the engine to be run at idle with the prop stationary) and it was engaged while the engine was shut down or at idle, the drag of a propeller that is braked and prevented from spinning is a fraction of an autorotating propeller (basically, the difference between a gyrocopter descending straight down with its rotor spinning and making lift, and a gyro with its rotor held stationary with the blades producing drag only and slowing the descent only slightly below falling object velocity).

A turboprop like that with blades flat and locked against rotating would probably be able to maintain control, and might even be able to maintain level flight (but probably not climb), as long as the blades are unable to start spinning and making negative lift. So in the end, I'd say the only way to save that situation would have required two things: a prop that can be braked, and time to figure things out and engage the brake.

$\endgroup$
2
$\begingroup$

The description of the accident says the propeller went to a flat pitch of 3°, which is still positive. At such angle, the air is trying to spin the propeller in the same direction as the engine, so the engine running helps the propeller spin. Only if the propeller went all the way to negative pitch would the engine be the air trying to spin it in opposite direction and therefore produce additional drag, but it appears that propeller was not built to allow negative pitch.

So I don't think it would have helped. It probably wouldn't have made much difference in the very flat pitch.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.