Re: Compressor Stall at Takeoff?

Date:         09 Dec 97 03:54:23 
From:         Steve Lacker <look@the.sig>
Organization: Applied Research Laboratories - The University of Texas at Austin
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Dick Bussiere wrote:
> When we began our takeoff roll, there was a loud "bang" from the
> rear of the plane.
>
> A few minutes later, the captain got on the loudspeaker and said that we had
> experenced a compressor stall in one of the engines. He said that it was
> common when taking off into a strong crosswind.
>
> Is this true? More importantly, when a compressor stall occurs, is there a
> loss of power in the stalled engine?

Although the mechanisms are different, you can think of a compressor
stall as having the exact same effect as a "backfire" through the
carburetor of a car engine (anyone besides me still drive carbureted
cars? :-) There is a *momentary* complete loss of power accompanied by a
"bang", but if no serious damage was done, the engine should come back
to full power almost immediately since the rotating components don't
have time to slow down very much.

Severe compressor stalls can damage the compressor by cracking blades or
stator vanes. Apparently in this case the engine gave no signs of any
ailment, so the pilot continued on. You did say it was a 737-200 which
would have Pratt & Whitney JT8D's, so short of throwing a load of bricks
into the inlet, there isn't much that will damage the engine enough to
shut it down :-) Of course, that could *also* mean it did suffer some
mild compressor damage but just kept chugging on....  It is possible
that 30 years of experience shows that an occasional compressor stall on
a JT8D is so unlikely to do any damage that its not worth aborting the
flight.

The explanation of a stall in crosswind also sounds reasonable, since
the airflow through the inlet would be disturbed, particularly on the
"downwind" engine I would assume. Some aircraft, such as 727-100's and
L-1011's are slightly more prone to compressor stalls in one engine (#2
in this case) than in the others because of unique features of the
inlet. In the 727 and L-1011, the inlet for #2 is atop the fuselage and
coupled to the engine via an "S" duct, which makes the flow into that
engine a bit more marginal than the others. The 727-200 addressed the
issue with a revised inlet shape for #2, and I don't know if anything
was ever done on the TriStar. In any event, it wasn't a severe problem
for either plane, since both have outstanding safety and reliability
records.

--
Stephen Lacker
Applied Research Laboratories, The University of Texas at Austin
PO Box 8029, Austin TX 78713-8029
512-835-3286 slacker@arlut.utexxas.edu (Remove the extra 'x' to mail me)