Re: 727 deep stall (Re: tip vortices *do* exist!)

From:         watson@win.tue.nl (Bruce W. Watson)
Date:         30 Mar 93 10:05:00 PST
References:   1 2 3 4
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In article <airliners.1993.282@ohare.Chicago.COM> rdd@cactus.org (Robert Dorsett) writes:
>A pilot can normally retard the throttles all the way back to idle
>without having to worry about the fuel controller or flaming out the engine.  
>The thrust at this setting can range from 300 lbs to 1000 lbs per engine.  
>
>The reason for all the "drag- generating laundry" is the need to slow from 
>very *high* speeds to relatively *slow* speeds in short amounts of time, 
>combined with the very *clean* design of most airliners--without such devices, 
>they would accelerate.
>
>All jet engines have a spool-up time from idle, usually under 8 seconds.
>I've never heard of a "safety setting" intended to reduce this spool-up time: 
>it would have to be at a relatively high thrust setting, which would help 
>defeat the purpose.  Lag times are simply a fact of jet engines that have to 
>be contended with.
>

   On a couple of the turbine aircraft I've flow, there was a minimum
spinup (aka spool-up) value on final. This was usually measured as one of
the turbine parameters (on some turbines it was 55% on N1). The idea was
both to be able to get quicker time to full (in the event of a go-around,
or to cope with some sort of wind shear situation), but also to get rid
of some of the throttle lag on the approach. This last use is particularly
important to avoid making large throttle movements, chasing the glide slope
all over the place.
 
>Again, allegations of a "deep stall" are some-
>what serious, since it suggests the airplane is in an aerodynamic condition
>it *can't* escape from.  In the case of the BAC-111, for example, aerodynamic
>effectiveness of the elevators was almost nil.  If the 727 is actually capable
>of such a stall, I'd like to hear about it! :-)
>
>---
>Robert Dorsett
>rdd@cactus.org
>...cs.utexas.edu!cactus.org!rdd

I didn't catch the original part of this 727 deep stall thread, but I _think_
I remember a 727 deep stall accident (the following is entirely from memory,
but I read about it some years ago in my Canadian aviation safety bulletin):
   One some cargo flight, the Captain and FO decided to allow the (type-rated
but rusty) FE flight the departure. As it turned out, they somehow forgot the
pitot heat. During the climbout, the pitot iced up, and with the static source
open the ASI began to act as an altimeter. With the airspeed ever-increasing,
and passing through the structural limits for flaps extended, the FE (flying)
continued to pitch up, while retarding the throttles. The end result was that,
by the time someone had managed to cross-check, the wind noise had died down
and they were indeed deeply stalled at a low throttle setting. I think the
way it ended, was with only a partial recovery, killing all 3 aboard.
   If anyone else knows the whole story (perhaps it was fiction ;-) I'd be
happy to see the corrections.
   Later,  
   Bruce