Re: hydraulic problems with DC-10's??

From:         rdd@cactus.org (Robert Dorsett)
Organization: Capital Area Central Texas UNIX Society, Austin, Tx
Date:         Wed, 25 Nov 92 06:58:52 CST
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In article <airliners.1992.32@ohare.Chicago.COM> kls@ohare.Chicago.COM (Karl Swartz) writes:
>In article <airliners.1992.30@ohare.Chicago.COM> weiss@curtiss.SEAS.UCLA.EDU (Michael Weiss) writes:
>>I have a hard time believing that an intact hydraulic system would have
>>prevented AA191 from crashing.  Let's face it, a wing-mounted engine falling
>>off produces such a rediculous unbalance that even full aileron wouldn't be
>>able to counter it.
>
>I don't see that ailerons have much to do with it -- the biggest
>effect would be a substantial yaw, which would require rudder input.

In the NTSB report on the DC-10 crash, a considerable amount of both yaw
and rudder were necessary to regain level flight, in the simulator tests--
80% right rudder and 70% right-wing-down aileron; roll angles didn't
exceed 30 degrees before recovery.  

Normally, given asymmetric thrust, you bank into the good engine(s): rudder's 
normally used to augment the ailerons as necessary to control sideslip.




>Having lots of altitude and airspeed to work with is certainly quite
>helpful, but isn't a requirement.  A few years ago a Piedmont 737-200
>lost #2 immediately after takeoff from O'Hare.  The pilots promptly
>declared an emergency, turned around, and landed several minutes later
>on another runway.  They didn't even realize that the engine had
>litterally fallen off until the got off he plane and looked.

There are actually two issues at work, here: one is the *power* lost by 
the engine.  To maintain level flight, the power required for flight must
equal the power available.  If the power available is less, one will start
to descend; if it's a lot less, one will descend faster.  The real issue is 
just power: it has little to do with where the failure was: losing two
of three engines on a 727 at MTOW means you'll go down, too.

The second issue is the moment produced by the combination of the "dead"
engine (with its drag) and the "good" engines.  This is generally a minimal
issue, assuming the airspeed is there, and the pilot applies correct 
technique.  Most transport aircraft can fly with all engines out on one side, 
although I do not know if this is an explicit regulatory requirement.  As 
long as the inherent longitudinal stability of the airplane (contributed
by the vertical stabilizer, rudder, wings, and fuselage) is sufficient to 
overcome the yawing moment, the airplane can be controlled.  So *correcting*
for a lost engine is a near-instantaneous correction, applied by the pilot, 
needing no altitude reserve.


During the El Al discussion on sci.aero, rec.av, and rec.travel.air, there
seemed to be considerable confusion between the role each factor took. 





---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd