Re: Two DC-9 aileron questions from a student pilot

Date:         27 Dec 96 04:41:05 
From:         "David G. Davidson" <gerhard@onramp.net>
Organization: http://rampages.onramp.net/~gerhard/tristar
References:   1
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journali@sprynet.com wrote:

> So what was happening here? Do airline crews check for "controls free and
> correct" like C-152 students do? Why the taxi with the control yoke turned
> all the way toward the right? I know it doesn't matter in a no-wind taxi
> which way the yoke is turned, but isn't it natural to neutralize the
> controls at some point during start-up or taxi? Why wait until the takeoff
> roll to do this?
>
> One more question: I know DC-9 ailerons are hydraulically assisted, but is
> there any direct physical link between the ailerons and the control yoke?
> I mean, would it be possible for the yoke to be in the neutral position,
> but the ailerons to be deflected, and the pilot not know about it?
>

The DC-9, MD-80 and MD-90 ailerons are not hydraulically assisted. They
use a plain-old control tab system, just a grown up version of the
system in that 152 you've been buzzing around in.

The control cables connect the wheel to the control tab, there is no
physical connection from the wheel to the aileron. Moving the wheel,
moves the control tab, which in turn moves the aileron. The ailerons are
free to flop around in the breeze as are the elevators (they also use
control tabs) on the DC-9 and MD-80. Keep an eye out for this and you'll
often see one elevator up and the other down.

Don't recall if the DC-9 has this but the MD-80 has a hydraulic elevator
actuator which forces the elevator to the nose down position if the yoke
is pushed all the way forward. This is to assist in recovery from a deep
stall.

The MD-90 has a fully hydraulic elevator system along with "pylon
flaps". These gems are located at the trailing edge of each engine
pylon. When the yoke is pushed all the way forward these flaps move down
to aid in deep stall recovery. Very hokey...