Re: DC-9 Flight Control

From:         gsmoff@Mcs.Net (Gary S. Moffitt)
Organization: MCSNet Internet Services
Date:         23 May 96 10:37:32 
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 I am pretty sure that all of these earlier aircraft had mechanical
> linkages to all of the primary flight control surfaces.  I also am
> pretty sure that these mechanical linkages were hydraulically boosted
> to easy in control of the aircraft.  Assuming a total power failure in
> the aircraft, are these hydraulic boosters shutdown?  If so the flight
> surfaces would become excessively hard to control.  If anyone out there
> has any experience with the design of these aircraft please give me an
> answer about this.  Could a fire in the main fusebox cause a total
> power fialure throughout th e aircraft.?

The DC9 is somewhat unique in that it was designed to be flown without
hydraulic power to any of the primary flight controls.  The control yoke
inputs actuate cables which actuate control tabs, the flight controls
respond opposite to the tab movements.  The control tab flies the control
surface.  This is one aircraft whose flight control forces do not change
with loss of hydraulic power.  There are of couse exceptions. On the MD80s
(I am not ssure about older DC9s)  there is hydraulic assist to the
elevator in the nose down direction only to assist in stall recovery and
there is hydraulic assist to the rudder which may be shut off with a lever
on the pedestal.  Neither of these hydraulic assists is necessary in
normal flight.

Gary S. Moffitt