Blackbird
Topic Author
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Joined: Wed Oct 06, 1999 10:48 am

Which Components Are Hydraulic (DC-8/707)

Fri Mar 01, 2002 5:10 am

Which control surfaces are hydraulic on the 707 and DC-8? I know the 727 was the first all-hydraulic aircraft so not all of the control surfaces were hydraulic on the DC-8 or 707.

Also, was stab-trim hydraulic on the 707 or DC-8? Or was it electric like the 727's?

-Kamarov
 
TechRep
Posts: 1877
Joined: Sun Jan 13, 2002 6:53 am

RE: Which Components Are Hydraulic (DC-8/707)

Fri Mar 01, 2002 10:47 am

Ok this is completly from memory so here goes:

DC-8 Hydraulic system:
Flaps (largest hydraulic user)
Spoilers (flight and ground)
Ailerons (bad leaker)
Slots (2 actuators per side, bitch to change)
Rudder (hell hole name says it all)
Horizontial Stab/Alt Stab (hydraulic/electrical)
Elevators

other:
Thrust reversers LONG DUCT(hydraulic actuated/ 12 PSI pneumatic assisted)
Thrust Reversers SHORT DUCT (Pneumatic)
Cargo Door (Douglas Door/Skydrol)
Cargo Door (Rosenbalm/5606)



So in fact all the primary and secondary flight controls are hydraulic. I think the complete Hydraulic system is 21.9 gallons and 12 gallons down to the stand pipe, with 9.9 gallons in reserve. The DC-8 uses a priority valve at 1750 PSI of reducing pressure a valve closes and only primary flight controls are available off the hydraulic manifold.

A large weakness on the DC-8 is the bogie trim compensator. It has no hydraulic fuse and the hydraulic line is under the landing gear bogie. If ruptured it will drain the Hydraulic system down to stand pipe in 3 seconds. It was always said, if you see the DC-8 taxiing with gear doors down your going to have a long day. The controls for hydraulic selection is on the Cash Register which includes 3 positions. Hydraulic pump can be selected from F/E position or Capt's position, however on some models no Capt's position is available.

As far as the B707, I have no idea about that aircraft other than the DC-8 is a better airplane.

TechRep

 
WhalePilot
Posts: 91
Joined: Sat Jun 16, 2001 12:28 am

RE: Which Components Are Hydraulic (DC-8/707)

Fri Mar 01, 2002 11:27 pm

Good job TechRep! You came so close to perfection, but the elevators are strictly mechanical.
 
Guest

RE: Which Components Are Hydraulic (DC-8/707)

Fri Mar 01, 2002 11:30 pm

The 707 had cable operated ailerons and elevator. The rudder was hydraulic with a manual reversion. The T. E. flaps, L.E. flaps/slats and spoilers were hydraulic. The stabilizor was electric. The stab actually had two motors, the primary controlled by the yoke switches or with manual handles on the center pedestal stab trim wheel, and the alternate motor used by the autopilot and mach trim system.
 
737doctor
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Joined: Mon Mar 19, 2001 4:52 pm

RE: Which Components Are Hydraulic (DC-8/707)

Sat Mar 02, 2002 3:20 pm

Yeah, I was gonna say that the DC-8 elevator system was mechanical, but apparently I was beaten to the punch.
Patrick Bateman is my hero.
 
TechRep
Posts: 1877
Joined: Sun Jan 13, 2002 6:53 am

RE: Which Components Are Hydraulic (DC-8/707)

Sat Mar 02, 2002 9:58 pm

I have seen the errors of my ways. I can now remember rigging that damn system thinking to myself, why did I mention elevators? The other info I believe was acurate.

TechRep
 
WhalePilot
Posts: 91
Joined: Sat Jun 16, 2001 12:28 am

RE: Which Components Are Hydraulic (DC-8/707)

Sun Mar 03, 2002 1:34 am

That's perfectly understandable TechRep, you have quite a good memory. Remember when i said that the elevator position indicator followup cable was the single longest cable in the whole plane.

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