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Which Components Are Hydraulic (DC-8/707)  
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Posted (14 years 3 months 2 days 17 hours ago) and read 4270 times:

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?


6 replies: All unread, jump to last
User currently offlineTechRep From , joined Dec 1969, posts, RR:
Reply 1, posted (14 years 3 months 2 days 11 hours ago) and read 4211 times:

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)

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.


User currently offlineWhalepilot From United States of America, joined Jun 2001, 91 posts, RR: 0
Reply 2, posted (14 years 3 months 1 day 22 hours ago) and read 4195 times:

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

User currently offline727pfe From , joined Dec 1969, posts, RR:
Reply 3, posted (14 years 3 months 1 day 22 hours ago) and read 4192 times:

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.

User currently offline737doctor From United States of America, joined Mar 2001, 1332 posts, RR: 35
Reply 4, posted (14 years 3 months 1 day 6 hours ago) and read 4172 times:

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.
User currently offlineTechRep From , joined Dec 1969, posts, RR:
Reply 5, posted (14 years 3 months 1 day ago) and read 4166 times:

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.


User currently offlineWhalepilot From United States of America, joined Jun 2001, 91 posts, RR: 0
Reply 6, posted (14 years 3 months 20 hours ago) and read 4166 times:

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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