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B-707 Hydraulic System Set-Up  
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Posted (6 years 5 months 3 weeks 3 days 14 hours ago) and read 4671 times:

How many fully redundant hydraulic systems does the B-707 have?

Andrea Kent

7 replies: All unread, jump to last
 
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 1, posted (6 years 5 months 3 weeks 3 days 12 hours ago) and read 4664 times:

The B707 has two hydraulic systems....the utility system and the auxilary system.

The utility system provides hydraulic power to...
Landing gear
Normal brakes
Nose wheel steering
Main landing gear truck leveling
Trailing edge flaps
Some spoilers

The auxilary system has two 28V DC pumps that provide hydraulic power to...

Some spoilers
Rudder

These two 28V DC pumps are normally operating at all times.

The two hydraulic systems are separate, however can be interconnected on the ground, for ground servicing applications, EXCEPT on those aircraft delivered to PanAmerican...in which case system interconnection is on the ground AND while airbourne.

Alternate flap extension is electric.
Leading edge devices are normally extended/retracted pneumatically.
No alternate extension possible.

Alternate/emergency braking is provided pneumatically in the event that the utility hydraulic system pressure is unavailable.

Note: There is NO hydraulic power assist to the inboard/outboard ailerons or elevators.
These are assisted by a special type of servo tab, called....balance panels.
The rudder also has balance panels for control assist in the event that auxilary hydraulic power is unavailable, however Vmca is greatly increased.

The horizontal stabilizer is electrically driven for trim applications.

NB. PanAmerican aircraft have hydraulic systems interconnection while airborne to enable very slow retraction of the landing gear, after takeoff, in the event that the main landing gear trucks are not level.
Required/desired by PanAmerican to avoid having to return for landing, after fuel dumping, on very long intercontinental sectors.
I have personally used this alternate procedure twice...very effective, as rails in the main landing gear wheel wells provide for leveling of the trucks...very slowly, during retraction, using reduced auxilary system hydraulic pressure.


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 2, posted (6 years 5 months 3 weeks 3 days 12 hours ago) and read 4656 times:

When you say "some spoilers" do you mean like the inboard set, or do you mean it helps extend them like half of the way?

Andrea Kent


User currently offlineFtrguy From United States of America, joined Aug 2003, 358 posts, RR: 0
Reply 3, posted (6 years 5 months 3 weeks 3 days 11 hours ago) and read 4647 times:



Quoting Blackbird (Reply 2):
When you say "some spoilers" do you mean like the inboard set, or do you mean it helps extend them like half of the way?

The utility system powers the outboard spoilers and the Aux powers the inboard


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 4, posted (6 years 5 months 3 weeks 3 days 10 hours ago) and read 4630 times:

Understood

Andrea Kent


User currently offlineRoseFlyer From United States of America, joined Feb 2004, 9666 posts, RR: 52
Reply 5, posted (6 years 5 months 3 weeks 3 days 6 hours ago) and read 4612 times:

Wow, thanks for the advice. I work on the 737 hydraulic system so its interesting to learn about the 707. Some of the 737NG stuff is still a carryover from the 707 days. Fortunately the redundancy aspect has definitely improved to improve safety.


If you have never designed an airplane part before, let the real designers do the work!
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 6, posted (6 years 5 months 3 weeks 2 days 20 hours ago) and read 4572 times:

411A,

Quote:
Note: There is NO hydraulic power assist to the inboard/outboard ailerons or elevators.
These are assisted by a special type of servo tab, called....balance panels.
The rudder also has balance panels for control assist in the event that auxilary hydraulic power is unavailable, however Vmca is greatly increased.

Technically when the B-707 was first built, even the rudder had no hydraulic boost either! From what I remember Boeing wanted to keep the design as simple as possible to make transition from prop to jet as simple as possible. Turned out though that the rudder wasn't particularly as effective as desired when dealing with an outboard engine failure during the takeoff run, plus the British demanded all sorts of requirements of the B-707 for it to be certified in the UK, which included a powered rudder with Q-feel, and a ventral-fin for improved directional stability.

(Out of curiosity, did the KC-135 have a hydraulically powered rudder from the get-go? -- If so, did it have artificial-feel?)

I thought the B-707 had both balance panels and control-tabs.


Andrea Kent


User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 7, posted (6 years 5 months 3 weeks 2 days 14 hours ago) and read 4547 times:



Quoting Blackbird (Reply 6):
Technically when the B-707 was first built, even the rudder had no hydraulic boost either! From what I remember Boeing wanted to keep the design as simple as possible to make transition from prop to jet as simple as possible. Turned out though that the rudder wasn't particularly as effective as desired when dealing with an outboard engine failure during the takeoff run, plus the British demanded all sorts of requirements of the B-707 for it to be certified in the UK, which included a powered rudder with Q-feel, and a ventral-fin for improved directional stability.

(Out of curiosity, did the KC-135 have a hydraulically powered rudder from the get-go? -- If so, did it have artificial-feel?)

I thought the B-707 had both balance panels and control-tabs.

Yes, the UK DEMANDED changes, and these were completed by Boeing.
David Davies had a very big stick, and used it wisely.
From Comet to Concorde, he certified 'em all, in the United Kingdom.

And, quite true, balance panels and individual surface control tabs.

Dunno about the KC-135, I'm not an AirForce guy.


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