411A From United States of America, joined Nov 2001, 1826 posts, RR: 9 Reply 1, posted (5 years 2 weeks 6 days 22 hours ago) and read 3311 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.
RoseFlyer From United States of America, joined Feb 2004, 8740 posts, RR: 52 Reply 5, posted (5 years 2 weeks 6 days 16 hours ago) and read 3259 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!
Blackbird From , joined Dec 1969, posts, RR: Reply 6, posted (5 years 2 weeks 6 days 6 hours ago) and read 3219 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.
411A From United States of America, joined Nov 2001, 1826 posts, RR: 9 Reply 7, posted (5 years 2 weeks 6 days ago) and read 3194 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.
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