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Dreamliner question
Just back from a week in Turkey, flew on TUIC/D. My first time on a 787 and have to say I was very impressed. Seat back IFE to keep the kids occupied, nice bit of extra legroom which being 6'4 was a godsend, and it seemed to ride turbulence a lot better than other aircraft.
One question I have for someone who knows, after pushback and engine start there was a loud whirring noise coming from somewhere underneath it sounded like. It went on for a good few minutes after we took off, then started up again during descent. Any ideas what it was? Are the flaps hydraulically driven on the 787 or could it have been electric motors to power them? Thanks in advance. |
I believe a design concept and novelty on the 787 was no hydraulics (not sure about the brakes tho) . So if you were seated mid plane then upto about twen mins after take off things like landing gear and doors plus staged flap retraction could all mean something big and electrical has to do its work. No expert so dont take this as gospel but pretty sure the 78 has minimal hydraulics.
Perhaps this will end up like the barking dog on the A320 where the power transfer unit hydraulic pumps make an odd noise often when taxying |
The 787 has plenty of hydraulics! There are two engine-driven hydraulic pumps and four electricly-driven ones. They power three 5000psi systems which connect to Landing Gear, Flaps, Slats, Flight Controls, Nose Gear Steering and Thrust Reversers. I suspect that what you are hearing are the electrical hydraulic pumps, which run continuously below approx 2000ft during take-off and landing. The system which the 787 eschews is an engine-bleed-driven pneumatic system (apart from inlet cowl and engine core anti-ice). Air conditioning and pressurisation is provided by four electrically-powered Cabin Air Compressors feeding two packs. The 787 electrical system is truly awesome. Each engine has two generators; there are two APU generators, three external power sockets, two batteries, a RAT and five engine-driven Permanant Magnet Alternators/Generators. In addition, each primary flight control surface has its own battery pack, to keep them moving in the event of a transient loss of electrical power during abnormal operations. The electrical system powers engine start, pressurisation, wing ice protection, stab trim and wheel brakes, in addition to the normal services like avionics and lighting. It also provides an alternate power supply for the flaps and slats. |
Originally Posted by eckhard
(Post 10239539)
I suspect that what you are hearing are the electrical hydraulic pumps, which run continuously below approx 2000ft during take-off and landing. Thanks for the comprehensive reply. That sounds about right. The noise started between engine start and flaps being lowered, and stopped shortly after the flaps were retracted, and then the opposite for landing. |
The C1 and C2 ELEC hydraulic pump selectors control pump operation. The two center pumps alternate as a primary pump and demand pump. The primary pump operates continuously after the second engine is started. The center demand pump operates under the following conditions: :on the ground for the first three minutes after the second engine is started, or from takeoff thrust set until radio altitude exceeds 2000 feet • flaps or slats are in motion, or during descent from when the gear lever is down and radio altitude is less than 2000 feet until groundspeed is less than 60 knots. Copied and pasted from FCOM... |
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