The 787 doesn't sound that quiet...

[UALdave]

http://www.youtube.com/watch?v=Asu6ifc6J7s
http://www.youtube.com/watch?v=qwhZhCtBaP4

What in the heck is causing that loud high-pitched noise?? Someone who posted in the second video said that it's a problem with the Rolls Royce engines, but I haven't heard anything about problems with any engines on the 787.

[LOT747-400]

To my understanding that's the electric hydraulic pump, nothing to do with the engines.

http://www.youtube.com/watch?v=snrE50LqDJM This video, you can hear it quite well. At the end you can hear it die down. Here is a comment made by a user on youtube from that video...
"That beeping/whining noise is not the engine.. The 787 has two fuselage-mounted electric motor hydraulic pumps which power the center hydraulic system. They are on the bottom of the fuselage in the WTB fairing, and can be heard in the cabin when they operate. They make a whining noise,or electrical hum.. But It wouldn't be constant however, generally only departure and approach."

-Phil

[UALdave]

Originally Posted by LOT747-400

To my understanding that's the electric hydraulic pump, nothing to do with the engines.

http://www.youtube.com/watch?v=snrE50LqDJM This video, you can hear it quite well. At the end you can hear it die down. Here is a comment made by a user on youtube from that video...
"That beeping/whining noise is not the engine.. The 787 has two fuselage-mounted electric motor hydraulic pumps which power the center hydraulic system. They are on the bottom of the fuselage in the WTB fairing, and can be heard in the cabin when they operate. They make a whining noise,or electrical hum.. But It wouldn't be constant however, generally only departure and approach."

-Phil

Gotcha. But, with regards to the hydraulics, isn't the 787 all fly by wire?

[Peter Kesternich]

"Fly by wire" only means that the control inputs from the cockpit to the control surfaces are relayed electronically, rather than hydraulically. Control surfaces are still mostly moved using hydraulics in most FBW-aircraft.

[Gabriel]

Originally Posted by Peter Kesternich

Control surfaces are still mostly moved using hydraulics in most FBW-aircraft.

I am still trying to figure one flight control surface that is NOT hydraulically powered in one FBW airplane. Maybe some THS?

[Peter Kesternich]

I think (though I may be wrong) that there are FBW aircraft where the spoilers are operated by electrical rather than hydraulical motors. Maybe somebody else can shed some light on that.

[Evan]

Originally Posted by Gabriel

I am still trying to figure one flight control surface that is NOT hydraulically powered in one FBW airplane. Maybe some THS?

Airbus FBW the THS and rudder can be mechanically controlled but hydraulically actuated. I think any large aircraft control surface must be hydraulically actuated, no?

[Evan]

Originally Posted by LOT747-400

To my understanding that's the electric hydraulic pump, nothing to do with the engines.

http://www.youtube.com/watch?v=snrE50LqDJM This video, you can hear it quite well. At the end you can hear it die down. Here is a comment made by a user on youtube from that video...
"That beeping/whining noise is not the engine.. The 787 has two fuselage-mounted electric motor hydraulic pumps which power the center hydraulic system. They are on the bottom of the fuselage in the WTB fairing, and can be heard in the cabin when they operate. They make a whining noise,or electrical hum.. But It wouldn't be constant however, generally only departure and approach."

-Phil

So they built a plane with calming mood lighting and then stuck a couple of screeching hydraulic pumps into it?

[LOT747-400]

Originally Posted by Evan

So they built a plane with calming mood lighting and then stuck a couple of screeching hydraulic pumps into it?

It's only for taxi, takeoff, approach/landing. Not for cruise, as I'm told.

[CcrlR]

Originally Posted by LOT747-400

It's only for taxi, takeoff, approach/landing. Not for cruise, as I'm told.

The electric pumps keep the hydraulic pressure at its normal pressure when the engines do not produce the required pressure to operate systems. If the switch is in auto, then the electric pumps will run when needed.

[Evan]

Originally Posted by Gabriel

I am still trying to figure one flight control surface that is NOT hydraulically powered in one FBW airplane. Maybe some THS?

Does the MD-11 LSAS count as FBW in pitch? I believe it has electrically actuated THS...

[Gabriel]

Originally Posted by Evan

Does the MD-11 LSAS count as FBW in pitch? I believe it has electrically actuated THS...

I really don't know, but I'd tend to think that the LSAS would control the elevator instead of the THS. Stability control requires quick inputs and the THS's tend to be slow.

That said, there are several airplanes with electric THS, that's why I flagged that control as a "suspect". I am sure the DC-9 and its derivatives (MD-80, etc.) have an electric THS (with motor and a jackscrew. It wouldn't surprise me if the DC-10 / MD-11 had it too.

[tsv]

If I was on a 787 I would just be relieved to hear the sound of the motors, how loud they were would not bother me, in fact the louder the better!

[Foxtrot]

Umm, THS?