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Flying back from DC today, one leg was on an A320. While taxiing, heard a noise very much like sawing a board with a hand saw coming from the back of the plane. It quit before takeoff.
Get on a small Embraer, the dang hydraulic pump is almost directly under the seats and it whines like a hound dog when taxing on one engine...don't know how many times I had to field that question during taxi operations while riding in the back.
In the old C-141 or C-130 you can actually see the hydraulic motors turning the jackscrews that move the flaps. And since those were built for cargo capacity and not passenger comfort {this comment will stimulate a LOT of comments from old timers who've sat in troop seats in the cargo hold} the noise is definitely even more noticable than an MD-80 or the like.
Thanks guys for the knowledgable answers. I didn't notice if they were taxiing on one engine or not. The fact that it sounded just like using an old-fashioned hand saw on a board - grunt, grunt, grunt - was unique.
It didn't worry me much as it didn't sound "malignant" - after a while a decent engineer develops an instinct about what kind of sounds mean trouble, and what kind are just noise. Or at least I have. Not always right, but mostly.
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Actually... It is the Rubber Band winding up. (So we say when flying Hobo Air... (Spirit)).
It is a pretty disconcerting noise while taxi-ing, especially when you notice the flight attendants are the only ones wearing parachutes.
I had only heard it in 319's till last week on a 320. (High power rubber band upgrade).
I thought it was a rotary compressor of sorts, but HYD makes me feel MUCH better
My next invention will be a HHV of some type (Hydraulic Hybrid). Very popular in Australia for Fire trucks and buses. Great idea... bit heavy for most cars, maybe I need to adventure into aircraft HYD systems for weight saving ideas! (Especially for the fluid and accumulators).
Oh for the great stuff we used to get at Boeing Surplus !! ARGH... closed
M3 and I need some small Hyd motors to mount on our '80's VW's axle shafts for braking and acceleration. I am obsessed with building a 75mpg Diesel MKI-III Scirocco.
In the old C-141 or C-130 you can actually see the hydraulic motors turning the jackscrews that move the flaps. And since those were built for cargo capacity and not passenger comfort {this comment will stimulate a LOT of comments from old timers who've sat in troop seats in the cargo hold} the noise is definitely even more noticable than an MD-80 or the like.
Thanks for the memories, Sir! Yep; the C-130 and C-141 were definitely built with passenger comfort low on the priority list... But, if you're quick when the aircraft reaches cruising altitude, the -60 hose makes a halfway decent bed... (the -60 is a small turbine engine that generates electrical power and air for equipment cooling and main engine starting for aircraft. It has a long air hose, stored coiled atop the unit that makes for a fairly decent mattress)
Flying back from DC today, one leg was on an A320. While taxiing, heard a noise very much like sawing a board with a hand saw coming from the back of the plane. It quit before takeoff.
Anyone know what that is? Some sort of pump?
Never heard a sound like this from an airplane.
First time I flew an Airbus was on a flight from Paris to Rome. That sound scared the crap out of me, because it only made it twice. Once when backing away from the gate, and then again as soon as we took off. I wasn't sure I was about to die or not. Since then I've flown on them dozens of times, they always make that sound.
So this power transfer unit is only in use when they are running on just one engine, right?
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)).
(the -60 is a small turbine engine that generates electrical power and air for equipment cooling and main engine starting for aircraft. It has a long air hose, stored coiled atop the unit that makes for a fairly decent mattress)
