Combining gearbox
Paul Hovnanian P.E.
> > is there any information about combining gearboxes. If two engines
> > power say one rotor how can this be acomplished without total
> > synchronization of the engines?
>
> The strength of the shafts automatically "synchronizes" the engines.
> The engines cannot turn at different speeds. Sort of like how the
> crankshaft on a multi-cylinder engine sychronizes the motions of the
> seperate cylinders/pistons.
I think some combining gearboxes are more complex than a simple hard
connection. I recall seeing something about the V22 having the
capability to drive both propellors through combining gears from a
single engine in the event of the opposite engine failing or being shut
down. This would imply the existence of differential gearing plus some
sort of limited slip or clutch system to prevent power from being fed
back into a disabled engine.
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Paul Hovnanian mailto:Pa...@Hovnanian.com
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Lynn Coffelt
> is there any information about combining gearboxes. If two engines
> power say one rotor how can this be acomplished without total
> synchronization of the engines?
>
> Achilleas
I seem to recall our X-18 VTOL at Edwards had four turboshaft engines in
two pods. The two engines in each pod drove a common gearbox and common
output shaft. The gearbox had some sort of differential arrangement that
permitted a difference of engine input speeds. It seems like there was an
"overrunning clutch" on each of those two engines that allowed one engine to
stop and allow the "good" engine to bravely carry on.
Although I was not connected in any way with the experimental, I had
heard scuttlebutt about the gearbox heating a lot with differential input
(engines not synchronized), and engine synchronization with early
hydromechanical fuel controls not an advanced science, there was a heavy
headwind to the whole Hiller (and maybe Fairchild?) project.
If I'm not too far from wrong, when we scrapped it, the 781 showed
about 20 flights with a total flying time of just over two hours. (two
frightening hours, I'll bet!)
Old Chief Lynn