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Old 9th Jun 2013, 12:28
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Uplinker
 
Join Date: Nov 1999
Location: UK
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My 2p worth is that hydraulics probably allow faster response, finer control, and far more power to weight ratio than a purely electric actuator.

Imagine a surface that has been commanded to move in one direction then has to stop and instantly move in the other - think inboard ailerons on a B767 for example, which move rapidly up and down on final approach. With an hydraulic actuator a valve just has to move a few mills either way to effect the change of direction. If the surface was being moved by an electric motor driving a screw jack; to reverse direction it would first have to bring the motor and a gearbox to a stop, then start up again the other way. So for each change of movement there would be the inertia of the whole drivetrain to overcome, and the system would not be as responsive as the hydraulic one.

There are linear electrical actuators available, but I don't know if these would be powerful enough.

This I suspect is why even the EHA's on the A380 still use hydraulics as the final operating force.

Last edited by Uplinker; 9th Jun 2013 at 12:28.
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