Re: LG wheel hydraulic drive motors

From:         (Winyard)
Organization: NSWC
Date:         09 Nov 94 00:51:22 
References:   1
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In article <airliners.1994.1657@ohare.Chicago.COM> mateos@minerva.cis.yale.edu (Matthew J O Scott) writes:
>Bill Simpson <news@aol.net> wrote:
>: I saw a paper that had been given at an SAE  A6 meeting  on  the use of
>: hydraulic motors  to  apply torque though gearboxes to landing gear wheels
>: and thus move the airplane on the ground.

...

>I don't see how or why this idea would fly. (Excuse me)
>1.  The weight penalty would be exceesive ...
>2.  Airlines are interested in fuel savings.  Yes, a hydraulic torque pump 
>running on APU juice would consume less fuel than all four fires on a jumbo, 
>but ...

Let's have some numbers!

1.  Assuming a 747, what is the fuel consumption of the normal number of main
engines running while taxiing between the gate and the end of runway,
including some allowance for waiting in line?

2.  How much on landing between the runway and gate?

3.  How much thrust is necessary to move a 747 at taxi speeds?

4.  What's the incremental SFC for a 747 APU?

With answers to these questions the fuel weight/cost penalties of current
practices can be brought to light.  ADDING a hydraulic motor might SAVE
weight!  Or maybe an electric motor would be better.

David Winyard
Annapolis, MD