taxi in reverse?

"James M. Knox" wrote in message ...
I always figured if I was building a homebuilt I would investigate some
relatively small motor/brake assemblies that are used on smaller electric
automobiles. May be WAY too heavy, but they make great brakes that don't
fade with heat ... *AND* you could just taxi out of the hangar (before
starting the engine).

My first thought when reading this was, "sounds cool!". And I started
to think it through. The motor part is clear enough, you can taxi
with electric power and not with the engine power. That'd lead to a
real difference in taxiing of course. You can't use engine power to
bring the rudder around for example. But this is workable, it just
becomes part of this plane's checkout procedure.

In the brake mode though, there's a problem. Either the motor/brakes
now work as generators or as motors in reverse. If the first, where
you put the power that's generated? Your battery's been charging off
the engine, it's already full and not drawing current. Your braking
power is directly related to the power you can cause to be used up on
something else. I imagine you can make your landing light really
bright or something... grin

The generator mode makes more sense in a hybrid aircraft, like hybrid
cars with regenerative brakes. But the problem with this is that
lightweight high-capacity batteries are not yet available.

If the brakes are operating as motors in reverse that solves the
generator problem. But it creates a new one. What happens if your
battery or electrical system dies? No brakes. But if you've got the
power, you should be able to get more braking from reversed electric
motors than current braking systems. Current braking systems convert
momentum to heat. Their braking capacity is directly releated to
their limit in heat capacity. Electrical reversed motors would have a
heat limitation, but the initial limiting factor would be the power
input.

Fun idea!

-Malcolm Teas