"PAW" wrote in message ...
wrote in message
...
In article , "PAW"
wrote:
This is a BS question, but I'm curious.

Not a BS question at all. You definitely could do this. Unfortunately,
the
hydraulic route will come at a price of reduced efficiency. You will
probably
loose 15-25 percent of your horse power. With this in mind, though, you
can
easily pick the proper size pump and motors to get the rpm of the
propellers
anywhere you want, with the engine running at what ever rpm it likes. Why
heck, you could even put small motors on the main wheels and use them for
brakes and to run the airplane backwards for parking. That would turn
some
heads.

best luck,
tom pettit



I was looking at some hydraulic motors the other day and was wondering
if
a pump and motor could be used to drive a prop. A crazy example; two
hydraulic motors and a couple pumps (powered with a mazda 13b maybe ??)
to
power something like a Cessna 337 in-line thrust type aircraft.
Understanding weight would be an issue, I'm wondering how it would, or
could
,work. I was looking at an Eaton motor that was rated at (up to) 3200 RPM
@
about 120 ft. lb of torque. Weight was 20 lbs. They have a pump (48 lbs)
that moves 42 gpm @ 4000 psi.

Is it possible? Single place would be fine.





That's a thought.... movement without the props turning. A Mazda 13b turbo
can do 250-300 hp EASY. Power available for the pumps shouldn't be a
problem. At least, *I *can't see how it could.

There are some commercially built single engined hovercraft that
use hydralic drive systems for the lift-fans. It allows excellent
control of porportionality of the lift function separate from thrust.
The upside is that it gives infinite variabilty and good packageing.
The downside is that appropriate systems are pretty expensive and do
add some weight and waste power but in larger craft this is not
excessive. But keep in mind that the lift function normally requires
around 30% of total power requirements in a large hovercraft and that
thrust is 70% which is of course by direct,mechanical drive so the
power losses from the hydralics are less significant than if used
everywhere.
I design/build racing hovercraft as a hobby and worship at the
church of "Light and Simple." The biggest real improvements have come
from learning how to make better components with composites. I have
tried about a 1000 ideas (and kept a few) but most of the progress has
been from making things lighter and better shaped - same as it ever
was.