"sidk" wrote in message
om...
One would not simply bolt a prop to a pump shaft... you will need to
add a suitable bearing and hub assembly which will surely weigh some
pounds.

Sid Knox



Actually, there are several brands that will handle a thrust load in excess
of 1000 lbs. But, a shaft to handle the loads properly would be the right
way. Not a big deal. The hub should be as light or lighter than any Rotax
PSRU, belt or planetary. I'd hope for 350-400 lbs of thrust per motor. More
would be sweet. Should be easy enough with the right hydraulic motor...
eh??? I'm pulling these numbers out of my ass hoping someone will tell me
where I'm screwing up... other than just telling me via e-mail I'm too lazy
to research it myself. Well, IMO, the USENET *was* a place to research....
at one time, many years ago.

Can not a 75 horsepower gas engine be replaced with a hydralic motor of
proper RPM and torque)?

Yes, I realize it takes more power, and depending on the quality and proper
sizing of the pump/motors, piping etc. etc., it's still less efficiant than
a direct drive. One place it would save weight is in the PSRU. I'd use a
Mazda 13b, no matter what (after years with them , I am convinced of their
reliability). PSRU are not light units themselves... EASY outweighting some
of the hydraulic motors I've seen. So, maybe the 250 lbs of weight that
would have went into a second engine could be swaped for the weight in
fluid,pumps ,motors add supporting cast members.

I'll get it sorted out.


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

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.