Is hyraulic drive posible?

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.

Sure, why not? Or you could use the engine to drive a generator which
would then drive electric motors to spin the props. Or you could do away
with the added weight and complexity and drive the props right from the
engine!

PAW wrote:
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.

Rip wrote:

Sure, why not? Or you could use the engine to drive a generator which
would then drive electric motors to spin the props. Or you could do away
with the added weight and complexity and drive the props right from the
engine!

You should patent that idea!

Mark Hickey

PAW wrote:
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.

"Mark Hickey" wrote in message
...
Rip wrote:

Sure, why not? Or you could use the engine to drive a generator which
would then drive electric motors to spin the props. Or you could do away
with the added weight and complexity and drive the props right from the
engine!

You should patent that idea!


I'm sure the USPTO will be unable to find any form of prior art and assign
the pattent in a heartbeat...
Rob

"Rip" wrote in message
. ..
Sure, why not? Or you could use the engine to drive a generator which
would then drive electric motors to spin the props. Or you could do away
with the added weight and complexity and drive the props right from the
engine!


And how might you suggest powering two props with *one* engine (when the
props are 12 feet from each other at opposite ends of the aircraft) via your
"less complex" methode of direct drive from the engine. Keep in mind a 13b
spins at 6000 RPM. Opps, gotta add a re-drive (or two). Thank you much for
your brilliant (and sarcastic) less complex answer.


PAW wrote:
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.

No problem! And I'll also suggest looking up the Aerocobra. WWII fighter
with the engine behind the pilot, machine gun firing through the center
of a tractor propeller. Aren't drive shafts wonderful!

PAW wrote:
"Rip" wrote in message
. ..

Sure, why not? Or you could use the engine to drive a generator which
would then drive electric motors to spin the props. Or you could do away
with the added weight and complexity and drive the props right from the
engine!



And how might you suggest powering two props with *one* engine (when the
props are 12 feet from each other at opposite ends of the aircraft) via your
"less complex" methode of direct drive from the engine. Keep in mind a 13b
spins at 6000 RPM. Opps, gotta add a re-drive (or two). Thank you much for
your brilliant (and sarcastic) less complex answer.


PAW wrote:

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.

"Rip" wrote in message
...
No problem! And I'll also suggest looking up the Aerocobra. WWII fighter
with the engine behind the pilot, machine gun firing through the center
of a tractor propeller. Aren't drive shafts wonderful!

PAW wrote:
"Rip" wrote in message
. ..

Sure, why not? Or you could use the engine to drive a generator which
would then drive electric motors to spin the props. Or you could do away
with the added weight and complexity and drive the props right from the
engine!





Yes, drive shafts are wonderful. I just don't like the idea of a shaft
running through where I'm trying to sit.


Here's the problem (IMO) with your response; I was asking about using
hydraulic motors. Several took my 3200 RPM speed as set in stone. I was
ONLY pointing out the fact Eaton has a full line of *lightweight piston
motors* that will handle speeds *UP TO* 3600 RPM at some decent torque
figures. A Mazda 13b is more than capable of producing the horsepower (plus
it's a lightweight water cooled engine) to provide the flow and PSI for
these little motors.

Anyhow, thanks for the "input". I'll stick with asking the engineers at
Eaton my questions because I'm obviously getting nowhere here. For the two
gents that provided information (Corky and Bob), Thank you.

Phil

Phil, sorry for the tongue-in-cheek answers. It's just that there is
very little new under the sun. In my admittedly misguided youth, I built
a one man helicopter, with the tail rotor driven exactly as you suggest
(variable speed hydraulic motor driven by a pump from the main engine, a
wankel from a snowmobile). I never had the balls to take the contraption
out of ground effect, but it did work. Hydraulics can be very efficient
at transporting considerable amounts of power from one end of a tube to
the other, but as others have pointed out, tend to be very heavy.
"Lightweight" is a relative term when speaking of industrial machines
(look at all of the effort involved in certifying aviation diesels, as
one example).



PAW wrote:
"Rip" wrote in message
...

No problem! And I'll also suggest looking up the Aerocobra. WWII fighter
with the engine behind the pilot, machine gun firing through the center
of a tractor propeller. Aren't drive shafts wonderful!

PAW wrote:

"Rip" wrote in message
om...


Sure, why not? Or you could use the engine to drive a generator which
would then drive electric motors to spin the props. Or you could do away
with the added weight and complexity and drive the props right from the
engine!





Yes, drive shafts are wonderful. I just don't like the idea of a shaft
running through where I'm trying to sit.


Here's the problem (IMO) with your response; I was asking about using
hydraulic motors. Several took my 3200 RPM speed as set in stone. I was
ONLY pointing out the fact Eaton has a full line of *lightweight piston
motors* that will handle speeds *UP TO* 3600 RPM at some decent torque
figures. A Mazda 13b is more than capable of producing the horsepower (plus
it's a lightweight water cooled engine) to provide the flow and PSI for
these little motors.

Anyhow, thanks for the "input". I'll stick with asking the engineers at
Eaton my questions because I'm obviously getting nowhere here. For the two
gents that provided information (Corky and Bob), Thank you.

Phil

"PAW" wrote

Anyhow, thanks for the "input". I'll stick with asking the engineers at
Eaton my questions because I'm obviously getting nowhere here. For the two
gents that provided information (Corky and Bob), Thank you.

Phil

Weight is still going to be the gotcha. Plus, don't forget an extra
radiator for cooling the hydraulic fluid. Hummm. Where do you suppose that
heat energy came from?
--
Jim in NC


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On Wed, 30 Jun 2004 23:53:15 -0700, "PAW"
wrote:

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.

So the engine drives a pump and the pump drives a hydraulic motor, and
the motor spins the prop, right? I'm thinking of the homebuilt
designers maxim: "Build it light and simplicate." In addition, you've
got the prop spinning at 3200 rpm which is kind of high and will mean
a smallish, noisy propeller that doesn't produce much low speed
thrust, which means long takeoff runs.

In addition, the weight of the items you mention will likely be higher
because you will need some means of cooling the oil, as it will be
working hard. There will also be the weight of the oil lines.

I'm not an expert but since you asked, here's a guess: Airplane
designers are a particularly ingenious lot. If it were possible to
utilize such a prop drive as you describe, I think someone would
probably have tried it by now. After all, we've had virtually every
other manner of providing thrust including photovoltaic cells coupled
to electric motors.

My guess is that your idea might work, albeit extremely marginally and
heat rejection will be a major issue, as will be efficiency due to all
the pumping losses incurred building pressure and converting the
pressure to rotational thrust. All for, in my opinion, relatively low
propeller thrust.

I'll bet a good mechanical engineer could compute the relative
efficiency of this design vs. a direct drive prop or PSRU driven prop.
That should be relatively painless and you'd know before buying any
pieces if this would be worth it or not.

Corky Scott