Is hyraulic drive posible?

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

Earlier, wrote:

...In addition, you've got the prop
spinning at 3200 rpm...

Well, that's one of the things that makes hydraulic drive sort of
compelling: There are plenty of variable displacement pumps that will
give you infinitely variable ratios. So there's no reason at all why
you would be constrained to 1:1 drive. Or even to any fixed ratio. And
the pumps and motors developed for airline and military aircraft
application offer some pretty good power/weight ratios. We're not
necessarily limited to the cast-iron lumps that Grainger sells for use
in industrial trash-smashers and the like.

...There will also be the weight of
the oil lines...

Well maybe the weight of the oil lines would be compensated by the
absence of shafts, belts, gears, etc...

One possible application might be for driving remotely-mounted
propellers for unconventional configurations, as the OP suggests.
Sure, for your typical aircraft of conventional configuration, direct
drive will probably continue to be best way to go. But perhaps for
retractable-propeller self-launch sailplanes, and other odd layouts,
the advantages of hydraulic drive might outweigh the disadvantages.

Bob K.

"Bob Kuykendall" wrote in message
om...
Earlier, wrote:

...In addition, you've got the prop
spinning at 3200 rpm...

Well, that's one of the things that makes hydraulic drive sort of
compelling: There are plenty of variable displacement pumps that will
give you infinitely variable ratios. So there's no reason at all why
you would be constrained to 1:1 drive. Or even to any fixed ratio. And
the pumps and motors developed for airline and military aircraft
application offer some pretty good power/weight ratios. We're not
necessarily limited to the cast-iron lumps that Grainger sells for use
in industrial trash-smashers and the like.

...There will also be the weight of
the oil lines...

Well maybe the weight of the oil lines would be compensated by the
absence of shafts, belts, gears, etc...

One possible application might be for driving remotely-mounted
propellers for unconventional configurations, as the OP suggests.
Sure, for your typical aircraft of conventional configuration, direct
drive will probably continue to be best way to go. But perhaps for
retractable-propeller self-launch sailplanes, and other odd layouts,
the advantages of hydraulic drive might outweigh the disadvantages.

Bob K.

Thanks Bob.

Hydraulic power was the only way I could think of to use one engine with
two drives in an in-line thrust design. Some of these motors are very
lightweight (IMO) and,as you said, are not the $150.00 cast-iron jobs from
Graingers. These are $2300.00 each. They're piston motors. They ( Eaton )
carry several that are rated from 2000 RPM, up to 3600 RPM... several models
to choose from. And, they have a ton of torque! :

Phil (on his way to the patent office) J/K

Hydraulic power was the only way I could think of to use one engine with
two drives in an in-line thrust design. Some of these motors are very
lightweight (IMO) and,as you said, are not the $150.00 cast-iron jobs from
Graingers. These are $2300.00 each. They're piston motors. They ( Eaton )
carry several that are rated from 2000 RPM, up to 3600 RPM... several models
to choose from. And, they have a ton of torque! :

Phil (on his way to the patent office) J/K
++++++++++++++++++++++++++++++++++++++

If one gears a clock motor low enuff...
it is said that one could pull the earth off axis.
Hardly a desireable speed for a prop.

There is no free lunch where torque is concerned.
Best be careful what is implied to the uninformed.

http://vettenet.org/torquehp.html
http://www.carcraft.com/techarticles/868/

P.S.
Rotsa' ruck at the U.S. Pat. Off.


Barnyard BOb --

"Barnyard BOb -" wrote in message
...


Hydraulic power was the only way I could think of to use one engine with
two drives in an in-line thrust design. Some of these motors are very
lightweight (IMO) and,as you said, are not the $150.00 cast-iron jobs
from
Graingers. These are $2300.00 each. They're piston motors. They ( Eaton )
carry several that are rated from 2000 RPM, up to 3600 RPM... several
models
to choose from. And, they have a ton of torque! :

Phil (on his way to the patent office) J/K
++++++++++++++++++++++++++++++++++++++

If one gears a clock motor low enuff...
it is said that one could pull the earth off axis.
Hardly a desireable speed for a prop.

There is no free lunch where torque is concerned.
Best be careful what is implied to the uninformed.

http://vettenet.org/torquehp.html
http://www.carcraft.com/techarticles/868/

P.S.
Rotsa' ruck at the U.S. Pat. Off.


Barnyard BOb --

You lost me. What gearing are you talking about? These motors would be
direct-drive.

Phil

"PAW" wrote in message ...
"Barnyard BOb -" wrote in message
...


Hydraulic power was the only way I could think of to use one engine with
two drives in an in-line thrust design. Some of these motors are very
lightweight (IMO) and,as you said, are not the $150.00 cast-iron jobs
from
Graingers. These are $2300.00 each. They're piston motors. They ( Eaton )
carry several that are rated from 2000 RPM, up to 3600 RPM... several
models
to choose from. And, they have a ton of torque! :

Phil (on his way to the patent office) J/K
++++++++++++++++++++++++++++++++++++++

If one gears a clock motor low enuff...
it is said that one could pull the earth off axis.
Hardly a desireable speed for a prop.

There is no free lunch where torque is concerned.
Best be careful what is implied to the uninformed.

http://vettenet.org/torquehp.html
http://www.carcraft.com/techarticles/868/

P.S.
Rotsa' ruck at the U.S. Pat. Off.


Barnyard BOb --

You lost me. What gearing are you talking about? These motors would be
direct-drive.

Phil

I am much of a lurker here but...It seems to me that a lot of the
naysayers are missing the point that you are proposing to drive -two-
props with -one- motor. There should be at least a break even if not
a savings in weight over -two- motors driving two props. I like
considering off the wall projects and have attempted a few myself,
mostly failures.

Harry K

(Harry K) wrote in message . com...

I am much of a lurker here but...It seems to me that a lot of the
naysayers are missing the point that you are proposing to drive -two-
props with -one- motor. There should be at least a break even if not
a savings in weight over -two- motors driving two props. I like
considering off the wall projects and have attempted a few myself,
mostly failures.


Actually, I'd charaterize it as driving two props with three motors.
Two hydraulic motors direct driving the props and one motor driving
the hydraulics.

I think a mechanical drive, like the chain drive the Wright Bros used,
would be more efficient.

--

FF

"PAW" wrote in message ...
"Bob Kuykendall" wrote in message
om...
Hydraulic power was the only way I could think of to use one engine with
two drives in an in-line thrust design. Some of these motors are very
lightweight (IMO) and,as you said, are not the $150.00 cast-iron jobs from
Graingers. These are $2300.00 each. They're piston motors. They ( Eaton )
carry several that are rated from 2000 RPM, up to 3600 RPM... several models
to choose from. And, they have a ton of torque! :

Phil (on his way to the patent office) J/K

But what was the original reason you wanted an in-line thrust design?
I've been keen on that layout (in-line) for fail-soft/reliability
benefits. I didn't like the idea of a single point failure in the
most likely place to have a failure (engine) meaning a forced landing.
If you use a single engine to drive 2 props, you don't get that
benefit.

There are some other bene's I could see though such as
1) Engine located at center of gravity perhaps on main spar
carry-through. So you could save some structural weight.

From an efficiency standpoint I think you're better off turning a
single big prop rather than 2 smaller ones.