Is hyraulic drive posible?

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 ...
"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.

Hydrostatic transmissions (hydraulic pump driving a hydraulic motor) are used all over the place for heavy equipment.
These are best for high torque, relatively low speed operation. A good aerospace quality pump will give you about 90%
efficiency, and the motor will be about 85%. Industrial pumps and motors typically are much less efficient. As someone
else said, the heat rejection will be an issue (we cool our pumps through heat exchangers inside fuel tanks sometimes).
You will be better off using direct drive from a couple of small engines than using a big engine and driving a pump then
driving a motor...

Our smaller pumps can spin up to 13,000 rpm (Apache helicopter) and deliver as much as 85 gpm @ 4500 psi (B2 bomber).
Our motors can deliver full torque at very low speeds (100 rpm)...

http://www.parker.com/ag/pdf/abexbrochure.pdf

--
Dan D.
http://www.ameritech.net/users/ddevillers/start.html


..
"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.

In article ,
"Blueskies" wrote:

Hydrostatic transmissions (hydraulic pump driving a hydraulic motor) are used
all over the place for heavy equipment.
These are best for high torque, relatively low speed operation. A good
aerospace quality pump will give you about 90%
efficiency, and the motor will be about 85%. Industrial pumps and motors
typically are much less efficient. As someone
else said, the heat rejection will be an issue (we cool our pumps through
heat exchangers inside fuel tanks sometimes).
You will be better off using direct drive from a couple of small engines than
using a big engine and driving a pump then
driving a motor...

Our smaller pumps can spin up to 13,000 rpm (Apache helicopter) and deliver
as much as 85 gpm @ 4500 psi (B2 bomber).
Our motors can deliver full torque at very low speeds (100 rpm)...

http://www.parker.com/ag/pdf/abexbrochure.pdf

--
Dan D.
http://www.ameritech.net/users/ddevillers/start.html


.
"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.




As Dan pointed out above, it is "possible," but not practical, as the
losses alone (pump + motor) reduce your efficiency to (.9 * .85) 76% vs
100% on a direct-drive system. In addition, you have the added weight of
the pump & motor and the added complexity of the overall system. Total
system reliability is the reliability of each component X the
reliability of every other component of that system. If you have three
critical components whose total reliability is .99, the system
reliability is .99*.99*.99 = .97.

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.

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

"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.

"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.