Is hyraulic drive posible?

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

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.

"Rip" wrote in message
...
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).




Not a problem. When I say "lightweight" I mean in comparison to most
motors. I see many that are 50-100 (or more) pounds. To me, a hydraulic
motor than weighs in at 20 lbs, spins at the proper speed without a gearbox,
and provide 100+ ft lbs of torque, is lightweight. Eaton *claims* 90%
efficiancy.


And I don't blame you for not getting out of ground effect. What was that
wankle good for... 50 hp?

"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

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.

"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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"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.