FLUID DRIVEN PSRU?

[Jringer]

I would like to know if there have ever been any successful fluid driven propeller reduction drives?

I have read that the steel geared units take a beating. Also, with steel on steel, the torque forces put a tremendous strain on the engine crank shaft. It would seem that a fluid drive could absorb a lot of this torque and surges and vibrations. When I was a kid I bought a Honda motorcycle that had a hydrostatic transmission that worked well. I didn't have to use the clutch if I didn't want to. Of course we all drive around with torque converters in our automobiles, so it made me wonder.

Thanks, John Ringer

[Jim Stewart]

Not that I've ever seen in the literature or in person.

It's hard to beat the existing designs for lightness and simplicity. You might want to look at the the DUC prop. It warps it's blades depending on RPM and air density. A clever design, but not entirely accepted yet.

[Jringer]

Thanks Jim. I think I may not have made my question clear. I was wondering if there was a fluid drive to drive the propeller. I was not wondering about changing the pitch. Although, the two functions could probably work together.
I realize the PSRUs have been engineered and reengineered many time over, I was wondering about a fluid drives ability to absorb the torque pulses, and vibrations, to relieve the strains on the crankshaft and steel geared PSRUs. Best regards, John Ringer

[snaproll]

John,
Several folks have tried this without success... Did it work - yes. Drawbacks - extra weight, power loss as it was about 95% efficient, friction loss, heat buildup in lines, etc. This is commonly used in the marine industry where large hydraulic pumps are used for multiple purposes including propulsion, and used in pumping systems, i.e as an example a Cat 130HP diesel drives the hydraulic pump and another hydraulic motor turns a Blackmer fluid pump (used on fuel barges). You will also find a great deal of farm equipment using hydraulic drives. With newer technology and materials available today, it might be worth the effort to develop a lighter version to turn a prop. In India, they now have autos on the road with pneumatic drives using compressed air tanks. Might want to research their systems for basics on propulsion and motor efficiency. Good luck. VR.. Don

[Jringer]

Thanks Don. I appreciate your information. I am familiar with hydraulics on farm equipment and heavy equipment, but I wondered about a PSRU application. It seems the problems are many. Maybe someone will come along with a new design that will overcome the problems and take some of the power pulse and vibration strain off the crankshafts. As you have probably guessed, I was thinking of the strains on the automobile conversion engines that break crankshafts, or break up their steel geared PSRU.
I was not aware of air powered cars in India. Who would have thought? It must take a big air tank and a very short trip! Ha-Ha. See! After thinking about air driven cars for awhile, my question about a fluid driven PSRU seems much more plausible.
Thanks again. Best regards, John Ringer

[snaproll]

John,
The prototypes used several 3000 to 4000 PSI tanks which provided 50+ miles range. Adapting a hydraulic or pneumatic pump to a crankshaft opens up a wide selection of possible engines for use which were previously unusable to drive a prop. Tata Motors ( http://www.tatamotors.com ) was one of the firms experimenting and developing the pneumatic drive. Might be worth you time investigating their technology for possible use. Good luck... VR Don Stits

[Jringer]

Thanks Don,
I went to the Tata web site. I was surprised. They own Jaguar and Land Rover, and they make big trucks, sedans and my new favorite the "Tata Magic Iris". (That one made me laugh!) I didn't see any information on air powered cars, but now that I know about them, I will look again. Again, thanks for the information. Best regards, John Ringer