This could be the answer to the question re a rotary and a hydraulic
tranny.
jd
Tom Kasmer and the Hydristor Featured in Business Week Magazine
The September 18, 2006 issue discusses hydraulic transmissions in
the
quest to save fuel in its "Science & Technology" section. The
full text
of the article is available online and can be read here
<http://www.businessweek.com/magazine/content/06_38/b4001082.htm>.
What are they claiming as an efficiency? The killer with most hydraulic
motor/pump combos is efficiency. For use in an aircraft anyway.
Bill Jepson
The weight and heat of driving a prop with hydraulics makes this
totally out
of the question on an aircraft. Have you ever seen the size of a
hydraulic
pump large enough to handle 300 hp? And the noise..... OMG are they
loud. In
the past I tested many pumps on a 50 HP electric test stand, and you
thought
a rotary was loud..... And then there is the complexity of pump, motor,
reservoir, pressure filter, scavage filter, case drain filter,
controls....
But what a speed brake, as you could stop the prop with the engine
running!
Larry
The Business Week author failed to convey the main reason that hydraulic
hybrid systems may make good economic sense. In a stop and go delivery
truck fleet the hydraulic hybrid system can recover most of the braking
energy that is normally lost. A hydraulic system can recover about 70%
of braking energy, whereas the best current electric systems can
recover only about 20%. Also, for a given power level, a hydraulic
system can be much lighter than an electric system.
The power density for a hydraulic system is around 5000 watt/kg and an
electric system is only around 600 watt/kg.
One possible aircraft use for the technology may be a rocket take-off
assist system that stores water in a hydraulic accumulator and squirts
it out the aircraft tail on take-off.
Aubrey Thompson
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