In rec.aviation.piloting Michael Ash wrote:
In rec.aviation.soaring wrote:
In rec.aviation.piloting Phil wrote:
I wonder if anyone has done any experiments with a hybrid drive system
for an aircraft. I am thinking of something like a 3-cylinder diesel
engine providing enough power for cruise, supplemented with a battery
pack and motor for takeoff and climb.
The advantage for hybrids comes from stop and go driving where the
battery is charged by regenerative braking.
There isn't much stop and go flying.
There is also an advantage which comes from only needing to size the
engine for cruise, not for acceleration, since you can suppliment the
smaller engine with the batteries during acceleration. Smaller engines are
generally more efficient than larger ones when putting out the same amount
of power.
If you are trying to say it takes less power to maintain speed than to
accelerate, yes that is true.
The advantage from the electric engine at cruise is that it uses zero
energy.
There were attempts to increase mileage of gas engines by turning off
uneeded cylinders at cruise. They didn't work that well and you still
had to move the pistons, the big crank, and all the rest of the stuff.
The other advantage is that the engine can stay in the engine's efficiency
band even when the RPM demanded of it is higher (acceleration) or lower
(initial start).
The transmission keeps the engine RPM within a limited range.
Hybrids have no effect on that.
However, these also don't help nearly as much on aircraft as on cars. The
difference between acceleration and cruise power on an aircraft is much
less than in a car, and aircraft engines tend to spend most of their time
in the efficiency band anyway, especially if there's a constant-speed prop
affixed. The extra drag caused by the extra weight of the batteries and
the rest of the hybrid system would probably outweigh any efficiency gain.
It doesn't help at all on airplanes.
The advantage to hybrids is they get better gas mileage.
They do that by using the deceleration to charge batteries which recovers
some of the kinetic energy instead of using it all to heat the brake linings.
--
Jim Pennino
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