At 18:07 30/10/2009, Morgan wrote:
Yes, but an electric tug doesnât have to carry
the equivalent of 100L of avgas like a
âconventionalâ electric aircraft would for
cross-country flying. If you allowed
regenerative battery charging, the tug could
completely exhaust its battery getting to 3000ft
and then recharge just enough on the way down to
allow for a go-around or hold. The battery +
motor should weigh much less than a 6-cylinder Lycoming.
Taras has built a scale model prototype - 40%
regenerative efficiency. 75W electric power to fly level.
The airfoil section on the prop must be
symmetrical to work as both a windmill and a
propeller. (The next time you meet an aerobatic
pilot droning on about symmetric airfoils, ask
him what airfoil is on his prop.) For the best
efficiency as a windmill, the prop needs to have
a large diameter and the delta-V (change in
velocity along a streamline) needs to be
minimised, indicating that a descent at close to
minimum-sink speed would be required for maximum energy recovery.
Todd (no relation) said:
This is the completely wrong thing to be putting
the electric motor in. The tug is the problem
not the solution. Its the GLIDER that needs to be electric!!
All this makes me wonder why we are talking about
lifting either the Internal Combustion engine or
the batteries into the air if we are really interested in energy-saving.
Surely a winch is the most sensible area to use
an electric motor to launch a sailplane, where
you can have as much weight and do not need to
shock-proof the charging system because they stay
fixed on the ground and the charging system can
be remote from the winch cable driving mechanism.
That's why we can have diesel winches that are so
cheap to run, though they can't do outlanding
retrieves or launch to a remote start point like a tug can.
Incidentally, aerobatic pilots (and they are
competing at Temora this weekend) may have
symmetrical wing sections to fly inverted - but
the propeller does not need this in-built
handicap unless it is intended to use it as an
in-flight brake, or to both push and pull the
aircraft (which would involve also changing the
direction of rotation, or at least a significant
reversal of pitch past the full-fine point to be
able to drive the airframe tail-first).
Wombat
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