Hybrid Engines??

The acceleration is still limited by the available power vs the total mass
of the glider and tow plane.


Possibly a better approach is to look carefully at propeller
efficiency in the initial acceleration. *In the ground roll where the
prop efficiency unlikely to be more than 25%.

Hmm, perhaps a better idea for a hybrid towplane than these hybrid
engines would be a tug with electric motors in it's wheels to quickly
get the party started... say up to 30mph or so before the prop is
providing primary thrust.

-Paul

PS. Noel, I definitely agree that battery/energy storage technology
needs to improve vastly (including $$$) for these to be truly viable
(read revolutionary) alternatives...

With two engines driving one propeller, does it count as a twin? ;-)

Bart

How about a catapult?

Mike Schumann

"sisu1a" wrote in message
...

The acceleration is still limited by the available power vs the total mass
of the glider and tow plane.


Possibly a better approach is to look carefully at propeller
efficiency in the initial acceleration. In the ground roll where the
prop efficiency unlikely to be more than 25%.

Hmm, perhaps a better idea for a hybrid towplane than these hybrid
engines would be a tug with electric motors in it's wheels to quickly
get the party started... say up to 30mph or so before the prop is
providing primary thrust.

-Paul

PS. Noel, I definitely agree that battery/energy storage technology
needs to improve vastly (including $$$) for these to be truly viable
(read revolutionary) alternatives...

bildan wrote:

Possibly a better approach is to look carefully at propeller
efficiency in the initial acceleration. In the ground roll where the
prop efficiency unlikely to be more than 25%. Touring motorgliders
like airplanes with fixed props are optimized for cruise, not
acceleration.

Small, high RPM props are very bad at very low airspeeds. Big, low
RPM props far better as are ducted fans. Note that helicopters use
huge rotors at around 300 RPM to slowly lift the entire aircraft
straight up. Other VTOL aircraft like the F35B use ducted fans which
are at their best below 75 knots.

The tiny prop is the weak link in current motorglider tugs. It
doesn't look as if it would be hard for the designers to lengthen the
landing gear by 25cm and ask Rotax to supply greater gear reduction
for a bigger, slower prop. A bigger prop would address the slow
acceleration.

The touring motorgliders I'm aware of have either an adjustable
propeller, or three position propeller (feathered, climb, cruise). I
would expect the ones used for towing to have the same; if so, the slow
acceleration may not be a propeller problem, but a power to weight
issue. Once airborne, their better aerodynamic efficiency makes up for
the lower power to weight, but that doesn't help the ground run.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* Sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On Mar 14, 2:54*am, Markus Gayda wrote:
How about using the propeller as a generator on the way down?
Recharge the battery. (of course you cant do that with a static prop)

THAT would be a real hybrid :-)

CU
Markus

Of course why not use all of the available energy? The turnstiles in
the New York subways are connected to generators that run the cars.

On Mar 14, 2:45*pm, Eric Greenwell wrote:
bildan wrote:
Possibly a better approach is to look carefully at propeller
efficiency in the initial acceleration. *In the ground roll where the
prop efficiency unlikely to be more than 25%. Touring motorgliders
like airplanes with fixed props are optimized for cruise, not
acceleration.

Small, high RPM props are very bad at very low airspeeds. *Big, low
RPM props far better as are ducted fans. *Note that helicopters use
huge rotors at around 300 RPM to slowly lift the entire aircraft
straight up. *Other VTOL aircraft like the F35B use ducted fans which
are at their best below 75 knots.

The tiny prop is the weak link in current motorglider tugs. *It
doesn't look as if it would be hard for the designers to lengthen the
landing gear by 25cm and ask Rotax to supply greater gear reduction
for a bigger, slower prop. *A bigger prop would address the slow
acceleration.

The touring motorgliders I'm aware of have either an adjustable
propeller, or three position propeller (feathered, climb, cruise). I
would expect the ones used for towing to have the same; if so, the slow
acceleration may not be a propeller problem, but a power to weight
issue. Once airborne, their better aerodynamic efficiency makes up for
the lower power to weight, but that doesn't help the ground run.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* "Transponders in Sailplanes"http://tinyurl.com/y739x4
* * * Sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" atwww.motorglider.org

Eric, it's a disk loading issue. Efficient props accelerate a whole
lot of air a little bit. Small props, regardless of pitch setting,
accelerate a little bit of air a whole lot. The solution to the low
speed efficiency issue is large diameter propellers turning slowly -
like 1000 RPM.

If you can make them work, ducted fans are in their sweet spot at
towing speeds. There's some blimps powered by ducted fans that claim
8 pounds of static thrust per HP - blimps fly at about towing speeds.
That's 800 pounds of thrust for 100HP which should get things rolling
quickly.

I think there are technologies on the horizon that might allow for
electric tugs as long as you were willing to charge them frequently.
The announcement this week in MIT's Technology Review of charging
times in seconds might be one of the breakthroughs.

At 09:54 14 March 2009, Markus Gayda wrote:
How about using the propeller as a generator on the way down?
Recharge the battery. (of course you cant do that with a static prop)

How about using the engine to run the generator on the way down? This
strikes me as one of the few advantages of the hybrid arrangement for a
towplane - give the engine something to do on the way back down. Load it
up, keep it working, keep it hot. Come down faster without worrying about
shock cooling an aircooled tug engine.

I also agree that this requires a prohibitively heavy battery array, but
with improving battery technology it might eventually work.

Oh, wait, wait, how about flywheel energy storage? Now *there's* a fun
idea - just *think* of the entertaining gyroscopic effects.

Jim Beckman