"Bill Daniels" wrote in message
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"Stefan" wrote in message
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Is anyone doing this?

In Europe, this is becoming more and more common. Towing works
astonishingly well with 100 hp and one of those new planes. The limit is
when the glider is very heavy (fully loaded two seater) or the runway is
very short and soft. Towing with 3 gal/hour and with remarkably little
noise is much cheaper and neighbour-friendlier, even if a tow it last
10% longer.

There are currently two categories of "new tow planes": Motorgliders
(such as the Super Dimona, in the USA called Katana XTreme) and modern
ultalights, as they are called here (see for example
http://www.remos.com/).

All in all, in Europe we strongly believe that this is the future of
towing.

Stefan

I don't believe an optimum design tow plane would look anything like a
touring motorglider. The key to performance and economy is the propeller.
It should be really big and slow turning. Remember, propeller blades are
just rotating wings. They work best at the L/D max just like a sailplane.
Think of a three to four meter diameter prop turning at 1000 RPM. The
touring motorglider airframes won't accommodate a prop that big.

I'm thinking of something that would look like an oversize ultralight with
the pilot way forward for the best view and a pusher prop over a low wing.
The wing would baffle what little sound the prop made so it should be very
quiet. A very slow prop could be easily driven with a tooth belt. 130 HP
should be more than enough for the heaviest 20 meter two-seater. A water
cooled Honda or Subaru engine might work great.

Bill Daniels


You may be right, from an aerodynamic point of view, but if it can work as a
motorglider/trainer too, then a club or FBO can use it more, and that helps
with the amortization/justification for buying it.

I think a towplane-only airplane would be a fairly low-wing loading canard,
towing from somewhere near the CG. Then tug upsets would become extremely
rare. Another weirdness of design would be to drive two overlapping props
(slightly offset fore and aft). The disc loading of each prop would be low,
like a big slow turning prop, but the gear legs wouldn't be so long. They'd
give up some efficiency to the overlap, of course.

But I don't think the market is big enough to support a dedicated tug
design. Compromising in the direction of a motor glider usable for training
or rides lets an operator get more use out of his investment.

Tim Ward