motorgliders as towplanes

On Tue, 10 Mar 2009 08:56:47 -0700, Mike the Strike wrote:

I observed a 100HP Lambada equipped with 13m wings being used as a
towplane in the 2000 Worlds in South Africa. It seemed to perform very
well despite the moderate density altitude. They were launching from an
asphalt runway and the ground acceleration was slower than most other
towplanes, but once airborne no difference was notable.

I think you mean the Samba, sibling of the Lambada. This has a a shorter
wing + extensions to bring it to 12m. These have been used by a number of
clubs in South Afria and a Samba was also used for a number of years at
Gariep Dam (towing everything up to ASH 25's).

Some of the feedback I heard from the Gariep operation:

- The short wings result in a bit more drag, which is a problem with
marginal tows. But their are no aileron extensions on the wing extensions
so in long wing configuration it lacks aileron authority for good control
in strong weather.

- That Samba had a manually adjusted variable pitch prop. The pilot spent
a lot of effort adjusting the prop during the take off run and the tow to
get the most out of it. They also tried an electric auto variable pitch
prop but the electric motor burnt out very quickly.

The Lambada and similar modern motorgliders are very light (300kg) -
nearly half the weight of the older designs

This can also be a problem if the glider gets out of position on tow. A/T
training might get quite uncomfortable.

I did some research into M/G tugging a few years ago and put together
some notes. You can read them at

http://www.zsd.co.za/ian/gliding/cgc...gs/mgtugs.html

and some feedback from tow tests that we did at our club.

http://www.zsd.co.za/ian/gliding/cgc.../towtests.html

We never bought the Samba mentioned in the 2nd article. In hindsight I
think we made the right choice as the airframe of the Samba is just too
light and fragile to survive getting "clubbed".

But later we bought a 2nd hand 80 HP Rotax Falke. We had it equipped with
a tow hook, and did a few tows with it. We have a long hard runway near
sea level. The 80HP was fine with single seaters but not safe with two
seaters so we stopped using it for towing. (But we do use it for
training.)

Now we have just up-graded it 100HP and fitted a tugging fixed pitch
prop. We are optimistic this will make it a useful tug. In a year's time
I might be able to give some more feedback.

The Falke is much heavier, more robust and easier to fly then the Samba.
It has already stood up well to a few years of club abuse. But the tow
performance is going to be less than that of the Samba.

(In the meantime we have no plans to sell our 180 HP Super Cub tow plane
and there is still lots of training work for the Motor Glider to do.)

Turbochargers and variable pitch props help make up for the lack of
displacement of the Rotax 4 stroke. But they both add complexity and
costs which might not work out well in a club environment. Perhaps one
day someone will persuade Jabiru to water cool their 120HP motor. That
should make the basis of a decent M/G tug.


Ian