Thanks all for the replies.

The reason I asked this, is that in some European contries, Diesel is
much, much cheaper than AVgas or Mogas. "Red" diesel is untaxed and
illegal for road use, but a towplane doesn't operate from roads.
Besides, diesel engines also run on Jet A-1, which here has tax
advantages, at least at the time.

Our club actually has a winch (most clubs in Holland do), but we cannot
use it during airport operation (=thermal) hours since we operate on a
busy, narrow airstrip with powerd aircraft operations. As AVGas is
getting very expensive (not only here, I guess...), the usual
Robin/Husky/... tow planes become more and more uneconomical. We now use
a Super Dimona (Katana Xtreme) to tow even our Janus C and ASH-25 from
the grass strip, but in heavy crosswind we sometimes can see the cars
too near below us. This motorglider however seems to be the only way to
keep our tow costs reasonably down.

At least for this part of Europe, I think a Diesel in a Robin-like
airframe would be a very nice replacement. Let's see what the near
future brings.

Olfert
Hornet A7