Hi Gordon,

I'm starting out with one of Tracy's RD1C drives, which is 2.85:1, and good
for way more power than I'll make wiht the single rotor. Unfortunately,
it's about 45 lbs stock. Speaking with Tracy, there's probably about 5 lbs
of weight that can be removed without losing any strength, and perhaps more
if you're willing to sacrifice strength in the drive. That wouldn't be a
problem for the single rotor, but if you ever wanted to use it on a two
rotor, it would be.

Richard Sohn has a running 12A single rotor now, and he's using a Hirth G-40
gearbox. At last report, his total engine weight was 170 lbs, which is
pretty great. He's custom made many of the parts on his engine to save
weight, and might produce them if it all works out well. He's currently on
a slow, and careful development and test program, and eventually plans to
put the engine in his Avid, which I believe is flying with a Subaru. It
will be interesting to see how the Hirth box works out, but I'm not sure how
much lighter it really is in the long run. I've asked Richard for the total
weight, but since so much of the adaptation is dependent on his custom end
housings, he hasn't been able to come up with a number. My guess is
something around 30 lbs total for the drive.

I asked about belt drives, and found that someone was making one for the
single rotor that David Atkins is selling. So far, I haven't heard any
reports of how that worked, if it even got finished. One other fellow who
makes belt drives told me that he refused to make such a drive for Atkins,
because it wouldn't be strong enough. His point was that the single rotor
is still full sized, and gives the same strength power pulses as the two
rotor does. Because of this, he felt the drive has to be as strong as the
two rotor drive. This does make sense to me, but I'm sure there has to be a
way to reduce the weight further.

FWIW, my plan was to bolt together off the shelf parts, and see what it
weighs. The Kolb Slingshot that I'll be using initially will handle the
weight, when flown as a single place, and with a BRS chute to balance the
CG. Once I get a worst case weight, then I'll start working on reducing it.

Cheers,
Rusty (hiding rotary info in the light twin thread)


What gearbox are you using? It seems like overkill to put one of Tracy's
boxes -- or something similar -- on a single rotor.

I would think a belt drive might be engineered that would be considerably
lighter -- expecially if you use the poly-v belts.