Hi!
I have run several of the old wankel model .They all run fine with as much power as the old K&B and HP .40 two-stroke engines.
They also throttle well. I used 10x6 props on them i the Nomad highwinged aircraft I had in the beginning of the eighties.
Fuel used were 5% nitro and 20% castoroil.
As for being heavy I dont agree, more like a modern .40 engine
( if you consider that heavy).
The more modern version of the OS wankel is more powerful than the older version and hasn't got the cooling ring, and it puts out more power too(1,27hp).
As for the large wankel seen in a Graupner catalog ...I´m nearly certain that OS made that too.
As for HP making wankels ... No! Only OS made modelwankel engines.
HP made fourstrokes with a rotaing valve mecanism at the top (.21 and .49) some 10 years ago. Now Mecoa makes these.


Regards!
Jan K
Sweden