Delta3,
I am enjoying this discussion - it provides me with the sanity check i often need as an engineer!
My own particular interest in applying turbodiesel engines to helicopters is to avoid the costs assoiated with gas turbines. This includes fuel and manufacturing, due to the materials required to raise TET. I actually see the turbodiesel as just another combustion chamber variation. I also appreciate that this is the objective of the rotary engine.
To answer your questions:
"1. Wankel versus MYT : same sealing problems ?"
See ammendment to post on MYT above. It's not an impractical engine, but i suspect that many of the issues that lead to the criticised Cummins example engine have been overlooked.
"2. (Diesel) in line versus radial : why did aviation petrol engines abandon radial designs despite of the weight and cooling advantages ?"
Probably because Frank Whittle and Hans Von Ohain showed the world a better way. The turbo charger has direct ancestry to the gas turbine, and is making aerodiesels viable. This new breed of aerodiesels are reintroducing the possibility of large multicylinder engines - no spark plugs to maintain...
"3. Two stroke loop > Two stroke uniflow > Four stroke : why are all racing engines moving to Four stroke ?. I would put uniflow in between 2 and 4-stroke: better but not fully efficiency, but added weight, height and complexity in line with 4-stroke."
About right. The Mercedes paper (SAE 981032) does not give weights, but compares loop scavenge, uniflow scavenge and 4-stroke (4 valve). The uniflow is shown to have similar specific power to the 4-stroke. The 4-stroke of course will not suffer any piston/ring lubrication oil getting into the combustion chamber. In practice 4-stroke is currently about 66% specific power of uniflow 2-stroke, but advanced turbo charging concepts will nullify that advantage.
"From the specs it appears to me that Zoche could power for instance a R44 type heli, without applying unproven techniques, need we more ?"
Well as you say the reliability needs to be proven. The general theme of the thread, while discussing the rotary engine, has been to explore future engine developments. I would say that Zoche points the way for big 4-stroke turbodiesel radials. Increase the boost, and reduce the size (and improve efficiency).
"... I am driving 7 years the wonderfully efficient CDI-engines ... and would not want to go back.."
It would take a serious development for me to trade up my VW diesel!
Mart