Ok world wide knowledge base, I need to find some candidate 3HP diesel engines. It will be going into a helicopter so "light" is a key factor, followed by reliability and no-fuss starting. Air cooled preferred, but will look at water cooled if I can handle the radiator weight.

-Greg

Light and diesel don't really go together very well. Yanmar would be a good small diesel candidate. I've got a spec sheet and they make a 4hp (L48EE) air cooled engine that makes it's power at 3600rpm. Dry weight is 26.5kg with a pull start. That's right around 58 pounds plus fuel and oil.

Yes, most small diesels are much too heavy. I need the weight to be around 10-12 lbs for the base engine w/o starter.

Thanks - Greg

10-12 lbs? You're almost going to be stuck in the realm of some kind of 2 stroke weed whacker or chainsaw engine or something along those lines. Good luck though.

Why not a microturbine? It's the only way you'll get the power to weight ratio you're looking for reliably.

http://www.wren-turbines.com/turboprop.htm
7.1HP at only 3.52 pounds.

Helicopters:
http://www.wren-turbines.com/Helicopters.htm

Started by looking at model aircraft diesels, but they don't go big enough (only about 1.5 HP) and aren't really reliable enough.

We have some of the micro-turbines and are looking at them, but the sfc is the pits (about 2.7#/HP-hr).

In the past we have worked with companies like Sonnex and UEL to convert gas/spark engines to heavy fuel (diesel) but none of them really fit this application.

If it was easy I wouldn't have had to invoke such a large support base to find a solution

Thanks - Greg

Ya, I can understand the fuel consumption aspect. The unit in my link above consumes about 3.62 #/HP-Hr, but that's at wide-open making 7.1 horsepower. If you only need 3HP, the smaller turbine consumes about 2.1 #/HP-hr. Probably still too much. Tough project.

Your next best bet is a small Ion Generator fueling a dispersive high-energy rotary powerplant. (I might just have to go patent that).