The guys who are very serious about 1/2A combat (that sounds so weird...) use Eastern European made engines call Cyclon and Flora that are $200+ each. Those that just want to have fun use a variety of other engines including VA's (I think no longer in production), Norvel (I know no longer in production) and a few have tried the Brodak 049 with an aftermarket head that uses a Nelson glow plug. The aftermarket head is sold by a guy named Doug Galbreth (sp?) and improves the RPMon the Brodak engine by 1,500. If you just want to get a feel for current 1/2A combat buy a Brodak Gladiatoralmost ready to fly 1/2A combat plane(I am fairly sure they are on their website but not in the catalog yet) the aluminum motor mounts and a Brodak 049.Without the aftermarket head the Brodak may not even have the power of a TD but you can break in the engine with the stock head and get a feeling for how the plane flys. There are better built ready to fly combat models but they are a bit harder to track down. Join the combat groups on Yahoo and just ask questions.
Bob