Combat Plane and Engine?
For club stuff we use stock engines like the OS.40fp. Put that on a Predator and you should be OK. We have VERY little damage and the planes fly good even on a very windy day.
Contest combat is as followed.
The Big boys fly B class with up to .30 sized engines.
The Scale guys use engines up to .26
The slow combat guys use stock .15's
Club stuff is sling what you bring.