RE: Bob Cat Copy Falcon 120 Jet
Mad,
It depends on which engine you'll be using. Most are using 5 degrees of downthrust, which is about right for a 14# class engine. If you're going with an 18# class engine then 6 degrees would be better.
I wouldn't raise the engine any more than necessary. Ideally it should be on the fuse center line.
I would think that (4) 3 mm. studs would be sufficient for a 14 or 18# engine.
I have a single tank (about a 300 cc.) for retracts (Robart) & brakes (BVM). Your requirements may vary depending on what brand you choose and which control valves you use.
Joe