As nice a plane as the F-82, as designed by Pat might be, it still would not be a classic legal twin. There are precious few that are, and as far as I can tell, they all have been mentioned in this thread.
Now, if you just want a twin stunter, there's a lot to be said for the concept. Pick your subject, and remember a few axioms. Things that always work as Bob Whitely says.
The nacelle legnth only needs to be long enough to hold the engine, and enough fuel to fly the pattern.
The tail needs to be long enough to balance out the weight of two engines, and their fuel tanks.
You should figure about 2 inches of clearance between the prop tips, and the fuselage.
Most who desire to design a twin, over power them. a pair of decent .20's will carry about 700 sq inches without hardly a problem. A pair of hot .15's will power a 620 sq inch plane.
Make sure there is no in-thrust in either engine.
Set the inboard engiines thrust line straight ahead, while giving the outboard engine a slight, 1 to 3 degrees of out-thrust.
Bob's things that always work should be imployed. A slight amount of down thrust is good, about 2 degrees plus or minus. along with a slight amount of positive incidence to the stab, will really help the plane fly well.
Properly rigging a twin is a more difficult procedure than most realize. Gordan Delaney has shown me that setting, and fixing the wing at 0-0 is the first step.
Next, set the nacells with the thrust line incidence where you have decided it should be. Make both thrust lines the same, as far as down thrust is concerrned.
Install the fuselage square to the wing.
Lastly, install the stab square to the wing. Make sure the distance from the flap hingeline, to the elevator hingeline, is equal, both sides of the fuselage.
Given a choice, simplify the control system, by mounting the bellcrank outboard when delaing with twin boomed, or double fuselaged designs. (P-38 and F-82 are good representatives of these styles.) The flaps and elevators will need to be stiffened up to resist twisting under heavy load, but it's not too difficult a task with todays materials.
Topic: Classic Twins ??? (Read 5391 times)
