jayseas

I have a some questions.

1.Why are some planes designed with the eng, wing and elevator all in a straight line?

2. Why are some designed with the wing higher than the elevator?




I hope this kind of states whay i'm trying to understand?
If not please respond with questions so i can clarify.
Jim

Jim Thomerson

Probably most stunt airplanes have the elevator above the wing. But some are all in line, others with stab below wing. I've seen some discussion, but all can be made to perform well. I generally put the tail higher than the wing because it is easier to line up the controls that way. One thing is that I want the vertical CG at the same level as the leadouts. The landing gear dangles down below, so I tend to put the thrust line on an inverted engine a little above the wing center line and the tail as above as looks good and lines up the controls.

On free flight models there is concern about keeping the tail out of the wing's downwash, but on a stunt airplane the down wash goes both ways with upright and inverted flight.

jayseas

(One thing is that I want the vertical CG at the same level as the leadouts)

Can you explain this?

Also, if i have the wing and elevator in line, do i have to have the thrust line inline with them or can it be alittle above?

Jim Thomerson

Lets say you have a high wing airplane with the bellcrank and leadouts in the wing. The engine, body, tail, landing gear, etc are all below the wing. So the CG will be positioned vertically well below the wing. This airplane will fly around with with the leadout guide lining up with the CG; with the wing flying at an angle to the control lines with the outside tip high. Not good.

As to the thrust line, I am flying a Herns Demon which is a low wing airplane with the thrust line (upright Fox 35) above the wing. The bellcrank is in the fuselage and the leadouts come out the side of the fuselage to a leadout guide on top of the wing. The leadout guide is about level with the vertical CG and the airplane flies fine.