I'm installing my engine on a 3d/funfly model and it seems that the engine can move up/down within the engine mount .
how can i determine the exact up/down thrust line(should the engine's shaft set parallel to the elevator/in relation with the firewall or any other starting point)

is there any good method to calc the thrust line angle ?

thanks

p.s
the engine is side mounted

Usually there is no up or down thrust. I would advive you to set it dead level, not up or down. It should work fine there. But see what other people say as well.

Zep, on my latest UCD.60 it appears that it will require a little down thrust from upline testing. I believe rcFp is referring to the engine placement in elevation regarding the thrust line of the plane. I have often wondered how this is determined and am curious to the answere as well. Joe

Yep, I was thinking about that vertical climb test. Usually I always prefer to have my surfaces dead straight, is I need to trim once I have I sort it out on ground so everything is nice and neutral and fly level on no trim. If I still have probs then its CoG or engine thrustline.

Zep, I am currently tuneing my thrust angle, not to be confused with thrustline, which I think rcFp was referring to. On the thrust angle, unfortunatly it is trial and error. You are on the right track by first ensureing that the control surfaces are set up properly. I have completed the vertical to check for right thrust and am now in the process of determineing if any up/down thrust is needed. Joe

thanks guys

but i was trying to figure out what is the plane's thrust line in order to install the engine before any test flight.
is this thrust line can be determine relatively to the plane's structure (like elevator)

If it were only that easy. Seems like a straight line from elevator to the vertical center would do it, but, like so many models they all appear to be placed differently. Some higher than others. I don't remember any to date that have been completly on center. Did you try the manufacturers web site for an E-mail link? Also, specifically, what model is it? Someone that has one may pick up on this. Joe

I'm guessing here, you want propwash on your stab, so if the wings are low you can have a more centered thrust, with mid wing you want a higher thrustline, with high wing the highest thrust line.

bear in mind the effect of drag on the wing, so if you have too high a thrustline with a low thick wing it will need up elevator to counter the down pitch from the wing at full throttle, then when you idle it will cause the nose to pitch up as drag on the wing is less. I would say keep the thrustline as close to the centerline of the wing as possible without blanking the stab.

best all round planes seem to be mid wing, stab just under tail fin, motor just above wing, tapered wing with very little dihedral gives best speed range with no coupling in knife edge. If its light enough you don't have to worry about tip stalling in spite of the tapered wings. constant cord wings have roll coupling problems.