I'm currently putting together a Sky Arrow .46 ARF from Nitro Planes. http://www.nitroplanes.com/neskyar14466.html . Those of you that have built a Nitro Plane ARF will know what I'm talking about when I say I do not trust anything stock from the box. You cannot count on anything being square or true. Especially this plane. I've had to modify, beef up, or square just about every step of the build so far.

Now however, I'm at the point of mounting the engine and have a question I am just not sure of the answer. What should the thrust angle relationship be. I've included a diagram I did in Windows Paint to show what I'm talking about and a pic of the plane in question.

Diagram A) The airframe out of the box has several degrees of engine down thrust. Being a top mounted engine I'm of the understanding that any thrust above the wing will try to push the nose down anyway so I really don't think it needs any more down thrust.

Diagram B) Recently I helped a guy set-up a very large Long EZE pusher canard. We put in several degrees of up thrust and it worked out very well. I'm thinking this would work well in my situation as well. Maybe not as much up thrust but I'm thinking a degree or two.

Diagram C) Or, should I just square everything up. I hesitate to do this because I've flown other pusher planes set-up this way and it seems the nose always wanted to push down on throttle up and zoom up when I let off. You could trim for cruise but everything else was off.

Don't pay any attention to the actual angles shown in the diagrams. I was just trying to illustrate the angle relationships in question. Not the actual amount of the angle. However, if you have an angle suggestion I'd like to hear it.

Let me know what you think,

Mike

BTW.... the side pic of the SkyArrow shows the engine pretty square to the wing but it is definitely not so in the example I got.

I'd tend to try it as the plans show it first. That is equivalent to a bit of downthrust on a conventional tractor layout. Now the resultant between the drag forces trying to rotate the wing into a more positive angle of attack and the engine trying to force it into a less positive angle, the forces will balance out at some speed. If you do not have any of the downthrust, the faster you go, the more it will want to pitch up.

I would go with A. Make certain the pusher prop is mounted correctly (rounded edge of prop is the Leading Edge and points to the direction of rotation). Remember that in a pusher application the engine will overheat if it is not in the air flying. I get my pusher Canard into the air within 30 seconds of engine start. For engine tuning I replace the prop with a tractor prop of the same make, diameter, and pitch. Good luck. Post your maiden flight report.