I am building a Fantasy III from Art Hobby. It has a thin, circular fiberglass airframe. Plans call for the motor to be installed pointing 2 degrees down from horizontal and 2 degrees to the right of the centerline.

What is your preferred method of laying out and installing the motor at small angles like these?

Cpt Crunch

For 2 degrees down thrust, I place two flat washers on each of the rear engine mounting bolts, UNDER the engine's mounting flange. For right thrust, I add 2 flat washers under the left side of the motor mount (on the firewall) to shim it to the right. Also, it is better to add MORE down thrust & right thrust, than it is not add enough. More won't hurt. Joe V

Thanks, Joe. That sounds simple enough!

Joe:

Could you explain to me what happens if there is not enough down thrust or too much down thrust. I flew a friends plane that climbed when throttling back and dove when throttling up. Is this not enough down thrust or too much? It seems know one at the flying field could answer that question. Please reveal the mystery of thrust angles.

Thanks.

K Sonn - The condition you describe could be caused by other things than just engine angle thrust. Specifically, I am thinking about the incidence angles of the wing and stab - have they been "Robarted"? Are they both zero-zero degrees? I have asked fellow modeler "Dr. Gravity" to respond to your inquiry as well, as I am by no means the highest authority on this subject. I just know that over the last 22 years, I have always been taught, and have always found to be true, a little extra down thrust (or right thrust) won't hurt. I hope "Dr. Grav" will contribute here, as well as our many other knowledgeable modeling friends. Joe V [email protected]

Diving when throttling up and climbing when throttling back are the classic symptoms of too much downthrust. You can explore the mysteries of this phenomenon at http://www.nsrca.org/. From their menu click the Technical button, then click Airplane Trimming.

Researcher, Majortom:

Thanks for the info.

Researcher has the right ideas. It is also possible that your Balance Point(CG) is too far aft!!
With tailheavy power planes...at mid throttle, it it dives handfs off after proper trim...it is tail heavy.
If nose heavy, it will climb with same trim settings. Sounds crazy...but thats how it works. Try balancing.
Dr. Gravity.

Thanks Dr. Gravity. We will experiment to see if we can figure the cause of the problem.