I have a question on mounting my motor to the fire wall. This is my first build and I'm building a Top Flite P-51 gold 60 size.
The instruction state the fuselage and firewall has the right and down thrust built in. (down 1.75 and right 1.60) On the firewall there is and off set to the right thrust but not one for the down thrust. Page 38 of the manual.

http://manuals.hobbico.com/top/topa0110-manual-v1_1.pdf

Question:
Should I go with the center point the they gave me?
or
Should I make a new line for the down thrust off the center line?


Thanks for the Help.

All of the Top Flite kits are very well designed and engineered. You should not have to modify what they have designed. The planes will have the proper thrust angles designed into the airframe. Build the plane according to the instructions.

Ken

Just an FYI thing, it's like Ken said, you build to the plans. Sometimes the instructions were written when the plane/kit was first designed and over time and testing small changes were made but the instructions were never changed. There was a time when 2 degrees right and down were the norm and a lot of kits had that built in. After a lot of testing it was discovered that it may have been too much or not needed at all and changed or removed from the kit. I have run into a number of kits that don't call for engine thrust at all, it's something the builder can add or subtract during there own flight testing. It's just something people doing builds should know about.

I know right thrust is for torque compensation, but if I understand correctly down thrust is for comensationof angle of attack to giving straight line thrust in level flight. If that is the case it would seem that a flat bottom wing trainner would not need much compaired to a fully symetrical wing. Flat bottom wings have lots of lift atzero AOA andsymetrical wings have no lift at zero AOA. I dont see how there could be a standard figure good for both. Maybe there is something I am misssing.

i thought down thrust was to compensate for the "balloning" affect at higher speeds, aka as the wing gets lift it wants to climb. so flat bottom wings tend to have more down thrust than say a profile? im not sure

This is what one of my books says about the down thrust in the glossary, Angle of the engine to prevent excess climb. Very short and simple. Today in most stunt planes you will find no built in thrust angle on the fire wall, it's a test and change as needed/wanted. If you have a lot of down thrust in the engine and you trim it for straight and level flight at something around half throttle then cut the throttle the plane will balloon up. Think about how it is trimmed for flight. Same thing happens on bipes if the wing incidence is off. When I would be doing the trim on a new bipe it often took a lot of trial and error before I could get everything straight.