SkySurfer motor mods final version

It took some time to validate the tunings on my SkySurfer.

In particular, the Centre Of Gravity and the appropriate propeller changed a lot from the initial setup.

I therefore had to modify my files for a correct propeller folding, and to have a plane behavior unchanged whether or not I use the motor.

It resulted in a sort of tube, glued in place in the glider fuselage where the motor should stand, and 2 motor plates to choose from depending on the propeller size.

Up to 7 inches propellers, the motor axis stays low in the tube, and the plate is completely included in, and screwed in place with an angle of 4° more than what the fuselage gives.

To mount a 8 inches propeller, the motor plate moves some millimeters backward and upward and adds 3° more raising the global value to 7°.

This way, the pushing force stays near to the COG point keeping an unchanged behavior of the plane with or without motor

The conception file includes also the cone and propeller folding li