RE: Top Flite Contender
Safebet,
Your choice of an OS .61 FX will work fine. The plans actually illustrate an OS .61 and an OS .40 LA. The Contender has a real thick airfoil so a pylon racer it will not be, regardless. My logic for using the .50 SX was: I had seen the Contender fly with .46 FX's and it performed very well. The .50 SX had more power than the .46, it fit the same foot print as the .46, and I really wanted to try the engine. Since I enjoy building airplanes and feel I do a good job at it, but I'm basically lazy, and really did not want to squeeze in the .61, I therefore opted for the .50 SX. Also you have a 10 OZ fuel tank and flying a .50 consumes less fuel and let's you stay aloft longer. Since you already have the OS .61 use it, it may even let you move the battery pack back where the plans illustrate.
Good luck, and enjoy the Contender.
Sledge_78 (Gerry)