I've come to the conclusion that planes this size need more power than a 26cc has to offer, and am not willing to load the weight of a 40cc on the front of the plane.

From my little bit of pattern experience, I agree that OS two strokes are the way to go - it seems to be the best option for power to weight ratio.

I think for the 73" plane, the OS 160 is the best choice, and a YS 170 would be great if you can afford it (high consumption of 30% nitro).

I have opted for the 69" plane and an OS 120 AX. I have that engine on a 9lb pattern plane and it is pretty darn impressive.

Thanks for the tips guys.