Dick I had always wondered about how the big 150cc engines fared on the front of some of the models. It's easier to visualize with a composite model, I guess we tend to think of them as stronger. But a really light built up airframe even if it is structuraly strong seems that it would vibrate apart. The only big engine I ever had was a Zeonah 35 or 45 or something like that on a World Engines Robin Hood. It had 1/4 inch thick ply sides and was built like a brick. Of course I put fiberglass over everything from the wing and landing gear forward. The motor shook like a wild creature and didn't ever get smooth.

I would guess the big twins might be smoother. I can see the airplane hanging on to the motor in the air but my mental airplane has the motor falling off when it lands.

With a full sized airplane you are tieing the motors into the steel tube structure which seems better able to handle the loads than something made of balsa.

What does your structure have to handle the loads of the motor and not shake apart?