RE: Four Strokes and Sport Flying
The interesting thing about 4-strokes that most people don't suspect is their weight. We are used to thinking of 4-strokes as being heavy, but when you get to the mid to larger 4-strokes, .61-.70-.91, they are actually lighter that the corresponding 2-stroke.
For example, a typical 2-stroke .61 weighs between 25-26 ounces with muffler. The .75 and .91s are built in the same case and weigh the same, 25-26 oz. A typical .46 weighs from 16.5 to 18 oz. Here are weights for 4-strokes in the .70-.91 range:
Saito .72 18.5 oz
Saito .91 19.7 oz
Magnum/OS .70 21-22 oz
OS/Magnum .91 22-23 oz
A plane designed for a 2-stroke .61 could need nose weight no matter what .70-.91 4-stroke you put in it.