I knew id have to draw a picture.You can use 4 sroke engines mounted in such a way as to have them turnning there same direction by using a center shaft with a gear that the prop would run on.As said,a twin would be configured as in post #12.
How about a 5 cylinder radial using just OS 4 Stroke engines.Nothing done to the engines.Check out the pic,then go to the thread and watch the video of this beast running.That will prove my point.I am going to make a twin like this as soon as i find 2 low priced,4 stroke glow motors then im going to convert them to gas.
I am also in the process of finding 3 -2 stroke engines the same size to build a 3 cylinder radial.Pretty easy.

http://www.rcuniverse.com/forum/m_57...Cengine/tm.htm