All:

Officially, anything with an engine less than 0,050 is 1/2A, then up to 0.15256 (2.5cc) is class A, B goes to 0.299, and C is up to 0.65. A long time ago C was up to 0.50 with D then going on to 0.65.

None of these classes are worried about too much anymore, and most competition classes have thrie own limits and exclusions.

And, as sturmvogel said, 1/4 A is accepted s meaning 0.02 power. Yes, there is also a 1/8A, for the 0.01 engines. But the 1/4A and 1/8A have never been "Official" classes.

Current definitions are very loose, with the 0.061 and 0.074 engines often being included in 1/2A, and some have even claimed 1/2A status for 0.09 and 0.1 engines. I think that's going a little too far, though.

Bill.