I understand all of that, Dick, But for planes in the 10-13lb range the 160 is the way to go. Not trying to say I'm right because it is all personal preference, but it is not worth the weight penalty for me when the 72" aerobats need as much help as they can get for a decent wing loading. 39 oz with pitts muff ready to go and it will be within a pound or so of thrust from a 40. I'll pay my $.90 per flight for that. I've read they are turning 20x6's at about 7200. Not bad for being 2000 below it's peak power. It will turn a 19x6 at about 8K, haven't put a scale on it but it feels like 18-20 lbs of thrust. 12 lb planes accelerate vertically.

If owners of 2.4's were posting rpms much higher than my 160 or Moki 1.8, I would have one, but they are not. The rpm I am seeing is about the same in the 18-20" prop range. When a 2.4 will turn a 20x10 in the 7000 rpm range, <4lbs for $350-$400 I'll be interested. Just by the numbers, the new 50s coming out are about the smallest I would go, and I have the "I wants" for the DA.

FYI, I truly respect your expertise in this field, Mr. Hanson, Thanks for your opinion.