Bill,
Tower Hobbies only has the APC prop in the 9x6 size. Do you know of a source for 9X5 APC pushers? The rear engine is a screamer in the air. It really unloads. Only the rear engine can be heard. There is no syncronization rhythm change and I miss that. I have not checked it with a tach while the front is running but it probably is up around 13,000 on the ground. I have wondered if some of the screaming comes from the wing acting like a drum. The trailing edge of the wing is just 3/16 inch from the trailing edge of the prop. Wish I had more room there. What do you think? I have a 9X4 to try on the front also. I added winglets to the wing and I think, but am not certain, that I imroved the takeoff performance. Rolls are faster in the air. Next weekend I'm going to put on the 9X6 prop again to see if I can credit the winglets for better takeoffs. I lost the front engine and the rear one just kept on screaming and I could maintain altitude. This one is a keeper. I'll have photos soon.