Sorry for all the posts... my wife is sick of listening to me talk about R/C airplanes...

Anyway, I've come full circle on this airplane with regard to the engine. After installing the Saito 72, I took it out to the field for some flight testing. Unfortunately, the plane didn't perform nearly as well as I hoped with this new powerplant. Uplines ran out of steam very quickly; the plane became mushy at the top of loops; etc. I tried using 15% nitro fuel and various props (even an APC 14x4W) with very limited improvements on vertical performance. I did some additional thrust measurements at home and found that the best thrust I could achieve was around 4lbs 10oz with a 14x6 prop. Although the FA-72 managed more thrust than the OS 50SX, it was far from providing the power needed to push around a 6lb 12oz plane.

So... I went back to the Saito 91 (after considering the new Saito 82a and an OS 61FX). I must say that I wish I had used the 91 in the beginning. Because I had to mount the engine as far back as possible, the CG on the plane actually moved aft, thereby allowing me to remove ~1/2 ounce of lead from the tail. The net result is that even though the FA-91 is 1 3/4 ounces heavier than the 72, my plane only weights about 1 1/4 ounce more. A quick measurement shows that I now get about 6lbs 10oz of thrust spinning a 14x6 prop... so I gain 2lbs of thrust while barely adding weight to the plane at all. One downside is that the 91 really sucks the fuel down so the little 10oz fuel tank only provides about 6-7 minutes of flight time.

A guy at the flight field told me to try 30% nitro in the Saito. He says he always uses 30% in Saitos and gains around 400-500 RPMs at the top end. I did some checking on the net and found that Saito says 30% is fine. Unfortunately, I also discovered that 30% nitro heli fuel is twice as expensive as the 15% stuff (almost $30/gallon for Coolpower). I might try it, but I imagine I'll stick to 15%.

Anyway, I can't flight test the plane until tomorrow because my club is hosting a helicopter fun-fly competition this weekend which is using the airplane runway. I can't wait to see how it performs tomorrow.

Dave