I realize Mr. Baxter does this sort of thing for a living, but I respectfully disagree that you have to turn the ST 90 at 12000 on the ground to successfully fly it. That may well be where the specs say it will develop maximum horsepower (not that H.P. means much with model airplane engines), but that will not necessarily be the best engine/airframe combination.

As an example, we used to fly the OS FSR or VF engines with 11x7 to 11x7.5 props, with tuned pipes, in the old "go fast" pattern style. These 61 engines would turn around 14500 to 15000 on the ground, probably coming close to the 17000 in the air that OS showed as the rpm to produce the HP figures in the specs. We found that we could use longer tuned pipes and go to 12x10 through 12x12 props, which quieted the noise down (noise rules came in) and the performance surprised most of us. OS did come out with long-stroke engines which may have turned the longer props even better, but the short-strokes did a admirable job. And they didn't fall apart from this use either.

With noise problems losing RC fields across the country, it makes some sense to turn lower rpms and cut the noise down. No desire to flame anyone here, just an honest difference in opinion based upon a long acquaintance with model airplane engines.

Clair