Think about what you wrote.

It's true of *any* engines.

In fact, an 0.049 "swinging a 13/6 @ 10 grand" will generate exactly the same amount of thrust as a 150cc gasser "turning the same prop at the same rpm"

The same prop will always generate the same thrust at a given RPM, regardless of what's turning it. It's *whether* the engine can turn the prop at those RPMs that matters.

In the case of a .90 like the ST, the 13x6 is really the *best* prop to harness it's useful power. Sure, you can run bigger props but they won't produce as much power.

What people seem to forget is that we generally grossly over-prop our engines because of noise and efficiency constraints.

Look at the manufacturer's figures -- they're often quoting the maximum HP at 15K-16K RPMs. To get those kind of revs out of a .90 you need to run an 11-inch prop.

My 175Kph "high wing trainer" has a TT61GP in the front. People can't believe how fast this thing flies or how much power I get out of that engine. How do I do it?

Well I only run 5% nitro but I don't load it down with a 12 or 13-inch prop. It turns a 11x7 at around 14KRPMs -- that puts it closer to the peak of its power curve but still allows the use of a prop that's efficient enough to make use of that power.

Yes, it's noisier than it would be on a 12x6 or bigger prop -- but I want power and prop it accordingly.