In the May issue of Model Airplane News, Dave Gierke ran a "shoot-out" between 10 standard muffler equipped, sport .60'ish engines.

Besides the power, reliability and cost effectiveness of the engines tested, we can all learn what the best props are, for these engines.

With the exception of the engines that were first and second in torque and in horsepower; the Fox Eagle .60 ABC and the Tower Hobbies .60 ABC (actually ABN) and the TT GP-.61 (which developed its maximum horsepower at lower RPM) all the other 7 engines developed their peak horsepower figures, at between 12,950 and 13,400 RPM.

When selecting the correct prop to use on an engine, we must take into account the model's weight and speed. But even more importantly, we must use a prop, which will spin statically at an RPM, which is around, or above the point of peak torque.
At the same time, this prop must, in top speed, level flight, spin as close as possible to the point of maximum horsepower.

If an engine makes its maximum horsepower at 13,000 RPM and "unloads" about 1,500 RPM in top speed level flight, it must be propped on the ground, with a prop that would spin as close possible to 11,500 RPM. No more. No less.

This, if maximum engine performance is to be realized in flight.

When the plane is in a dive, the engine will exceed the maximum horsepower RPM.
But this will prevent excessive speed in the dive, because due to the excessive RPM, the engine is making less horsepower.

Selecting a prop that will keep the engine at the point of maximum torque, will maximize the static thrust developed by the engine.
But static thrust is important only in static situations; hovering, for example. It is much less important in the dynamic, other 99% of the flight envelope of most models.

Unless you are flying a 3-D model, where maximum static thrust is a must, prop the engine for maximum dynamic horsepower.

If you fly a large, heavy, high drag model, use a prop with a pitch of 4-6 inches that would spin at 11,500 RPM on the ground.
If you have a lighter, slicker ship, use a 7-10 inch pitch prop, that would spin at 11,500 RPM on the ground.

This all goes for an engine that develops its maximum horsepower at 13K RPM. If your engine is at its best at only 12K, prop it at 10.5K static. if your engine makes its best horsepower at 15K, prop it at 13.5K static.

There are other propeller manufacturers besides APC. Master Airscrew, Bolly, Zinger and Top Flight, just to name a few.
If you cannot find a prop from one manufacturer, which fits the prescription, you can always try another manufacturer.

Sincerely,