A question to knowledgeable aviation people . . .

Not all of them, no. Small aircraft, like Dusty, would be fitted with a reduction gearbox to limit the rotation speed of the propeller to a safe speed. Maru says near the end that he has an epicyclic gearbox, which is very efficient, but very complex and difficult to fix.

The better question would be why Dusty, now a world famous air racer, would not opt to have his engine and gearbox replaced, or why he was not aware that he was using parts that were so difficult to repair or replace. Logically, a plane that would be flown over oceans would be checked for such a vulnerable failure point.

The aircraft that the "Dusty" character is based on (Cessna Ag Cat?) actually uses the P&W turboprop engine, not a piston engine.

That being said, there's lots of piston engines that use reduction gearing. For example, Rotax engines are ubiquitous in LSA/ultralight planes and generally operate at much higher RPMs than you'd want to swing a prop. I think most of the small 2-strokes use reduction grearing. There are a few larger Lycoming/Continental engines that use reduction gearing but I think it's uncommon.

Thanks for sharing your knowledge, Longbow503 and tatohead. The fact that Maru says near the end that he has an epicyclic gearbox, shows that the Pixar screenwriters were trying to lend credibility to the story scenario to avoid disappointing the aviation enthusiasts that are watching the film.

But, Longbow503's observation shows that this story scenario is flawed for consistency with the events in the first planes film.