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Small GA-Aircraft like a Cessna 172 or a Piper PA-28 have an engine similar (I think) to the one of a car.

But why don't planes have a gear and a lever to change the gear?

  • Would'nt they achieve a faster prop speed by doing that?
  • Would it be possible?
  • Would it be useful?

Gear lever of a car

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Because there is no link between the wheels and the engine.

When the car is moving slowly, wheels turn slowly so the engine must turn slowly as well. However piston engines do not work below certain RPM, so the gear switching must be implemented even for small cars.

Propeller can always turn at the speed sufficient to sustain the engine running. If the plane moves too fast (or must stand in place), wheel brakes can be applied.

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  • $\begingroup$ "When the car is moving slowly, wheels turn slowly so the engine must turn slowly as well." Sorry, but that's a completely inaccurate analogy of how an engine/transmission works. When the car is stopped is the engine off? You can place your foot on the brake in a car as well, car stops, engine keeps running. In many cars there is no direct link between the engine and the wheels either, the torque converter is in the way (which uses fluid to couple them together). $\endgroup$ – Ron Beyer May 3 '17 at 13:58
  • $\begingroup$ Ae, stop the car by placing foot on the brake and watch your engine still running ... $\endgroup$ – h22 May 3 '17 at 14:29
  • $\begingroup$ The question is about the difference between cars and planes. Most often both have wheels. $\endgroup$ – h22 May 3 '17 at 18:25

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