Tired of breaking propellers on belly landing airplanes? This is probably the solution you need.

Most modern fixed wing electronic speed controllers (ESCs) have the ability to actively slow and stop a propeller inflight by lowering the throttle to minimum setting. This ESC brake function must be turned on using one of several methods.

There is a great deal more force and likelihood of impact of a windmilling (spinning) propeller and therefore more chance of it breaking even on a normal belly landing.

This video discusses the basic physics of why this happens and how to activate your ESC brake.