After reading Fred Pearce’s famous article “Rubber – All You Need to Know” in the March and April, 1979 Model Aviation magazines I decided to build a torque meter to investigate this topic. The rubber motors we use to power our little airplanes seem very simple; you wind them up and let them unwind. Actually they are very complex. As you wind them up, the torque increases, but it increases along a curve. When the motor unwinds, the torque decreases along a similar but lower curve. Future windings and unwindings are not along the same curves. The rubber will return to almost its original state if left to rest overnight. It is important to understand these things to fit a rubber motor to an airplane and propeller and manage its energy for long flights.

A typical torque meter consists of a piece of steel wire that is fixed at one end and has a hook at the other into which a rubber motor is introduced. As the motor is wound, the torque causes the steel wire to twist. An indicator needle attached to the wire near the rubber end indicates the amount of twist against a scale. You can find many torque meter designs with a search on the internet.