Intro: Second Life of Broken Propeller for Rc Model Planes
Beginner pilots of radio-controlled model airplanes know how often it happens to break a propeller. And even propeller-saver adapter does not always help. One weekend when I had broken my last propeller and the shops were closed, an idea to build an adapter for broken propeller blades came to my mind.
This adapter is based on a cylindrical piece of plastics with height 10 mm and diameter 18 mm with a center-hole for motor axis. On this cylindrical piece of plastic on opposite sides there are 2 grooves at 30 degrees angle made with a hand saw as symmetrical as possible. These grooves will host the propeller blades. The correct angle of the grooves is such that the thin ends of the propeller blades are at 0 degrees climb angle. Groove direction must be chosen correctly such that propeller blade is turning with a leading edge forwards.
The broken ends of the propeller blades must be grinded so that they look equal. Then a 3 mm diameter hole is drilled on each blade. This hole is for the plastic screw that will hold the blades in the propeller adapter. There are two M3 threaded holes in the propeller adapter to hold the blades. The blades are quite free to move in the grooves but the centrifugal force during the rotation aligns them. No balancing was done to this propeller after assembling. There are two more plastic screws on the sides of the adapter for fixing it to the motor axis or for attaching a rubber ring of the prop-saver.
The re-born 7x3 propeller test on a CD-R motor powered electric plane show that it is having good thrust and is only slightly lauder then a new one. It has survived several crash landings and nothing and the blades did not brake. The demonstrated adapter for second life of broken propellers can be a valuable thing for beginners who do not need the maximum performance but instead endurance during the landings.