Sage Model Engines
“Tapper” Stirling Engine
This engine is a Ringbom type Stirling engine designed by James R. Senft from the book “Miniature Rinbom Engines”
The odd aspect of this engine is that it has a free displacer piston. Tapper is heated by an alcohol flame about the size of a birthday candle. After about 15 seconds of heating, if the flywheel is nudged into motion it begins to oscillate back and forth. After another 15 seconds the engine goes into full stroke operation. After passing over top dead center for the first time it begins to run with continuous rotary motion. The top speed of the engine is about 900rpm. The engine runs well in either direction. If left unloaded the engine will reach it’s overdriven limit and runs erratically but a slight load will return it to a rhythmic tapping operation. It is obvious to the casual observer that the displacer is free of mechanical connection with it’s upper end seen bobbing up and down driven by varying vacuum and pressure pulses in the cylinder. The hot end cylinder which houses the displacer is made from stainless steel to withstand the flame.The displacer is a closed but hollow tubular assembly much like a closed cigar tube and is free floating in the hot cylinder. The power piston is grahite and so requires no lubrication. It’s cylinder is brass. The two cylinders are connected by a piece of tubing at the top.