Sagita Sherpa hot air-powered helicopter in the ULM-VLR (Ultra Léger Motorisé – Very Light Rotorcraft) class. Is based on the TDR transmission system technology, to simplify the helicopter design for better reliability, safety and profitability.
How Sagita’s engine works:
The engine drives a compressor that takes in air at the rear of the fuselage.
Part of the compressed air feeds the engine, the balance bypasses the engine, collects the heat of the cooling system and is eventually mixed with the engine’s exhaust gases in order to raise the temperature to 100°C (212 °F).
The hot compressed air is then sent to the rotor and expanded in two contra-rotating Ljungström type turbines.
Each of these turbines drives directly one of the two contra-rotating coaxial rotors. The air exits the turbine through a circumferential gap between the two rotors.
The transmission system requires no lubrication, no cooling and no tail rotor drive. Its efficiency is about 85%.