Self launching glider packs a retractable jet engine
By Darren Quick
August 12, 2010
Gliders that have engines which can be used for take-off to remove the need for catching a tow to altitude by an airplane or a winch are quite common now. Such engines are usually of the electric or small-piston motor variety, but New Mexico-based company, Desert Aerospace, has gone a step further by fitting a glider with a retractable jet engine.
The ‘BonusJet’ is a two seat, high performance, self-launching glider based on the TST-14 sailplane produced by TeST in the Czech Republic. It features a PBS TJ-100 turbine engine (also produced in the Czech Prepublic) on a retractable pod located directly behind the cockpit. The jet engine, which is designed for use in unmanned aerial vehicles, folds down into the fuselage once soaring altitude is reached. A cooldown period of 1.5 minutes is required after engine shutdown before retracting the engine.
Once the engine is drawn into the fuselage retractable doors close over it to form an aerodynamic covering and leave the craft looking like any other glider. Three switches in the cockpit control all the engine's extend/retract/start functions: one opens and closes the doors, one extends/retracts the engine and the last starts and stops the engine.
The engine weighs 42 pounds (around 1/3 the weight of equivalent piston engines) and produces 240 pounds of thrust but does burn through more than 20 gallons per hour. The BonusJet can carry 24 gallons of fuel, giving it a jet-powered flight time of around 1.5 hours. Although, with initial flight tests using the engine showing a climb rate in excess of 900 ft/minute the pilot shouldn’t have to run the engine for very long to reach soaring altitude and the team is projecting a sea level climb performance approaching 1,000 ft/minute.
Desert Aerospace also projects a sea level takeoff distance of 500 ft., with the craft achieving takeoff distances of approximately 700 ft. in tests at the company's home airport in Moriarty, New Mexico, which is at an elevation of 6,200 MSL. The company says this makes the BonusJet's takeoff requirements considerably better than any other motorglider it has compared it with, such as the Stemme, DG-505 and ASH-26E.
Desert Aerospace says phase one flight tests have been completed but is continuing to measure performance with the BonusJet flying regularly as a soaring aircraft. In the near future, the company plans to start selling the BonusJet at a price it says will be much less than existing self-launching gliders from more expensive German manufacturers. Currently the company is projecting a cost of around US$175,000, including jet engine installation, basic instruments and trailer.
Check out the videos below to see the BonusJet in action.