So far microlights and self-launch gliders have been propeller driven. Small jets have been used before but poor static thrust means take-off runs are impractically long and fuel consumption high.
In gliders, engine and propeller systems that erect create so much drag that should the engine fail to start work load increases and flight safety rapidly deteriorates, especially when low. Electrically driven nose mounted folding propellers have recently appeared, but the battery systems these need are heavy, costly, weigh the same whether full or empty, and have limited life before expensive total replacement is required. Affordable light-weight long-lasting battery technologies appear some way off yet.
Small jets are simpler, commonplace and more reliable, but relatively thirsty. Suitable fuels are, however, very cheap, and you carry only as much fuel as you need for the planned sortie.
Small jet turbines cannot accelerate quickly enough to provide a reasonably short take-off. To supplement turbine thrust we are electrically driving the main wheels to provide the initial sprint needed to quickly reach take-off speed. Once at flying speed the turbine can efficiently power the climb away.
Small turbines are compact and light weight with few moving parts and low vibration when compared to reciprocating engines. A fixed engine installation removes all of the weight and complexity inherent in retractable petrol engine and propeller systems.
Turning the engine on (and off) is a simple automated procedure. A small airscoop is all that opens (and closes), the engine itself remains inside the fuselage, so in flight the turbine can be turned on and off easily with glide performance little affeced.
Our engine is the AMT Titan producing max thrust of 390N. This engine is a tried and tested unit with a long in-service record.
Maintenance is on-condition and most routine maintenance and inspection can be pilot/owner conducted in accordance with the engine manual provided.
Various fuels may be used including domestic kerosene, diesel (incl agricultural, recycled and bio-diesel types) paraffin, JetA1 and JP4.
Take-off and climb to 2500’ should consume about 6.5 litres of fuel (e.g. domestic kerosene at 45p/litre – Dec 2014) – a low launch cost. At cruise or cruise/climb the turbine thrust is reduced to about 20% and fuel consumption is less than 500cc/minute.
Planned fuel capacity is currently 34 litres (may change) and again, to reduce complexity, the wings are dry with all fuel in one fuselage centre section tank.
Our high-torque brushless motor (image of motor at left) is a standard unit customised for our use profile and with a purpose built controller from the motor manufacturer for true technical compatibility.
The motor provides the initial pre take-off sprint, quickly accelerating the aircraft to flying speed. The short peak output for the sprint means required battery capacity is minimised reducing weight and cost.
Electrically driven wheels also provide for taxi capability before take-off and after landing – without running the turbine.