An internal combustion engine for unmanned air vehicles that uses a disk rather than pistons is undergoing bench testing. The project aims to develop a 16.3kg (36lb) powerplant that generates 77hp (57kW).

Development of the nutating engine has been supported by the US Army and US Air Force Research Laboratory. A single disk wobbles as it rotates inside a housing so that its edge pitches up and down, creating voids that increase and decrease in volume as it spins.

The wobble is known as nutation and the voids take the place of piston cylinders' combustion chambers. The bench-tested engine is a steel construction, gasoline-fuelled first-generation prototype.

"The Army research laboratory wanted it for UAVs," says US company Kinetic Reseach and Development president Michael Boruta. "We are doing combustion studies to understand the thermal dynamics. We are slowly getting closer to the [16.3kg] target."

Boruta's Ilinois based firm has developed the engine as part of a joint venture with another US company, Baker Engineering.

The engine's designers claim a nutating disk has a smaller contact area compared to a piston, will deliver a flatter torque profile and provide 270 degrees of compression on the 360 degree rotation of the shaft.

Boruta adds that with a two-disk system the engine would be the equivalent of an eight-cylinder engine and the injection system design will be key for using heavy fuel.

The joint venture is currently building a second-generation aluminium engine. Another goal for the engine is volumetric, to fit a 103hp unit within 0.02m3 (1ft3). The 77hp engine would have a 0.021m3 volume.

Source: Flight International