Tests using heavy fuel are under way for an aluminium nutating engine that could deliver the power density that the US military requires from its internal combustion powerplants.
A nutating engine uses a disk that "wobbles" inside a housing so that its edge pitches up and down, creating voids that increase and decrease in volume. The wobble is known as nutation and effectively each disk takes the place of four pistons as each disk has four voids.
The aluminium version is considered the second generation, following a first-generation steel prototype. Development of the nutating engine has been supported by the US Army and continues to be by the US Air Force Research Laboratory (AFRL).
For AFRL an 150hp, 40.9kg (90lb) aluminium nutating engine is being developed by Illinois-based Kinetic Research and Development as part of a joint venture with another US company, Baker Engineering.
Nutating engines are expected to achieve a power density that would enable a 14.7kg (32.5lb) powerplant to produce 50hp (37.3kW), which the US military says cannot be matched by other internal combustion systems. A 50hp engine with a mass of 14.7kg has a power to weight ratio of 1.54. However Kinetic and Baker's aluminium nutating engine will achieve a power to weight ratio of 1.6 if its combustion tests are successsful.
According to Kinetic Research and Development president Michael Boruta, "this [aluminium] engine would be good for a [General Atomics Aeronautical Systems] Predator size class of [unmanned air vehicle]," and he added that testing is now "concentrating on combustion" with a focus on "different spray patterns, fuel injection methods and timings".
As well as UAV propulsion for near-term applications the US military is also interested in nutation for electrical power generation.
The companies are also developing a smaller 7hp version for miniature munitions propulsion for the AFRL. This has a single disk, the larger aluminium powerplant has two, and after six months of testing the 7hp engine hardware is now being manufactured. The company has another contract, with the US Defense Advanced Research Projects Agency, for a single disk 8hp engine purely for power generation.
Source: Flight International
