Small wonder

A UK developer of innovative model aircraft engines looks set to cash in on an increasing global appetite for small, fuel-efficient motor scooters.

Dorset engineering firm RCV Engines has been supplying its Rotating Cylinder Valve (RCV) internal combustion engines to model plane enthusiasts since 1997, but now a larger and more advanced version of the system is expected to appear on scooters manufactured by Taiwanese company Motive Power Industry (MPI).

Brian Mason, RCV’s head of product development, claimed that the technology provides distinct potential benefits over conventional two and four-stroke engines in terms of increased performance and improved fuel consumption.


And with exhaust emissions regulations forcing manufacturers to abandon polluting two-stroke engines in favour of more expensive four-stroke units, Mason said that the technology is well-suited to a number of small engine applications.

While the engine shares the same induction, compression, power and exhaust strokes found in a conventional four-stroke engine, the big innovation lies in the way that the cylinder is configured.

In a conventional IC engine, gases enter and leave the cylinder via poppet valves in the head which are operated via a mechanical valve train. The cylinder in the RCV, however, is suspended between two bearings, and is driven by the crankshaft either via a gear train or toothed belt drive system. A gear at the base of the cylinder meshes with a reduction gear on the crankshaft which causes it to rotate at half of the shaft’s rotational speed around the piston.

At the top end of the rotating cylinder there is a single port leading to the combustion chamber. This is surrounded by a fixed timing ring with three radially arranged ports; inlet, ignition and exhaust. This simple valve arrangement serves the combustion chamber as the engine cycles through the conventional four cycles. The rotating cylinder is effectively combined with the rotary valve in a single component.

Mason added that because most of the major components of an RCV engine are identical to those of a conventional four stroke, the engine is relatively simple to manufacture.

The engine configuration is fundamentally similar to that used on the high-performance Sleeve Valve engines used on a number of world war II aircraft. However, while these engines delivered impressive performance benefits, wider take-up was limited by the problem of effective valve sealing. Typically, close tolerances were relied upon to achieve sealing during operation.

This made such engines both relatively expensive to manufacture as well as requiring lengthy and controlled warm-up procedures to avoid seizure.

Sealing system

Mason claimed that his company has solved this problem with the development of simple cylinder valve sealing system which employs essentially the same basic principles as used in piston rings. The seal mechanism contains just four, low-cost components and to accommodate the thermal expansions typical of engine operation, the valve has an ‘active’ sprung sealing mechanism.

RCV has already developed a prototype 125cc engine for MPI, which Mason claimed has exceed all performance expectations. He said he is confident that he will soon be announcing a major deal to license the technology to the scooter maker.

The company believes the technology has massive potential in parts of southern and eastern Asia where the market for small motorbike and scooter engines is huge.

Indeed, India alone produces more than six million two and three- wheeled vehicles each year, most of which are equipped with engines of less than 250cc.

Mason added that RCV is also investigating opportunities in the power tools and forestry markets. He said that promising discussions are underway with a number of interested companies, and that the company hopes to demonstrate a chainsaw powered by its engine within the next few months.