If you've been lucky, clever, or even perhaps a bit crafty, I expect you have managed to acquire some interesting model-flight goodies for Christmas. Those who can properly manage this sort of opportunity generally ensure that 'what I get is what I want', to purloin and corrupt the computer jargon, so hopefully you have got that particular kit, radio, gadget or tool that you have been so heroically doing without until this festive season!

If all else fails and justification is required (and it's funny the way it so often is!), there is always the 'Christmas present to myself' approach, and that one definitely ensures the perfect answer to your needs.

Having said all that, I'm not telling on what basis I have gained my latest acquisition - a beautiful new engine for the SIG Citabria model which I will be starting to build from the beginning of February, once my new garage/workshop has been delivered and erected.

This is the item in question; the RCV60-SP 4-stroke rotating cylinder valve engine from RCV Engines of Wimborne, Dorset, UK. The engine has just one more moving component than a 2-stroke engine - the rotating cylinder itself. The cylinder is suspended between two bearings, allowing it to rotate freely around the piston; the piston and crank are entirely conventional. A gear formed around the base of the cylinder meshes with a 2:1 reduction gear on the crank. As the piston reciprocates and the crank turns, the cylinder rotates around the piston at half engine speed.

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 4 cycles: induction, compression, power and exhaust. Ignition is achieved through a standard 4-cycle glow plug exposed once only during each complete cycle.

The rotating cylinder is effectively combined with the rotary valve in a single component, hence RCV - rotating cylinder valve. A shaft attached to the cylinder rotates at half engine speed producing high torque and facilitating use of larger and quieter scale propellers.

The rotating cylinder is in-line with the axis of rotation of the propeller, producing an extremely streamlined shape and small footprint as this front view shows, so that the RCV60-SP fits within most small diameter cowlings, giving a typical cowl clearance radius of just 36mm. The engine has behind-the-prop starting using a special top-start adapter similar to those frequently used on model helicopters, but smaller. Coupled with the recommended use of a remote glow connector, it keeps the starting process well behind the prop, making it somewhat less hazardous than is sometimes the case!

RCV claim that use of modern materials and the beneficial honing action between the piston and rotating cylinder minimises any internal wear. With no complex overhead poppet valves, the 4-cycle RCV engine design has proved to be inherently reliable - I just hope they're right!

The RCV60-SP replaces the RCV60 Plus which was apparently in production until August 2000. I do not know exactly what modifications may have been made, although I have been told that the new engine has a thicker and stronger mounting backplate than the earlier model and there is now a nipple fitted to the exhaust to allow the fitting of a pressure feed line to the fuel tank.

The technical information given here is taken from the manufacturer's sales literature and website, where details of their range of engines and propellers can also be found - www.rcvengines.com