Cox Model Engine - The Engines

The Engines

The Cox .049 Engine is a 2-stroke internal combustion glow plug engine. These engines use a glow plug to heat the fuel/air within the cylinder to start. Once running it is disconnected and operates in the same manner as a diesel engine. The self ignition is due to the heat produced from the compression of the air/fuel mix, and the catalytic reaction of the platinum element in the glow plug and the methanol in the fuel and does not depend in any way upon the continued use of the battery. Fuel intake to the engine is controlled by a simple needle valve and venturi system. Fuel/air mixture intake to the crankcase is controlled via a reed valve or rotary valve depending on the engine design.

In a reed valve engine the valve is drawn open by suction as the piston moves upward on the compression stroke. As the piston moves down on the power stoke, the pressure in the crankcase causes the reed valve to close. The fuel air mixture in the crankcase is then forced past the piston via the transfer/bypass ports in the cylinder. One characteristic of a reed valve is that the engine will run in either direction; an advantage for a "pusher" model but a disadvantage if the engine is finger started, as it may start in the wrong direction. (The Cox engines employed a starting spring which kept fingers free of the propellor and generally ensured correct rotational direction.)

On rotary valve engines the process is similar except instead of a reed, a rotary valve is used (incorporated in the crankshaft), which opens and closes as the piston moves up and down. The rotary valve is more efficient and adjustable (at design time) as there is a larger and clearer path to the crankcase than in the reed valve setup, but such engines can run in only one direction; pusher configurations require a special propellor, sometimes difficult to find.

The fuel used to power the engine is called Model Engine Fuel, a mixture of methanol (70%-40%), castor oil (20%) and nitromethane (10%-40%).

The Cox line of reed valve engines designed prior to 1960 used a rear reed valve induction system. In the late 1950s they played around with rear rotary valve induction (as used in the RR1) before moving forward with front rotary valve induction for their Tee Dee and Medallion lines.