A well-rounded performer

Model Airplane News, Jul 2002 by van Mourik, Dick

FINAL APPROACH

Scratch-built engines are rare in RC models, and radials are even rarer. Designing, building and operating your own 5-cylinder radial is daunting, to say the least. Dick van der Veldt of the Netherlands picked up the gauntlet, and the result is the Penta 54 engine you see here. The story of this engine starts in 1999, when Dick was shown a German plan for a radial engine while visiting a fellow club member. At the time, Dick was building an 18-percent FW-190, and no available radial engine would fit the model without protruding through the cowl.

Although nothing was wrong with the basic layout of the engine on the plan, Dick wasn't satisfied with the construction. Furthermore, the diameter was too large for his purposes, so he decided to design his own radial. An engineer by profession, Dick had access to all the machinery needed for such a massive job, so he drew up his design and started construction in July 1999.

The prototype 5-cylinder radial had a bore of 23.4mm (0.92 inch) and a stroke of 24mm (0.94 inch), giving it a displacement of 52cc (3.15ci); hence, the designation "Penta 52." Because it was to be fitted in the FW-190, the engine diameter could not exceed 230mm (9.05 inches). It used valves, pistons and piston rings from the popular Saito FA-50 as well as a SuperTigre Mag carburetor and O.S.-type "F" glow plugs.

The engine features some interesting design aspects, including a completely separate front and rear crankcase. Lubricating the valve gear can be a real problem with this kind of engine, but Dick solved this by using a separate oil chamber in the front of the crankcase. This allows the engine to be run on fuel with relatively low oil content. He used Saito pistons, and he made the linings out of nitrated C 45 steel, honed for better surface quality. He made the valve rods (a sensitive part of any 4-stroke engine) of hardened steel. The radiuses on the lower end run in a small hemispherical dent in the cam rod.

The cam plate itself is made in two separate pieces that are bolted together; this enables the engine to be run in the opposite direction when the inlet and exhaust sides are reversed and the two parts of the cam plate are repositioned. This makes the engine suitable for twin setups.

The entire concept is well designed and allows adjustments to be made without modifications to the basic engine. For instance, different carburetors can be fitted, and experimenting with these requires only that you loosen three small screws.

The engine first ran on New Year's Day 2000, which means that the engine went from concept to working model in about six months-an amazingly short time, considering how much of the engine was homemade. It was put through its paces on a test stand, where the results were very promising. At only 5.8 pounds, the engine turned a Menz wooden 20x8 prop at 7,000rpm and was able to run as low as 1,500rpm. No glow driver was needed at lower rpm.

Dick decided to build a small run of six engines. He made some minor improvements to the prototype Penta 52; the revised design was renamed "Penta 54." Saito valves were again used on the 54, but Dick made his own pistons and rings. The aluminum pistons have been anodized to improve their mechanical properties. While he was at it, Dick increased the bore slightly, and this added horsepower; the engine now turns a Menz 20x10 prop at 7,000rpm.