ZDZ 40 RV-L

MODEL AIRPLANE NEWS ENGINE REVIEW

A powerful, lightweight gasoline engine with rear induction

The popularity of gasoline engines used in giantscale models is at an alltime high. There's no question that they are reliable, easy to start and adjust and economical to operate. If there's anything about them to criticize, it would be that the average gas burner is big and heavy when compared with equally powerful 2-stroke glow engines. This is because most popular gas engines can be traced back to industrial applications such as chainsaws, lawn trimmers and other power tools. This is no longer the case with the new generation of engines specifically designed for model airplane use. They are lighter and more compact and enjoy great popularity, especially with the scale-model building fraternity.

RC Showcase (RCS) specializes in designed-for-model-airplane-use powerplants and offers many excellent lightweight and powerful engines. (See my RCS 1.40 engine review in the December 2000 issue). RCS also distributes the ZDZ engine line that includes the 40, 60, 80, 120 and 160cc engines. For this review, I ran the new ZDZ 40 RV-L engine. Let's take a closer look.

FIRST IMPRESSION

The first thing you'll notice when you hold the 40 RV-L in your hands is that it just doesn't look like a gasoline engine. It's more like a high-performance glow engine with its narrow front end and rear-intake layout. The engine is also very light for a 40cc (2.4ci) gas burner-2.9 pounds without ignition system! A reason for this is that it comes equipped with an electronic ignition system; there's no magneto, coil, or condenser. In general, I prefer rear-intake engines because their internal layout produces a very strong crankshaft, and these engines can be concealed easily in a scale airplane's cowl.

The ZDZ 40 is not just a rear-intake engine; It is equipped with a rotary-disc intake valve (see sidebar on next page). Another nice feature is its 6-bolt prop-hub assembly; it improves scale appearance and prop-attachment security. There is no single-bolt option for the engine, nor is it recommended by RCS. All things considered, the 40 RV-L looks and feels like a high-quality piece of equipment.

ENGINE CASE

Another reason the engine is so light for its size (the "L" in its name stands for "lightened") is its three-piece, investment-cast cylinder and crankcase. The engine is manufactured with very little unnecessary material while still maintaining adequate support for the piston and main bearings. The cylinder and rear end plate are bolted to the crankcase and sealed with gaskets. The cylinder has three transfer ports molded into place, and the internal surface of the cylinder (there is no sleeve) is plated with Nikasil. This material is used in highperformance marine and motorcycle engines and is

a durable blend of siliconcarbide and nickel. The plating is very hard and slippery (minimizing internal friction) and has good heattransfer properties. The forged piston and connecting rod are connected by a hefty wristpin that's held in place with two C-clips. The flat-head piston has an iron ring, and both the upper and lower ends of the connecting rod are equipped with caged roller bearings for reduced friction.

The solid crankshaft is supported by two large SKF sealed ball bearings and has a large counterbalance web and crankpin. Because the crankshaft is not drilled out and machined to form a front intake valve, it remains rigid and strong. The front end of the shaft is drilled and threaded for the propalignment shaft that also secures the prop hub assembly in place. A slot is milled into the front of the shaft to fit a I-inch-long key that prevents the hub from turning around the shaft.

The rear end plate is also equipped with a caged roller bearing that supports the rotarydisc intake valve. The steel valve is held in place with a pan-head machine screw, and a slot cut into the front face of the di sc mat es with an extension pin that protrudes from the main crankpin. The large intake passage is cast in place and is directly fed by a Bing 48 pumper carburetor. Two bolts hold the carb in place, and a phenolic spacer separates it from the case and prevents the carb from getting too hot. If you remove the carb, be sure you reinstall it so that the pressure transfer holes in the end plate and spacer line up with the carburetor's pressure-induction hole. If they don't line up, the carb will not function properly.

IGNITION SYSTEM

My engine came with a Brisk UR17 resistor spark plug and a nicely designed locking collar. You slip the plug into the collar before you screw the plug into the cylinder head. A small setscrew tightly secures the metal spark-plug cap within the collar. The cap can be quickly and easily removed-no clumsy twisting and tugging required here!

The high-tension spark-plug lead is covered with a metal shielding that helps prevent ignition "noise." The Falkon ignition module has a compact metal case and features a microprocessor-controlled advance/retard function. Its voltage range is from 4.5 to a maximum of 6 volts. Because a fully charged pack can deliver more than 6 volts, 5-cell NiCd packs without a voltage regulator are not recommended by RCS. I used a Fromeco Reliaswitch (available from RCS) with my 5-cell, 1000mAh battery pack. At full throttle, the average current drawn from the ignition battery is about 600mA.