These engines use a special type of fuel that not only provides the energy for combustion, but also serves as a coolant and lubricant. It’s basically alcohol mixed with oil and a touch of nitromethane. Other than the plug and fuel, glow engines work the much the same way as any other internal combustion engine, but there are some distinct differences that are important to know. Two Stroke vs. Four-Strokes Engines There are two types of nitro RC engines used with radio controlled airplanes. There are two cycle (2-stoke) and four cycle (4-stroke) nitro engines. A two-stroke RC engine fires every time the piston reaches the top of the cylinder while a four-stroke engine fires every other time.

Four-stroke engines fire every other revolution which produces a very low pitched growl that sounds a lot like a full-scale airplane! For this reason most large aerobatic and giant scale planes including warbirds use 4-stroke engines. Four-stroke nitro RC engines are also easier on fuel consumption. Four stroke engines can be a bit more tricky to tune than 2-stroke engines. This is really a non-issue if you invest in a good tachometer. Four-stroke nitro RC engines produce more torque at lower RPM’s compared to a two-stroke RC engine.

This means that four stroke will use a much larger diameter propeller than a two-stroke engine. Ball Bearings vs.

RC model airplane engines. When talking about model airplane engines for radio control use, by far the most common type is the glow plug engine, often also called a. Better Sources Chris Bernard Pdf Creator. Two-stroke petrol engines are preferred when mechanical simplicity, light weight, and high power-to-weight ratio are design priorities.

Bushings Some nitro RC engines are available with ball bearings supporting the crankshaft while others have bushings that support the crankshaft. It is easy to tell if a nitro RC engine has bearings or not just by looking at it. Take a look at this O.S. 46AX engine above.

The area highlighted red is where the bearings sit in the housing. 46LA engine on the right does not have bearings.

Although bushed engines are cheaper, they are not nearly as powerful or efficient as engines with bearings. This is because the bearings do a much better job of minimizing friction than bushings do. ABC Nitro RC Engines There are two different ways that nitro RC engine manufactures seal the piston with the sleeve in the bore. It is critical that the piston and sleeve form an airtight seal in order for the engine to produce compression. Some RC engines simply have a ring that goes around the top of the piston that seals with the iron sleeve. This is called a “ringed” engine. To the left is a cross sectional view of the piston/sleeve assembly of a ringed engine.

It is greatly exaggerated in order to illustrate how a ringed piston seals with the sleeve. The portion in red is the ring.

Some nitro RC engines have an aluminum piston that moves in a tapered chrome plated brass sleeve. This type of engine is called an ABC engine for Aluminum, Brass, and Chrome. The above image on the right is extremely exaggerated to show you what the piston/sleeve assembly looks like at ambient temperature. At ambient temperature the inside diameter of the sleeve is slightly smaller at the top of the stroke. The fit between the piston and sleeve gets tighter as the piston rises.

When the engine gets to operating temperature the top of the sleeve expands and the sleeve is no longer tapered. The reason the top of the piston expands is because it sees all of the heat from the combustion. The bottom of the sleeve is much cooler and does not expand nearly as much. When the top of the sleeve expands the piston will fit perfectly with the sleeve at both the top and bottom of the sleeve. Murex mx3 user manual free. When the engine is cold the sleeve only seals with the piston when the piston is near the top of the stroke. This can make ABC engines a little more difficult to start, especially in cold weather.