Introduction to Nitro RC Engines

"What YOU need to know for choosing the best Nitro RC Engine
for your radio controlled airplanes!"

Nitro RC engines are the most popular type of RC engines. It is common for people to refer to all types of RC engines as “Gas” engines. RC engines that burn gasoline do exist and are primarily used to power large scale RC airplanes.

The vast majority and most popular type of RC engines burn nitro-methane fuel. This airplane fuel is commonly referred to as “glow” fuel because the engines use glow plugs to ignite the fuel.

You can learn more about the different types of glow fuel here. Nitro RC engines are sometimes referred to as “glow” engines for the same reason.

Two Strokes vs. Four Strokes

Ball Bearings vs. Bushings

Ringed vs. ABC

Engine Sizes

Engine Accessories

Operation & Maintenance

Tuning the Engine

Storing the Engine

Where to Buy Engines

Two Stroke vs. Four Strokes

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 RC engines. A 2-stroke RC engine fires every time the piston reaches the top of the cylinder. A 4-stroke fires every other time.

Because the 2-stroke fires every revolution it has a high pitched whining sound when running. Two-cycle engines are cheaper and require less maintenance because there are fewer moving parts. The design of a 2-stroke engine is very simple as camshafts and rocker arms are not needed to open and close the valves. Two-stroke RC engines have a higher power to weight ratio than 4-stroke engines. Most beginners start with a 2-stroke engines because they are cheaper, easier to maintain, and easier to tune.

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 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 engine. 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. Bushings

nitro engine ball bearing Some nitro RC engines are available with ball bearings supporting the crankshaft. Others have bushings that support the crankshaft. The picture to the right is what the bearings look like. There are two sets of bearings. One set in the front and a larger set in the back.

I've never had a bushed engine and don't have a picture to show you. A bushing is nothing more than a bronze or brass disc with a hole in the center for the shaft.

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 to the left. The area highlighted red is where the bearings sit in the housing.

If you look at this O.S. 46LA engine to the right you can see that the housing does not have these places for the bearings.

Ringed vs. ABC Nitro RC Engines

ABC nitro powered engine

There are two different ways that nitro RC engine manufactures seal the piston with the sleeve. 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. The picture to the right is 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.

ABC nitro powered engine 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 picture to the left is exaggerated to illustrate 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. 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 whether. ABC engines are more tolerant if you accidentally run the engine slightly too lean.

nitro-engine ring The repair cost for a ringed nitro RC engine is much less that that of an ABC engine. The ring itself is usually the only thing that fails in a ringed engine, provided that you run the engine with the correct fuel mixture. The rings are very easy to replace and are inexpensive. The cost for replacing the ring is typically under $20. To rebuild an ABC cylinder you will need to buy a new sleeve and new piston. As with anything, the sum of the individual parts of an engine cost a lot more than the whole. It is usually not economical to rebuild an ABC engine.

The benefit of an ABC engine is that the break-in time is a lot shorter. An ABC engine will tolerate the occasional lean run, as where a ringed engine will be damaged immediately with a lean run. The benefit of a ringed engine is that it can be rebuilt relatively cheap. A ringed engine will tend to hold its maximum power longer than an ABC engine which slowly decreases in power as the sleeve and piston wear. If you’re new to the hobby I recommend getting an ABC engine. It is much more forgiving and easier to break in. It’s worth noting that just about all four-stroke engines are ringed engines.

Nitro RC Engine Sizes

Hanger9 Alpha40 Trainer RC airplane When you buy a nitro RC airplane it will always have a number associated with it that gives you an idea of what size engine it will need.

For example, the Hangar 9 Arrow 40 would require at least a “40 size” nitro RC engine. The size of the engine corresponds to the displacement of the cylinder.

Evolution.40NT

The Evolution .40NT would be a good fit for the Hanger 9 Arrow 40 nitro RC airplane. An engine slightly larger than the number on the airplane will certainly give the airplane a little more spunk! However, you should never exceed the maximum recommended engine size for any airplane. The maximum recommended size is usually slightly larger than the size of the airplane. For example, the Hanger9 Alpha 40 could be flown safely with a "46 size" engine.

Since a four-stroke RC engine has a lower power to weight ratio you will always need a slightly larger 4-stroke engine then the actual size of the airplane. A 40 size airplane may require a 60 size four-stroke engine. Go by the recommendations of the airplane manufacturer when sizing the engine.

Accessories Needed for Nitro RC Engines

To start your nitro RC engine you must have some means of spinning the propeller. You can either use a chicken stick or an electric starter to flip the propeller. But never ever use your fingers unless you are wearing thick leather gloves. These engines won’t hesitate to put a gash in your fingers! Trust me I know! If the carburetor settings are off you may be flipping that prop with a chicken stick until the end of time before it fires! Everyone has days when their engines just won’t cooperate even with a 12-volt starter. An Electric starter really is a necessity when flying glow-powered airplanes. Save yourself the headache and go ahead and order one ... You will thank me later!

Secondly, you will need a way to provide power to the glow plug. You can use either a glow igniter or a glow plug clip. Both an electric starter and a glow plug clip require a 12-volt battery.

Most people buy a flight box which houses the 12-volt battery and power panel. The power panel clips to the 12-volt battery and supplies power to the starter, fuel pump, and glow igniter. If you stay with the hobby you will definitely have a flight box like everyone else.

When I started flying my goal was to get an airplane in the air with the least amount of money possible. It was hard enough convincing my wife to let me buy the airplane, radio, and engine! So I got by for a little while with a glow stick, electric starter, and a hand fuel pump. I had an old 12-volt car battery that I used to power the starter. This was not exactly an optimal set up, but it got me by until I could save money to buy a flight box, power panel, and a 12-volt battery!

Operation & Maintenance of Nitro RC Engines

A nitro RC engine will last you a lifetime if properly operated and maintained. On the same token, the engine could last a very short time if not cared for properly. The life span of your engine is in your hands.

Breaking in the Engine

Just like any other type of engine, nitro RC engines need to be broken in. While very close tolerances are held when the parts of these engines are machined, a break-in process is needed to allow the moving parts to be “mated” with one another. During this process the piston and sleeve wear together to conform with one another. ABC engines typically require a shorter break-in time than ringed engines.

Some engines such as the Evolution Engines Trainer Power System are broken in at the factory. Regardless of what type of nitro-powered engine you have, it is absolutely critical that it be broken in properly. This critical first step will have a great impact on the life of the engine!

Here you can find more information on how to break in your engine

Tuning the Engine

The most important thing to know about nitro RC engines is that they are cooled and lubricated by the fuel. You, the operator, determine how much fuel is going to the engine by adjusting the needles valves.

If the needle valves are adjusted too “lean”, the engine is not getting enough fuel for lubrication and cooling. The quickest way to destroy an engine is to run it lean! If the needles valves are adjusted too “rich” it means that too much fuel is going to the engine. When the mixture is rich the engine may not run at all, or it will with a lot less power than it's capable off.

The mixture should always be slightly rich to be completely sure it doesn’t lean out while in the air. Finding that sweet spot where it's not too lean and not to rich is called tuning your engine.

Here you can find more information on how to tune nitro RC engines.

Storing the Engine

At the end of each day at the field you need to make sure all of the fuel inside the engine has been burned. When the glow igniter in place, flip the engine over until it no longer fires. This is easy to do with an electric starter.

If you will not be using the engine for an extended period of time (over a month), it is a good idea to run some after run oilthrough your engine. This will prevent the inside of the engine from developing rust.

Where to Buy Nitro RC Engines

If you know what you're looking for, which you do because you have read this page, you can generally save quite a bit of money by shopping on eBay. Just be cautions and make sure the seller has a good feedback rating, especially when buying used engines.

Below are nitro engines currently on eBay. They are arranged by manufacturer. Make sure to click on View all at the bottom of each to see the entire selection.

and start bidding now!