Ever looked at a model airplane and wondered what makes it roar to life? It's all about the engine, and understanding their size can feel like deciphering a secret code. For most of us who tinker with radio-control (RC) airplanes, the heart of the machine is often a glow-plug engine. You might hear them called 'nitro' or even 'gas' engines, and it can get a little confusing.
The term 'gas' is a bit of a catch-all, especially in North America, where it usually means gasoline. 'Nitro,' on the other hand, often comes from the world of RC cars and refers to glow-plug engines that use nitromethane in their fuel. While true gasoline-powered 'gas' engines are gaining popularity in the RC airplane scene, glow-plug engines are still the most common.
Now, let's talk about how these engines work, because just like their full-size counterparts, they come in two main flavors: 2-stroke and 4-stroke. Think of it like this: a 2-stroke engine fires its spark plug once every single turn of the crankshaft, while a 4-stroke takes two turns to get one firing. You can usually spot a 4-stroke by those little external pushrods that operate its valves – a simpler 2-stroke engine doesn't have those.
Historically, 2-stroke engines have been the go-to for RC planes. They're generally more powerful for their size, easier to get running and maintain, and, well, cheaper to buy because they're simpler to build. If you're just starting out with a trainer plane, it's very likely designed for a 2-stroke.
However, that doesn't mean 4-strokes are out of the picture. They're fantastic for planes that need a bit more torque at lower speeds and, importantly, they're much quieter. That lower, more realistic rumble makes them a favorite for scale models that mimic real aircraft. You might also notice that when manufacturers suggest engine sizes, a 4-stroke recommendation will usually be larger than a 2-stroke for similar performance. For instance, a '46' size 2-stroke might be replaced by a '61' size 4-stroke. It's all about balancing speed versus 'grunt' – 2-strokes tend to push planes faster, while 4-strokes offer more pulling power.
So, how do we actually measure these engines? For glow-plug engines, the size is usually given in cubic inches, but expressed as a number representing 1/100th of that. So, a .40 cubic inch engine is simply called a '40,' and a .61 cubic inch engine is a '61.' You'll often find this number stamped right on the engine's crankcase. Planes are often designated by the same numbers, meaning a '40 size plane' is built to accommodate a 40-46 engine.
Gasoline engines, on the other hand, typically use cubic centimeters (cc) for their size, like a DLE-85, which is 85cc. When comparing a 4-stroke to a 2-stroke, as a very rough guide, you can expect the 4-stroke to need about a third more displacement for equivalent power. Of course, modern engines are getting more efficient, and there are always variations between brands and specific models, so this is just a starting point.
When you're looking at glow-plug engines, you might also encounter terms like 'ringed' and 'ABC.' This refers to how the engine seals its compression. A traditional 'ringed' engine uses a piston ring, much like a full-size car engine. An 'ABC' engine, however, uses a tapered sleeve and different materials – aluminum for the piston and brass for the cylinder – to create the seal without a ring. It's a subtle difference in engineering, but it affects how the engine performs and wears over time.
