Why Are Paramotor Engines Usually 2-Strokes?


If you’ve ever flown a paramotor, then you know that characteristic whir of a two-stroke engine powering you forward through the air. I love that sound! That’s not the only reason 2-stroke paramotors are so popular though.

Why are most paramotor engines 2-strokes? Paramotors use 2-stroke engines instead of other types of engines such as electric or 4-stroke engines, because they are cheaper to make, easier to fix, and have a better power-to-weight ratio compared to other kinds of engines.

But have you ever stopped to wonder exactly why two-stroke engines are usually used to power our paramotors? Today we will take a look at the reasons why this is so, as well as the downsides of two-stroke engines, and where the sport may be headed in the future.

Power and Weight

The main reason paramotors use two-stroke engines is that they pack the most power into the least weight. When you think about it, it makes sense: When you are flying, your biggest need is to have the power to climb higher and to get to where you are going.

This need competes with a different need, which is that when flying you need your engine to be as small as possible and weight as little as possible.

Generally, when you are trying to make an engine more powerful, you need to make the engine heavier and give it more volume. So you can see how these two needs are competing at each other.

Two-stroke engines give the most power for their weight – the most bang for your buck you could say – when compared to the other types of engines out there.

It does it because of how two-stroke engines work. “Two-stroke” means that the engine pistons have two movements that they make per cycle: they move up and they move down. The gas ignites and the piston is pushed back, and then more gas is loaded as it is compressed again.

When you compare this to the movements that a four-stroke engine makes, you can see where the power difference comes from. Four-stroke engines make four movements per complete cycle.

They inject the gas as the piston compresses it, ignite the gas and let the explosion push the piston back, release the exhaust, and move the piston back to the starting position to allow the gas to enter again.

Even if you don’t fully grasp all of these technical details, the main picture is easy to see: whereas two-stroke engines burn gas every time they are compressed, four-stroke engines burn gas every other time they are compressed.

This means that they are burning fuel in half as many cycles as a two-stroke engine, and thus they give about half the power output for the same size engine.

To get the same amount of power, a four-stroke engine usually weighs about 50% more than a two-stroke engine with an equivalent power output. That is a major jump, especially in an aircraft, where weight is a very large concern.

Since a two-stroke engine makes for the best balance between these two needs – the need to have a low weight and a high power output – it is clear to see why it is a very popular engine for paramotoring.

Cost

Two stroke engines are also just cheaper to make. They require less complexity, fewer parts, and less space. Because they require fewer materials and time to make, the cost comes out lower.

Size

Weight is a big factor when flying, but so is size. Two-stroke engines pack more power into less space than other engines, and therefore you can get away with a smaller engine when flying with a two-stroke.

Easier To Repair

Because two-stroke engines have reduced complexity compared to other engines, they are easier to work on and cheaper to get repaired when they break.

If you are mechanically inclined, it means that the average person has a higher chance of being able to fix it themselves.

This is actually handy when you are a paramotorist because most places don’t just have a paramotor repair shop you can go visit whenever something goes wrong (although your local lawnmower shop may be able to help you out).

Cons

All of this isn’t to say that two-stroke engines are the perfect little engines without any downsides.

For all of their benefits, they actually have a few significant drawbacks, which have caused some people to take a second look at four-stroke engines on paramotors (which we will look at later on in the article).

Shorter Life

Two-stroke engines wear out faster than four-stroke engines do. This has to do with the fact that they don’t have a built-in lubrication system to keep everything oiled.

With a four-stroke engine, like with your car’s engine most likely, there is a separate chamber for the oil. When it is time to change the oil, you can dump out the old oil and put in the new oil.

With a two-stroke engine, you don’t do this. They don’t have separate chambers for the lubricating oil. When you use a two-stroke engine, you need to use gasoline that already has oil mixed in with it. This oil keeps everything pretty lubricated as the gasoline burns.

This lubrication provided by the oil in the gas mixture keeps the engine from immediately dying, but it is still not as good as having full-strength oil doing the lubricating. This is why two-stroke engines do not last as long.

It may actually surprise you how fast these motors can go out. While most will get you at least 300 hours of flight time, 500 hours of flight time is considered pretty old for a paramotor engine.

Inefficient

Remember when we discussed how the two-stroke engines push out the exhaust and spray in the new gasoline at the same time? Well, this makes it possible for some of the gas molecules to escape out with the exhaust without ever even being burned.

This is a loss of energy you have already bought and is a source of inefficiency for two-stroke motors.

They Burn Oil

Two-stroke engines need oil mixed in with the gasoline. Exactly how much will depend on the exact mix ratio of your engine, but it is usually around 2 to 3 ounces per gallon that you will need to mix in.

Paramotors burn about a gallon of gas per hour of operation, and so this means that you will have to buy a whole gallon of oil for every 50 or so hours of flying.

More Pollution

Two-stroke engines let a little bit of the gas/oil mixture slip out every time the piston cranks.

This, combined with the fact that they burn overall less efficiently and with the fact that they burn oil as they run, means more chemicals and pollution are released into the air when compared to the emissions of a four-stroke engine.

But Wait – What are People Saying About This New-Dang-Fangled Four-Stroke Engine?

That’s right, there is a new chapter in this story. Recent engine technology has allowed a few manufacturers to come out with a four-stroke paramotor engine. Some people are calling them the “best engines ever.”

While I can’t personally vouch for them, because I have never flown one, their basic statistics are impressive: their fuel consumption is about two liters per hour (which is almost half of the standard gallon per hour that most two-stroke paramotor engines require).

Even so, it’s power output is in the same range as normal engines, at around 30-35 horsepower. And most that I have looked at so far weigh just about the same as the traditional engines do.

So what’s not to like? I honestly don’t see any reasons why four-stroke engines will not continue to increase in popularity with time. While their cost is higher, so it is with every new technology. I am excited to see what can come of this welcome development.

So I hope you have a quick understanding of the reasons why most paramotor engines are two-strokes. Traditionally, they pack the most power for their size and weight.

But four-stroke engines with newer technology are starting to challenge the status quo and may change everything in the future. We will just have to see how this all plays out!

Related Questions:

Do the sparkplugs in paramotor engines fire every cycle? The sparkplugs fire every cycle in any two-stroke engine. This is because gasoline needs to be burned every time the piston is compressed. However, in a 4-stroke paramotor the piston goes around twice in the engine, so the spark plug fires every other rotation. Electric paramotors do not have spark plugs.

Are there any electric paramotors? Electric paramotor motors do exist, but they are very expensive and not widely used. Instead of buying gasoline as fuel, you only need to spend a few hours recharging the battery. They are very reliable and do not require a lot of maintenance, but the gap between the lesser power and flight time of an electric paramotor compared to a gasoline paramotor is too great for many people. Most electric paramotors have an hour of flight time, tops.

Geoff Southworth

I am a California native and I enjoy all the outdoors has to offer. My latest adventures have been taking the family camping, hiking and surfing.

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