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Turboprops and piston engines are two of the most common airplane engines. Let’s examine turboprop vs piston engines to see the differences and which is better.
Turboprop engines and piston engines have one major thing in common — they use propellers to generate thrust. Turboprops use a turbine spun by exhaust gasses to spin the propeller, whereas piston engines use the rotation of a crankshaft to directly spin the propeller.
Piston engines have been around since the early days of flight, whereas turboprops are relatively new on the scene. So it’s safe to assume that these two engine types are entirely different from one another. In this article, you’ll learn what each one is, how they work, the differences between them, which one is safer, and which engine design is better.
At SkyTough, we strive to publish nothing but the best, most helpful content on the web for our readers. For an article topic like this one, that involves a combination of extensive research from us and discussion with (and input from) other experts in aviation. So when you’re done reading this expert comparison, all of your questions about turboprop vs piston engines will be answered.
What Is A Turboprop Engine?
A turboprop engine is a type of jet engine, or gas turbine engine — jet and gas turbine often refer to the same thing. But they do still use a propeller, hence the name turboprop. The easiest way to think about a turboprop engine in this comparison is to think of a turboprop engine as a crossover between a normal jet engine that you see on many types of planes and a piston engine. We’ll of course touch on the latter shortly.
Like all jet engines, a turboprop streamlines the internal combustion process of the engine into a blur of simultaneous operations. Air enters through the front of the engine through the intake and then passes through a compressor (or a series of compressors), where both its pressure and temperature are greatly increased.
The air then moves along into the combustion chamber where jet fuel is introduced and mixed with the hot pressurized air. The mixture combusts and the explosive force jettisons the hot exhaust air towards the rear of the engine. With a turboprop, this exhaust gas is used to spin a turbine at the backside of the combustion chamber rather than being shot out the back and used as thrust.
Connected to the turbine is a shaft which then goes back towards the front of the engine and enters a gearbox. The gearbox is where the magic happens, as it takes the rotation from the turbine and steps it down to much slower speed which is usable by the propeller. The propeller’s rotation and speed are what is used to generate the thrust that enables the plane to fly.
What Is A Piston Engine?
Even though both types of planes are distinguished by having a propeller, a piston engine airplane does use any type of jet engine — unlike a turboprop or turbofan-powered airplane. While they’re both internal combustion engines and have the same general thermodynamic process, the ways that they operate mechanically are vastly different.
Rather, you can think of a piston airplane engine as something far more similar to the engine in your car. As long as your car uses an internal combustion engine (i.e. isn’t electric), then your car’s engine is similar to the piston engines that airplanes use. The only real difference is that the airplane’s piston engine drives a propeller and your car’s engine powers the drivetrain.
That said, piston engines require the same general things as a turboprop: air, fuel, and combustion. Air enters the engine through the intake and makes its way into the combustion chamber. In a piston engine, the combustion chamber is the cylinders of the engine, where the piston operates. Hence the term piston engine.
The piston is attached to a connecting rod which is attached to the crankshaft. As air enters the cylinders, fuel is also injected. When the crankshaft spins and causes the piston to reciprocate, the compression stroke of the engine causes combustion between the fuel and air, forcing the piston back up, which then in turn causes further rotation of the crankshaft.
The crankshaft is then connected directly to the propeller and causes it to turn at the same rotational speed, with no gearbox necessary. As the propeller turns, it begins generating the thrust necessary to power the piston airplane and get it up into the skies.
Turboprop Vs Piston Airplanes: What Are The Differences?
Now that you have a bit of background information about the two types of engines that differentiate a turboprop from a piston airplane, it’s time to really compare the two in detail and check out any similarities and differences. We’ll focus on four major categories to compare the two planes: how the propellers are driven, efficiency and limitations, performance, and safety.
Let’s dive right in and get to the good stuff — turboprop vs piston airplanes.
As you’ve likely realized by now with how much of the above sections was focused on the engine types, the ways that the engines work are the single biggest differences between the two planes. To take that a step deeper, the real difference between the two engines is how they drive the propellers.
Since much of this was laid out in more detail above, I’ll spare you some of the effort. Here’s a quick summary and comparison between the two.
With a turboprop, a turbine is spun at high speeds by the exhaust gasses following the combustion of fuel and air. As the turbine spins, a shaft connected to it runs to a gearbox where the rotational speed is stepped down to something far more usable. From the gearbox, an output shaft then goes to the propeller and spins it to the needed speed to generate thrust.
With a piston engine on the other hand, the reciprocating motion of the pistons force upward motion on the connecting rods which then turn the crankshaft. And the cycle begins again. But while the crankshaft is turning, the propeller is connected directly to it and rotates at the same speed that the engine is turning in order to generate the thrust needed.
Although both planes and engine types use propellers to generate thrust, turboprops have the ability to produce much more power than a piston engine. But more on that later.
Like many of the factors that go into deciding which engine is better, it takes a bit of effort to dig deep enough to see which one is really more efficient. This is because both types of engine can be more efficient than the other in a given set of circumstances — a turboprop can be more efficient than a piston engine, and a piston engine can easily be more efficient than a turboprop.
While not true in 100% of the cases, there’s a general rule of thumb when it comes to the efficiency of these two engine types. Turboprop engines seemingly get more efficient as their size increases, while piston engines are usually most efficient the smaller they are. Think about a car. In most cases, a 4-cylinder engine is going to be far more efficient than a big V8, right? That’s exactly the same as for piston airplane engines.
To take that rule of thumb a step further, we can think about similarly sized engines at the same time, but one of each type. Not only do piston engines become less efficient as it gets bigger in general, but they’re also less efficient than turboprop engines of a similar size. As engine size decreases, a turboprop will be less efficient than a similarly sized piston engine.
So more or less if you haven’t gathered by now, it’s almost entirely dependent on the specific airplane, the way it’s used, what goals you have for the airplane, and of course the engine and its size. In some cases a turboprop is a more efficient engine, whereas other cases the more efficient option will be a piston engine.
The series of parameters that most of you are probably interested in during this comparison between these two types of planes are the ones that deal with performance. I’m talking about power, speed, and altitude. This is the type of information that you’ll likely be basing some of your opinion on, especially if you’re in the market for an affordable plane.
In terms of pure power output, a turboprop has the capability of producing more. This harkens back to the efficiency stuff from earlier, because bigger engines usually produce more power. And since turboprops are far more efficient as engines get bigger, they can keep producing more and more power when a piston engine will fall off and be unable to keep up.
To give you an idea, the most powerful piston airplane engine is the Lycoming XR-7755. This 36-cylinder behemoth put out a respectable 5,000 hp. That’s certainly a lot for a piston engine, but not for a turbine engine. The most powerful turboprop ever is the Russian Kuznetsov NK-12, which put out 15,000 horsepower — three times as much.
Keep in mind that both of these power outputs pale in comparison to what the biggest jet engines in the world can produce. But that’s another topic for another day!
How fast airplanes fly and their power are usually closely related to one another. So you might be thinking that turboprops travel faster than piston airplanes. That is true in most cases. In an apples to apples comparison, a plane equipped with a turboprop will usually be bigger, more powerful, and faster than a piston airplane. But at the extreme end of the spectrum, it’s actually a lot closer than you might think!
Turboprops operate at their most efficient at subsonic speeds, falling off around 500 mph or so. And you don’t have any piston engines operating at supersonic speeds! However, the Grumman F8F Bearcat reached a speed of 528 mph in 1989 in New Mexico. So when it comes to maximum speed, turboprops and piston airplanes are almost neck and neck. But in most cases, the turboprop will get you there a little faster!
Similar to how fast turboprops and piston airplanes fly, how high the planes fly follows a nearly identical pattern. In most cases, a turboprop flies higher than a piston airplane plain and simple. Turboprops tend to operate at their most efficient at altitudes between 20,000 and 30,000 feet. Piston airplanes usually have a service ceiling of about 12,000 to 15,000 feet.
But just like with the speed comparison from above, the extreme ends of the spectrum tell a different story. While turboprops can’t really go too much higher than their cruising altitude because the air is too thin to spin the turbine, a piston airplane has been much higher. Way back in the 1930s, a Caproni biplane with its piston-powered engine reached an astounding altitude of over 56,000 feet.
We all know that one of the most important aspects of anything related to flying and aviation is safety. If given the choice, you always want to opt for the safest airplane and design possible, because there’s no reason to choose anything else. So is a turboprop safer than a piston airplane?
The main safety concerns of these two types of planes come down to points and modes of failure. With a piston engine, there are so many moving parts that go in different directions. Up-down, left-right, rotational, etc. With all these different movement types and parts touching one another, there is a heightened risk of vibration failure and lots of parts that could fail.
In a turboprop, on the other hand, the biggest point of failure is the gearbox. Because if that fails, then the propeller will spin far too fast. Although a turbine engine may actually have more parts, the reason that there are less modes of failure is because they’re all pretty much rotating and moving in one direction, which greatly reduces the risk of excessive vibration.
While both types of planes are safe overall, I have to give the nod to a turboprop as being just a bit safer in most cases.
Turboprop Vs Piston Airplanes: Which One Is Better?
At this point in the article, there’s really only one thing left to answer: which type of plane is better?
I wish I could give you a direct, definitive answer. But the trust is, that’s just not possible. It really will depend on what you’re wanting to do with the plane, how far you’ll be traveling, what you’ll be hauling, what the conditions are, and more. In most of the categories listed above, the turboprop is the slight winner.
But those comparisons were all mostly made in the general sense. If you’re planning on flying the plane with a smaller payload capacity, or shorter distances/slower speeds, then a piston airplane might be the better choice. They’re also typically much cheaper as well!
So use this information to help you determine which one is better for you, but there’s no way to definitively answer which one is better than the other!