Most people know the horsepower rating of their automobile; however, many wonder, how much hp does a plane have, and is this even a fair comparison to make?
To express the thrust force of a plane in horsepower, we need to understand how a piston engine functions differently from a jet propulsion engine. The hp of every plane can vary. According to calculations, while the jet engine of a Boeing 777 has a horsepower of 30,843, the jet engine of a Boeing 747 has a horsepower of 59,934.
This article will outline the answer to the question ‘how much hp does a plane have’ by discussing how an automobile engine is different from a jet engine. Moreover, by explaining in some detail how a jet engine works, the article will provide a better understanding of why an aircraft’s propulsion is necessarily expressed in a different way than horsepower. By the end of the article, while you won’t have a specific answer to the question ‘how much hp does a plane have,’ you will better understand why this comparison doesn’t make much sense.
Our experts in jet engine propulsion systems have come together to articulate this rather complex subject in a simple manner that just about anybody can understand. So, without further ado, let’s get right into it!
How Does a Piston Engine Work?
A piston engine, also known as an internal combustion engine, differs from aircraft or jet propulsion engines. Combustion is a fancy word for burning and refers to the chemical process by which a fuel and air mixture is used to release energy. Notably, a piston engine works through the paired ignition and combustion processes, both of which take place within the engine itself.
This energy is then partially converted into work, which shall then drive the automobile forward. The energy released from the combustion of the fuel-air mixture is converted into work within a fixed cylinder with moving pistons inside it. In a nutshell, the expanding gases released from the combustion reaction push the pistons, which provides the force needed to turn the crankshaft. Ultimately, this work is used to drive the car’s wheels as the automobile’s crankshaft connects the moving pistons to the drivetrain that drives the wheels to turn.
Piston engines or internal combustion engines are also known as four-stroke cycle engines. This is because the process of turning combustion into work requires four basic strokes. These are intake, compression, combustion, and power stroke. Exhaust is also the last element of this cycle and involves the release of the combusted gases.
Lastly, it is worth noting that the power output of an internal combustion engine is expressed in watts. Traditionally, the term horsepower is used to express the power output of a piston engine, and 1 horsepower is equivalent to 746 watts.
How Does an Aircraft Engine Work?
Just as the crankshaft in an automobile works to drive the wheels, the crankshaft in a plane is used to run the propeller. However, other than this, a jet propulsion engine works very differently from internal combustion or piston engines.
Like any other vehicle, the job of the jet propulsion engine is to convert the energy latent within fuel into kinetic energy, which will drive the jet forward and help it soar through the air. However, the process by which a plane does this is not similar to how a piston engine works.
To start, large fans or turbines facing the front of the aircraft turn and suck cold air into the engine, forcing it through an inlet. This slows the air down to a large extent which is necessary for the second step.
A second fan, referred to as the compressor, increases the pressure of the air by squeezing it. This, in turn, allows the temperature of the air to increase significantly.
The wing of the plane has within it a fuel tank that contains liquid fuel known as kerosene. As the compressor squeezes the air and increases its temperature, the fuel tank squirts kerosene into the plane’s engine.
Just behind the compressor lies a combustion chamber. Here, the compressed air mixes with the kerosene, causing it to start fiercely combusting. This, in turn, releases hot exhaust gases, thereby generating an even more dramatic temperature increase. At this point in the process, the mixture can reach a temperature of 1650°F.
The hot exhaust gases are made to rush past a set of turbines, causing them to start spinning very rapidly. The blades of the turbine are connected to an axle that runs across the length of the engine. This axle connects the turbine, compressor, and fan to one another, so when the turbines start spinning, so do the fan and the compressor, thereby allowing the process to continue with even greater efficiency.
The tapered design of a plane’s exhaust nozzle allows the released gases to accelerate to speeds of 1300 mph. Therefore, the hot air leaving the engine from behind is traveling at over twice the speed of cold air entering the compressor from the front. This difference in force is essentially what powers the plane. In essence, the backward moving exhaust gases are what provide the plane with thrust, allowing it to move forward.
How Much Hp Does a Plane Have?
So, now we understand how a jet propulsion engine produces thrust to drive the aircraft forward through the air. The vector of this force of thrust, another word for its direction, is equal to the direction in which the aircraft is traveling.
Below are the horsepower ratings of some common types of planes:
Unlike in an automobile, in which the engine’s thrust is expressed in horsepower, the power of a jet engine’s thrust is expressed in either Newtons, pounds, or kilograms of force. 1 Newton is equivalent to 0.225 pounds and 0.102 kilograms of force.
For example, the jet engine used on a Boeing 747, known as the General Electric GEnx 1B, produces a thrust of 75 pounds, 34.019 kilograms, or 333.617 Newtons. While this may seem like an enormous amount of force compared to the thrust that drives an automobile, note that a typical space shuttle launches itself into the earth’s upper atmosphere with a thrust of 7.3 million pounds.
Therefore, the comparison between a commercial aircraft and a piston engine is not a straightforward one. These are essentially two completely different types of engines as they produce thrust in entirely different ways. In order to compare the thrust of a jet propulsion engine with that of a car engine, we would first need to convert this thrust into shaft power. This will allow us to get an idea of how thrust can be expressed for the piston engine’s crankshaft.
This conversion requires us to consider the other forces acting on an aircraft as it soars through the air. These forces are aircraft weight, lift, speed, and drag. Taking these into account can allow us to theoretically derive a quantity to express the Watts produced by a jet propulsion engine.
Doing the calculations, we find that the jet engines of a Boeing 777 produces approximately 23 Megawatts when cruising and that too in an aircraft at maximum capacity. Using a conversion of 1 Megawatt as equals to 1341 horsepower, we can say that the jet engine of a Boeing 777 has a horsepower of 30,843 horsepower.
In the end, we find that comparing the thrust of a jet propulsion engine to the horsepower of a piston engine is quite a complicated matter. This is mostly due to the different physics that apply to a car when compared with an aircraft. The thrust of a piston engine is hence expressed in watts or horsepower. Meanwhile, the thrust of a jet propulsion engine is expressed in pounds, kilograms, or Newtons.
About THE AUTHOR
Alex has logged close to 400 hours on his own Piper Cherokee and enjoys bush flying as it offers a chance to test out his skills in difficult situations. His favorite trip, and one he makes regularly, is to the Red Deer Forestry Airstrip.Read more about Alex Costa