Learn about propulsion
What is propulsion?
Propulsion is the action of pushing (or pulling) any given object. In the context of aerospace, propulsion is the study of propelling aircraft through the air, providing thrust. This is done, of course, through the airplane’s engines.
Airplane jet engines: the basic principles
All jet engines used in airplanes work on the same basic principles: air comes in the front, goes through the engine, and gets spit out the back. But how does this process work?
The compressor compresses the air coming in the engine’s intake, increasing its pressure. The compressed air, now moving quickly through the engine, is combusted, meaning that it gets mixed with fuel and set alight. The fiery, fast-moving air is then shot out the back through the engine’s exhaust nozzle, providing thrust. There are a multitude of ways to get this process done, and it can be different for each type of engine.
An engine with no moving parts: Ramjet
A ramjet engine is special since it has no moving parts, unlike most other types of engine. Since there’s no fan to suck air in, ramjet propulsion only works if the aircraft is already moving forward. This is why, in Maverick’s Mach 10 speed test, he only engages ramjet during the flight, not on the ground. Ramjet is often used in aircraft that are meant to achieve higher speeds, like the “Darkstar”.
A ramjet engine uses a special inlet to compress the incoming air rather than a compressor (due to the high speeds that the air is moving at). The compressed air then goes through a combustion chamber, getting mixed with gas. The mixture is then ignited and sent out the back of the engine, producing thrust.
What about propellers?
Propeller engines work differently from jet engines, and generally achieve slower speeds. However, for shorter, slower trips, propellers are far more fuel-efficient. So how do they work?
The National Air and Space Museum invites us to “think of a propeller as a spinning wing.” Wings harness a difference in air pressure to generate lift. A propeller is also just essentially a series of wings using that difference to generate lift, “but in a forward direction.” In fact, if you look at the cross-section of a propeller, it has the same rough shape as a wing.
Non-air breathing engines
So far, all of the engines covered have required air to work properly. However, there is another type of engine: non-air breathing engines, or rockets. These engines are found in spacecraft – vehicles that travel outside of our atmosphere and therefore have little to no access to air.
How do rockets work?
A rocket, in extremely simple terms, ignites huge amounts of fuel in a combustion chamber, then spits it out the back at insanely high speeds, creating thrust due to Newton’s Third Law of Motion. In order for a rocket launch to be successful, the thrust produced has to be enough to offset the weight of the rocket + fuel + payload.
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