Aircraft propulsion is a fascinating topic, there are many types of engines and propulsion systems,
many of which use the combustion of fuel, we also have a new generation of electric propulsion,
which still has a long way to go to be deployed in mass,
but small aircraft and other specially equipped planes are using it right now.
Did you know that a glider can fly without an engine?
to learn more, watch my video about gliders on the top right corner.
Let’s start with the most common type of engine, the piston engine.
It’s the same type of engine used in cars,
the piston engine is very reliable and has been used in airplanes from the beginning of aviation.
Pistons can be arranged in many ways, and you can have as many as
you can fit under the engine cowling, they can be inline, opposed, V type or
radial. The more cylinders you have the more power output you’ll get, but also more fuel consumption.
If you don’t know how an engine works I’ll show you real quick with this animation. Normally
we’ll find a 4 stroke engine in airplanes, this means that the cycle has 4 stages to complete,
the mixture of fuel and air goes into the cylinder and then the intake valve closes, the piston goes
up and compresses this mixture, that’s the compression stage, from there the spark plug
ignites the mixture and the combustion generates a small explosion that pushes the piston down,
that’s the combustion stage where the power is generated, the last stage is the exhaust,
in which the exhaust valve opens and the residual gasses exits the cylinder, the process repeats.
In cars, you’ll normally see the cylinders arranged in line or in V, but in airplanes
we can also have other arrangements including opposed and radial. The main difference with these
arrangements is the cooling and aerodynamics, see how a radial engine is exposing all the cylinders
directly to the airflow, thus it doesn’t need an extra cooling system since it will be cooled
by the air, but this arrangement will produce a lot of air drag slowing the plane down during its
flight. Many early airplanes used this kind of engines to simplify the cooling problem.
The other kind of arrangements, especially the V type, will allow for a slimmer design and
better aerodynamics, but the cooling will be more critical, relying on more complex cooling systems,
but totally worth it if you want to get the maximum speed out of the engine.
To go faster, a piston engine won't do, you need a better technology,
for that we can use rocket engines, but they are inefficient, and they burn fuel too quickly.
Jet Engines or turbines came along and they were the answer to the speed and power problem,
after many years of development they were ready to be deployed, first being used during the second
world war, but after the war ended, the technology kept improving to the point it was very efficient,
reliable and perfect for its use in many variants of engines types and aircraft.
The turbine uses a lot of small blades rotating at high speed, the engine takes air from one end
and forces it through different stages where it’s compressed and mixed with atomized fuel,
then ignited, the expansion of the gases will escape towards the back forcing the rotation of
the next set of blades in the turbine which at the same time turns the whole system.
Notice the similarity on the 4-stroke engine cycle, in the turbojet engine
we have the air intake, the compression, the combustion and the exhaust stages,
but this is happening continuously, not like in a cylinder where every stage is
defined by the stroke of the piston and then the explosion is the combustion.
Nowadays, there are many types of jet engines, they are, turbofan,
Turbojet, turboprop, turboshaft and Ramjet engines.
The most used in civil aviation is the turbofan engine, in this type of engine there’s a large
fan at the front that sucks the air in, most of which is used to generate thrust,
and only a small percentage actually goes in for the combustion stage, the advantage of this
kind of engine is that is a lot quieter and more efficient for subsonic speeds.
The turbojet engine is the one we saw in the first example,
and all the air that gets in from one end goes through the whole process,
it’s very powerful, very noisy but somewhat smaller than the turbofan engine.
The turboprop engine uses the power from the turbine
and through a gear box the rotation is transmitted to the propeller,
Compared to turbofans, turboprops are most efficient at flight speeds below 725 km/h
(450 mph) because the jet velocity of the propeller (and exhaust) is relatively low. Modern
turboprop airliners operate at nearly the same speed as small regional jet airliners but burn
33% less fuel per passenger. However, compared to a turbojet (which can fly at high altitude
for enhanced speed and fuel efficiency) a propeller aircraft has a lower ceiling.
And compared to piston engines, their greater power-to-weight ratio (which allows for shorter
takeoffs) and reliability can offset their higher initial cost, maintenance and fuel
consumption. Also as jet fuel can be easier to obtain than aviation gasoline in remote areas,
turboprop-powered aircraft like the Cessna Caravan and Quest Kodiak are used as bush airplanes.
The turboshaft engine is similar to the turboprop,
but it’s connected to a big shaft and it’s normally used for helicopters, the workings of
the whole system is practically the same, it can also be used for military tanks and even boats.
Lastly, we have the Ramjet engines, these engines are more like a rocket with the
difference that they can only produce thrust once they have a fast airflow to start working,
in other words the airplane have to be flying already at a fast speed for this engine to work.
This engine does not have a set of blades like the turbines, it has very few moving parts, and
it relays on its shape to slow down the supersonic air at the intake to a subsonic speed, driving the
air to a compression stage and then burning the fuel with this compressed air to generate
supersonic thrust towards the nozzle. This engine is used in the SR 71 blackbird, although you might
wonder then how can this airplane take off if the ramjet engine can only work at supersonic speeds?
Well this airplane has a turbojet nested inside the ramjet, it’s a 2 in 1 solution. Once the plane
reaches the speed needed, then there’s a bypass in the engine that will work mostly as the ramjet,
it is a bit more complicated than that but I suggest you watch the videos from
other YouTube channels, which links I’ve provided in the description below
to have a more detailed and better understanding on how the engines work in the SR71 blackbird.
I could keep talking about other types of propulsion systems for aircraft,
like the new electric motors, in which the only limitation we have now is the amount of energy we
can store in our current battery technology, but it promises a great future for electric aviation.
But I think this deserves an entire new video on its own. I only will mention few
weird propulsion systems that are not practical or not developed enough to be use in aircraft.
Going back in time, we have a steam propelled aircraft, one of the most successful was the
BESLER biplane, but the steam engine was heavier, less efficient, and more complex than conventional
internal combustion engines, it could not compete with them and thus was never put into production.
Human powered aircraft is another peculiar type of propulsion, but it is completely possible,
only in good weather conditions and if the person is not tired.
Then we have rocket propulsion, to go at the fastest speed possible, but for a brief moment.
And the final one I’m going to mention is the ion propulsion, a very new technology.
And that’s it for this video, if you have another type of engine in mind you
would’ve like me to mention just let me know in the comments bellow.