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.
