Profile image

Engine Types: Part 1 (How Engines Work)

Mod Squirrel  4.6 years ago

Background

One of the most important components in an aircraft capable of sustaining flight without the use of thermals is of course the engine. One of the fundamental forces acting on an aircraft is drag. Drag is countered by thrust and when these two forces are the same, the aircraft enters an “equilibrium”. If in this state the thrust force increase, the aircraft accelerates until the amount of drag again equals the force of the thrust. Similarly, if the thrust is reduced, drag decelerates the aircraft until the thrust equals drag again.


The 4 Fundamental Forces in Powered Flight

How an Engine Works

Now given the stark contrast between the different types of engine, it might come as a surprise to know that they all operate the same on a fundamental level. In order to generate power an engine needs to perform the following tasks:

  • Suck or draw in air from its environment.
  • Compress the air it’s sucked in.
  • Inject fuel into the compressed air and ignite the mixture.
  • Expel the exhaust from the ignited mixture.

This process can be simplified in the commonly used expression of “suck, squeeze, bang, blow”.

An Illustration of “Suck, Squeeze, Bang, Blow” in a Piston Engine

Types of Engine

There are two main types of engine in the aerospace industry, Gas Turbine Engines and Piston Engines (also known as reciprocating engines). The main difference between these to engine types is how they generate their thrust.

Piston Engine Operation (typically connected to a propeller for thrust):

Gas Turbine Engine Operation:

Gas Turbine vs Piston

Gast turbine engines are by far the most favoured in the commercial aviation industry over piston engines because they’re:

  • More efficient at high power operation
  • Produces a lot of thrust
  • Have a wide variety of variations for different operating conditions (hint at a future post?)
  • Produce less vibration and mechanically more efficient (everything moves around a single point)
  • Better operational characteristics at high altitudes
  • Lightweight

Piston engines still have some advantages over Gas Turbine though:

  • More efficient at low power operation
  • Significantly cheaper
  • Use less fuel idling
  • Easier to overhaul
  • Probably less catastrophic if something goes wrong (i.e. components aren’t going to spin off and embed themselves into the fuselage, thus potentially severing other components.)

These differences in effectivity somewhat isolate the two types of engines to different markets. Airliners and military aircraft typically experience harsh operating conditions (flying at high speeds and altitudes). Weight saving and efficiency is often the key factor on whether an aircraft is suitable for a particular role. Comfort (a lack of vibration) is also a particularly important factor for the commercial airline market. Price is also less of a concern when compared to the private consumer markets. Thus, Gas turbine engines are the natural choice for these roles.

By contrast, aircraft owned privately (by one or two people, or a small company like a flight school) often don’t need or benefit from high altitude performance, especially for short flights such as typical training flights or recreational flights. In these instances, flying below the clouds for nicer views, etc is more beneficial. Owners of private aircraft are generally also a lot more restricted in terms of how much they can afford to spend on an aircraft as they don’t have the backing of a large company with millions to throw around. These owners often don’t have speed as a priority either. Thus, the piston engine is a natural choice for private owners.

Conclusion

While there are exceptions and partial crossovers in delivery of thrust (e.g. Turboprop engines. A gas turbine that drives a propeller, instead of a piston engine driving a propeller), both main types of engine clearly have their place in the aviation industry with each sporting advantages and disadvantages, making them more effective in their own environments and so attractive to different markets.

Next Post: Engine Types: Part 2 (Axial Flow Jets)
Previous Post: Why Creating a Unique Aircraft Design is Difficult

  • Log in to leave a comment
  • Profile image
    14.6k Graingy

    @Tookan
    Oh, I could tell.
    It's just... y'know... a little bit "silly"

    one year ago
  • Profile image
    9,303 Tookan

    @Graingy
    It's a (dirty) rhyme used to describe the 4 stroke piston cycle of an engine, suck is the intake stroke where an engine sucks in a gasoline/air mixture, squeeze is the compression stroke where the piston of an engine goes up to its Top Dead Center and compresses the air/fuel mixture, bang is the power stroke where the spark plug of an engine ignites the air/fuel in the cylinder, and blow is exhaust.

    one year ago
  • Profile image
    14.6k Graingy

    “suck, squeeze, bang, blow”
    what

    one year ago
  • Profile image

    Is there a way to put mixture in your builds?

    1.8 years ago
  • Profile image
    3,965 HyperViper

    Nice

    3.7 years ago
  • Profile image
    Mod Squirrel

    @Chancey21 Fuel injection is basically the digital equivalent of a carburettor. The carburettor uses mechanical components (pressure, flotation, etc) to create the fuel/air mixture. Fuel injection on the other hand uses a fuel pump and various sensors to establish the appropriate amount of air to mix with fuel.

    +1 4.5 years ago
  • Profile image
    69.2k Chancey21

    Can you please explain what the difference is between carborated and fuel injected is?

    4.5 years ago
  • Profile image
    14.6k Viper3000ad

    Thanks for the feedback. It's a fantastic opportunity to cover some questions that i always had. The air in higher altitude is less denced and cooler, how a piston engine without spark plugs manage to keep correct mixtures. Is the fuel more like diesel in witch with enough compression autoignits? They have some sort of small turbines to heat and compress the incoming air? Do diesel aviation engines have spark plugs ?
    I hope I don't get you tired with all that question storm...

    4.6 years ago
  • Profile image
    Mod Squirrel

    @Viper3000ad Avgas is used in piston engine aircraft, although that's likely to change in the future due to environmental concerns. Jet A1 is most commonly used for commercial jet powered aircraft, although Jet B is used in cold climates due to lower freezing point. I think JP8 fuel is used for military aircraft,.

    4.6 years ago
  • Profile image
    14.6k Viper3000ad

    Great article. What type of fuel is best for a piston aviation engine? The new diamond d42 for example has two diesel props. Can compressed liquid gas used in a aviation?

    4.6 years ago
  • Profile image
    47.9k Sm10684

    @Tully2001 I'm honestly starting to like you now /_\ wankels are the best

    4.6 years ago
  • Profile image
    Mod Squirrel

    @Strucker Don't worry I'm secretly scared of the fish too

    4.6 years ago
  • Profile image
    25.9k Strucker

    Never knew that.
    Ok you now my fav mod.
    Because the fish scares me

    4.6 years ago
  • Profile image
    Mod Squirrel

    @WNP78 thanks, man!

    4.6 years ago
  • Profile image
    Dev WNP78

    Excellent article! I fixed the typo in the first sentence for you.

    +4 4.6 years ago
  • Profile image
    6,235 Loopy200

    This is great! Really helped me understand how the piston engine and gas turbine works, quite simple actually.

    +1 4.6 years ago
  • Profile image
    Mod Squirrel

    @Nerfaddict I have plans to cover jet engines all in one post. Also ioinc wind and ion engines provide very little thrust for an typical aircraft.

    4.6 years ago
  • Profile image
    35.0k AdlerSteiner

    Suck, Squeeze, Bang, Blow

    4.6 years ago
  • Profile image
    40.1k Awsomur

    This is really good falling asleep material.

    Jk it was interesting

    +2 4.6 years ago
  • Profile image
    29.0k Nerfaddict

    @Squirrel while I would like let you know there are other engine types such as:
    -ion
    -scramjet
    -ramjet
    -ionic wind
    Something tells me questioning against a moderator is a not so good idea

    4.6 years ago
  • Profile image

    "How an Engine Works"
    RAPID FIRE BOOM BOOM BOOM BOOM BOOM SHHCUUUUCHCUCUCHCHCU CHARLIE IN THE TREEEEEEES BOOMBOOMBOOMBOOMBOOM FIRE EXPLOSIONS SCHUSCHUSCHU
    we are driven by explosions

    +3 4.6 years ago
  • Profile image
    13.0k CruzerBlade

    how does helicopter transmission work?

    4.6 years ago
  • Profile image
    Mod Squirrel

    @HarryBen47 Don't worry, I still have ideas for more informative articles. I have plans to cover gas turbines in more detail, as well as configurations, etc. Aerospace has a lot of aspects to it and while I don't think I'll cover them all, I'll try to cover the important things regarding aircraft design since it's appropriate for the site/game.
    .
    If you (or anyone else reading this for that matter) has something they'd like to see me cover, feel free to suggest it and at the very least, I'll cover it in an article or (if it's a large enough topic) dedicate a post to it.

    +1 4.6 years ago
  • Profile image
    12.6k HNL47

    Make more of this pls it is very useful

    +1 4.6 years ago
  • Profile image

    Totally can’t wait for other power plants like motor-jets and stuff like that.

    +1 4.6 years ago
  • Log in to see more comments