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Thread: ? re: FSX turboprop engine inlet area

  1. #1

    Default ? re: FSX turboprop engine inlet area

    Hi guys,

    Seeking to understand a commonality I'm seeing with all native FSX turboprops and most others. In [turbineenginedata], the parameter 'inlet_area' is typically set to 1.0, which I'm understanding that to indicate the dimensional area of the ducted inlet in square feet.

    Looking at other turbine-driven aircraft (jets, turbofans, etc.), this variable is indeed variable and goes up logically (a Learjet will have a ~4'^2 area whereas something big like a 747 will have a huge area).

    Is a global 1'^2 inlet area right for turboprops?
    Uich gwennen na'wanath ah na dhin,
    an uich gwennen na ringyrn ambar hen.

  2. #2
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    The inlet_area=1 for turboprops is fairly standard. I just compared the KingAir to a P3C Orion and the air inlets are small compared to fanjets like the 747 or 737. For a bigger turboprop you can adjust the size if you want, but most developers decided that 1 was good enough.
    Mr Zippy Sent from my keyboard using "Whackamole", NudgeAKey + 2 Fingers

    No flight Sim installed until I get a new computer.

  3. #3

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    Quote Originally Posted by mrzippy View Post
    The inlet_area=1 for turboprops is fairly standard. I just compared the KingAir to a P3C Orion and the air inlets are small compared to fanjets like the 747 or 737.
    I suppose there's reasons for that.

    1. Invoking Bernoulli's Principle to force a massive amount of air through a small restriction*.
    2. The debris gate at the inlet would be pointless if the inlet was larger.
    3. The propeller.

    Quote Originally Posted by mrzippy View Post
    For a bigger turboprop you can adjust the size if you want, but most developers decided that 1 was good enough.
    Ahh, the dichotomy of being ultra-realistic vs. messing around with details that do not matter as much to the onboard physics engine.

    Thanks for the quick reply. Was wondering if there was indeed a method to the madness, and I'm reminded yet again that turboprops are still turbine engines though they suck everything through a stir straw before the bang and blow stages.

    * These are details that were most likely slept through in high school physics.
    Uich gwennen na'wanath ah na dhin,
    an uich gwennen na ringyrn ambar hen.

  4. #4
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    Actually, the physics is fairly straightforward:https://en.wikipedia.org/wiki/Turboprop

    In aircraft, like the 747, 737, using a turbofan engine, it needs to suck in mass quantities of air to be mixed with fuel and burned to become exhaust thrust.

    In a turboprop, less air is needed to mix with the fuel to provide power to the propshaft and the thrust is provided by the prop.
    Mr Zippy Sent from my keyboard using "Whackamole", NudgeAKey + 2 Fingers

    No flight Sim installed until I get a new computer.

  5. #5
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    In aircraft, like the 747, 737, using a turbofan engine, it needs to suck in mass quantities of air to be mixed with fuel and burned to become exhaust thrust.
    Actually, in a turbofan, the air that goes to combustion is only a small portion of the air that is needed, and the rest goes to the "fan" which acts as a kind of specialized propeller. This NASA article has a very helpful diagram and a good explanation of the operation of a turbofan: https://www.grc.nasa.gov/WWW/k-12/airplane/aturbf.html and you can even run various animations (airflow, temperature, pressure) to visualize it further. You can contrast it with this page on turbojet engines: https://www.grc.nasa.gov/WWW/k-12/airplane/aturbj.html and this page on turboprops: https://www.grc.nasa.gov/WWW/k-12/airplane/aturbp.html

    They also have a page on the core gas turbine assembly: https://www.grc.nasa.gov/WWW/k-12/ai...btyp/etcs.html

    Finally, here is a link to NASA's Beginner's Guide To Aeronautics, which is aimed at Middle to high school students (and link for younger ones, as well): https://www.grc.nasa.gov/WWW/k-12/airplane/index.html

    Good stuff there.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  6. #6
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    Thanks, Larry! You always come up with good stuff!
    Mr Zippy Sent from my keyboard using "Whackamole", NudgeAKey + 2 Fingers

    No flight Sim installed until I get a new computer.

  7. #7

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    Good stuff; thank you guys.

    It does go to prove some of my observations of these turbofan engines -- especially on, for example, the P&W P1500's powering the Airbus A220 -- the hot section is tiny in comparison.
    Uich gwennen na'wanath ah na dhin,
    an uich gwennen na ringyrn ambar hen.

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