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Thread: NACA intakes for carb induction - pros and cons?

  1. #1
    Join Date
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    Default NACA intakes for carb induction - pros and cons?

    Rather than risk derailing the Tsunami rebuild thread I thought I'd start a new one.

    When watching the excellent home movies about Tsunami's construction I noticed she began with a NACA intake on the top cowling which later became a more standard trunk intake a la Allison Mustangs. I asked about the reasoning for that and I think it was answered.

    As far as I'm aware - bearing in mind my relatively small knowledge bank compared to many members here - only Stiletto and Miss Ashley II featured NACA intakes for induction (I'm not terribly interested in MAII's NACA radiator intake in this thread).

    Is losing the Mustang Smile in favour of a NACA intake a practical decision? If so, is it for drag reasons or does it help the carb "breathe" more?

    It certainly makes for a sleeker nose which must be cleaner for racing and I'm curious to learn if this is true and, if so, why more inline racers haven't adopted it.

  2. #2
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    Default Re: NACA intakes for carb induction - pros and cons?

    There was a third...

    Vendetta used a downdaft induction system for the same reasons as Tsunami and MAII --wing location. As far as I know this intake location was not done for efficiency. I'm actually guessing that in the case of Tsunami...

    I never heard anything about how the Vendetta version worked -- John had bigger issues in 1988.

    Neal
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  3. #3

    Default Re: NACA intakes for carb induction - pros and cons?

    MA2 and Critical Mass are certainly among the the most "raciest" (my iPad almost crashed trying to figure out how to spell that word). The rule has always been that form follows function and beauty is in the eye of the beholder. It would be awesome if reality was a video game. I remember walking past the MA2 pit in the very early morning and being gobsmacked about how perfect the airplane looked and how tidy and professional the whole thing looked (I was jealous, my little toolcart had to sit outside all night). The Dwelles are a great group and their airplane looked like it might go super-sonic if someone ever put the spurs to it. But the truth is the Bearcat was better looking and Strega and the clones that follow it are very sexy, Tsunami was on a strong trajectory to upset the standards but unfortunately it's progress ended abruptly.
    Last edited by knot4u; 12-04-2021 at 08:11 PM.

  4. Default Re: NACA intakes for carb induction - pros and cons?

    This report has some CFD pictures to help with visualizing. But the conclusion is about the same as in the Tsunami thread. The benefit of a NACA duct is less drag than a protruding scoop. The downside is you lose mass flow. And a racer needs a lot of air mass flow. And lastly there is no real drag benefit of a NACA duct on this portion of the aircraft. ie a NACA duct isn't saving any frontal area or even wetted area.

    Notice no one in biplane or IF1 uses a NACA duct to feed the carburetor. But they will use a NACA duct to feed their oil coolers. The applications and requirements for the airflow are different.

    https://ntrs.nasa.gov/api/citations/...9930090318.pdf

    https://www.scielo.br/j/jatm/a/TnXSN...at=pdf&lang=en

    https://ntrs.nasa.gov/api/citations/...9930085733.pdf
    Last edited by CubersWrist; Yesterday at 05:16 PM.

  5. #5
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    Default Re: NACA intakes for carb induction - pros and cons?

    Quote Originally Posted by wingman View Post
    There was a third...
    How could I forget Vendetta?! Thanks Neal.

    Quote Originally Posted by CubersWrist View Post
    The benefit of a NACA duct is less drag than a protruding scoop. The downside is you lose mass flow. And a racer needs a lot of air mass flow. And lastly there is no real drag benefit of a NACA duct on this portion of the aircraft. ie a NACA duct isn't saving any frontal area or even wetted area.
    Thanks for your post Thomas, I really appreciate the links.

    So is there a drag benefit to losing the standard Mustang intake under the prop? Or does it just make the aircraft look fast?

  6. Default Re: NACA intakes for carb induction - pros and cons?

    Hypothetically if you could eliminate the scoop you would reduce drag. But in practicality the engine needs to breath. So in all likelihood whatever system replaces the smile will be less efficient and therefore heavier.

    ie you could load up a bunch of compressed air tanks into the plane. So it?d be a ?blowoff? rather than boil off. More aerodynamic but your adding lots of weight and complexity for the same if not worse performance

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