How much drag do king posts cause?

Discussion in 'General Experimental Aviation Questions' started by HumanPoweredDesigner, Sep 8, 2009.

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  1. Dec 17, 2010 #21

    autoreply

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    I meant something else.

    If we have a 18% thick airfoil with a drag of 0.004 and a 36% thick airfoil with a drag of 0.0075, it's still beneficial to take the fatter one. For struts and landing gears, buckling/bending is the loading condition and the critical dimension is the thickness of the airfoil. I'd be surprised if the lowest-drag struts would have a thickness below 25% actually.
     
  2. Dec 17, 2010 #22

    Mac790

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    Sorry Jarno that I didn't get you at first time, I had a small surgery in previous week in hospital, lost about 6-7 KG in week, and can't eat proper food for another 7-10 days, I'm very weak and my brain doesn't work as it should. You were talking about chord vs thickness relation, better known as fineness ratio, 1/3 is probably the best idea, but wouldn't it be 33,3% instead of 36%.

    Seb

    edit: for whatever this software is worth for 33% 0.34, for 36% 0.40
     

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  3. Dec 17, 2010 #23

    topspeed100

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    It is really amazing video.

    One question.

    If you have the round strut in 45 angle to the wind..how much is the drag reduced ?

    I mean it is 9 times compared to the airfoil like symmetrical shape....will it be 50% less ?

    -----

    I came to realize these huge powers as I designed a retractable gear ( for my previous design )...and found out that the gear when nonretracted actually created more drag than the whole airframe combined.
     
  4. Dec 17, 2010 #24

    orion

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    No, it'll be pretty much the same if the span or height it covers is the same as a strut that's perpendicular to the flow. Actually, due to the increases wetted area, the swept one may actually have a higher drag count.
     
  5. Dec 17, 2010 #25

    topspeed100

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    Ok Orion,

    I was not spesific enough.

    If the lenght of the object is the same ? Will the 45 degree angle reduce the drag significantly ?
     
  6. Dec 17, 2010 #26

    topspeed100

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  7. Dec 17, 2010 #27

    Jan Carlsson

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    With the round strut dressed in an airfoil you reduce drag to something like 1/3 - 1/10 of the drag of the tube. depending of how well you do it.

    the question of tilted tube, 45 degree, isn't that 1,414 times longer? in direction of air flow.
    it need to be 3,5-4 times longer then its t.

    The optimal chord lengt in the spread sheet found above is in direction of air stream!

    Jan
     
  8. Dec 17, 2010 #28

    orion

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    Some, after all, if you rotated it 90 deg it's drag would go to nearly zero. But if you do that, what other compromises do you create?

    But really, drag reduction due to sweep is more a transonic phenomenon, not low end subsonic.
     
  9. Dec 17, 2010 #29

    Hot Wings

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    One question.

    If you have the round strut in 45 angle to the wind..how much is the drag reduced ?



    I believe what you are asking is what would be the Cd be of an ellipse with a finesse ratio of 1.414?

    I thought it would be a quick find on the web (don't have access to my library at the moment) but the closest I could come with a quick search is page 18 of this:

    http://www.yildiz.edu.tr/~atayil/Bolum11.pdf

    The drag of a stranded aircraft cable may be considerably different than the same diameter solid wire when presented to the air flow as an ellipse.
     
    Last edited: Dec 17, 2010
  10. Dec 17, 2010 #30

    HumanPoweredDesigner

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    That's how I compare airfoils for wings. All else being the same I'd rather have a wing that has less cord.
     
  11. Dec 20, 2010 #31

    topspeed100

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    Thanks gentlemen !

    I also try to present taildagger version and struts there are tilted.

    I am drawing a really small plane and the problem is that sans pilot the plane will go automatically to tailspoon. Taildagger doesn't look that good, but might be lighter with less drag.
     
  12. Dec 29, 2010 #32

    HumanPoweredDesigner

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  13. Dec 30, 2010 #33

    topspeed100

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  14. Nov 9, 2014 #34

    henryk

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