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Thread: Holes in Spoiler or Not

  1. #16
    Registered User John.Roo's Avatar
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    Re: Holes in Spoiler or Not

    Hello!
    We tried air brakes with and without holes and my subjective feeling is that with holes was efficiency of air brakes better.
    It means - higher drag.

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    Best regards!
    Martin
    Last edited by John.Roo; March 2nd, 2019 at 12:29 AM.

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  3. #17
    Registered User pictsidhe's Avatar
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    Re: Holes in Spoiler or Not

    I've read at least one paper on experiments with holes and without. Possibly on dive brakes. Either NACA or British ARC.

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    Registered User Hot Wings's Avatar
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    Re: Holes in Spoiler or Not

    The only thing I can add with regard to holes or not:

    The ones without holes stung more.

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    School policy at one time was to wear a belt. I was a bit of a nonconformist.
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    Re: Holes in Spoiler or Not

    Quote Originally Posted by plncraze View Post
    Look at the speed brake on Maupin\Culver's Windrose. Pops up from the top of fuselage. Probably is held down by air pressure.
    that type is what was added to the Carbon Dragon when they decided to add one as an after thought. My thoughts here are that is purely drag and does not spoil the lift..... All of my glider experience has been with aircraft with "spoilers" on the wing.

  6. #20
    Registered User pictsidhe's Avatar
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    Re: Holes in Spoiler or Not

    Here's a 42 summary to peruse.2614.pdf

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    Re: Holes in Spoiler or Not

    Quote Originally Posted by pictsidhe View Post
    Here's a 42 summary to peruse.2614.pdf
    Its a pity not more of the R&M reports are online, they tend to be very useful / interesting.
    Last edited by Mad MAC; March 3rd, 2019 at 02:18 AM.

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    Registered User cluttonfred's Avatar
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    Re: Holes in Spoiler or Not

    Does anyone know a good source for those RAE reports online or in book form?
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  10. #23
    Registered User pictsidhe's Avatar
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    Re: Holes in Spoiler or Not

    The RAE ones are hit and miss. Quite a few are on the Cranfield site, but I have failed to find many referenced ones anywhere online. I'd love to know of another source. The British Library in London could be worth trying a shopping list at. NACA stuff is far more available. I have acquired a few books with extracts from some. They often cover topics that NACA hasn't looked at.

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    Re: Holes in Spoiler or Not

    Quote Originally Posted by pictsidhe View Post
    Here's a 42 summary to peruse.2614.pdf
    There it is. 33% round perforations gives 10-12% reduction in drag as the price for a big reduction in vibe effects on the rest of the plane. Other venting also makes for improvements with vertical slots decreasing the depth of wake. Cool.
    Billski's opinions expressed here are available free and may be worth the money you paid for them. Understand that they are based upon a successful combination of education and a lifetime of experience using that education, but I can not know everything about your circumstances. Your choices are yours alone, and you must be the final judge on what you do. No whining...

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    Re: Holes in Spoiler or Not

    Choices Choices...I read it highest drag and lift reduction no holes or slots......So now will the vibe effects tare off the fabric in the aft half of the wing? Guess I could see how much it affects it and add holes later? NE speed is 65 mph and stall is reported 19 mph.....pretty low Reynolds numbers,.....not 400 mph dive bomber.

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    Registered User wsimpso1's Avatar
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    Re: Holes in Spoiler or Not

    I was thinking that if you get big oscillations with a solid brake, and you give up a 10 percent drag to get a much smoother ride when brake is extended, it would be a decent trade. If you build with no holes and get big vibration amplitudes at an annoying frequency, well, you might remove the brake panels and put a bunch of good sized holes in it to settle it down... And if you get buffeting that lines up with the resonant frequencies of anything else in the airframe, you had better be prepared to do something to drive the vibe frequency someplace else.

    The reason holes and slots work so well, is there is still a lot of drag getting air around the edges of the vents. And it suppresses vibration so well because each hole, slot, or edge is shedding vortices at its own rate and strength. Since every holes sees a somewhat different velocity field, every hole will have a different shedding rate and strength. Odds are pretty good that instead of a couple big vortices on a regular cycle, you will have a whole bunch of different vortices shedding at different rates.

    I think I would be prepared to change things once I get flying, and be prepared for losing 10-12% of solid brake drag to make it pleasant flying. Then if it turns out your speeds are so low that vibe is no big deal, BONUS!

    Billski
    Billski's opinions expressed here are available free and may be worth the money you paid for them. Understand that they are based upon a successful combination of education and a lifetime of experience using that education, but I can not know everything about your circumstances. Your choices are yours alone, and you must be the final judge on what you do. No whining...

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