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Thread: Help with slat design

  1. #1

    Help with slat design

    Hi EAA fellows!


    I'm starting with a friend the design of an STOL ultralight. We would like to add a leading edge slat, and we are thinking in one that could be retracted to have a clean profile to increase cruise speed. This means that a regular profile should be modified to have slat and wing profile in his shape (we are thinking in NACA 4416)... Does any body knows some books that explains slat design? any start point to this endeavour? Any help will be highly appreciated.


    -Chacalextreme.

  2. #2
    steveinindy's Avatar
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    http://zenithair.com/kit-data/ht.html A chance to learn from the reigning master of GA STOL himself. Read the entire series and you'll come away off to a pretty good start.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  3. #3
    pylon500's Avatar
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    You will also find that there is a movement away from slats / slots to better wing sections and the use of vortex generators where needed, less drag and definitely less weight.

  4. #4
    steveinindy's Avatar
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    Quote Originally Posted by pylon500 View Post
    You will also find that there is a movement away from slats / slots to better wing sections and the use of vortex generators where needed, less drag and definitely less weight.
    With STOL aircraft though it's hard to beat the pros of a slat because you're not going to get anywhere near the same benefit from vortex generators or even the best designed wing sections (without the serious tradeoffs of things like nasty stall characteristics, undesirable pitching moments, huge drag levels, etc). A fixed slat isn't going to add that much weight and isn't going to knock the performance of something already intended to be low and slow (after all we are talking about an ultralight here). What adds weight is the gear related to retracting them like you see in the big iron.

    Unless the OP is a trained aerodynamicist (which, judging by his request, he is not), his best bet is to go with a slat and then use the vortex generators at what they are best for in GA: correct problems that are identified during flight testing after the aircraft is built.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  5. #5

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    The industry is disagreeing with you. Vortex generators are light, easy to install, and have a great bang for the buck. You see vortex generators on Super Cubs and Huskys. Slats that are fixed force a full time performance penalty and movable slats are more mechanically complex than you think. Take a look at a Helio. You have to design the mechanism so that the springs are chosen correctly and the roller mechanisms for the support arms never jam on their rollers. And to select the correct springs for a moveable slat you have to calculate the dynamic Q for the speed that you want the extension to occur at, deduct the mechanical resistance in the system, etc.....

    The industry answer is that VG's are common and slats are not. Hmmmmm......

    Best of luck,

    Wes
    N78PS
    Last edited by WLIU; 04-20-2012 at 04:04 AM.

  6. #6

    Post help with slat

    Thanks everybody for reply, is great to start receiving answers.

    I read the articles from Chris Heintz and they are great. However, from the design point of view, we need more detail about the slat profile, its location relative to the main profile, and the gap between both, to optimize the lift coefficient. I have found some papers in the NTRS (NASA technical report server), and seems that much of the design of this devices require the use wind tunnels. I'm still trying to find some book or paper which explain a reliable design methodology, but I haven't had luck yet. The idea of vortex generators looks pretty good and lightweight, could be good to test them once the plane is ready, I think that they are easy to install. What about mix both? does the high angle of attack attained with slats minimize the effect of vortex generators? In other hand, we are thinking to avoid an automatic deflection system, we are planning to use a manual system deployed by the pilot at certain velocity if he wishes to land slow. Could this be dangerous?

    Thanks again, please continue posting

  7. #7

    Shocked

    by the way, look at this video:

    http://www.youtube.com/watch?v=nKU0uQki5Dc

    i
    n the minute 3:33 you can see a Helio Courier open and closing his slats! cool! agree that design a reliable system like this is very hard, they open and close when they need, even if it is in one wing only...

  8. #8

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    My friend had a Helio Courier, and I am pretty sure that the wing leading edge slats were just spring loaded and opened when the air flow over them got slow. I don't think the pilot had any control on when or how much they opened , just like a ME 109.

    The owner of the Helio thought it was a great plane, even though he kept in on an 6000 ft paved strip and never landed on a short runway or carried any big load. The plane was really noisy.'
    Another friend had a Maule and they were always claiming which one was faster( really, neither one was very fast). Finally one day we went on a long cross country trip and there they were , side by side, and so slowly it seemed to take 10 minutes the Maule barely pulled ahead.
    Last edited by Bill Greenwood; 04-20-2012 at 11:16 AM.

  9. #9
    kscessnadriver's Avatar
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    Quote Originally Posted by WLIU View Post
    The industry is disagreeing with you. Vortex generators are light, easy to install, and have a great bang for the buck. You see vortex generators on Super Cubs and Huskys. Slats that are fixed force a full time performance penalty and movable slats are more mechanically complex than you think. Take a look at a Helio. You have to design the mechanism so that the springs are chosen correctly and the roller mechanisms for the support arms never jam on their rollers. And to select the correct springs for a moveable slat you have to calculate the dynamic Q for the speed that you want the extension to occur at, deduct the mechanical resistance in the system, etc.....

    The industry answer is that VG's are common and slats are not. Hmmmmm......

    Best of luck,

    Wes
    N78PS
    To claim that the industry answer is VG's is a sham. The only industry that does that is the super low end, low production, low money making world of GA. Those who use airplanes to make money all use movable slats.
    KSCessnaDriver
    ATP MEL, Commercial Lighter Than Air-Airship, SEL, CFI/CFII
    Private SES

  10. #10
    Even we don't have any money, neither a factory, we would like to try retractable slats. Part of the challenge!, and thanks Bill, that confirms that the design of the Courier is very complex to start with. Manual system is the way to start...

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