KF Airfoils :: explained by Dave Powers

Discussion in 'Scratchbuild Talk' started by Dredogol, Nov 9, 2009.

  1. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

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    Alright, here is a collection of videos by Dave Powers explaining and testing everything about KF Airfoils.

    NOTE: "KF" == "Kline Fogleman", where K = "Richard (Dick) Kline" and F = "Floyd Fogleman"


    KF Testing...

    How to make a KF Airfoil...
    [video=dailymotion;x7rgy1]http://www.dailymotion.com/video/x7rgy1_how-to-make-a-kf-airfoil_tech[/video]
    Flight Report #1...
    [video=dailymotion;x7rtkf]http://www.dailymotion.com/video/x7rtkf_kf-flight-report-1_tech[/video]
    Flight Report #2...
    [video=dailymotion;x7ripv]http://www.dailymotion.com/video/x7ripv_kf-flight-report-2_tech[/video]
    Phone Interview w/ Dick Kline (part 1)...
    [video=dailymotion;x7sahx]http://www.dailymotion.com/video/x7sahx_how-dick-came-up-with-the-world-rec_tech[/video]
    Phone Interview w/ Dick Kline (part 2)...
    [video=dailymotion;x7sgyb]http://www.dailymotion.com/video/x7sgyb_the-kf-paper-airplane-out-flies-the_tech[/video]
    Phone Interview w/ Dick Kline (part 3)...
    [video=dailymotion;x7shk8]http://www.dailymotion.com/video/x7shk8_the-kf-effect-in-cars-trucks-and-go_tech[/video]
    Phone Interview w/ Dick Kline (part 4)...
    [video=dailymotion;x7shl3]http://www.dailymotion.com/video/x7shl3_daves-future-plans-for-the-kf-wing_tech[/video]
    Phone Interview w/ Dick Kline (part 5)...
    [video=dailymotion;x7shse]http://www.dailymotion.com/video/x7shse_personality-types-and-super-heroes_tech[/video]

    ==================================================
     
  2. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

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    Lastly, I would like to finish off by posted a picture of the 4 KF airfoils Dave used in his testing, and links to various sites talking into more technical details as to HOW the KF airfoil works.

    [​IMG]

    -- Kline Fogleman Airfoil Study (our banner is in the article! :))
    http://cmreel.com/?page_id=82

    -- (7) KF Airfoils w/ design descriptions & RC uses
    http://depronrc.com/aeroplanes/artic...gleman-airfoil

    -- Basic "Stepped Airfoil" design theory
    http://www.acsol.net/~nmasters/vortex-lift/step.html

    -- KF Airfoil Velocity/Magnitude pressure tests using CFD Simulation w/ Video Results
    http://slfcfd.sourceforge.net/airfoil_KFm2.html

    -- RexResearch.com - KF Airfoil Design Concepts and Patents
    http://www.rexresearch.com/klinfogl/klinfogl.htm#ultim

    -- NASA Technical Reports in 1974 (26-page "BAD" report)
    http://ntrs.nasa.gov/search.jsp?N=0&...Kline-Fogleman

    -- (American Society of Civil Engineering) - Aerodynamic Performance of Airfoil w/ Step-induced Lift Augmentation
    http://cedb.asce.org/cgi/WWWdisplay.cgi?9800003

    -- "Slipping the Surly Woods": by Dick Wood
    http://www.rcgroups.com/forums/showa...mentid=1288605

    ::: NOTICE :::
    The (76+) posts below has been shortened from the (3768+) posts from the "KF Airfoil" topic at RCGroups.com

    "See how the KF Airfoil designs matured since August of 2006..."

    -- KF Airfoil Design discussion (76+ posts)
    http://www.rcgroups.com/forums/showp...8&postcount=84 - (1 image)
    http://www.rcgroups.com/forums/showp...2&postcount=87 - (1 CFD image)
    http://www.rcgroups.com/forums/showp...&postcount=109
    http://www.rcgroups.com/forums/showp...&postcount=120
    http://www.rcgroups.com/forums/showp...&postcount=122 - (1 image)
    http://www.rcgroups.com/forums/showp...&postcount=133
    http://www.rcgroups.com/forums/showp...&postcount=153
    http://www.rcgroups.com/forums/showp...&postcount=155
    http://www.rcgroups.com/forums/showp...&postcount=159 - (2 PDF using "JavaFoil")
    http://www.rcgroups.com/forums/showp...&postcount=160
    http://www.rcgroups.com/forums/showp...&postcount=180 - (1 image + 1 PDF using "JavaFoil")
    http://www.rcgroups.com/forums/showp...&postcount=218 - (2 images)
    http://www.rcgroups.com/forums/showp...&postcount=220
    http://www.rcgroups.com/forums/showp...&postcount=225
    http://www.rcgroups.com/forums/showp...&postcount=234
    http://www.rcgroups.com/forums/showp...&postcount=259
    http://www.rcgroups.com/forums/showp...&postcount=260
    http://www.rcgroups.com/forums/showp...&postcount=280
    http://www.rcgroups.com/forums/showp...&postcount=337
    http://www.rcgroups.com/forums/showp...&postcount=340
    http://www.rcgroups.com/forums/showp...&postcount=342
    http://www.rcgroups.com/forums/showp...&postcount=360
    http://www.rcgroups.com/forums/showp...&postcount=364 - (rroyce == Dick Wood :eek:)
    http://www.rcgroups.com/forums/showp...&postcount=367 - (1 image)
    http://www.rcgroups.com/forums/showp...&postcount=420
    http://www.rcgroups.com/forums/showp...&postcount=422
    http://www.rcgroups.com/forums/showp...&postcount=436
    http://www.rcgroups.com/forums/showp...&postcount=453 - (1 image)
    http://www.rcgroups.com/forums/showp...&postcount=480
    http://www.rcgroups.com/forums/showp...&postcount=491
    http://www.rcgroups.com/forums/showp...&postcount=499
    http://www.rcgroups.com/forums/showp...&postcount=535 - (1 image+ data)
    *** http://www.rcgroups.com/forums/showp...&postcount=542 - (5 CFD images)
    http://www.rcgroups.com/forums/showp...&postcount=546
    http://www.rcgroups.com/forums/showp...&postcount=556
    http://www.rcgroups.com/forums/showp...&postcount=620 - (1 data using "JavaFoil")
    http://www.rcgroups.com/forums/showp...&postcount=624
    http://www.rcgroups.com/forums/showp...&postcount=667
    http://www.rcgroups.com/forums/showp...&postcount=668
    http://www.rcgroups.com/forums/showp...&postcount=672
    http://www.rcgroups.com/forums/showp...&postcount=673
    http://www.rcgroups.com/forums/showp...&postcount=675 - (1 image)
    http://www.rcgroups.com/forums/showp...&postcount=679
    http://www.rcgroups.com/forums/showp...&postcount=692 - (2 articles)
    http://www.rcgroups.com/forums/showp...&postcount=697
    *** http://www.rcgroups.com/forums/showp...&postcount=751 - (Optimal KF Airfoil Design Specs)
    *** http://www.rcgroups.com/forums/showp...postcount=1366 - ("")
    ***
    http://www.rcgroups.com/forums/showp...postcount=1369 - ("")
    http://www.rcgroups.com/forums/showp...&postcount=777 - (1 image)
    http://www.rcgroups.com/forums/showp...&postcount=797 - (3 images)
    http://www.rcgroups.com/forums/showp...&postcount=806
    http://www.rcgroups.com/forums/showp...&postcount=815
    http://www.rcgroups.com/forums/showp...&postcount=834 - (1 image)
    http://www.rcgroups.com/forums/showp...postcount=1111 - ("")
    http://www.rcgroups.com/forums/showp...postcount=3584 - ("")
    http://www.rcgroups.com/forums/showp...&postcount=845
    http://www.rcgroups.com/forums/showp...&postcount=858
    *** http://www.rcgroups.com/forums/showp...&postcount=893 - (Dick Kline KF-Airfoil LOGO)
    http://www.rcgroups.com/forums/showp...postcount=1116 - (1 image)
    http://www.rcgroups.com/forums/showp...postcount=1157
    http://www.rcgroups.com/forums/showp...postcount=1165
    http://www.rcgroups.com/forums/showp...postcount=1220
    http://www.rcgroups.com/forums/showp...postcount=1221
    http://www.rcgroups.com/forums/showp...postcount=1351 - (3 "heavy" articles into 1 summary)
    http://www.rcgroups.com/forums/showp...postcount=1479 - (Wind erosion on Rocks == Wing design Idea)
    *** http://www.rcgroups.com/forums/showp...postcount=1549 - (Adjustable KF Airfoil Height w/ Servo)
    http://www.rcgroups.com/forums/showp...postcount=2046 - (1 image)
    http://www.rcgroups.com/forums/showp...postcount=3595
    http://www.rcgroups.com/forums/showp...postcount=3599
    *** http://www.rcgroups.com/forums/showp...postcount=3609 - (resources by :: "Tony65x55")
    http://www.rcgroups.com/forums/showp...postcount=3629 - (1 image)
    http://www.rcgroups.com/forums/showp...postcount=3635
    http://www.rcgroups.com/forums/showp...postcount=3648 - (1 image)
    http://www.rcgroups.com/forums/showp...postcount=3655 - (2 images)
    http://www.rcgroups.com/forums/showp...postcount=3659
    http://www.rcgroups.com/forums/showp...postcount=3661

    http://www.rcgroups.com/forums/showp...48&postcount=2 - (MAIN POST)
    http://www.rcgroups.com/forums/showp...54&postcount=9
    http://www.rcgroups.com/forums/showp...9&postcount=54
    http://www.rcgroups.com/forums/showp...4&postcount=55
    http://www.rcgroups.com/forums/showp...7&postcount=56
    http://www.rcgroups.com/forums/showp...1&postcount=74
    http://www.rcgroups.com/forums/showp...1&postcount=84
    http://www.rcgroups.com/forums/showp...&postcount=196
    http://www.rcgroups.com/forums/showp...&postcount=215
    http://www.rcgroups.com/forums/showp...&postcount=218
    http://www.rcgroups.com/forums/showp...&postcount=219
    *** http://www.rcgroups.com/forums/showp...&postcount=221 - (3 University Airfoil Databases)
    http://www.rcgroups.com/forums/showp...&postcount=225
    http://www.rcgroups.com/forums/showp...&postcount=229
    http://www.rcgroups.com/forums/showp...&postcount=230 - (3 CFD videos)

    -- KF Airfoil advantages w/ Wingtip Devices discussion (3 posts)
    http://www.rcgroups.com/forums/showp...postcount=3562
    http://www.rcgroups.com/forums/showp...postcount=3563
    http://www.rcgroups.com/forums/showp...postcount=3571




    -- "JAVA FOIL" program download...
    http://www.mh-aerotools.de/airfoils/javafoil.htm

    -- KF Airfoil Thickness Calculation Formulas -- (2 EXCEL Spreadsheets)
    http://www.rcgroups.com/forums/showp...&postcount=930
    http://www.rcgroups.com/forums/showp...postcount=2211

    -- (8) KF Airfoil design comparison on Straight Wing w/ Evaluation Scores -- (2 PDF files)
    [Test #1] -- http://www.rcgroups.com/forums/showp...postcount=1593
    [Test #2] -- http://www.rcgroups.com/forums/showp...postcount=1651

    -- KF Airfoild CFD Simulation showing Primary/Secondary Laminar Separation Boundaries -- (PDF file)
    http://www.rcgroups.com/forums/showa...mentid=2167940

    -- Sample Depron KF Airfoil w/ detailed measurements -- (1 image)
    http://static.rcgroups.com/forums/at...g?d=1178420779

    -- Air pressure values on 2 regular airfoils -- (2 images)
    (original post) => http://www.rcgroups.com/forums/showp...postcount=1575
    http://static.rcgroups.com/forums/at...g?d=1202108413
    http://static.rcgroups.com/forums/at...g?d=1202108458

    -- How to make a KF Airfoil from Foam -- (1 image)
    http://static.rcgroups.com/forums/at...g?d=1254484513



    ==================================================

    If you guys find more (technical) links about this topic, please feel free to post them here! :D
     
  3. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

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    Okay... now I'm really tired of this thread, ROFL.
    I'm done with my part of this forum for a while.
    I hope other members here will help out and find some things I may have missed? @_@

    BTW, I only did a "skim" of these posts, so I may have missed a "few" important posts, but I really don't care anymore!
    Try reading 4000+ posts in 1 day.
    Uhh...


    Anyways, I left off on (page #252, post #3768) on this forum:
    http://www.rcgroups.com/forums/showt...58321&page=252

    And on (page #16, post #238) on this forum:
    http://www.rcgroups.com/forums/showt...117276&page=16


    Hope this INFO is useful for members here...
     
  4. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

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    [​IMG] DavePowers [​IMG]

    Oh verrrry helpful! Thank you!
    __________________
    ~ Dave Powers
    RCPowers.com



    --------------------------------------------------
    Kos-Mos [​IMG]
    Thanks a lot. I just learned a whole bunch in this thread.

    And using a KF step foil might just solve an issue I had with a scratch built plane. Since it is based off an anime plane, it "should" not fly. This specific one has FSW that are too small for the plane... using KF steps might help it.

    Also, I will post results of using KF on FSW setups.
     
  5. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

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    crshbandit
    So any of u 3D guys try adding the KF airfoil to your foamie to improve harrier type manuvers? Seems like it would be a simple add on that would improve performance. Is there some formulas to calc. what the cord should be and the thickness of the added airfoil? Not an engineer here so more simple more better!:)

    ----------------------------------------
    BtownG
    Originally Posted by crshbandit

    This is what I found. Sorry it's not the best quality, if you open it in a new window you can actually read what it says.
    [​IMG]

    ----------------------------------------
    MoTheG
    The KF-AF is not a good AF but they are better than just a foamplate.
    Just the foam ist very bad, so even the KF-AF is much better.
    The trick with the step can lower the drag at a certain AoA, but only if it is done just right.
    The Drag from 2°-3° can be reduced to 1/3
    This works great at Re=600k :
    X Y
    1,00000000 0,00000000
    0,99000000 0,00800000
    0,97000000 0,00950000
    0,95677000 0,01000000
    0,90451000 0,01150000
    0,83456500 0,01500000
    0,55200000 0,01500000
    0,40500000 0,01400000
    0,40000000 0,01900000
    0,30000000 0,01800000
    0,25000000 0,01700000
    0,16540000 0,01593800
    0,09549000 0,01500000
    0,04322700 0,01494660
    0,01800000 0,01420000
    0,00900000 0,00998000
    0,00000000 -0,00000000
    0,00900000 -0,01000000
    0,01800000 -0,01300000
    0,04322700 -0,01503000
    0,65450850 -0,01503000
    0,75000000 -0,01500000
    0,83456500 -0,01450000
    0,90451000 -0,01102000
    0,95677000 -0,01000000
    0,97000000 -0,00950000
    0,99000000 -0,00800000
    1,00000000 0,00000000

    It is practically a flat plate with a step at 40%.
    But notice that the step is only about 0,06" (0,5%).
    This is NOT a 0.25" plate glued onto another, this is two layers of thin cardboard.

    Here something else than the KF-AF, this is like KF no magic.
    Drill a 0.02"-0.03" hole every 1" at 40% into your 0.25" foamplate wing. this will not increase lift but it will decrease drag and increase the stall angle.
    Also don't forget to give the leading and trailing edge an 45° angle surface facing up, this will give it much more lift: (details matter! anything will fly but there are big differences in small changes.)
    -____-----.____
    |____| -> /____\
    Again: this is not a "real" wing but it will work. :skipper: has a real wing.​


    ----------------------------------------
    MoTheG
    the KF2 is fully turbulent and the step makes the airflow disconnect from the surface.
    I don't understand the hype. If you have a wing that is always stalled then you will not notice a stall happening. :nope:
    small steps can reduce the drag, but huge steps like that will give the wing a constant stall.
    Try the trick with the tiny holes in the wings. that is not a myth but a prooven concept.​


    ----------------------------------------
    mobackwudsflyer (guest)
    Just wonderin. How's the best way to construct foil's. Watched dave use em and fully undestand the benefit's as I'm not new to aerodynamic's and flight. Would just like to know the construction process.

    TY for any links or advice.

    ----------------------------------------

    MoTheG
    Originally Posted by mobackwudsflyer
    you mean how to build them?

    1. the old way is to make ribs, wing panels front- and back- ledge and span paper or foil over it.
    2. if you use foam you can use light one like styrofoam and cut and sand it into shape as a full body.
    3. Or if you can get your hands on thin elastic foam like 4mm EPP you can bend it around ribs.
    I use method two. Real planes are build with method one.​

    ----------------------------------------
    mobackwudsflyer (guest)
    I was mainly askin about the kf step airfoil's for the flat foam plane's. When dave was testin the different one's he just kinda slipped it on the wing and taped it in place. I was just wonderin how he made them.

    Sorry if I wasn't clear. Durin the day while I'm waitin for load's at the quarry I watch the you-tube video's on my phone and read, post on the forum's. I live way out in country and only have dial-up so it's almost impossible to watch vid's at home.

    Thank's again for the info.
     
  6. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

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    AHHHH !!!!!
    When I was merging the posts, I lost BOTH posts, including the main KF airfoil post I spent over 10-hours on making.

    Thank GOD I was able to backtrack to view the original page and copy/paste it back to this format...

    Sorry guys, but at least we didn't lose the data!
    (I gota be more careful next time...)


    *** MERGED / MODIFIED POSTS ***
     
  7. MoTheG

    MoTheG Airman

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    KFm1

    could someone write about the KFm1 ?
    Dave didnt find it to be a good choise and I havent read any one praising it.
    It doesnt seem to have a place in RC-flight.
     
  8. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

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    I think it's because most RC airplane hobbiests are going to Speed or Maneuverability.

    IMHO, I think the KFm-1 is more for gliding planes.

    It might be a good test to put KFm-1 on Glider foam planes (no motors), and see how it performs.
    Also, I think it'll have to be a DELTA design wing, or the effect might be negative (my opinion)
     
  9. bshupe

    bshupe Rookie

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    I have a question. If the KF 4 is breaking the laminar airflow over the trailing edge of the wing reducing drag etc why not just make the wing the size of the stepped section of the KF? It would seem that the lower part of the step is no longer creating lift if the air being released from it off the back edge of the step. Im sure Im missing something here so please explain if you dont mind.
     
  10. MoTheG

    MoTheG Airman

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    there is so much wrong or missing here that I cant even start to explain.
    try to read more and then come back with better questions.
     
  11. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

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    Your question applies to ALL versions of the KF-m airfoils...

    If you did more reading from the 2nd post, you might understand more...
    http://www.rcpowers.com/forum/showpost.php?p=14309&postcount=2

    However, let me use the KFm-2 (top step) as an easy example:
    [​IMG]

    As you see from this diagram, the black area is the actual airfoil design.
    The blue/cyan colored lines are where lift occurs, and the green point is where the laminar boundary separation occurs (where lift ends).
    The white hashed area is where the negative air-pressure bubble is formed due to the step from the KFm airfoil.

    After airflow passes the KFm "step" point on the airfoil, the air AFTER that point actually "sticks" to the negative air-pressure bubble "THINKING" it is still part of the physical airfoil.
    By looking at the CFD diagram (line colors), it is clear that LIFT does occur over that air bubble and "pulls" that part of the airfoil up.
    (How/Why this is the case, I personally do not know because I'm not an aeronautical engineer.)

    Compared to a flat plate airfoil, having that KFm step actually improves the lift coefficient of the wing. It is also an EASY construction method, and you MUST have a "sharp" Leading Edge for this to work properly. Also, the KFm step needs to stop at 40% of the airfoil chord length.

    Of course, a REAL smooth airfoil design is preferred, but exact/optimal construction is much harder to achieve with foam.

    Now, because of the air bubble location, you can see the control surfaces on the trailing edge is not getting optimal airflow. If the control surfaces DO move, the High Pressure airflow (on the bottom of the wing) has a greater effect than the negative low pressure on top of the airfoil.
    In short... control surfaces WITH a KFm 1-3 airfoil will respond with less authority than a regular flat-plate foam airfoil.

    The KFm-4 actually IMPROVES control response, because there is an equal sized air bubble on the upper/bottom sides of the airfoil. Compared to a flat-plate airfoil, the KFm-4 WILL respond better.
    This is why Dave (on his KFm airfoil test vids) noticed rock solid responses during his turns.

    Hope this helps explain HOW the KFm airfoil workds, and why it is preferred over a regular flat-plate airfoil.
     
  12. bshupe

    bshupe Rookie

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    Thanks for the additional, very detailed info. I hope I didnt come accross as combative, I was just asking a basic engineering question based on the idea that a significant part of the KF design is to reduce drag which reducing the airfoil area would also do. I am trying my best to understand the ratio between the reduction in drag : the increase of lift and the overall performance improvement of either or both.

    Thanks again!
     
  13. steverc

    steverc Rookie

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    Dredogol,

    Trying to understand this, at least to a degree, so thanks for your explanations.

    One thing though, your colored diagram looks like a KF2, and you stated 'the KFm step needs to stop at 40% of the airfoil chord length', i am going to assume you mean 40% from the leading edge, but the KF2 diagram earlier on states 50% of chord length?

    You also said 'MUST have a "sharp" Leading Edge for this to work properly' - Do you mean sharp edge as in, not just the vertical edge of a piece of depron? so it could be a curved edge, or a 45 degree angle cut, or two 45 degree cuts to create sharp edge at the mid vertical, or i guess, do you mean a real thin edge?

    Thanks again for taking the time to list all this stuff.
     
  14. slick8086

    slick8086 Rookie

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    clarification

    Sorry if this is obvious to every one else, but I'd like to make sure I'm understanding this properly.

    The step distance should be 7%-9% of the chord.
    [​IMG]

    So if I wanted to use a single piece of 1/4" blue foam for the top plate to create the step, my minimum chord will have to be (roughly) 2-3/4" for a 9% step?
     
  15. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

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    40% is considered optimal length for the KF airfoil (leading edge to trailing edge [including the control surfaces])

    Basically, you cannot have a flat "block" at the leading edge.
    It has to be AT LEAST a sharp edge up front.
    The BEST result is a rounded edge, where the upper edge is higher / more rounded.
    Look at some KF airfoil diagrams to see what I mean.
     
  16. MoTheG

    MoTheG Airman

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    What it is good for

    Here is what the KF is good for:
    it is good for planes that have a deep wing and fly slow (or at least are supposed to be able to)
    an example of such a plane is the RCPowers YF-23 model, it's wings are as deep as they are wide (low aspect-ratio) and it can do the delta-style (drag-lift/vortex-lift) slow flight.
    People who tested the KF-AFs on normal wings (high (>2) aspect-ratio) did not find benefits.
     
  17. bshupe

    bshupe Rookie

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    I dont want to start an argument but I have seen some guys online (youtube vids and thier website) that use the KF wing type on parkjet planes that they fly into the 150 mph range with great high-speed handling. Admittedly, they kind of suck at low speed but much of that is because they have no flaps or other controls that would assist slow speed flight at landing etc. Fact is, they crash an awful lot at launch and landing but they perform like few other R/C planes I have seen at the speeds they fly.

    Im just adding another facet for consideration.
     
  18. MoTheG

    MoTheG Airman

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    hardly a parkjet at 150mph.
    how do you know that another wing would not have been significantly better(faster)?
    how do you know it is not just a 2kW powersystem?
    hardly an argument here.
     
  19. bshupe

    bshupe Rookie

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    I didnt say another wing would or would not be better or faster. What I said was in contradiction to your comment "Here is what the KF is good for" effectively putting it into a little box.
     
  20. bobdabilduh55

    bobdabilduh55 Top Gun

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    This just in from our buddy Dick Kline concerning New Wind-Tunnel Tests of his KF Airfoils.
    Here is his email to me….

    Bob ...

    I thought that you might be interested in this report.

    ~ Dick

    http://www.ripublication.com/aasa/aasav3n2spl_11.pdf

    School of Aeronautical Sciences, Hindustan University, Padur, Chennai, Tamil Nadu, India.
    Abstract
    This paper investigates and compares the flow over a typical scaled down model of Kline-Fogleman airfoil with a baseline airfoil model at different angles of attack in low subsonic speed. The intent of this study is to evaluate flight performance of one model of the NACA 23015 airfoil and one Kline-Fogleman variant of the NACA 23015. The airfoil models are fabricated with a chord length of 165mm and with a span of 300mm. Aerodynamic characteristics are studied at a free stream velocity of 25m/s in subsonic (blow down type) wind tunnel with the test-section size of 600 x 600 x 2000mm. It is an open cycle, intermittent suction type Wind Tunnel and makes use of the compressed air provided by a compressor. It has a maximum speed of 50m/sec and a compression ratio of 9:1.The settling chamber of the tunnel is of dimensions 1.8 x 1.8m2. Measurements of static pressure revealed the quality of flow field experienced over the models.
    The values of lift & drag coefficients for the airfoil in consideration with NACA 23015 shows stall characteristics at an angle of about ? = 150. The Kline-Fogleman airfoil resists stall even at an angle of ?=450. In fact it doesn’t stall completely but levels of with a very minute L/D ratio. This leveling off is observed for a range from ?=450 to ?=600. The Kline-Fogleman airfoil not only resists stalling for very high angles but also prevents the free fall usually observed at critical angle by leveling off.
    The KF airfoils and derivative 'stepped' airfoils have gained an enthusiastic following in the world of foam constructed radio controlled model aircraft. This study pushes the utility of KF airfoil further more by applying its typical step over the NACA 23015 airfoil.

    3. Conclusion
    An attempt was made to investigate and compare the flow over a typical scaled down models of NACA 23015 airfoil and Kline-Fogleman airfoils at different angles of attack in subsonic wind tunnel. NACA 23015 airfoil and its Kline-Fogleman variant (KFm2) was developed in Burma teak wood. Both were tested in wind tunnel for pressure tapping and the e lift and drag forces were calculated.Aerodynamic characteristics were studied at a free stream velocity of 25m/s in subsonic (blow down type) tunnel. Measurements of static pressure revealed the quality of flow field experienced.It was then found out through comparison that the Kline-Fogleman variant with a step at 50% chord length possessed superior lift characteristics as shown in the graph in Fig 6. More importantly the KFm2 variant resisted stalling even for very large angles of attack. The KFm2 did not stall till angles of ?=450after that it leveled off with a good L/D ratio.This can be of very good use as leveling off prevents the accidents caused by free fall at critical angles.
     
    F1wanabe likes this.
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