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Thread: Fun Wing Tip Experiment (uploaded for Skywagon)

  1. #1
    Seaworthy's Avatar
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    Fun Wing Tip Experiment (uploaded for Skywagon)

    The original wings are TCOW extended squaretip. The extended portion is all in the fiberglass tip.The spar ends are the same span as Piper's.

    The new aluminum wing tip has 2-1/2"more span. The rib is completely exposed. The yarns flow straight back in most flight attitudes except during stall

    when the outboard row curls up and outboard.
    The other wing tip is the standard TCOW(Backcountry) tip. What would you expect to find? Which has

    more drag? Lift? Would you expect a cruise speed difference? Higher or lower?
    What do you guys think? After a while I'll tell you what I found. In the

    meantime I'll be making another new tip for the other side to balance the two wings.


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    Last edited by Seaworthy; 06-23-2020 at 11:06 AM.
    Marine Corps Aviation since 1966
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    skywagon8a's Avatar
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    Thanks Tom, I just can not manage to post pictures from my camera through the computer to this site.
    N1PA

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    BC12D-4-85's Avatar
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    I might try sealing the rib end w/o a tip with something to reduce turbulence drag. Maybe a thin polycarbonate plate. I've had those Horner/Hendricks tips on two Supercubs - one was already on and one I had installed - and they didn't seem to harm performance other than some aileron sluggishness after with non-extended controls. They are an early CallAir Ag design later fitted to Pipers.

    Edit: Here's links to two PDF files regarding the CallAir agplane evolution. The first is an overall analysis of flying characteristics and lift distribution. Page 14 discusses the wing planform. The tips were probably added (?) to the A-9 and B-1 to improve spray swath distribution plus control vs the original rounded design. The second PDF discusses the history of CallAir with Chapter 3 on the A-9 and B-1.

    https://apps.dtic.mil/dtic/tr/fulltext/u2/671079.pdf
    http://lincolncountywy.org/archives/...e,%20(749).pdf

    Gary
    Last edited by BC12D-4-85; 06-23-2020 at 03:49 PM.
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    skywagon8a's Avatar
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    One of these new A-4s was delivered to the operator at the Clark Airport in Hanover Mass in 1958. On the day it was delivered, the new owner took me for a ride in it. He was a WW2 P-47 Ace. There was a jump seat behind the pilot for the ground crew to ride to the job site.

    This airplane had flat plates on the wing tips. He used it for several years supplementing two Stearmans, one of which also had flat plates on the wing tips (National Hi-lift wings). Little did I know at the time, that many years later I would own all three planes. The Callair was no longer airworthy as the tubing in the fuselage and the fertilizer didn't get along together.
    N1PA
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    ask frank how it works?
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    BC12D-4-85's Avatar
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    Perhaps Lil'Cub's focus is going slow not fast. He originally had tips and flat plates according to the pics available. Weight is everything when lift and power are fixed.

    Sky...which wing flew slower at stall and in cruise. Maybe one needed more rudder due to added drag? We await the results. It'll be fun to see if the flat end does as well and the price of used tips drops.

    Edit: In link #1 - Post #3 they analyze the effect of a large radius leading edge added to the Clark-Y airfoil. It apparently extended below the LE, and above 80 mph caused some issues that they detail with a suggested fix (fair in the lower rear of the cuff). But for the intended use it helped performance.

    Gary
    Last edited by BC12D-4-85; 06-23-2020 at 06:18 PM.

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    Jerry Burr's Avatar
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    Seaworthy. Yes make another tip. They have to be the same or the test is no good. You have to test pairs together. Otherwise the minute you touch the rudders the test is junk. I added 28 lbs to one wing at the lift strut juncture and planned to test one tip at a time. The tip with the weight. In doing so you have to keep both feet flat on the floor. When doing so, the wing with the weight was the light wing. In other words it rolled away from the weight. P-factor thing. Bad test. Tested in pairs worked great. Jerry
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    BC12D-4-85's Avatar
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    A typical gen aviation wing can't easily be sealed to air pressure or it would expand or compress as altitude changes unless compensated. The upper and lower surfaces experience differential pressure, but it's likely the lower surface vs internal wing pressure above, and the upper vs the same internal pressure below....not upper vs lower directly in low altitude unpressurized aircraft.

    Exposing a wing tip shouldn't affect that dual surface pressure differential and overall circulation affecting lift and drag, but might add-subtract lift and drag plus local internal pressures from disturbed airflow at the exposed tip.

    Experiment and verify Pete.

    Gary
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    skywagon8a's Avatar
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    Quote Originally Posted by Jerry Burr View Post
    Seaworthy. Yes make another tip. They have to be the same or the test is no good. You have to test pairs together. Otherwise the minute you touch the rudders the test is junk. I added 28 lbs to one wing at the lift strut juncture and planned to test one tip at a time. The tip with the weight. In doing so you have to keep both feet flat on the floor. When doing so, the wing with the weight was the light wing. In other words it rolled away from the weight. P-factor thing. Bad test. Tested in pairs worked great. Jerry
    Jerry, Seaworthy made the post for me because of my inability to post pictures. Rudder and stick position do effect the results. Keep the opinions and analysis coming. This test was only the first step in a series of tests which is expected to provide something more than you have seen here yet. Stand by, I'll tell you later. In the meantime I thought this would be fun and so far it is on track.
    N1PA
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  10. #10
    BC12D-4-85's Avatar
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    For fun put a cam inside the open wing looking out and tuft the rib supports as well to note local flow. Make the lower tufts longer so they can wrap and twist about up and back more. Color yarn by location. Maybe a cam on the float lift fittings looking out on top of the wing.

    Gary
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  11. #11
    skywagon8a's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    For fun put a cam inside the open wing looking out and tuft the rib supports as well to note local flow. Make the lower tufts longer so they can wrap and twist about up and back more. Color yarn by location. Maybe a cam on the float lift fittings looking out on top of the wing.

    Gary
    Good idea Gary, Someone with camera expertise is welcome to come with his camera to help make this happen.
    N1PA
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    Quote Originally Posted by BC12D-4-85 View Post
    Maybe a cam on the float lift fittings looking out on top of the wing.

    Gary
    Something I had not thought of. The top of my plane has a few 3/8-24 threaded hardpoints. I should make a streamlined mast to get a camera up a few feet or so when it comes time to fly this.
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  13. #13
    BC12D-4-85's Avatar
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    Here's a basic wind tunnel test of three wingtips. Not much change noted among the choices. I assume the square end was closed over: http://acversailles.free.fr/document..._wing_tips.pdf

    Edit: Dr. Hoerner's Tech Report 5752: https://apps.dtic.mil/dtic/tr/fulltext/u2/a800374.pdf

    Edit: Note the Hoerner tip did not have an extended rear span unlike the tips on Sky's Cub above. There are disclaimers for the effects of airspeed, aspect ratio, and airfoil shape.

    And a Supercub.Org Classic on tips. See both pages: https://www.supercub.org/forum/showt...11-madras-tips

    Gary
    Last edited by BC12D-4-85; 06-25-2020 at 01:19 PM.

  14. #14
    Steve Pierce's Avatar
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    What happened to the really old thread where Jerry posted pictures of his test rig and tufted wings in flight?
    Steve Pierce

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    Will Rogers

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    Wing Lift Distribution

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    Gary,


    The lift distribution graph is excellent. Interesting how prop wash has a stronger effect further towards the tips at higher speed. Makes sense with the air being less "sticky" at the higher Reynolds Number; so the higher speed prop wash can more easily accelerate the air further out towards the tips.

    Thanks for the Tech Report.

    Jonny







    Quote Originally Posted by BC12D-4-85 View Post
    I might try sealing the rib end w/o a tip with something to reduce turbulence drag. Maybe a thin polycarbonate plate. I've had those Horner/Hendricks tips on two Supercubs - one was already on and one I had installed - and they didn't seem to harm performance other than some aileron sluggishness after with non-extended controls. They are an early CallAir Ag design later fitted to Pipers.

    Edit: Here's links to two PDF files regarding the CallAir agplane evolution. The first is an overall analysis of flying characteristics and lift distribution. Page 14 discusses the wing planform. The tips were probably added (?) to the A-9 and B-1 to improve spray swath distribution plus control vs the original rounded design. The second PDF discusses the history of CallAir with Chapter 3 on the A-9 and B-1.

    https://apps.dtic.mil/dtic/tr/fulltext/u2/671079.pdf
    http://lincolncountywy.org/archives/...e,%20(749).pdf

    Gary
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  16. #16
    BC12D-4-85's Avatar
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    These reports have value but do take some struggle to understand. Mississippi State did lots or research via Prof. Raspet, Cornish, and Bryant among others. Cal Center (pers. com. from Charly @ Crosswinds STOL) and Gordon Mandel used the info I was told years ago. Here's one referenced that would also be interesting but I can't find an online source.

    Smith, Michael R., Roberts, Sean C., and Patrick, John D., Evaluation of the Piper PA-18 Agricultural Aircraft.
    Research Report No. 63, Aerophysics Department, Mississippi State University, State College, Mississippi, September 1965.

    Of course today it takes real experiments like Peter N1PA has proposed here to investigate further options.

    Gary

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    30 years ago my neighbor flew a cub with a normal bow-tip wing and a wing with a squared off droop tip ( Hendricks I think). He said he could tell no difference in flight. He was a full time commercial pilot and no novice.

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    I have wanted to stay out of this, but I guess I am not.
    For a straight wing aircraft the wingtip for the most part does not matter.
    If you read allot of Hoerner's design theory, and follow this with the work of Mike Arnold and Burt Rutan. Keep in mind Burt has had many very able minded people in his employ.

    Look at Arnold's AR5 and the AR6, look at the tips used on two of the lowest drag planes ever made. Simple rounded tips.
    Arnold's AR5 did not even run a spinner. It has been proven the stagnant air around the prop hub has little to no effect on drag. They are pretty and they can make a good profit.
    Even Hoerner, late in life published papers that once there was true data on his various tip designs, they made little to no difference.

    Where a wingtip can make a difference is on a swept wing. Not only do the sell seats, but they save a few pounds of fuel, less than the few hundred pounds of seats sold. Freighters have little need for real fancy tips. A simple upturn will do. Freight dosen't care.

    Just wait till you see what my plane will have

    The wing tip essentially does not matter. Companies offering droop or upswept tips make their best money if they hire very good marketing people.

  19. #19
    mike mcs repair's Avatar
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    Fun Wing Tip Experiment (uploaded for Skywagon)

    Quote Originally Posted by CharlieN View Post
    the wingtip for the most part does not matter..
    This!!



    Sent from my iPhone using SuperCub.Org mobile app
    Last edited by mike mcs repair; 07-04-2020 at 06:27 PM.
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  20. #20
    BC12D-4-85's Avatar
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    Anecdotal conversations with folks that fly SEL or SES low vs high - light vs heavy - seem to favor more wing span and area especially at altitude. Makes sense that aspect ratio. I've had both stock and extended and the benefit of extended wings for me was takeoff and landing on floats. Speed was drag limited anyway and efficiency not a factor.

    Guess we'll see what the tip design here brings. I never did remove the tips and just fly the wing extension. That in itself as an experiment may be revealing.

    Gary
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    As Gary says, take the squared off wing offering more area, now move the aileron out as far as possible, now extend the flaps.
    Now those wing tips give you more lift and the ailerons are more responsive.
    Pete, follow up here with the data you have.

  22. #22
    BC12D-4-85's Avatar
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    Pete's third pic shown in the intro is an open ended extended wing. I wonder if that's the final design (like Frank Knapp's Lil'Cub now has)? Above I mentioned sealing it...but maybe a sealed vs unsealed experiment is on his list.

    Gary

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    Frank's biggest concern is weight. For all we know Lar's would not sell him the lightweight cloth to cover the ends of the wings. The Oratex RC plane covering is all we need.
    FWIW I love the video of Frank in his back yard opening the throttle and the plane takes off, with no wings. Sorry I am not good chasing links.
    Pete did some tuft testing to improve the gaps on his plane, good stuff. I know he will follow up. There is allot more improvement in what he chased down than what different tips will offer.

  24. #24
    BC12D-4-85's Avatar
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    Back when C.G Taylor designed the early E-2 Cub he did the wing right. Then the J-2 came along and ever since we've been trying to fix it or make it better. J-2 left and earlier E-2 right.
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    Soooooo when we are talking wing tips are we including the last two rib bays (round tip wing), or are we just talking about two full bays normal rib profile with a tip on the end, or the STC that uses normal rib but shortens spars. If wing size did not matter we would all be looking for pacer wings because they are lighter.
    DENNY
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    My opinion, that answer would be goal oriented. Low speed or wide range of speed operations, add the ribs and build long.
    Better cruise, shorten it.
    I would expect most people hare would build the longer version.

  27. #27
    BC12D-4-85's Avatar
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    Pete has a CS prop and big mill to drive it. Speed the goal? Buy a fast low drag airplane. Floats? Drag hinders improvements unless float deck to wing angle can be optimized for design (done that here with +3/4" longer rear struts vs higher wing lift). Control? The rate of roll and adverse yaw between builds will inform. No change detected between tips? Don't make a bird nest available via an open end.

    Edit: prop isn't CS but ground adjustable. Thanks Pete for the correction below.

    Gary
    Last edited by BC12D-4-85; 07-05-2020 at 12:19 PM.

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    skywagon8a's Avatar
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    This is fun, keep the talk coming.

    My prop is a ground adjustable not CS. It is currently set to produce just under 2700 rpm at wide open throttle level flight. The second test is getting close which will be a duplicate of the first test with the opening on both wings instead of just one.
    N1PA

  29. #29
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    FWIW. When I built mine 25 yrs.ago, I went with full ribs all the way to where the tip of the bow would have been and left it square. I did have about a 2" tail tip outboard of the aileron which was pushed out, and ended up with 86" for flaps. The square tip was fabric covered. I flew it that way for a few yrs. and then added some very shallow droop tips. The ONLY difference that was obvious to me was that the tips lightened the aileron pressures slightly. Have always been very happy with the leverage of the aileron being outboard for lifting a float out of the water sooner that you might be able to do otherwise. I never could tell if the droop tip offered a little more cushion in ground effect. Maybe? Or maybe it just looked a little more finished? When i was competing at the Greenville Fly In in the late 90's and early 2000's it still had the squared off tips and was still beating all comers off the water, including the 180hp super cubs. It sure kept the boys guessing. LOL
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    Steve Pierce's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    These reports have value but do take some struggle to understand. Mississippi State did lots or research via Prof. Raspet, Cornish, and Bryant among others. Cal Center (pers. com. from Charly @ Crosswinds STOL) and Gordon Mandel used the info I was told years ago. Here's one referenced that would also be interesting but I can't find an online source.

    Smith, Michael R., Roberts, Sean C., and Patrick, John D., Evaluation of the Piper PA-18 Agricultural Aircraft.
    Research Report No. 63, Aerophysics Department, Mississippi State University, State College, Mississippi, September 1965.

    Of course today it takes real experiments like Peter N1PA has proposed here to investigate further options.

    Gary
    Raspet was killed in a Super Cub that had a vacuum cleaner motor run off the engine and the suction was run through a double windshield and a series of precision holes drilled in the leading edges. They had a problem with these holes getting clogged. alked to an engineer that worked with him and another person that was a builder of his designs. Unfortunatley all but one have passed on and he is in his 90s.
    Steve Pierce

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    Quote Originally Posted by CharlieN View Post
    I have wanted to stay out of this, but I guess I am not.
    For a straight wing aircraft the wingtip for the most part does not matter.
    If you read allot of Hoerner's design theory, and follow this with the work of Mike Arnold and Burt Rutan. Keep in mind Burt has had many very able minded people in his employ.

    Look at Arnold's AR5 and the AR6, look at the tips used on two of the lowest drag planes ever made. Simple rounded tips.
    Arnold's AR5 did not even run a spinner. It has been proven the stagnant air around the prop hub has little to no effect on drag. They are pretty and they can make a good profit.
    Even Hoerner, late in life published papers that once there was true data on his various tip designs, they made little to no difference.

    Where a wingtip can make a difference is on a swept wing. Not only do the sell seats, but they save a few pounds of fuel, less than the few hundred pounds of seats sold. Freighters have little need for real fancy tips. A simple upturn will do. Freight dosen't care.

    Just wait till you see what my plane will have

    The wing tip essentially does not matter. Companies offering droop or upswept tips make their best money if they hire very good marketing people.
    How about the tufted tip pictures Jerry posted years ago? Looked like from that the the droop tip wing had the air flowing over the aileron and the tip bow wing had it spilling off the end of the tip.
    Steve Pierce

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  32. #32
    BC12D-4-85's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    Raspet was killed in a Super Cub that had a vacuum cleaner motor run off the engine and the suction was run through a double windshield and a series of precision holes drilled in the leading edges. They had a problem with these holes getting clogged. alked to an engineer that worked with him and another person that was a builder of his designs. Unfortunatley all but one have passed on and he is in his 90s.
    Some of the PA-18's boundary layer suction experiment (and other STOL test summaries) is also available here: https://www.sae.org/publications/tec...ontent/670245/ I have a copy and it's a good read especially the bibliography for further links.

    Wonder if reversing the air flow through the small suction holes would have unclogged them?

    Gary

  33. #33
    Farmboy's Avatar
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    Speaking of blown wings. With the advent of modern compact and lightweight leaf blowers, maybe old ideas will now work?

    A friend posted this as a joke, but if used differently....

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    Transmitted from my FlightPhone on fingers...
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  34. #34
    BC12D-4-85's Avatar
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    Seal the Cub upper flap fairing to wing and outboard exit. Drill holes along the rear edge or under the rear lip. Pressurize the inboard fairing entry with electric blower to energize flow over deflected flap. Drink more coffee then go test.

    Gary
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  35. #35
    skywagon8a's Avatar
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    Quote Originally Posted by supercrow View Post
    .... then added some very shallow droop tips. The ONLY difference that was obvious to me was that the tips lightened the aileron pressures slightly. Have always been very happy with the leverage of the aileron being outboard for lifting a float out of the water sooner that you might be able to do otherwise. I never could tell if the droop tip offered a little more cushion in ground effect. Maybe? Or maybe it just looked a little more finished?
    When the droop tips were installed on this airplane, initially I could find absolutely no difference in the flight characteristics. This was a case of the original rounded tips being removed and the droop tips being screwed on. After going through all of the usual flying antics trying to find something, I did. Power idle glide, full flaps, gear up, descending steep banked turn to a landing on the water. During the flare to arrest the sink rate while still banked I noticed a bit more cushion than with the original tips. A definite improvement in this condition. Normally this plane would not have a cushion in that condition so would just settle through the descent making a solid landing. This was only noticeable in a banked descending turn. During a power idle wings level landing there was no noticed difference.

    This airplane has 68" longer wing span than the original Seabee as well as 8 feet more total flap length. These droop tips on a stock Seabee may have further improvements, I have not had the opportunity to fly the single engine Bee with droop tips. I have flown them with no alterations, tip plates, 12" and 24" extensions. All three of those were an improvement. As those of you who have flown the Seabee know, it glides like a streamlined anvil. Any extra on the tips helps.

    N1PA
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  36. #36
    skywagon8a's Avatar
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    Test #2
    The other wing with it's extended tip. The two tips extend the span by 3" over the original square tip. The extra 3" provides 15.3# of lift enough to support the weight of the new extensions. The wingspan in this condition is 37'3".

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    What are your thoughts as to any differences between this configuration and two tips like the one below?

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    These two pictures are to show the flap and aileron configuration and how they are different from a stock PA-18. Maximum flap deflection is 56 degrees.

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    Finally manged to post a picture.
    N1PA
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  37. #37
    BC12D-4-85's Avatar
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    How does it fly with the change?

    Gary
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  38. #38
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    Quote Originally Posted by BC12D-4-85 View Post
    How does it fly with the change?

    Gary
    I still have two more alterations and tests in mind before I comment. Though last evening I thought of a third. That third one will take some research and construction time. Still thinking on yes or no on that one.
    N1PA
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  39. #39
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    Test #3

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    Open wing tip covered with fabric.
    N1PA

  40. #40
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    Test #4

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    Added fence below wing tip ending at trailing edge. This is a water spray rail for the EDO 3500 floats.
    N1PA
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