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Thread: Experimental Cub Kit with Slotted Wing 180 Hp and Big wheels any suggestions on kits

  1. #161
    skywagon8a's Avatar
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    Quote Originally Posted by RVBottomly View Post
    I saw that in an earlier picture taken from above and thought the same thing. But then there are Junkers flaps that are out there on their own.

    It does seem like it would add drag in cruise.
    My thinking is that the leakage would move the center of lift forward which would pitch the nose upward increasing the fuselage drag.
    The Junkers is a rather dirty airplane aerodynamically.
    N1PA

  2. #162
    Southern Aero's Avatar
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    RV

    What you have shown there is very similar to what I have going on with the stretch. At flaps 12-15 it will already have the lower slot exposed, its sealed at 0. Upper slot begins to open between 20-25. At 40-45 both slots exposed. I can get 48-50 degrees with this configuration. Upper seal is a mylar strip to flex with aileron surface and keep seal 0-minus 5.





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    ......... It doesn't cost any more to go first class! You just can't stay as long.
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  3. #163
    skywagon8a's Avatar
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    Southern Aero, What airfoil are you using? I experimented with moving the ailerons up in cruise on my 185. This was easy with the electric drooping system. In any position other than neutral the cruise speed was slower.
    N1PA

  4. #164
    Southern Aero's Avatar
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    sky

    Ha, its been a "secret" .......... Same as yours, just a little thicker ................. 13.5%. The -5 reflex to 12-15 degrees will be manual with electric flaps and electric trim. Something has to be electric or you would run out of hands on a go around. A lot of folks have been asking for info and pics. I'll get some pics up as soon as I get something "presentable". The fuselage is mostly done, looks like a bunch of rusty, burned up tubes at the moment and the basic wings are done. Will drop the fuselage down from hangar beam soon to finish interior/stringer attach stuff, mate everything up and build the struts.
    ......... It doesn't cost any more to go first class! You just can't stay as long.
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  5. #165
    RVBottomly's Avatar
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    Quote Originally Posted by Southern Aero View Post
    RV

    What you have shown there is very similar to what I have going on with the stretch. At flaps 12-15 it will already have the lower slot exposed, its sealed at 0. Upper slot begins to open between 20-25. At 40-45 both slots exposed. I can get 48-50 degrees with this configuration. Upper seal is a mylar strip to flex with aileron surface and keep seal 0-minus 5.
    Thanks for posting those images! That looks really cool. The mylar strip is something I hadn't considered.

    Now I want to pry a little more--are you using slats as well? I seem to remember you had drawings for the L14.

  6. #166
    RVBottomly's Avatar
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    Quote Originally Posted by flyrite View Post
    For landing considerations only, Might be best to try and mimic ground effect vehicles. You very seldom see any kind of slotted flaps on those. One of the reasons I thought it more effective to eliminate any slots and deflect as much air towards the ground as possible. Seems to me any slight loss of lift by elemenating the slots on a flap would more than be made up for by capturing under the wing in ground effect as much air as possible and smoothly deflected downwards.
    flyrite, that reminds me of a question I've had for a long time on your plane. Did you have the bottom flap before adding the split flaps? If so, how effective was that by itself?

    I was thinking it would have a lot of ground effect.

  7. #167
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by RVBottomly View Post
    ...

    Now if I can find a picture of the Rev 3 wing. All I've been able to find is tantalizingly low on detail.

    Vic
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  8. #168
    RVBottomly's Avatar
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    Thanks Mike! Now I have something to study.

    Vic

  9. #169
    Southern Aero's Avatar
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    Now I want to pry a little more--are you using slats as well? I seem to remember you had drawings for the L14.[/QUOTE]

    Yup, but slats not slots as on the L14 very similar to the Helio
    ......... It doesn't cost any more to go first class! You just can't stay as long.
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  10. #170
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by Southern Aero View Post
    Now I want to pry a little more--are you using slats as well? I seem to remember you had drawings for the L14.
    Yup, but slats not slots as on the L14 very similar to the Helio[/QUOTE]

    Not me. My customer. Yes on slats.


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  11. #171

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    Quote Originally Posted by skywagon8a View Post
    Southern Aero, What airfoil are you using? I experimented with moving the ailerons up in cruise on my 185. This was easy with the electric drooping system. In any position other than neutral the cruise speed was slower.
    Did you raise the ailerons too?

  12. #172
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    Quote Originally Posted by mike mcs repair View Post
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    mike, Is there going to be a fairing (gap seal) installed on the trailing edge after covering or is the shape going to remain as it is shown in the picture?
    N1PA

  13. #173
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    Quote Originally Posted by CharlieN View Post
    Did you raise the ailerons too?
    Charlie, I have an electric aileron drooping system. For an experiment I rigged it in order to move the neutral position of the ailerons in flight. This because Maule was advertising a reflex flap position for cruise. So I thought that I would see what would happen by reflexing the ailerons or with a slight droop. Any position other than in line like Cessna built it slowed the cruise speed. The up position dumped the trailing edge lift which is why I'm having reservations on that Rev 3 flap system.
    Last edited by skywagon8a; 03-25-2019 at 05:41 AM.
    N1PA

  14. #174

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    Ahh, yours was on the ailerons, I have not read all of last nights posts yet so I missed that. I had expected this was reflexing the flaps which are more commonly done.

  15. #175
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    Quote Originally Posted by skywagon8a View Post
    Charlie, I have an electric aileron drooping system. For an experiment I rigged it in order to move the neutral position of the ailerons in flight. This because Maule was advertising a reflex flap position for cruise. So I thought that I would see what would happen by reflexing the ailerons or with a slight droop. Any position other than in line like Cessna built it slowed the cruise speed. The up position dumped the trailing edge lift which is why I'm having reservations on that Rev 3 flap system.
    Sounds like an interesting experiment. My flaps reflex slightly, but I don’t think I cruise fast enough to see a difference in speed. The airplane changes pitch attitude though.

    I would guess that reflexed flaps might work better than ailerons due to washout, but that’s just a guess.
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  16. #176

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    Reflexing really only plays it's hand with airfoils with a fair amount of pitching moment. An airfoil with any cusp on the underside truly needs to be reflexed.
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  17. #177
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    Quote Originally Posted by CharlieN View Post
    Reflexing really only plays it's hand with airfoils with a fair amount of pitching moment. An airfoil with any cusp on the underside truly needs to be reflexed.
    That makes sense, thanks!

  18. #178
    Southern Aero's Avatar
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    Quote Originally Posted by CharlieN View Post
    Did you raise the ailerons too?
    Yes. But with that said............ with this airfoil it may not be that beneficial. Testing will tell. If I get 3-4 knots out of it, it will be worth while. The "mixing system" will give me about 18-20 degrees total movement of flaps and ailerons. If the -5 works well, great. If not, it can be adjusted back to zero and not used to reflex. Reflex worked on the Maule but it has the same airfoil as the Pipers. It just killed some lift and got rid of some trim drag.
    ......... It doesn't cost any more to go first class! You just can't stay as long.

  19. #179
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    Quote Originally Posted by Southern Aero View Post
    Yes. But with that said............ with this airfoil it may not be that beneficial. Reflex worked on the Maule but it has the same airfoil as the Pipers. It just killed some lift and got rid of some trim drag.
    There is one very big difference between the two airplanes. The Maule has a fixed stabilizer with trim tabs on the elevator. Reflexing the flap will effect the fixed position drag of the stabilizer. The Pipers have a movable stabilizer which neutralizes it's own drag generating position. Reflexing a Piper wing trailing edge will do nothing. Which is why my 185 slowed down with the ailerons deflected in either direction.
    N1PA
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  20. #180
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    Quote Originally Posted by RVBottomly View Post
    flyrite, that reminds me of a question I've had for a long time on your plane. Did you have the bottom flap before adding the split flaps? If so, how effective was that by itself?

    I was thinking it would have a lot of ground effect.

    Yea , Bottom flap before split flaps. No noticeable lowering of stall speed, But was great for popping off ground and providing drag for landings. widened the cord to be flush with the bottom fuselage when deployed.

  21. #181
    Southern Aero's Avatar
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    I agree with you about the fixed and not stabilizer. I may not run a jack screw in mine TBD. But trim is drag no matter how you get it, the wing has to carry that down load depending on your speed and weight, the farther your CG is from the center of lift the more you trim. I am just going to see how much difference it will make. Reflexing the ailerons only is about the same as washing out the wing more............ more drag as AOA would need to be slightly higher, wouldn't it? Do you agree a "flat" wing will be a little faster than a "washed" wing? The version I'm working with will reflex the entire rear of the wing, not just the flaps or ailerons but both. But the gain it may have might not be worth the effort. If not, I'll adjust the "mixer" to be a manual motion for 0 to 15-20 and electric for the rest.
    ......... It doesn't cost any more to go first class! You just can't stay as long.

  22. #182
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    Quote Originally Posted by Southern Aero View Post
    ... But trim is drag no matter how you get it, the wing has to carry that down load depending on your speed and weight, the farther your CG is from the center of lift the more you trim.
    Not quite. If you have a fixed stab and a trim tab on the elevator there will be just one CG location and speed when all three surfaces are aligned in the minimum drag position. At any other CG there will be some deflection between the three creating an increase in drag. With a trimming stabilizer there are infinite CG locations where the two surfaces will be aligned in the minimum drag position.
    Your idea of adjusting the trailing edge of the wing for trimming purposes is not something that I have given much thought. It will be an interesting experiment. I can see how it will allow an expansion of the CG location while retaining a minimum drag on the fixed stabilizer and trim tab tail.

    I have not found that changing the washout of a wing by small amounts makes any noticeable amount of change in drag.
    N1PA

  23. #183
    Southern Aero's Avatar
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    I'm sure there are some other guys in here that have rigged a Cub wing flat, makes a little difference. ......... especially clip wings, I always rig them flat.
    ......... It doesn't cost any more to go first class! You just can't stay as long.
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  24. #184

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    SA,
    Are you going to have any adjustment in the horizontal for tuning or development? Flat surfaces or airfoil?
    In the planes I have designed and built in the past I have failed to get the tail right a few times, and that was when I was better with math than I am now.

    With allot of pitching moment an airfoil in the tail surface has value. This pitching moment might only be present at high loads when the flaps are deployed, granted trim drag is not important here.

    I am expecting enough unknowns in my build that a portion of my flight testing will be to see if my horizontal and elevator are "in plane"during cruise, not to mention not running out of reserved authority throughout the flight envelope .
    Variations of this will be many factors with CG relationship to Center of pressure with relation to pitching moment. Something that obviously is ever changing.

    Wing twist, a simple rectangular wing should essentially be flat. If you are going to have any LE devices there is no need for twist. The LE device will hide any harsh caricaturists. Or should at least.

    MIT, the university did an intercollegiate contest to actually determine the twist withing a rectangular wing for maximum performance. The result was the wing was not actually "flat" but twisted down slightly mid span and back up a the tip. The final outcome turned out that the type of tip used offered more variables than the twist distribution spanwise. I wish I could find the link to that study.
    Other variables involved were variations in spanwise flow, something that also varies with each change of loading on a wing as well as wing tip design.

    My wing will be flat. I am not good enough to calculate the up twist of the tip on my rectangular wing.

    Anther note, this may bust some theories.
    People have used different airfoils on fabric wings with the belief they could have laminar flow.
    Unfortunately laminar flow is not just front to back flow but it has a spanwise contingent as well. With the rise and fall of spanwise flow over the crest of a rib pretty much ensures the flexible surface of a fabric over ribs will not achieve the low drag of a laminar wing.

    Heck very few aluminum skin wings truly have laminar flow anywhere near as close to what theory says they might.

  25. #185
    skywagon8a's Avatar
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    Quote Originally Posted by Southern Aero View Post
    sky

    I'm sure there are some other guys in here that have rigged a Cub wing flat, makes a little difference. ......... especially clip wings, I always rig them flat.
    SA, We are beginning to get deep into the weeds away from the topic of the thread. Charlie has given a good explanation. Here is a deep weed read if you have the time: http://www.wainfan.com/wingdes.pdf Barnaby Wainfain is a well known engineer who has a regular article in Kitplanes magazine.

    We all know (or should know) that a rectangular shaped wing (Cub) has the most benign stall characteristics of any other shape due to the fact that a stall begins at the inboard trailing edge progressing forward and outboard. This ensures that the ailerons continue to provide control as deep into the stall as possible. The main purpose of washout is to ensure that the ailerons maintain this control in order to meet certification requirements.
    You rigging the wings flat on the clip wings makes sense in that a clip wing's primary purpose is for those who like to perform aerobatics. Shorter wings will promote a faster roll rate. Rigging them "flat" will help the tips stall sooner thus improving certain aerobatic characteristics. Yes there are some who rig their wings flat, some who rig them with as much wash-in as possible in order to give the outboard portion of the wing more angle of attack on takeoff and landing. These folks need to be aware that there is a possibility that they could run out of aileron control when they are in a tight low speed position. They had better be good rudder users.

    I take from your discussion that you feel that there is less drag when the wing is rigged with no washout. Do I understand correctly? If so, I doubt that the small amount of drag difference would be noticed without sensitive measuring equipment on a aerodynamically dirty Cub. You are a savvy guy, does the airspeed move any more than the needle moving from one side of the mark on the airspeed indicator to the other?
    Last edited by skywagon8a; 03-26-2019 at 07:18 AM.
    N1PA

  26. #186
    BC12D-4-85's Avatar
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    One very experienced local Cub pilot preferred flatter than factory wings. Not sure how much but they looked flat. His belief was that it reduced the "mush" when lifting off or landing. He spent lots of time loaded on skis where AOA was limited and at altitude in mountainous terrain doing game surveys. He was also a competent aerobatic pilot that (in my words) was willing to deal with any resulting changes in slow flight and stall behavior. One man's opinion.

    Re: Barnaby's article. He claims that adding leading edge camber doesn't increase lift at a given AOA. I'd like to see some confirmation.

    Gary

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