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Thread: Short Take-Off.

  1. #81

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    Idlete

  2. #82

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    Here is my theory on the PA-12 aileron and roll rate.

    1) The PA-12 aileron has more travel both up and down.
    2) The longer chord allows the sharp leading edge of the aileron to extend below the wing and cause drag when the aileron is up.

    Theory on Big V.G.'s

    1) Don't need to be mounted as far forward on the leading edge to work, becuase they can start working on the disturbed air from the leading edge cuff sooner.

    2) On a stock cub wing you will not see any difference. The nice thing about micro VG's is that if you have a Crosswinds STOL leading edge cuff you get a different set of instructions for mounting them farther forward.

    3) BLR VG's will not decrease power on stall speed with full flaps on the long flapped PA-12 wing with leading edge cuff when mounted in accordance with the STC.

  3. #83
    Don
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    Pa-12 has a differential belcrank in the aileron control system. Aileron has more up travel than down. Should have less adverse yaw but don't know if this would increase roll rate. Neither 12 or 18 have very good ailerons. Maybe the 12 is alittle better???

  4. #84
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    Sorry guys, all your speculation, and I should have just mentioned that the 180 HP -12 I flew is flying on a PA-18 aileron.

    And it's roll rate is nearly that of my Dad's VG'ed PA-14.

    Dave Calkins.

    Anyone notice how many hits this thread has taken?

  5. #85

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    delete

  6. #86
    stolmaster
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    Up or down nose pitch with flap deflection

    The pitching up or down on a cub has to do with the span of the tail in comparison to
    the span of the flaps. The air being drawn down over the flaps impacts the top of the
    tail in a downword angle causeing the nose to pitch up. As you exstend the flap out
    you will reach a piont where you get no pitch up or down. Exstend it farther and you get
    down pitch. This point will very some with speed and power setting. To test this for your self take a cub or J3 up and while in smooth air pull down on the aileron cross cable
    above your head, nose down. This is hard to do if there is much tension on your
    ailerons cables. Caution do not pull hard enough to damage anything.

    Wayne

  7. #87
    Jerry Burr's Avatar
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    Big/Little V.G.'s

    Hi Diggler. I sure enjoy your posts. I will try to answer your question of big / small V.G.'s. In the Micro layout, I couldn't find any difference between the two at the stall. In that configuration, the area of chord you are dealing with is so small that the small ones work fine. And I knew that I was going to catch (flack) about the wing covers. So I was happy that the small ones did the job. The big ones are more looks/marketing. On the BLR however, they had to use the big ones. In fact up on top of the spar where they are mounted they would work better if they were 2.5" tall. Then they would work with power and flaps, not just at 0-thrust. They both help the ailerons at approach speeds. Jerry.

  8. #88
    PA12driver's Avatar
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    Ok so what if any would I gain by putting Charly's leading edge on my PA12 with STD PA18 flaps?

    Second, would I get any better flare control with a larger Elevator (Hendrix)?

    Thanks,

    Tim

  9. #89
    Dave Calkins's Avatar
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    FOR JERRY:

    Or do the VG's under the horizontal stabs. make all the difference, or at least enough to negate use of the enlarged tail-feathers some guys have?????????

    And what about airfoiled horizontal stabs???

    I saw a thread listed in the discussion index on airfoiled stabs., but haven't checked it out yet.

    Dave Calkins.

  10. #90
    RedBaron's Avatar
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    I talked to a guy that had the long flaps on a SCub, and he was complaining that sometimes the airflow over the tailfeathers was disrupted and in gusty winds it was so bad it caused more than a little puckering...Made sense to me, anyway he has gone back to standard flaps. Extended to the fuse of course...
    Sound like a safety issue anyone?
    Andy

  11. #91
    Dave Calkins's Avatar
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    Somewhere on this site we had a discussion about the turbulence caused by the extra 3" of flaps extended INBOARD to the fuselage. 'Nuther 3 inches is what the thread was titled.

    Back to the airfoileed, VG'ed, or enlargened tail:

    I checked out the airfoiled tailfeather thread and didn't find an answer.

    It seems like since we know we want "lift" on the tail in a certain direction (down, of course), we'd design an airfoil cross-section that would work FOR us. Or would we just get along with a stock symetrical "flat plate" of an airfoil, and mask the problems with the "magical" vortex generator??

    Piper designing for simplicity, light weight, and low-cost aside, where are we on this issue??

    Dave Calkins.

  12. #92
    Gary Reeves's Avatar
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    Seems to me that someone (hint hint) working with slots and slats could take a look at turning the gap between the horizontal and the elevator into a slot shape that would close at full up and open on the way down . Both the change in angle of attack on the elevator and the coanda effect of the designed slot would at least unstall the elevator.

    Gary

  13. #93

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    Ribs

    Anybody know anything about the Riblett GAU 613-66" wing that D&E advertises? I e-mailed them to ask for some names of people that have bought them so I could find out how they worked but haven't received an answer.

  14. #94
    Jerry Burr's Avatar
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    Tails and Tales.

    Hi Dave. When I was testing V.G.'s on the wing, it was clear that the wing efficiency was improved to the point that the tail (horizontal/elevator) no longer had the authority to stall the wing. The problem had to be corrected before further testing could proceed. I am currently using a PA-20/22 balanced tail. The fix according to Mr. Dodge, and a requirement on one of his STC's was to install the 6" longer PA-18 tail. I rejected this because of the additional weight and the increased twisting moment on the fuselage. Cost was also a factor. It was only logical that the V.G.'s caused the problem (with the wings) that they should be able to fix the problem (with the tail). I installed them under the horizontal and the problem went away. Later when the wing testing was complete, I revisited the tail and removed all of the V.G.'s that were not necessary, leaving only enough V.G.'s to completely stall the wing for 3 point landings. (with power). The weight of the additional V.G.'s was 1.6 oz. I believe that 95% of the stock engine/wing PA-18's will get along fine with a stock tail if flown using the techniques outlined in the { Landing Short Over A 50 Or 100 ft. Obstacle } thread. I don't believe that power off or ( 0-thrust ) landings have any place in the STOL world. In addition to giving the tail more authority on approach, using power makes it less likely that the engine will falter (fart) when a burst of power is needed for a power flare. For the other 5% or those with modified wings, the large squared tail with V.G.'s is about the limit for a practical application. An all flying tail (stableator ) is probably the best, but it and it's mounts are heavy. The real problem to deal with at high AOA is that the stabilizer acts like a Delta Fin and tends to push the tail up (you can see Delta Fins under the tail of the new Lears) as the elevator is trying to push it down. At some point they just cancell each other out. The easiest way to solve this is to reduce the size of the stabilizer. (( For those that have BLR kits and have installed the plates on the fuselage that effectively INCREASE the size of the stabilizer, please don't ask me for ways to increase the elevator effectiveness. You have created your own problem )). A simple/light method would to add an airfoil to the bottom leading edge of the elevator. A slat if you will. They were used on Polish built Storches. They would be simple to add to the existing structure. The inverted airfoil that some STOL types use, are hard to adapt to the Cub. They have to be both large and light and on a Cub STRONG. The Cub tube and fabric is about as sturdy and simple as you can get. If I had elevator problems, I would probably test the elevator slat first. Wayne is involved in this problem on his STOLMASTER Slat kit. And he will probably have a lot to add to my simple musings.

  15. #95
    stolmaster
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    Slated or sloted tail feathers

    Gary, Ok i'll take the bait. The slat on the tail has been used with good success. The
    problem with it on a cub is draging your tail through the brush. I know we would'nt
    this but fact is fact. Still it would be the best and simplest on a cub. Just got told
    I have to leave. Will be back with what i a'm doing with this problem
    Wayne

  16. #96
    CubCouper's Avatar
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    How difficult would it be to test an inverted airfoil on the stab surface? Say, peel the fabric, and attach a thin rod (maybe 3/16 or so) across the ribs on the bottom side. This would create a slight airfoil shape once the fabric was shruck back on.


  17. #97
    Wayne Mackey's Avatar
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    Slats or ?? tailfeathers

    Gary, Remember 95% of the toys i make are installed on Exsperimental aircraft so testing isn't as much touble. I think i have come up with a way to clamp a slat on
    18 tailfeathers with out damage to the fabric. We know it works but how much.
    I have been using long flaps as well as drooping ailerons. With my slats we can
    droop them about 23 degree's and keep fair control. We all know the wind can be
    a problem here so i make my system so I can disengage the droop at any time in
    flight. Anyhow I have a big pitch control poblem when the plane is in the light weight mode.
    With the PA18 tail and the power on no problem, but with the power off keeping
    the nose high is prettie tuff. My plan is to make a panal in both stabilizers that
    comes up like the elevater. In doing so it will decrease the size of stabilizer and
    increase the size of elevater. At high angles of atack or desent the stabilizer
    counteracts elevater. This system will be controled by the flaps, more flaps more
    up panal. What fun! Wayne

    Cubcouper, In the mid 70s we made PA18 tail with an airfoil . We didn't gain enough
    to be worth the trouble. Good luck , hope yours is better than ours.

  18. #98
    DON
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    I'm building an experimental cub. I'm seriously thinking about a symetrical airfoil on the tail surface, hoping to decrease drag and improve control authority at low speed. I believe closing the gap between the elevator and horizontal stab would also help. Anyone got any ideas for a add on "gap seal" for my bushmaster I'm flying now.

    Don

  19. #99
    cubdrvr's Avatar
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    How about the clear tape that completely covers the gap between elevator and stab...............I've seen it on aerobatic aircraft. Would it help or hurt on a cub?

  20. #100
    Jerry Burr's Avatar
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    Elevator gap seal.

    The fabric seal between the stabilizer and the elevator does help. It is a pain to maintain, unless it is a stits tape or that sort of thing. The drawback is that it feeds higher elevator forces back through the system and into the stick. Hit a real hard air bump and it will take the stick right out of your hand. It's just another compromise. Jerry.

  21. #101
    Gary Reeves's Avatar
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    Stolmaster,

    After I thought about a slot between the horizontal and the elevator, I also realized that it if worked well enough to get the elevator flying, but not the horizontal, you could create a control reversal.

    -something like your comment about the elevator and horizontal countering each other at high rates of decent-

    I can't quite figure out the location of your slat. My ideas for a tail slat have always been eliminated by the leading edge geometry.

    Gary

  22. #102
    WAYNE MACKEY LR
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    tail slats

    Gary, I would biuld a slat the shape of a cub wing with about a 4 or 5" cord and install
    it upside down with the flat side up about 4" away from the elevater. The slat would be
    about 15% of it's own cord ahead of the elevator hing point. It will have to be notched
    around the flying wires. Testing to be safe it would be installed on one side only to see
    the affect, and the other side would be unaffected.
    stolmaster

  23. #103

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    Blast from the past. A fun tread to revisit, for sure. I know Denny Martel passed away last winter and later in the year I remember his Cub being for sale, as is/where is, with a sick engine in Yakutat. Who ended up with that Cub? Anyone here?

  24. #104
    Jerry Burr's Avatar
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    The airplane is at KBVS at present. Adding a lot of parts to the sale and will try again. Don't know what she will ask this time. Jerry B.

  25. #105
    cubdriver2's Avatar
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    Great thread. Looking back 12 years its amazing looking at S2Ds picture that he hasn't aged a bit .

    Glenn

  26. #106
    Steve Pierce's Avatar
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    I agree Glenn. cubdrvr sent me a roll of that tape and now I finally get to install it on my own Super Cub. Like old movies, there is lots of good, old stuff on this website.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  27. #107
    S2D's Avatar
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    Quote Originally Posted by cubdriver2 View Post
    Great thread. Looking back 12 years its amazing looking at S2Ds picture that he hasn't aged a bit .

    Glenn
    I'd tell you my secret to youth but then everyone would look as great as I do.
    I may be wrong but that probably won't stop me from arguing about it.

  28. #108

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    Anybody know why the cambered tail on a Stearman is mounted upside down?

    But back to short takeoffs, this little critter could get off shorter than anything I know. Couldn't get the camera far enough away to include his wingtips, but you can get an idea of his size from the man standing on the ladder by his head.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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