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Thread: Gap seals

  1. #1

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    Gap seals

    Has anyone added gap seals to their rudder and elevator on a pa-18? Did you notice a significant improvement in authority?
    Last edited by womblesd; 11-12-2020 at 03:24 PM.

  2. #2

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    I added the cub crafters gap seals and did not notice any change. However, I do have a well rigged plane, VG's on the tail, and adjust my trim for pretty much hands off landing/takeoff/level flight. If you don't trim much you may notice some improvement . Every cub seems to fly different. Borrow a set 5 min to put in, and see if it helps.
    DENNY
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  3. #3
    skywagon8a's Avatar
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    Stick some duct tape over the slots to see what happens.
    N1PA
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  4. #4
    mvivion's Avatar
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    I put a set on a PA-11 and couldn't tell any difference. As Pete noted, stick some easily removable tape on the gaps as an experiment and see what you think.

    MTV
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  5. #5
    Bill Rusk's Avatar
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    Here is an older write up on the CC gap seals


    Gap Seals

    This year at Oshkosh Cub Crafters introduced their new Gap Seals for the elevator and rudder. They are still working on the STC so they are only available to the experimental crowd at this time. I had the opportunity to test them at New Holstein on several aircraft (many thanks to you guys for trusting me with your baby for a while) both before and after installation. They work very well improving the control effectiveness and also lightening up the control forces. I was quite impressed. I did suggest to Jim at CC that when he writes the STC paperwork to try to get approval to install them on the Rudder only, Elevator only, or both as the user desires. Thus if you wanted a gap seal on your elevator but not on the rudder you would have that option rather than having to do both because that is how the STC is worded. I guess we will see how it works out when they get the STC.
    The gap seal is a plyable rubber that is extruded into a hourglass shape and is wedged/fits between the stabilizer and the elevator/rudder. It is held in place by fit and friction. I did not have any come loose at NH nor on my aircraft but you could put in a little adhesive if you wanted. It takes about 5 minutes to install these things and no tools at all. There is no detectcable friction or binding in the controls with the gap seals in.
    This is a really slick idea that works. Increased elevator authority at high AOA (ie in the flare) is really nice. It definately makes it possible to get the tail down first on three point landings and you don't have that feeling that you are running out of elevator in the flare. I predict that you will see these on just about every cub when the STC is done. Here are a couple of photos.

    And a link to the post with pictures
    https://www.supercub.org/forum/showthread.php?22553-Building-a-Smith-Cub&p=477660&viewfull=1#post477660

    I like them, and in my opinion I believe they are a light weight, simple addition, that helps the performance. Like VG's. Light, and simple, performance enhancement.

    Bill Rusk
    Very Blessed.
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  6. #6
    RaisedByWolves's Avatar
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    Back when I was flying my cub daily and had a pretty good feel I flew one afternoon for a few hours, put them on, flew some more and took them off and flew again. I noticed no change. My cub is light weight and has vgís. Same as above I trim for hands off.


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    cubdrvr's Avatar
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    Blenderm
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    Scooter7779h's Avatar
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    I like them on the -12. Had to buy the STC to use for a Field Approval. Dang FA was 3 pages long.... Anyway, it seems to have a more solid pitch and rudder authority, and the tail picks up better. Keep in mind I have a belly pod, and Micro Vgs, on a -12. It is pretty subtle difference though, but an improvement IMHO.
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    Two pieces of Blenderm sticky to sticky so the cross section is like the cloth hinges on old U-control models. No possibility of pulling or binding. I've used 1 inch glider tape but Blenderm is at any pharmacy.
    What's a go-around?

  10. #10

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    I added the Cubcrafters seals on elevator and rudder before I added VG's. I personally think the elevator response is more "linear" than without the seals. That is the best way to describe it. It makes the flare smoother in my opinion but your mileage may vary. With both VG's and gap seals on my PA-18-95 a power off stall is a mush with no break.

  11. #11
    BC12D-4-85's Avatar
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    I put these on my Taylorcraft - https://www.aircraftspruce.com/catal...apsealtail.php - the elevator gap is a bit tighter than a Cub. With just a small trim tab on the left elevator these helped make them a bit more effective in landing. Also keeps winter snow and ice from building up in that gap when parked. In flight - not much change but have VG's under the stabilizers.

    Gary

  12. #12
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    After a renovation that included VGs and big tires, I was unable to get fully into the 3 point attitude at low landing speeds in ground effect - I would always touch down mains first and it would hop a little bit because there was not enough elevator authority to plant the tail. After adding the elevator gap seals, I not only can touch down properly, I can add a little power and taxi down the runway with the tailwheel on the ground and mains off (not recommended, but still).

    You lose a little elevator 'feel'. Without the seals, there is a soft feeling in the stick where the elevator starts to give up because of the airflow through the gap. I think Pops Dory mentioned this in another thread. Like everything, it is a tradeoff.
    The modern equivalent of the phrase "lions led by donkeys" is "innovation led by lawyers".

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    Steve Pierce's Avatar
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    I need to pull mine off and see if I can tell. They have been on to long.
    Steve Pierce

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  14. #14
    Bill Rusk's Avatar
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    I love the elevator seals but I felt the rudder did not benefit as much. I did not like the rudder "feel" with the seals. It felt too light to me. PERSONAL OPINION FOLKS.

    Way back when CC was doing the pre STC testing I flew them a lot on different cubs, on and off, etc. I recommended to Jim Richmond that he write the STC paperwork in a way that allowed you to use the elevator seals with, or without, the rudder seals, to give folks the option. Don't know if that is the case or not as I have not read the STC paperwork.

    I only have the elevator seals on my cub.

    Just another opinion.

    Bill
    Very Blessed.

  15. #15
    PerryB's Avatar
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    Quote Originally Posted by Bill Rusk View Post
    I love the elevator seals but I felt the rudder did not benefit as much. I did not like the rudder "feel" with the seals. It felt too light to me. PERSONAL OPINION FOLKS.

    Way back when CC was doing the pre STC testing I flew them a lot on different cubs, on and off, etc. I recommended to Jim Richmond that he write the STC paperwork in a way that allowed you to use the elevator seals with, or without, the rudder seals, to give folks the option. Don't know if that is the case or not as I have not read the STC paperwork.

    I only have the elevator seals on my cub.

    Just another opinion.

    Bill
    That was exactly my first impression. I liked the modest improvement in elevator authority, but the slightly increased sensitivity of the rudder put me off a bit, at first. After a few trial flights I decided to remove them (rudder). Apparently I had become accustomed to them, because as soon as I removed the I missed them. I put them back in, go figure.
    After Monday and Tuesday, even the calendar says WTF !
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  16. #16
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    The CC STC reads you can fly with the rudder and/or elevator seals independently, but the elevator seals cannot be asymmetrical. I like mine. I also have VG's on the tail, but did notice a difference.
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  17. #17
    skysigns's Avatar
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    humm i like them on my cubs

  18. #18
    skywagon8a's Avatar
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    Quote Originally Posted by PerryB View Post
    That was exactly my first impression. I liked the modest improvement in elevator authority, but the slightly increased sensitivity of the rudder put me off a bit, at first. After a few trial flights I decided to remove them (rudder). Apparently I had become accustomed to them, because as soon as I removed the I missed them. I put them back in, go figure.
    You have peaked my curiosity. Not just you Perry, but anyone here who is using these gap seals. Is or has it been your habit to use or not use your stabilizer trim during various segments of flight? For example, when you are down wind in the pattern and close the throttle. Do you ever move the trim before you touch the runway? Or do you just muscle the elevators to get the desired result?

    I ask, because I have never found a lack of elevator authority in a Cub where I could point the issue to the gap between the two surfaces. A fixed stabilizer airplane, perhaps?
    N1PA

  19. #19
    spinner2's Avatar
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    Quote Originally Posted by skywagon8a View Post
    You have peaked my curiosity. Not just you Perry, but anyone here who is using these gap seals. Is or has it been your habit to use or not use your stabilizer trim during various segments of flight? For example, when you are down wind in the pattern and close the throttle. Do you ever move the trim before you touch the runway? Or do you just muscle the elevators to get the desired result?

    I ask, because I have never found a lack of elevator authority in a Cub where I could point the issue to the gap between the two surfaces. A fixed stabilizer airplane, perhaps?
    My answer would be no, I do not change trim in the pattern. I also donít close the throttle until I am stopped. I dial in nose-down trim and leave it there. I like the feel of pulling back on the stick and releasing it at touchdown rolling up on the mains.

    I've had the seals in since 2011 and rereading an old post Iíd made on the CC site I commented that I felt the seals effect was like put a couple MPH headwind over the elevator. Landings can be flatter at the same speed or slower in the 3-point.

    I also like the rudder seals.
    "Fast is fine, but accuracy is everything." Wyatt Earp
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  20. #20
    skywagon8a's Avatar
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    Therein is the difference. I am of the camp of closing the throttle, setting up a glide, trimming out any control pressures and gliding to a landing. Whether the engine continues to run or not makes no difference. Of course there are times when this procedure is altered, not many. This technique I have used in airplanes of all sizes with success.
    N1PA
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  21. #21
    sjohnson's Avatar
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    Quote Originally Posted by skywagon8a View Post
    You have peaked my curiosity. Not just you Perry, but anyone here who is using these gap seals. Is or has it been your habit to use or not use your stabilizer trim during various segments of flight? For example, when you are down wind in the pattern and close the throttle. Do you ever move the trim before you touch the runway? Or do you just muscle the elevators to get the desired result?

    I ask, because I have never found a lack of elevator authority in a Cub where I could point the issue to the gap between the two surfaces. A fixed stabilizer airplane, perhaps?
    I use stabilizer trim in my Cub. In my experience, the elevator gap seals only come into play in ground effect, tail low, low airspeed.
    The modern equivalent of the phrase "lions led by donkeys" is "innovation led by lawyers".
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    mvivion's Avatar
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    Dang, I guess my wife has been right all along....she's always said I was an insensitive kinda guy.......

    MTV
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  23. #23

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    Quote Originally Posted by skywagon8a View Post
    You have peaked my curiosity. Not just you Perry, but anyone here who is using these gap seals. Is or has it been your habit to use or not use your stabilizer trim during various segments of flight? For example, when you are down wind in the pattern and close the throttle. Do you ever move the trim before you touch the runway? Or do you just muscle the elevators to get the desired result?

    I ask, because I have never found a lack of elevator authority in a Cub where I could point the issue to the gap between the two surfaces. A fixed stabilizer airplane, perhaps?
    My PA-18-95 pattern and landing goes like this:

    1. On downwind leg, even with the numbers, throttle back to 1500, 7 cranks to trim nose up and that yields ~60 mph with flaps at zero on my Cub (cause there ain't no flaps lol).

    2. Base to final turn complete, roll one more crank nose up slowing to 50 which for me yields a steep stable approach and shortest landing roll, because energy management starts when you turn final. Any energy on final has to be spent in ground effect unless to spend it before you hit ground effect.

    3. Begin to add back pressure just before crossing the fence to achieve 45 mph and keep adding back pressure to time it so that when I enter ground effect (half the length of the wingspan) I am at 35 mph and slowing and then just above touchdown pin the stick all the way back and it drops on a 3 point and rolls about 50-75 feet on the grass with 29" tires and bungees. It will seem weird to pin the stick back but if you are 35 mph or under it will not stall and fall and bounce, I promise. Don't pin the stick 15 feet up, I am talking about the point where you are like 2 feet above the runway and slow. Too fast and it will climb and fall. This is where practice is required to get the timing right.

    Note: I usually push the carb heat in just before crossing the fence so I am ready to reject the landing if it is a short landing area. I also do that with 10,000 feet of runway to make it a habit.

    4. If you want a wheelie, don't pin the stick back, nudge forward just before touch and hold it on the mains.

    Note: On final if you sink, add a burst of throttle but leaving that in usually means landing long so just a burst. If you are high reduce throttle and leave it out. Don't change the attitude and don't dive.

    IMO and as a CFI I teach that the steep stable approach is flown without lots of muscle on the controls on final, you should only adjust bank and rudder angle to compensate for cross wind, and adjust throttle for sink or too much height and the pitch picture (and resulting airspeed) stays the same. Otherwise you are fighting too many variables and the result is a long landing that misses your mark, or an unstable approach that ends in a poor landing.

    I know this thread is about gap seals but adding them made this procedure work much smoother for me and more predictable on the elevator authority at flare.

    Also, these speeds are approximate, especially below 50 mph because instruments vary, pitot angles force inaccuracy, etc. They are for reference only. The picture in the windshield i what matters and once you define it, it becomes more accurate than the instrument.

    This has worked for me for 30 years on 2 cubs so it might work for you. When I fly HP airplanes, I disregard all this stuff and fly the V-Speeds, lol.
    Last edited by sdischer; 11-26-2020 at 12:39 PM.
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  24. #24
    RaisedByWolves's Avatar
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    Quote Originally Posted by skywagon8a View Post
    Therein is the difference. I am of the camp of closing the throttle, setting up a glide, trimming out any control pressures and gliding to a landing. Whether the engine continues to run or not makes no difference. Of course there are times when this procedure is altered, not many. This technique I have used in airplanes of all sizes with success.
    After installing the Thrustline I never change the trim except when the load changes. I slow down, could use trim, and then pull a notch of flaps and itís back to hands off. Slow down more another notch and back to hands off


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  25. #25

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    I think a big part of that is having the flaps. No-flap airplanes need a lot of trim IMO. My J3 is exactly the same, lots of trim. I can not speak to the thrustline mod although the ones I have seen or spoken with claim it greatly improves the airplane in all configurations which makes you wonder why it wasn't designed that way.
    Last edited by sdischer; 11-26-2020 at 02:54 PM.
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  26. #26
    jrussl's Avatar
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    Quote Originally Posted by RaisedByWolves View Post
    After installing the Thrustline I never change the trim except when the load changes. I slow down, could use trim, and then pull a notch of flaps and itís back to hands off. Slow down more another notch and back to hands off


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    Thatís the same way I fly my SuperCub. Except I havenít installed the Thrustline mod............yet.

    Jeff


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