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Thread: Rudder trim tab

  1. #1
    C-GZUP Jorfarms's Avatar
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    Rudder trim tab

    I would like to install a trim tab on my rudder so I donít have to rest my foot on the right pedal for the whole trip. Has anyone done so and if so how. Nervous about drilling holes. My plane is on floats mostly
    The bad news is time flies. The good news is that your the pilot.

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    supercrow's Avatar
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    Rudder trim tab

    If mostly on floats you might consider adjusting the water rudders just a little. They are large enough to make very effective trim tabs without loosing their effectiveness in the water. You could drill the trailing edge of the rudder for number 4 stainless screws and attach that way,(prob. 3 screws), but the water rudders require no drilling and work very well with very little adjustment.
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    Just bend the LE of the vertical stabilizer like Piper says to.


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    courierguy's Avatar
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    I taped a 1/4" diameter length of aluminum tube, guesstimated it at about 6" long "would be about right", on the TE of my exp.'s rudder, on the same side as I was holding foot pressure. Once I found it was about perfect in all conditions, or close enough anyway, I hot glued it onto the fabric.

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    cubdriver2's Avatar
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    Quote Originally Posted by dgapilot View Post
    Just bend the LE of the vertical stabilizer like Piper says to.


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    Tabs are ugly and not needed, bandaid for misaligned vertical fin

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  6. #6
    C-GZUP Jorfarms's Avatar
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    I have a Ugly tab on my other plane and it works great, but nervous thinking of drilling holes in that very small tube in the rudder. I think the water rudder idea sounds very simple and easy to do. Thanks for the advice
    The bad news is time flies. The good news is that your the pilot.

  7. #7
    www.SkupTech.com mike mcs repair's Avatar
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    Rudder trim tab

    You can adjust the vertical fin as mentioned above. Or adjust the floats... rudder tabs are not a good solution. They just compensate for the actual problem


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  8. #8
    C-GZUP Jorfarms's Avatar
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    Ok I have to ask, just how would you adjust the vertical fin, I prefer to fix it right and not patch fix. But I was just dreaming and looking at Carbon Cubs and they have a trim tab.
    The bad news is time flies. The good news is that your the pilot.

  9. #9
    skywagon8a's Avatar
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    Quote Originally Posted by dgapilot View Post
    Just bend the LE of the vertical stabilizer like Piper says to.
    Only do this when the airplane is on wheels. The airplane MUST fly straight without the floats first.

    Then when the floats go on you will know what to adjust to make it fly straight. Follow supercrow's advise. Before adjusting the water rudders double check the rigging of the floats. Sometimes the floats/airplane combination just won't fly straight. Then tweaking the water rudders solve the issue.

    Sometimes the floats are rigged straight, but a little to one side. This can make the plane wing heavy, but fly straight. This can then make you need rudder to fly straight. Why is the rudder needed in this case? There are a number of possibilities.

    Be certain to do the rigging check while cruising with the power you normally use. Changing the power setting effects the trim, particularly noticeable on the higher powered airplanes.

    There are many adjustments when rigging floats to an airplane, each effecting the other. You must be very fussy and analytical when deciding just what part to adjust. It can be adjusted to fly straight and still be wrong or it can fly straight and be right, your choice. The right way will make the plane fly more efficiently. You may even see some speed differences.

    Once done correctly, making the seasonal change overs is simple as long as you pay attention.

    Glenn is right, trim tabs are band-aids.
    N1PA
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    Steve Pierce's Avatar
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    Quote Originally Posted by courierguy View Post
    I taped a 1/4" diameter length of aluminum tube, guesstimated it at about 6" long "would be about right", on the TE of my exp.'s rudder, on the same side as I was holding foot pressure. Once I found it was about perfect in all conditions, or close enough anyway, I hot glued it onto the fabric.
    Might note that this advice is on a RANS S7.
    Steve Pierce

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  11. #11
    Steve Pierce's Avatar
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    I adjust the leading edge of the vertical stab per the rigging instructions. Here is an older thread with that advice along with trim tab size, material thickness etc. 3 holes and #6 PK screws is how I have seen it done on Cub Crafters Cubs.

    https://www.supercub.org/forum/showt...udder-Trim-Tab
    Steve Pierce

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  12. #12
    C-GZUP Jorfarms's Avatar
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    Wow thanks again, good advice skywagon I won’t do anything major till I check it out on wheels. It is just a minor amount of pressure I have to apply to center the ball so it’s not out much. I have 180 hp in it and the plane is still the way I bought it, not sure when I’ll have it on wheels. For now the water rudder idea sounds good.
    thanks again,
    The bad news is time flies. The good news is that your the pilot.

  13. #13
    courierguy's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    Might note that this advice is on a RANS S7.
    Yes, but the concept works on any plane, and doesn't require drilling any holes and maybe looks less obtrusive, even unpainted like mine. Using tape, it is a good way to experiment, as it's surprisingly effective. I like the bending of the vert stab too, didn't know that was a recommended way to fine tune but it makes perfect sense.

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    cubdriver2's Avatar
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    One day I took off in my J4 and need a big foot of rudder. I thought it must of gotten damaged while docked. Went back and one of the rudder return springs had come unhooked from the firewall. 2 min fix

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

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    skywagon8a's Avatar
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    Quote Originally Posted by courierguy View Post
    I taped a 1/4" diameter length of aluminum tube, guesstimated it at about 6" long "would be about right", on the TE of my exp.'s rudder, on the same side as I was holding foot pressure. Once I found it was about perfect in all conditions, or close enough anyway, I hot glued it onto the fabric.
    Hmmm? Interesting ! That's a new one to me.
    N1PA

  16. #16
    skywagon8a's Avatar
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    Quote Originally Posted by Jorfarms View Post
    Wow thanks again, good advice skywagon I won’t do anything major till I check it out on wheels. It is just a minor amount of pressure I have to apply to center the ball so it’s not out much. I have 180 hp in it and the plane is still the way I bought it, not sure when I’ll have it on wheels. For now the water rudder idea sounds good.
    thanks again,
    Try changing the power setting up/down, see what happens.
    N1PA

  17. #17
    Steve Pierce's Avatar
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    Quote Originally Posted by courierguy View Post
    Yes, but the concept works on any plane, and doesn't require drilling any holes and maybe looks less obtrusive, even unpainted like mine. Using tape, it is a good way to experiment, as it's surprisingly effective. I like the bending of the vert stab too, didn't know that was a recommended way to fine tune but it makes perfect sense.
    That is my preferred way of rigging a rag and tube Piper with a jack screw trim system. I hate external trim tabs and would rather make the surface go the way it needs to.
    Steve Pierce

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    Just an FYI, the forward fitting on the Howard vertical stabilizer was slotted so you could move it left or right as needed to trim, then clamp the bolts down tight to hold it in place. Granted that is the trim for one speed, but you only need it trimmed for cruise. Does the same thing as moving the Piper vertices stab leading edge.


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  19. #19
    C-GZUP Jorfarms's Avatar
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    I could change the power setting but it’s a cub on floats, it’s slow or slower. I changed props and now I’m going 10 mph faster but the yaw is still the same. I should take it off floats and then I would then know if it’s the plane or the addition of the floats.
    The bad news is time flies. The good news is that your the pilot.
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  20. #20
    skywagon8a's Avatar
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    In the meantime using a level, compare the front spar carry through tube to the two bottom screws which hold your turn and bank (or what ever the ball is attached to) in the instrument panel. If the ball isn't installed correctly, you may be fixing something which doesn't need fixing. Sometimes your mind is thinking one thing is in error when it is really something else.

    I had a friend who was having a similar issue as yours with his Cub on wheels. When I looked at it, both lift strut forks on one side were screwed in and the other side were screwed out. The plane flew straight but the ball was always out. The answer was, the fuselage wasn't hanging evenly under the wings. Adjusted both forks, each the same number of turns on one side problem solved.

    If you have a smart level you could compare the bottom of both wings to the spar carry through tube. Check under the front spar where the leading edge skin is flat between the ribs.
    N1PA
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    Steve Pierce's Avatar
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    Does it fly hands off just not feet off? If so bend the leading edge of the vertical fin and it will fix your problem. Done it a 100 times and it works and is how Piper did it and described in the rigging instructions. I think trim tabs are lazy.
    Steve Pierce

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    Will Rogers

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    skywagon8a's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    Does it fly hands off just not feet off? If so bend the leading edge of the vertical fin and it will fix your problem. Done it a 100 times and it works and is how Piper did it and described in the rigging instructions. I think trim tabs are lazy.
    Yes Steve, if on wheels. If it is crooked on wheels, then when floats are installed you will be incorrectly correcting an error. It must be right on wheels first.
    N1PA
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    On a related note. Could someone tell me where in reference to what is the correct neutral aileron position? With the stick centered, where are the ailerons supposed to be and what reference point do you use to measure it?

    I know of a cub that changed the aileron neutral deflection position and it required rudder to keep the ball centered afterwards. Suspected that one aileron was deflected differently. It flew hands off, but needed a bit of left rudder.
    Last edited by MoJo; 10-26-2020 at 09:32 AM.

  24. #24
    www.SkupTech.com mike mcs repair's Avatar
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    Rudder trim tab

    Quote Originally Posted by Jorfarms View Post
    Wow thanks again, good advice skywagon I wonít do anything major till I check it out on wheels. It is just a minor amount of pressure I have to apply to center the ball so itís not out much. I have 180 hp in it and the plane is still the way I bought it, not sure when Iíll have it on wheels. For now the water rudder idea sounds good.
    thanks again,
    You MUST first check that the ball is telling you the truth(gauge is leveled with plane in level flight attitude, and equal dihedral)


    Sent from my iPhone using SuperCub.Org mobile app

  25. #25
    Steve Pierce's Avatar
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    Quote Originally Posted by MoJo View Post
    On a related note. Could someone tell me where in reference to what is the correct neutral aileron position? With the stick centered, where are the ailerons supposed to be and what reference point do you use to measure it?

    I know of a cub that changed the aileron neutral deflection position and it required rudder to keep the ball centered afterwards. Suspected that one aileron was deflected differently. It flew hands off, but needed a bit of left rudder.
    With the bottom of the wing, trailing edge of the flaps. Do not try and dink with the vertical fin until the airplane flies hands off in rol via aileron rigging or you will be chasing your tail till doomsday.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

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    Steve Pierce's Avatar
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    Quote Originally Posted by skywagon8a View Post
    Yes Steve, if on wheels. If it is crooked on wheels, then when floats are installed you will be incorrectly correcting an error. It must be right on wheels first.
    No dealing with rigging back and forth between floats and wheels so did not know that. I would rig it and then rerig if needed on wheels or just add a trim tab and go back and forth if that is how the airplane will be operated. The float plane I maintain is on amphibs and does not go back and forth to wheels.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

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    Quote Originally Posted by Steve Pierce View Post
    With the bottom of the wing, trailing edge of the flaps. Do not try and dink with the vertical fin until the airplane flies hands off in rol via aileron rigging or you will be chasing your tail till doomsday.
    Are you saying that a straight edge off the bottom of the wing at the inboard end of the aileron would be flush?

  28. #28
    Steve Pierce's Avatar
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    Sort of, the wing is a bit concave on the bottom. If the wing is built right it will line up with the outboard aileron bay tip rib.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  29. #29

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    Quote Originally Posted by Steve Pierce View Post
    Sort of, the wing is a bit concave on the bottom. If the wing is built right it will line up with the outboard aileron bay tip rib.
    Thanks Steve.

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