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Thread: New landing gear tracking?

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    RCharles's Avatar
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    New landing gear tracking?

    How should the wheels be installed on a stock L21B with 800x6 tires so as to have the plane track straight with the tail wheel centered? Just installed new Univair stock gear and taxing everything feels fine but at landing speed touchdown the plane wants to feel as though it has gotten a gust of wind from the right requiring control inputs to stop the drift to the left . The nose is being held pointing straight down the runway but the plane still feels as though it is being blown by a wind from the right until it slows down with breaking...should the wheels be parallel,toed in ,toed out,or what? Or does the pilot just need some dual instruction? Help please.

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    Try landing on the opposite runway and see if it’s tracking or wind.

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    cubdriver2's Avatar
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    It's supposed to be a little challenging, otherwise everyone would be doing it ;- )

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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    Parallel. Take a simple tape meaure and check front center and back center. On your tires any toe in more than about 3/4" will give you trouble. Much better to have less than 1/2" difference, but zero is the desired.
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    RCharles's Avatar
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    Quote Originally Posted by bob turner View Post
    Parallel. Take a simple tape meaure and check front center and back center. On your tires any toe in more than about 3/4" will give you trouble. Much better to have less than 1/2" difference, but zero is the desired.
    Thanks Bob , I thought that would be the answer but now confirmed.

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    Steve Pierce's Avatar
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    I found that 1/2" toe in on 31" Dessers was a bear. How did the plane react prior to the gear swap? When I repair fuselages we weld the gear fittings on with them parallel.
    Steve Pierce

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    The issue with Cub style gear is there is no adjustment possible unless bending the axles is possible?? I have heard of folks putting a long pipe over the axle and adjusting the toe in by carefully bending the axle with the long pipe. Is this an accepted practice?

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    RVBottomly's Avatar
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    Quote Originally Posted by Phil Kite View Post
    The issue with Cub style gear is there is no adjustment possible unless bending the axles is possible?? I have heard of folks putting a long pipe over the axle and adjusting the toe in by carefully bending the axle with the long pipe. Is this an accepted practice?
    That's basically the practice--most use heat. But I don't think it is the axle you are bending. It's the tubes attached to the axle that actually bend a little.

    Heating up the axle itself sounds like an opening to all sorts of troubles. My opinion only, based on making landing gear for my homebuilt.
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    What RV said! I have a similar issue that we looked at exactly as you described and came to the same conclusion as above. No predictable way to control the bending site!

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    tramcking

    [Q
    iIs there a way to shim the wheel angle at the attach point some way. to move it left or right.plane has double puck Cleveland breaks .?

    UOTE=Kid Durango;803076]What RV said! I have a similar issue that we looked at exactly as you described and came to the same conclusion as above. No predictable way to control the bending site![/QUOTE]

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    Steve Pierce's Avatar
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    Quote Originally Posted by RCharles View Post
    Just installed new Univair stock gear and taxing everything feels fine but at landing speed touchdown the plane wants to feel as though it has gotten a gust of wind from the right requiring control inputs to stop the drift to the left .
    How did the plane react prior to the gear swap? Was the gear the only thing changed?
    Steve Pierce

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    Will Rogers

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    RCharles's Avatar
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    [QUOTE=Steve Pierce;803155]How did the plane react prior to the gear swap? Was the gear the only thing changed?
    [/QUOTE

    that was all that was done.checked today and showed 1/4 inch toe in at front of tires with tape measure.Hit or miss. Question is ,what direction are the headed in...maybe both slightly left? Time for a laser I guess'

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    Bearhawk Builder's Avatar
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    Snap a line down the center from the spinner tip to the tail post, clamp a straight edge to the brake discs and measure 40" forward of the axle center. .350 inch difference to the center line at 40 inches is .5 degrees toe in which I find is perfect. Heating the cluster is the only way to go, get it cherry red and let it cool slowly. PIA but well worth the effort, it will change the ground handling dramatically.


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    I go 1/8" toe in 18" forward of the axle on the Taylorcrafts that I work on, they taxi perfect without squatting. I wound up using a piece of 5' well pipe to bend the gear into submission to get it there. Tim

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    RCharles's Avatar
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    Here is what I did today .The result was a bit hard to believe if I did this correctly. I shot a laser line down the center of fuselage and marked the laser dot on the hanger door. Then put a straight edge along side each wheel with small lasers attached to each and marked where they showed on the door. The plane was in level with the tail in what would be about a tail low wheel landing position.The LEFT main wheel laser dot measured 5 inches further from it to the center , than the right main wheel laser dot. The hanger door was 61/2 ft from the front of the wheels each the same....LEFT WHEEL WAY OUT THERE PULLING TO LEFT? Is this a valid way to get an idea what going on?

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    Seems to me it would be. I can’t see why it would be any different going forward rather than down, as long as everything was at the same ‘altitude’.
    Tim: how did you control where the gear bent? Or can you tell where it bent?
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    RVBottomly's Avatar
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    Quote Originally Posted by RCharles View Post
    Here is what I did today .The result was a bit hard to believe if I did this correctly. I shot a laser line down the center of fuselage and marked the laser dot on the hanger door. Then put a straight edge along side each wheel with small lasers attached to each and marked where they showed on the door. The plane was in level with the tail in what would be about a tail low wheel landing position.The LEFT main wheel laser dot measured 5 inches further from it to the center , than the right main wheel laser dot. The hanger door was 61/2 ft from the front of the wheels each the same....LEFT WHEEL WAY OUT THERE PULLING TO LEFT? Is this a valid way to get an idea what going on?
    Just to be sure, I'd do it from the brake disks--or from rims without tires. From what you have observed there is a lot of misalignment. But it is good to take the tire variables out of the equation.

    I did something similar on my homebuilt--measuring with a straight edge against the tires. The variation was quite noticeable when you turned the wheels 90 degrees and tried again.
    Last edited by RVBottomly; 05-16-2021 at 10:08 PM.
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    You are correct indeed ,the tires do not work well so shot the lines using the rotors and got better readings but still showing toe out on the left side .Seems like every time we measure we get some other reading.Checked the rotors with the laser and they are running true. So what the ...?
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    So just a thought. If you move the plane forward you have the actual ‘toe-in’. But if you push it in backwards the tires could put a little torque on things because of the geometry. It would be a small change, but I sure notice it.

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    skywagon8a's Avatar
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    This thread is confusing. You had a properly operating stock Cub on which for some reason you decided to install new landing gear. Why did you install new gear? Also since it apparently was functioning properly with the old gear, your new Univair gear appears to have an issue. What is Univair doing to fix their gear?

    There appears to be some information missing in your request for help.
    N1PA

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    RCharles's Avatar
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    The answer is simple.The old gear was put on the cub in 1954 and the aircraft appeared to have been under water at one time because the fuselage hade to be replaced in 1994 but the gear was not. So I felt it was time to do so.
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    hotrod180's Avatar
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    Quote Originally Posted by Kid Durango View Post
    So just a thought. If you move the plane forward you have the actual ‘toe-in’. But if you push it in backwards the tires could put a little torque on things because of the geometry. It would be a small change, but I sure notice it.
    Are you using greased plates under the wheels?
    Double layer trash bags can be substituted.
    Cessna Skywagon-- accept no substitute!

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    Quote Originally Posted by skywagon8a View Post
    ...You had a properly operating stock Cub on which for some reason you decided to install new landing gear. Why did you install new gear? Also since it apparently was functioning properly with the old gear, your new Univair gear appears to have an issue. What is Univair doing to fix their gear?
    Who's to say that the gear which was removed hadn't been tweaked to track straight sometime in the past?
    The Univair gear might be right on the money, maybe the attach fittings or the fuselage are off.
    Cessna Skywagon-- accept no substitute!
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  24. #24
    RCharles's Avatar
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    last check done today .it seems a both wheels are pointed left . the left wheel is toed out5/16 inch and the right wheel is toed in by 9/16 0f an inch... both going to the left.So no wonder it wants to take of in that direction on landing?

  25. #25
    Bearhawk Builder's Avatar
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    When you roll the plane forward a toed in tire will ride up and narrow the track a toed out tire will do the opposite to a point. Roll it back and the opposite happens. You need to establish a proper track width and do your measurements at that width otherwise your numbers will change. If you’re confidant of your angles start with that left gear and bend it straight. It may be all you need

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    hotrod180's Avatar
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    Quote Originally Posted by Kid Durango View Post
    .....Tim: how did you control where the gear bent? Or can you tell where it bent?
    If it matches up with the fuselage fittings at the top,
    and the axle is at the correct angle at the bottom,
    does it really matter where it bent?
    Cessna Skywagon-- accept no substitute!
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    Truth be told - I don’t know! I’ve wondered and worried about it enough that I was afraid to try it on mine. I was concerned with changing the geometry as the gear swings, perhaps having something in a bind. Thanks though.

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    Crash, Jr.'s Avatar
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    Leave good enough alone before you go twisting up a good set of gear. The toe difference is minimal and the fact that it's pointing both to the left isn't likely causing the plane to veer any such way. If 1/2" of toe and 7/16" left was causing cubs to veer off the left side of the runway there would be a whole lot more cubs off in the weeds. If you look at any cub out there close enough you'll find similar or worse measurements of the gear alignment. Cessnas are often even worse but they don't throw themselves off the runway on landing somehow.

    I know this might be a touchy subject but is it possible that landing technique has something to do with your plane veering left? What's your landing speed? Can you just put in a bit more right rudder when flaring to keep the plane straight?

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    I have flown several taildraggers with 3/4" toe in, measured on 6" or 8" tires front to back. They are nowhere near as stable as a good set of zero toe in legs.

    I have an orphan Cub gear leg that was removed from a ground loop Cub. I would love to have a simple measurement technique to see if it is tweaked without having to put it on an aircraft.

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    skywagon8a's Avatar
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    Quote Originally Posted by bob turner View Post
    I have an orphan Cub gear leg that was removed from a ground loop Cub. I would love to have a simple measurement technique to see if it is tweaked without having to put it on an aircraft.
    Try leaning it against a wall with the axle parallel to the floor. Measure the gear bolt bushings distance from the wall to see that they are the same. Then using a carpenters square see if the axle is perpendicular to the wall.
    N1PA

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    RCharles's Avatar
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    tracking gear

    Quote Originally Posted by Crash, Jr. View Post
    Leave good enough alone before you go twisting up a good set of gear. The toe difference is minimal and the fact that it's pointing both to the left isn't likely causing the plane to veer any such way. If 1/2" of toe and 7/16" left was causing cubs to veer off the left side of the runway there would be a whole lot more cubs off in the weeds. If you look at any cub out there close enough you'll find similar or worse measurements of the gear alignment. Cessnas are often even worse but they don't throw themselves off the runway on landing somehow.

    I know this might be a touchy subject but is it possible that landing technique has something to do with your plane veering left? What's your landing speed? Can you just put in a bit more right rudder when flaring to keep the plane straight?
    Well sir , anything is possible , but with over 1200 hrs in this airplane and the fact that this problem just showed up with the addition of a set of new landing gear , I do not think that is the problem. I will consider making plans for some additional instruction though....
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    Steve Pierce's Avatar
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    I wonder if somehow the Univair gear is tweaked or is the fuselage tweaked and the old gear was tweaked to correct it. I wouldn't settle for what you have. I would want to get to the bottom of it. Bushwheels can hide a lot of sins in the geometry. the 800s do not.
    Steve Pierce

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    Steve thank you for your concern here. The fuselage on my airplane was replaced in 1994 by Jim Soars at Rocky Mountain Air frames. He built up a new fuselage with the L21 window configuration from drawings I made off my old fuselage that was completely rusted out and not airworthy . He had the PMA authority for Piper and they may still have.My plane was built in 1954 for the Italians. I just purchased new landing gear within the last 6months ,had them covered and put them on the plane. That is when the problem showed up. the gear was purchased from Univair. I have talked with them about the problem ...

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    They are good folks. Every now and then a jig slips or a new welder joins the picture. If it isn't right they make it right.

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    Steve Pierce's Avatar
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    If you have a way to hoist the airplane or even if you don't use long bolts in the gear and then measure between the front gear attach bolts and the rear attach bolts and make sure your fuselage at the gear fitting is square. Gear fitting can get tweaked just like gear.
    Steve Pierce

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    Just to be sure your fuselage fittings are properly located, I would measure from centerline of fuselage to center of each bolt hole, and then also check diagonal measurements fitting to fitting. Eliminate as many possible errors before you start bending things!

    I usually check track in both the level and 3 point attitude. Depending on the geometry of the fuselage, it can be different (I don’t think this is an issue with Piper fuselages) and worth checking.


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    RCharles's Avatar
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    Talked to Univair today and they assured me that the jig they use is spot on. They jig it with zero toe in or out ...straight ahead. They said some one must have made a hard landing in my plane and damaged the fuselage. Not likely as it was built with an Alaskan modification to strengthen the gear attach points and the entire fuselage is 4130 . So then , How the heck does one TWEEK the gear if it is all welded together. I am not going to heat it up red hot and bend it , so what else could possibly be done to correct the problem ... Can't fly it with both wheels pointing the same way !

  38. #38
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    Quote Originally Posted by RCharles View Post
    Talked to Univair today and they assured me that the jig they use is spot on. They jig it with zero toe in or out ...straight ahead. They said some one must have made a hard landing in my plane and damaged the fuselage. Not likely as it was built with an Alaskan modification to strengthen the gear attach points and the entire fuselage is 4130 . So then , How the heck does one TWEEK the gear if it is all welded together. I am not going to heat it up red hot and bend it , so what else could possibly be done to correct the problem ... Can't fly it with both wheels pointing the same way !

    Fly it out to @StevePierce, he can fix it

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    I had some lift struts where the jig had slipped and the welder got careless. When I presented them with hard evidence (careful, documented evidence) they were extremely quick at fixing it without cost to me (other than painting and installation). I knew something was wrong, but it took me a year to figure it out.

    Anybody else might have said "too bad - you should have checked them when you first got them."

    I am impressed!

    Start precision measurements. If you do the above "wall" trick, let us know how it works. I will try that tomorrow - I have five gear legs laying around, but maybe not a good wall?

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    Bearhawk Builder's Avatar
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    Don’t want to heat it? Trust me it’s the only way to bend that cluster.
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