New landing gear tracking?

tracking gear

Crash said:

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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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....

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 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 ...

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.

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.

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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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 !

RCharles said:

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 !

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Fly it out to @StevePierce, he can fix it

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?

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

I have a gear jig. Factory gear drops right in it and the bolts push right in. I also have a set of heavy duty Univair Super Cub gear. If either one can help you let me know.

Just something to throw out there, fuselage fittings bend easily and not all new fuselages are straight.

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.

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The only gear fitting mod I know of is the heavy duty front fittings and those are from Airframes.

RCharles said:

Talked to Univair today and they assured me that the jig they use is spot on......

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Would you expect them to say anything else? :roll:

Steve Pierce said:

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.

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OK,Checked the gear attach points and all spot on. Also checked the left gear leg by running a laser light down the front of the left forward gear leg and out the axle as suggested by the Univair folks and the axle is out of alignment so far that the laser point is not visible on the end of the axle. Showing a large toe out that confirms all our other tests.Doing the same test on my old gear the laser line runs straight out the center of the axle showing that the axle has no toe in or out but is straight tracking as it should be and like Univair claims their jig to be set.They have not once in all our conversations mention that there is a chance the jig they used is out of alignmemt .Up to this point they have been trying to tell me that the plane has been through a hard landing and the fuselage is bent or some other problem that has caused this.Maybe even damaged in shipment? Really? Be careful folks and I have learned my lesson and do not have some one cover your gear until you have checked them out mounted and tracked .

First, once you present them with actual evidence, I am sure they will make it good.

Second, the laser idea sounds great. Tell us more - you align the pointer along the forward edge of the gear leg and look for parallel? How does the pointer disappear behind the axle? Can you post the photos that you will send to Univair, showing the laser test?

Hot digs - I am testing my spare gear leg as soon as I figure this out! Mine may have been tweaked during a horrific ground loop - very faint wrinkes in the fabric. Other side was demolished, so we replaced both. Not my airplane; I just did a lot of the work.

Place the laser on the top of the forward gear leg and shoot down the center of the tube. The axle is just an extension of the forward gear leg.Now you will have to jockey the laser here a little to get it onto the axle but you will see how it will run straight on out the the center of the axle if it is jiged at zero degrees no toe in or out.I think this is a fool proof way to tell what you have.I wanted to take a video of this but do not know haw to post it .If that line is left or right as it goes out the axle you will see whether it is toed left or right iE forward or back from roughly 90 dgrees in relation to the center line of your plane...Now you must have the weel assembly removed...

Got it! I shall try tomorrow. I will take the camera. Neat! Thank you!

I tried with a pointer. The torque plate flange stops the laser (of course). Then I stretched a string and sighted down that. Looks ok.
Apparently there are lasers that are planar, as opposed to "spot." That is probably what Univair meant, but I would guess there is more to it than just turning the laser on. It would have to be clamped exactly vertical.

I use a laser mounted on a tripod and fully adjustable for laying out straight lines for painting. It can lay a vertical or horizontal line or anything in between. Would work great for this gear examination.

Here is the best way I know how to check gear alignment.

1.We have determined that the left gear is toed out and the right is toed in.
Measured at 70 inches ahead of the wheel the left is about 2 3/8 inches further from the center line than the right wheel.
2 .The right wheel is toed in very slightly at about 1/2 inch we think and that is ok.
3.I am gong to jig the new left gear before removing it and then see if the old gear will fit in that jig.I expect that it will not. If it does then I will be sure we have entered the "twilight Zone" ....
4.The old gear will be hung from the same mounts that the new just came off of and have flown on the airplane for 1300+ hrs without pulling to the left!
5.I plane to then return the gear Univair and request that they replace at least the left gear that is jigged true and straight.And I will verify same before I cover it!

well here is the latest info I have on my tracking problem , I shipped my new gear and my old gear to univair as they requested and they ,after putting my old gear in thier jig, said that it did not fit, and basically that I was SOL.This is what the said
Your original gear.
"Axle is bent toe in

The main tube in line with the axle measuring from the holes where the long strut attaches to the hole in the forward gear attach is 1/8” longer which would affect the camber of your axle.
This gear we are unable to put in our jig due to the above issues. The top attach bolts are in line the same as our gear. We are guessing that maybe someone has adjusted the axle or maybe this gear has been worked on in the past? Our inspector also said maybe the gear attach fittings could have been welded a bit off and it wouldn’t take much to need that axle to be adjusted".
nivair gear.
"With the fabric on the gear still slides right into the fixture we have been manufacturing them in since the mid 60’s.

Axle and main tube are both in line with no toe in or toe out.
Both the Piper original drawing and the Univair prints call out the leading edge tube and the axle to follow the same center line.

So to answer your statement of our gear being toe out, compared to your gear with being toe in and different camber and our gear being neutral it would look toe out. The bad news is that Univair would not be able to make a gear to fit your needs for your aircraft as we would have to build it not using a jig and then it would not be able to be certified since it would not conform to a Univair print or Pipers gear print. You might look at the gear fittings as our inspector had mentioned as you said you have toe in on the right and toe out on the left something seems a bit off and with as much as your gear is tweaked at the axle it was adjusted at some point in time.

Sorry this is probably not the answer you want to hear but I do want to thank you for sending in your gear as well so we can see where the problem may be at. Like I said over the phone we sell these gears for the cubs and have done so for many years using the same jig and prints since 1967. With how many we sell of these gears there would be receiving a bunch of negative feedback if there was a manufacturing issue."

SO,I have two landing gear [left side] that came off of 1954 model L21B aircraft.One off of my plane and another from a friends airplane that are basically identical and are tracking almost straight.
I have been flying the airplane for over 25 years with the gear that they were sent along with the new ones I just purchased them .The problem with controlling the plane on landing started with the new gear installation. All the mounting points are spot on!
SO, at some time in the past piper aircraft must have changed the jig configuration.If anyone with a 1954 or early cub purchases one of these gear they are not going to be toed probably .It is highly unlikely that I have the only two gear that are different...Comments welcome please ?

Blast, inspect and recover your gear and install it. We jigged several L21 fuselages in my jig and they fit perfectly. We also installed a few sets of Univair gear on said L21 without issue. I would suspect your fuselage might have gotten tweaked over the last 67 years.

Steve ,thanks for the post. but, I had this fuselage built for me by Jim Soares at Rocky mountain Airframe in 1994and at that time he was building frames for Univair. If you ordered a piper super cub fuselage at that time it was built by him.When I recieved the finished product in Atlanta I had the airplane restored complete with new fabric,cables, wiring,etc,all except landing gear.It was the original gear as far as I know.
I also have another set of gear from a 1954 L21B like mine and it's left gear test on my plane near perfectly straight like my old gear that univair is talking about that I sent them along with the new gear that is different.The 1954vintage gear looks to be from a slightly different jig.
Now univair bought Rocky mountain at some in the past after Mr. Soares passed away. I have heard that univair bought the jig and many of his tools.Anyway Any body who purchased a frame from piper back then got one just like mine made by Jim Soars I think.I have checked the frame and it is fine!

Take 2 3/8" rods, sharpen one end of each to a point and slip them into the two gear attach fittings and measure the distance from the front and rear.

One thing I would not do is cover whatever gear you decide to use until you have put it on the plane and make sure it works.
Denny

We have run a 15/16th rod thru the attach lugs and they are very straight .A 3/8 rod is a bit tight.All three gear we have . have mounted easily.The left hand leading edge upper bolt is the only one that the bolt needs a little coaxing in each case.

RCharles said:

We have run a 15/16th rod thru the attach lugs and they are very straight .A 3/8 rod is a bit tight.All three gear we have . have mounted easily.The left hand leading edge upper bolt is the only one that the bolt needs a little coaxing in each case.

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Not what Steve is suggesting. He is asking you to check gear lug parallelism between the two sides on your fuselage.

Edit: And even if the two sides are parallel to each other, they might not be parallel to the horizontal reference line per the Piper prints. Please report back what you ultimately find!

Gordon,This frame was built in 1994.When I got it I mounted the gear from my plane built in 1954 and flew it for over 25 years that way ..The only thing that has changed is the new univair gear.When you put these new univair gear next to the older piper gear there is actually a difference in the length by 3/8 inch .?

Go back to my post #36! Your fuselage has been around since 1994, lots of things may have happened in that time. Verify the location of all the fuselage gear fittings for parallelism and location for and aft. With the fuselage level, drop a plumb line (or laser) down to the floor from the centerline of each fitting, and make your center line from the firewall to the tail post. Measure from the center of the fuselage to each fitting and verify they are all the same. Then measure the diagonal from left front to right rear, and then from right front to left rear. Those measurements should be the exact same, or your fuselage fittings are off. Don't forget to also check the cabane attach fitting locations as well.

Get the drawing for the gear and verify the measurements for the gear if you don't believe Univair. If the gear is correct, then the only thing that can be wrong is the fuselage.

How do your new and old gears compare to this drawing?

http://www.supercubproject.com/drawings/pdfs/A3310136.pdf