Model IV-1200 factory tube landing gear alignment discussion

[GWright6970]

I have done a search on here and in the internet regarding toe in and toe out. I checked my gear out per the excellent photo procedure on here, and found that my 1993 factory tube gear has BOTH sides with a toe in of about 1/2 inch to the aircraft center line, on 8 inch wheels and 21 inch Nanco tires.

There are at least 3 of us builders in search of your experience and knowledge!

Before I embark on disassembly and attempting to bend these axles, I wonder just how necessary this is. I can put up with the tire wear on the outsides. My questions revolve around if people are successfully landing aircraft with this much toe in, or any amount of toe in? Did you ever measure the toe in loaded, and in the 3 point attitude? Have those with positive camber (tire top is outward from the fuselage) had to ever adjust the camber also? How did you successfully correct the toe in or camber? Did bending the axle result in having to make modifications to the brake calipers, etc?

It is my hope to have this thread be dedicated to factory tube gear experiences. Thank you!

FYI.. my Kitfox is now registered, and after I address this issue, I will be proceeding to the Airworthiness Certification process... super close!

[avidflyer]

Here is my take on it. If you are running right down the runway straight and level, then the tires will be scrubbing themselves off more or less the same amount with the toe in you have. But then you start a swerve to the right, weight will shift to the left wheel somewhat, and maybe the left wing goes down some as well. Both of those things will add more weight on the left wheel, and less on the right wheel. Where is that left wheel pointing (considering the toe in you have)? I would say it's trying to steer you more into the swerve rather then neutral or the other way, which toe out would do. That's why I would say neutral or just a slight bit of toe out is the way to go. I'm no expert, but like everyone else, I have an opinion, and this is it! :-) JImChuk

PS when I measure the toe in/out, I make a mark in the center of the tires, and measure off that mark when it's straight ahead to a center line or the other tire. Then rotate the tires back 180 degrees and measure from the same mark again. That should be way more accurate then measuring off the sidewall of the tires.

[GWright6970]

Jim,
Thank you. I agree with all of your response. I measured as per your procedure, from center of tire to center of aircraft line that was determined by a set of plumb Bob's off the center of the prop, and the tailwheel spring attachment bolt.

I wonder what those who are flying with toe in can add to this discussion?

Thanks Jim!

[rv9ralph]

On my Model 3, I had toe in on the left and neutral on the right. On landing the aircraft wanted to divert to the right so hard the I could hardly keep it straight... it was a struggle.

To measure I used a straight edge (6 foot level) on the rim of the wheel. To get an accurate line, I used 3/4" nuts as stand-offs from the rims to the straight edge.

By whatever means, make both neutral.

The method of correcting by putting a pipe on the axel and tweaking to straighten in not intended to bend the axel, it is intended to twist the landing gear.

Ralph

[Auster]

You were also asking about tyre wear with positive camber e.g. top of the tyre further out than bottom. I have the standard grove gear and wheels with 8" Air Trac tyres on my S5 Outback. After a little more than 400 landings, almost all of those on tarmac, there is very little tread on the outside of the tyres and plenty remaining on the inside. This weekend I will swap the tyres around and start wearing the other side.

Does my experience match others with this set-up?

[GWright6970]

Ralph,
What method did you use to correct your alignment?

Excellent information, thank you!

[Slyfox]

On my Model 3, I had toe in on the left and neutral on the right. On landing the aircraft wanted to divert to the right so hard the I could hardly keep it straight... it was a struggle.

To measure I used a straight edge (6 foot level) on the rim of the wheel. To get an accurate line, I used 3/4" nuts as stand-offs from the rims to the straight edge.

By whatever means, make both neutral.

The method of correcting by putting a pipe on the axel and tweaking to straighten in not intended to bend the axel, it is intended to twist the landing gear.

Ralph
but if you have the grove gear, I think you can get shims from kitfox to kick the wheel in or out.

[GWright6970]

Auster,
Good idea on rotating your tires to compensate for wear. Have you ever measured for toe in or out?

Thank you for relating your experience!

[rv9ralph]

Ralph,
What method did you use to correct your alignment?


Well, that goes to two things. First, I corrected my gear to remove the toe in. It was not difficult due to non-standard gear. There was a horizontal plate that attached the axel to the gear structure that allowed adjustment.

The final correction was that I replaced the stock with Grove gear, then checked the alignment and used the grove shims to achieve proper alignment.


Ralph

[PapuaPilot]

You always want to check the toe in in relation to the wheel hubs like Ralph said, don't check it at the tires.

Tires typically wear on the outboard side and rotating them is a normal procedure to maximize the wear and life of a tire. The outside wears because the is the part that touches on the landing as the wheels spin up. As the plane gets heavier the landing gear spreads out and the wheels go from a positive camber to approximately zero. The picture is for cars but it give you an idea of what camber is.

23955

[HighWing]

First regarding camber, I never worried about as my thinking was like Papua Pilot's sort of like camber yes while empty, but get in and presto - perfect alignment.

Coincidentally, by first Model was also a 1993 model - delivered in March of 93.

Grover,
Your question has all the details of my experience. While I was in the build phase, Skystar issued a service bulletin regarding alignment of the early IV landing gear. Essentially it was to fasten the fuselage to the floor as an anchor point, then drop plumb lines and using chalk lines mark all the measuring points. I used a saw horse-like support under the lift strut attachments and a welded fixture that supported the tailwheel and was bolted to the hangar floor for security and to counteract the bending forces. The geometry of the supports raised the main gear wheels for wheel removal to expose the axle. A square placed against the axle gave the alignment sighting against the square to a tape measure placed about 10 feet forward of the axle and aligned perpendicular to the center chalk line - both sides. A measurement between both axles gave the desired cross measurement. After the deviation was determined a piece of copper pipe was placed.over the axle to help preserve the threads and a long pipe was placed over that and the gear alignment began. As Grover suggested, it was the axle that bent rather than the gear structure and washers were strategically placed to bring the brake calipers in line with the axles. This procedure was as described in the service letter. I flew with the original bungee gear for a year or two without any issues, then switched to the Hammerhead gear. My take on the early Kitfox models and the number of ground-loops with corresponding high gear collapse rate had to do with either poor tooling alignment or poor welding technique resulting in a very poor quality bungee gear. When designing the cabane gear we once made, I used an original IV bungee gear to set longitudinal wheel positioning and that gear was extremely toed in - something like 3/8 inch at the length of the bungee arm.

[Auster]

Auster,
Good idea on rotating your tires to compensate for wear. Have you ever measured for toe in or out?

Thank you for relating your experience!

We did measure back when the plane was built. about ten years ago, and I think it was neutral but I will check again tomorrow when it is in the workshop. It isn't the easiest plane to keep straight on take-off or landing but I just put that down to it being a Kitfox and that I have to work a bit harder than in other taildraggers. Will report back.

[efwd]

Believe I recall you said you have a toe-in condition. If that's correct, then the handling characteristics you describe are precisely what you would expect with a toe-in condition from what I have read. I believe it is recommended to be neutral or slight toe-out for this reason. I bought shims from Kitfox. They aren't the cheapest peices of aluminum (less $$ than Grove) but my airplane tracks true down the runway.:D I believe I did the deed with two shims.

[rv9ralph]

Here is a picture of the nonstandard gear. Note the horizontal plate the axle is attached to. This in turn is attached to a plate on the gear weldement by 4 AN3 bolts, which allow adjustment for toe in/out.

Ralph

23960

[GWright6970]

Ralph,
That is the way to do it! I wish ours was designed like yours! Thank you for posting this! Yeah, I'm envious!! LOL!!

[GWright6970]

Lowell,
I must be blind, because I can't find either a Service Letter, nor a Service Bulletin on this issue. I will hopefully be finishing up my specialty Kitfox trailer in the next two weeks. You may find me at your front door again!

Thank you Lowell, I would have never made it this far if it were not for your unselfish assistance and mentoring!

[rv9ralph]

Ralph,

That is the way to do it! I wish ours was designed like yours!

They are for sale.

Ralph

[t j]

Back to the original question.

The Model 4 standard tube landing gear should have neutral or slight positive (1/4 inch or so) camber when the fuselage is leveled. This is with the airplane empty or even with two 200 pounders sitting in the seat. The bungees will stretch to give it negative camber in a hard landing but only for a second.

Using a six foot cheater on the axle to bend the gear or the axle to adjust toe in has been done by some builders. I chickened out when I tried to do that for fear of damaging the gear or the fuselage. I wish I had known about the option to install shims like Ralph did on his gear.

Here's the thread on that. https://teamkitfox.com/Forums/threads/2802-Wheel-alignment-a-photo-tutorial?highlight=wheel+alignment

[HighWing]

Lowell,
I must be blind, because I can't find either a Service Letter, nor a Service Bulletin on this issue. I will hopefully be finishing up my specialty Kitfox trailer in the next two weeks. You may find me at your front door again!

Thank you Lowell, I would have never made it this far if it were not for your unselfish assistance and mentoring!

Definitely not blind, Just misled a bit. I did the search and found the original source. It was an article written by Kitfox Guru, Mark Budak and published in the Kitfox times of April 1996. I posted a link to a PDF of the Kitfox Times below and also in the sticky for the older documents. My approach to the correction deviates a bit, but the set-up and measurement description is pretty much the same.

[GWright6970]

To all, my update:

First, and most importantly, THANK YOU everyone for discussing this.

All along, I have used the "Tom Jones" method of determining the values on toe in/out. I employed the cheater pipe on the axle method to align the left gear, but chickened out when the pipe appeared to be bending too much, and the Kitfox said "ouch." I then removed the axle, inserted the appropriate length into a section of 3/4" galvanized pipe representing the landing gear depth, and a different length of pipe over the portion of the axle representing the axle going through the wheel. I triple checked my Mark's on the axle end, showing me how it was to be bent. I then applied the "Tom Jones" sledgehammer to it. One hit was all it took! It bent the axle 1/4".... I reassembled the wheel, and presto, the 1/2" toe in has been removed. This then required the Lowell Fitt brake assembly realignment procedure with a couple washers.

The wheel rotates free and aligned.

Thank you Ralph for your fair offer to purchase your adjustable gear, in case I destroyed mine.

Again, thank you everyone!

[HighWing]

Good thinking. I wonder if I would have been so intuitive if I had been aware of the axle bending history. I probably tweaked mine in 1996 or 7.

[4Hummer]

To all, my update:

This then required the Lowell Fitt brake assembly realignment procedure with a couple washers.

The wheel rotates free and aligned.

Again, thank you everyone!


Care to share this "Lowell Fits brake assembly realignment procedure" ?

[GWright6970]

Care to share this "Lowell Fits brake assembly realignment procedure" ?

4Hummer.... it is simply placing a regular 960 washer between the landing gear's brake attachment plate, and the brake caliper plate at the two places that either align the brake plate to a corrected toe in or toe out. For me, I placed a washer at the two forward points to align for my bent rearward axle that corrected my toe in condition.24050

24051
I apologize for my slow response! I was not able to get the REALLY GOOD photos with either my camera or my phone!

[Scot]

Hey Everybody-

Thanks to this thread I have been able to make my brand-new Kitfox behave correctly. It is a project dating back to 1993 with bungee gear, and I obtained the Airworthiness Certificate on Jan 6 (of all days). I got my TW endorsement in April, but still have no Kitfox time. During a number of high-speed taxi tests on the stock bungee gear, with tailwheel off the ground, it was an absolute BEAST to control and keep anywhere near the centerline. I was so afraid of it I thought I could never fly it and was considering selling.

My intuition took over, and I found this thread regarding wheel alignment. Upon checking, I discovered my pilot-side wheel was toed-in more than 2 deg. It was visibly apparent just looking at it without measuring devices. After considerable hand-wringing, I figured there was nothing to lose by attempting the cheater-bar method.

Using a beefed-up multiple layered bar consisting of plastic over the axle to protect the threads, 4' steel bar over the axle, and 7' aluminum alloy over the steel, I began exerting MAXIMUM force on the gear leg to remove the toe-in. After several attempts which ended with losing foot traction on the cement floor, I got serious and began bracing myself against other things I could find to stack up. Even with the most pressure I could exert, it would always spring back to the original position. With each try, I was replacing the wheel and seating the bearings just enough to get an accurate reading.

Then I began to get serious, and was able to feel a little bit of "give" in the landing gear weldment. Upon reassembly, I discovered that I was half the distance to the goal. I then gave it another back-busting heave, and felt it give again. Upon checking, it was aligned at nearly zero toe-in.

I took it to the airport, and did some high-speed taxi runs. The difference was literally unbelievable. It was a different aircraft. I spent 1.5 hrs. doing high-speed taxi runs along both taxiways, tailwheel in the air, getting to liftoff speeds while holding it on the ground. I suddenly feel that I can definitely fly this aircraft.

Thanks to all of you who contribute to these forums, it is an amazing resource for all with problems with, of all things: EXPERIMENTAL AIRCRAFT.

[DesertFox4]

Scot, glad it worked out. I went through the same process on my first Kitfox, a model 3, back in 1999. Got right up to putting the bar on the axel to “adjust” it and stopped. Just couldn’t do it. Figured I’d really mess it up worse. Put a Grove gear on and never looked back. Made an airplane out of it immediately. Glad you went for it with great results. So many incredible experienced members on TeamKitfox.com. They continually make me and my moderators proud to keep it running. Enjoy your “new” Kitfox.
Thanks for the update too. It could be very beneficial to others.

[GWright6970]

To "close the loop" the aircraft lands and takes off tracking beautifully. No strangeness...

Lowell Fitt and Joey Meyers dropped by my hangar today to discuss our aircraft builds. I thanked Lowell again for his procedure to align the calipers with the disc if you have to bend an axle to align your gear.

I pointed out to Lowell that while the washers really helped, the alignment was not perfect. After about 6 landings and applying the brakes to cure the pads, "The pads" wore themselves into compliance! No problems.