s24789

s24789

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OK big screw up on the installation of the gear legs on our -7A. We noticed that the tires were REALLY wearing on the outsides. Consulted the forum, and found that this is somewhat common. Then looked over the plans (checked twice during build) and found that there is in fact a left nad right gear leg. We knew it. I guess the paper sticker came off or we are ignorant when installing the brakes and wheels.

Anyway we have convinced ourselves the we have considerable toe-in due to the gear leg switch. We have flown and now need to correct the problem. Looking for advice about jacking aircraft high enough to facilitate the swapping of gear legs. We have the standard Harbor Freight ram jacks but I do not think they will get the wing high enough. Anyone else been as dumb as us and how did you correct it ?

Thanks
phelps
 
First of all, I hope you are wrong about the legs but it sounds like you have done your homework. :(

Second, I am not sure how high you have to be to remove the gear legs but the HB jacks can get it lifted fairly high.
 
Kevin,

I am with TKATC.
I don't think you have a problem with the gear leg.
I know there is a left and right. I think they are the same.

I have the same issue with my left side. Tire wear on the
outside and the right is fine.
I am now rotating them at 40 landings to help the left side
wear out. Also running at 40 PSI. It does pull to left when
tire pressure is not maintained at 40.
The only way to fix the problem is to heat it up and bend it.
Which I am not going to do.
Also you can't shim the 7A gear legs because they are round
vs the 8 that are flat.

I hope this helps.
Did look at DWG 34A

My .05
 
Left = U-701A-L
Right = U-701A-R

Most (A) models have outside tire wear over a period of time.
 
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Kevin,

I seriously doubt that you switched the left and right gear legs. Yes, the left and right gear legs are different from each other (mirror image). And the geometry is such that if you swapped them you'd end up with ridiculously wrong gear geometry. It wouldn't go unnoticed.

Some outside wear on the tires is to be expected, simply as a result of the gear geometry as it was designed.

Furthermore, it seems that some RV's experience greater uneven tire wear than others, likely due to variation in the gear geometry within tolerance. On mine I found some measurable difference in toe between left and right. My right main has 0 deg toe (this is nominal), and my left has 1.3 deg toe-in. Discussed this with Van's, and they indicated that the bend in the gear leg has a specified tolerance of +/-2 deg, so it's within spec, and nothing can be done about it anyway short of drastic measures (either replacing or re-bending and re-heat treating the gear leg).

Kevin, have you actually measured how much toe-in you have? I suggest doing that and getting a better assessment of your situation before you start taking parts off the airplane.

-Roee
 
Tires make a difference too

My first flying was done with the main gear tires that came in the kit. It wasn't long before the outside wear was noticeably more than the inside and it was time to disassemble and flip the tire on the wheel. As it was, the new outside wore down fairly quickly.

For the next set of tires, I went with Desser monster retreads - these are a brute of a tire. After about as much flying on these as I got out of the first set, I can't see a difference inside to outside - no need to flip the tire yet.

One thing - these might be slightly larger than the kit tire - if you still can, leave some room.

FWIW.

Dan
 
Lift clearance

I also hope you are not reversed L & R. Check your current toe in for proper spec + or - 2 deg., as mentioned.

If you do need to lift your RV to remove legs, option as follows:

Build up the needed height with cribbage, (short lumber) to place your regular wing jack on.

Next, build a ramp with 8 foot long (2x6's) for your main wheels to rise to the same level as the cribbage stacked to place the jacks on.

Once the plane is at its position to be jacked, then proceed to jack the plane until the tires are off the cribbage. At this point you just remove the cribbage under the tires and you effectively gain the height needed by the removal of the cribbage. This is quite easy. Feel free to contact me for any clarification of above. Keep us posted on what you find out.
 
There is no way they could be switched and still be flyable. The toe out would be close to 30degrees if they were installed on the wrong sides.

Also, one easy way to check is, the hole for the brake mount should be level with the ground when installed. If you had them on the wrong side, it would be vertical (Or at least close to vertical).

If you are really concerned about tire wear, you may be able to work with Van's or their supplier to figure out if something is just on the edge of the manufacturing tolerance or if there was indeed a problem with one of the parts.

How many hours and landings do you get out of a set of tires right now before you have to change or flip them?
 
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Working with Ken at Van's. Discovered our perceived problem Saturday at noon and could not wait till monday to find out if we screwed up. We have about 40 landings all on asphalt. They maybe could go Another ten before having to get flipped. Ken gave us some more things to check and we will do them tonight. I am backing up from the ledge now. Thanks for the help
Phelps
 
s24789 said:
Working with Ken at Van's. Discovered our perceived problem Saturday at noon and could not wait till monday to find out if we screwed up. We have about 40 landings all on asphalt. They maybe could go Another ten before having to get flipped. Ken gave us some more things to check and we will do them tonight. I am backing up from the ledge now. Thanks for the help
Phelps
Click to expand...

Please keep us up to date on this issue. :)
 
I have some comments regarding Van's kit tires and Van's leg/mount geometry - my personal experience that stretched over several months.

The legs are different - you will not be able to install the legs on the wrong side and have a plane that will roll. Tires will toe-out severely.

Tire wear on the outside is a result (in my research) of the leg/mount geometry.

I raised the plane off the ground (wing jacks and center spar jack) to measure the toe-in. Van's stated (as did the leg manufacturer) that the legs should have a 0 to 1/2 degree toe-in when no weight is on the legs. Mine is about 3 degrees toe-in on each leg.

I tried new legs to no avail and even measured the legs against the manufacturing drawings. They were correct, given the dearth of tolerances. I believe it is all in the consistency of the top leg hole that is pre-drilled at Van's then final drilled by the builder, while the legs are subcontracted out.

I have switched to Desser retread tires, keep them inflated at about 33 psi, and am getting much better tire wear (certainly much better than the Van's kit tire wear). I also switched to "almost landing" 2 or 3 times for each landing to keep my landing practice up. I do "not quite touch and gos".

Next step will be a 38 - 40 psi, per other posts on this thread.

Hope this helps.

Francis
65 hours on my RV 7A - next is the painting.
 
Jacked the airplane last night, removed the wheels to rotate the tires and verified we did NOT swap the legs left to right. The brake flange bolt is horizontal on both legs. Just swagging the numbers it looks like three degrees of toe in. Now I am dejected.
Phelps
 
onther point of view

Kevin,
I'm no test pilot, but spent a LOT of time messing with the toe-in on our old Jodel F-11 ( taildragger). ...seemed the thing always wanted to head for the weeds! (Turned out that a lot of it was aerodynamic rudder blanking on roll-out, and crappy 'locking' tailwheel mechanism, and my technique).
If you look at a protractor, 3 degrees ain't all that much! Heck, I drift more than that on every landing if there's the slightest crosswind. ( no, I'm not perfect!)
Yes, it looks like a mile when you put straight edge on it, (and zero would be better.)
The gear also 'hangs', ( just not as obvious as a C185) so the first contact will be on the outer radius regardless of toe ( in my observation). At 60 mph, that's a lot of rubber left on the road each time.
Consider when you do tight turns, there's also potential for a fair bit of scrubbing, especially if doing it at any speed...this is where higher pressures probably help.
my .02 FWIW
 
Ken (both of them) from Van's and Richard from Langair hit a home run. The gear legs showed up at 1700 on Monday. Installed the brakes and wheels and gear. Airplane was off jacks by 2300. The gear is noticably better. Will report tire wear results.

phelps
 
Gear update

A little over 5 hours and 10 landings on the re-drilled gear legs and the tires look brand new. Our toe in problem has been scratched from the chalk board. On to the next concern, sealing slider interface. Thanks Ken from Van's and LangAir
Phelps
 
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