CTLS Main Gear Toe in?

[Doug G.]

I am sitting here looking at my main gear and wondering if the metal wedges that are between the gear leg and the axle are supposed to be creating toe in, or making the wheel straight (maybe slight toe out)?

I have noticed the plane seems squirrelly when I am taxing but took it to be the nature of the beast, but now I wonder...

The only thing I can find is the Parts and Assembly manual and it looks there like they are facing the other way (toe in).

Thanks

[Anticept]

Aircraft mains need to have a TINY amount of toe in. It keeps them from being squirly on taxi and landing. Make the toe as miniscule as possible, because wear greatly increases with toe.

[Doug G.]

Not much option. The spacer can only be turned two ways. One direction makes them straight (or pretty close now that I have measured) and the other makes them toe in. (I can't really tell how much without changing it.)

[Anticept]

Not much option. The spacer can only be turned two ways. One direction makes them straight (or pretty close now that I have measured) and the other makes them toe in. (I can't really tell how much without changing it.)

 

If you are referring to the metal spacers, leave those alone. You can make corrections to the metal spacers with your own out of thin fiberglass and epoxy layups and sand them to the degree of correction, or order them from FD. You might be allowed to machine the metal spacers, but that you would have to confirm with FD.

[Doug G.]

What I am wondering is if someone, before I bought the plane, might have put them on wrong. Should they be thick forward the front or back? Currently the thick side is toward the front.

 

I am trying to verify that they are on correctly since the picture in the P & A seems to show them the other way, but it is not conclusively clear. I hoped someone here could tell me before I head home. Otherwise I will call FD tomorrow.

[Anticept]

Do whatever it takes to get the toe as close to correct as possible. Generally the metal spacers alone aren't enough. Both of our CTLS have a few fiberglass spacers for fine correction.

[LS Bruce]

Any good tricks on measuring the toe?

[Doug G.]

What is correct, do you have a source for the specs?

[Tom Baker]

I just installed a set of Matco's on a CTLS, and if you put the spacers in wrong you will definitely know. I did look at another CTLS that had an extra shim that may have been for adjustment.

[Doug G.]

So Tom, which way does the wedge go?

[Anticept]

Doug: You need to place it in a way that gives you toe-in, but an absolutely minimal amount. Fraction of a degree. If no orientation works, then you need additional corrective spacers.

 

 

Any good tricks on measuring the toe?

 

 

First you need a large straight edge, several feet long, to go between the wheels. Straighter is better.

 

OR, you can use one of those sweeping lasers used for wall layout.
 

You also need two sets of plates with grease between them. The aircraft will sit on the plates, and you move it forward and back a couple times for a few inches, so it allows the wheels to shift to their natural position.

 

Carpenter's square and protractor.

 

Place the straight edge/laser in front of the wheel against the rubber. If you are using a laser, you need to make sure the laser beam and emitter are the same distance from the wheel rubber on both wheels.

 

From there, you can set a carpenter's square up against the wheel, rubber and all, line the square's corner up with the laser beam, and measure the angle. If you want a more specific measurement, you would need to find a way to make this work by only touching the wheel rims, but generally that's overkill.

[Doug G.]

I think that turning them around would produce about 1/8" of toe in on each side. As they are they seem very straight. (Measuring the same grooves in the tire front and back gives 63" in both places.)

[Runtoeat]

Do I need to dig up my laser alignment photos again - nah, won't go there.

[Doug G.]

I really thought I was asking a simple question.

[Anticept]

See my edit for how I do it. It's more precise that way, but it's marginally more complicated.

 

I think measuring the rims instead would be better though for your method, Doug G, if you have precise measuring equipment. You'll need to use a little trigonometry to determine the angle, or the acceptable distance difference. EDIT: Scratch that. If both wheels were 45 degrees off to the same direction, the measurements would still be the same, even though clearly the wheels are not correct. My method uses the aircraft lateral axis as drawn between the mains with the straightedge/laser as reference. It does rely on the wheels themselves being in line with each other, though, but it shouldn't be a problem. The last and most complicated, but most accurate method, is using multiple plumb bobs dropped from buttock line 0 on a leveled airplane, straight edges on the tires going forward to back, and measuring perpendicular off the imaginary line drawn between the plumb bobs to the straight edges. Then measuring from where you met the straight edges to the center of the wheel axle and using trig.

 

EDIT: Also, toe in is preferable to toe out, period. Toe-out on aircraft main wheels causes squirreliness. As a side note, in cars, a front wheel drive car desires toe-out (countering the tendency to understeer), while a rear wheel drive desires toe-in (countering the tendency to oversteer). Again, we're talking a fraction of a degree.

[Anticept]

I think that turning them around would produce about 1/8" of toe in on each side. As they are they seem very straight. (Measuring the same grooves in the tire front and back gives 63" in both places.)

 

See my edit above. I just realized your method is inaccurate and shouldn't be used.

[Runtoeat]

Doug, I've spent a lot of time aligning my main gear after installing Matco system.  Honestly, the human eye is hard to fool.  A suggestion is to just stand back from the plane and sight where your wheels are pointing.  If you think one or the other or both aren't pointing in a parallel direction to the general center or your fuselage, add a little shimming and see how the plane tracks during high speed taxi.  Roll the plane forward before checking to put wheels into normal set. This is obviously "backyard mechanic's" method and there is the formal alignment method described in the FD manual.  Another way to set toe is this method from a previous thread:

http://ctflier.com/index.php?/topic/2576-choosing-tires-requesting-opinions/?p=30180

[Tom Baker]

So Tom, which way does the wedge go?

That was a couple weeks ago, and I don't remember which way the thick and thin sides went. I can go look at my airplane if you really need to know. If they are installed wrong you will have obvious misalignment.

My quick and crude method of checking toe is a 6' piece of 2" aluminum angle on two blocks of wood and a carpenters square.

[FlyingMonkey]

The Matco setup on my CTSW required one washer on each lower bolt on both sides to correct excessive negative camber.  Additionally to correct toe-in the right wheel needed a washer on the upper front bolt.  The left toe-in was much worse, and I needed two washers (the max allowed) on both front bolts.  I might have gotten away with less washers if I had shaved them into wedge shapes before installing, but this seems to be working well.

 

Before the change to Matco I was burning through tires (they were wearing on the outside very badly) in about 20 hours, not kidding.  I now have about 20 hours on the new setup and the tires still look good with no abnormal visible wear.  I also switched to the 8-ply Aero Classic tires; they have a flat tread area instead of the rounded 6-plys and I think that helps as well.  I do not find the ride painfully harsh, even at Roger's recommended 45psi.

[Doug G.]

Just talked to Dave Armando at FD. he says the thick part goes to the front (which means they are correct on my plane) and that toe in is a bad thing. (He didn't say it, but I suspect toe out is also.) So l guess the taxiing issue is just the nature of the beast.

He did suggest checking the bearings on the pedals under the mushroom to see that they are in place after I told him it felt like I needed more right pressure to turn on the ground than left.

[Anticept]

I am going to retract some of my statements about aircraft toe.

 

It appears that both cars and planes differ based on how they are built. Everything from gear design, to where the drive power comes from, tires, nosewheel vs tailwheel, etc. Things like piper cubs need toe in, because the bungie suspension needs tucking in to help stability. Whereas others might need toe out to help in turns or stability from ground looping.

 

Here's a good explanation for generalization:

 

 

Just get it as straight as friggin possible!