cessna 170 wheel alignment with 180 legs

[pilot1]

Hi just a question
I bought a cessna 170 ragwing and also have felt like I have the hardest airoplane in the world to fly. I have a lot of tailwheel landings being a glider tug pilot and having over a thousand landings and takeoffs in Super cubs, Callairs and Scouts in all kinds of conditions but I just excepted that you dont land a c170 in a crosswind ( especialy after I ground looped it with 2 children and an adult aboard, Broken tail wheel cloth damage to tip and one elavator slight bent no prop strike. and a very dinted ego ) Now if it is blowing or possible crosswind I dont fly Mabe you guys have the answer. Also My aircraft was fitted with Cessn 180 main legs do you know of this mod and would it have any effect on the wheel alignements you guys have suggested here

Steve

[blueldr]

Get the book out and check the wheel alignment. Especially the toe in or toe out. It is critical.

[pilot1]

Will the 180 legs make any difference

steve

[blueldr]

Steve,
The type of gear legs will not make a difference. Off runway excursions are generally caused by mis-alignment, specifically, toe in or toe out beyond limits.

[pilot1]

Thanks BL, I will try to check alignment this week_end
2. How to check alignment IVE copied this of this site but Ive seen other peopl talk about loading up to max weight and useing geased trays or newspaper Yet this method says empty what are your thoughts?

Steve.

The first step is to make sure that the wheels are in a neutral position. In other words make sure you have relieved all effects of turning or pushing the airplane around the hanger floor. To do this, push the airplane forward in a straight line for a few feet. Avoid doing this on wet cement. The toe-in and toe-out checking is done at the factory at the wheel flanges. A simple check fixture can be manufactured for doing this checking. A simple but accurate checking job, without a check fixture, can be done as follows: Place a straight edge across the front face of the tires and then place a carpenter's square backward from this straight edge on the outside of either tire. Then measure inboard from the carpenter's square to the rear and front flange of the wheel. The difference in this distance will indicate the amount of toe-in or toe-out existing on that wheel. The original setting as measured above on the various model airplanes at their empty weight is listed below. The first figure is the amount of toe-in which we try to get and which is the ideal setting. The tolerances are indicated next to each figure.

SHIP EMPTY WEIGHT

MODEL DESIRED TOE-IN TOLERANCE
120 & 140 1/16" 0 TOE-OUT 1/8" TOE-IN
170 0 0 TOE-OUT 1/16" TOE-IN
190 & 195 1/16" 0 TOE-OUT 1/8" TOE-IN

3. How adjustments are made

The adjustment is made with wedge shaped shims that are installed between the axle assembly and the landing gear spring unit. These shims are tapered in two directions so that they result in variations of toe-in as well as camber. There is no specific reading or setting which we try to maintain as far as camber is concerned as experience indicates that any reasonable variance in camber does not in any way affect tire wear. Tire wear is apparently the result in greatest proportion to misalignment in toe-in.

The following shims are available for the various models.


MODEL 170

At present, one special shim is available. The following table lists the partnumbers for the shims and the bolts that are necessary for their installation.

0541111 Shim Main landing gear
AN5-22A Upper Bolts
AN5-23A Lower Bolts

Again the correct position of the wedge is very important. The thickest corner is to be installed for ward and up. Additional 140 shims are to be used as required.

[GAHorn]

The alignment should be done at 2000 lbs, and should strive for ZERO toe-in/out.

[c170b53]

What changes with the increase in weight of the a/c? with respect to toe in or out? In other words does the I can imagine the castor changing. Has anyone tried light vs heavy and can come up with a measured difference.

[cessna170bdriver]

What changes with the increase in weight of the a/c? with respect to toe in or out? In other words does the I can imagine the castor changing. Has anyone tried light vs heavy and can come up with a measured difference.

The difference between caster and camber always has and always will confuse me, so I looked it up: http://www.ozebiz.com.au/racetech/theory/align.html

If I interpret the site correctly, "caster" only applies to wheels that steer, and is the angle to which the steering pivot axis is tilted forward or rearward from vertical. That's the important one on our tailwheels.

"Camber" is the angle of the wheels to a vertical axis. Toe-in/out (the easy one to remember) is the angle of the wheels to a longitutinal axis. With a 170 in the three-point attitude, the gear legs extend forward at an angle, so they have a longitudinal component as well as a vertical one, so spreading them would affect both camber and toe-in/out.

Miles

[c170b53]

Sorry I screwed up my lost post I was thinking camber not castor. I agree that loading the aircraft would spread the gear and change the camber that being the angle of the axle to the ground in the vertical plane. Its the toe in thats difficullt to see altering when the gear spreads. The toe in in my mind would be the angle of the axle to the gear leg in the horizontal plane. Would the gear not have to twist to alter that relationship?

[cessna170bdriver]

Sorry I screwed up my lost post I was thinking camber not castor. I agree that loading the aircraft would spread the gear and change the camber that being the angle of the axle to the ground in the vertical plane. Its the toe in thats difficullt to see altering when the gear spreads. The toe in in my mind would be the angle of the axle to the gear leg in the horizontal plane. Would the gear not have to twist to alter that relationship?

What you are saying is true only when the airplane is in whatever attitude it takes for the gear to be vertical, that is, with the axles in the same vertical plane as the attach saddles. In this attidude the gear flexes in a plane perpendicular to the ground. If you spread the gear the tops of the wheels will camber inboard with no change in "toe".

Now imagine the airplane 90 degrees tail down from the original position, with the wheels directly in front of the attach saddles. In this attitude the gear flexes in a plane parallel to the ground. Now if you spread the gear, the gear will "toe out" relative to ground, with no change in camber relative to the ground.

The normal three point attitude of the airplane is somewhere between these two extremes, so, relative to the ground, when you spread the gear, you increase both the camber and toe-out relative to the ground.

Does this very convoluted explanation help anything?

Miles

[pilot1]

Thanks to the excelent advice from this web sight I have checked my wheel alignement empty but with full fuel and found that one leg is forward by about 15 mil ( about 3/4 inch I think) when measured from a point centre of the tail to the same relevent point on the landing gear leg with triangulation also the wedges have the thickest section pointing down. the left leg had about 1/4 inch of toe-out and the left leg was about neutral. I will put about 220 Kg of water filled plastic containers in the cabin and unload the gear then recheck and get back to you with the result P.S somebody else Wrote that they had 1/8 inch of toe-in and when loaded up it went to zero so I'm guesing that I will have more toe out on both wheels and that would explain a lot of the handling problems
( I hope ).

Steve

[zero.one.victor]

Besides the toe-out (castor) factor, I don't imagine that one MLG being forward of the other helps things. It may not cause too much problem, but I wonder what effect that has when for example the tail comes up on the takeoff roll, or comes down after a wheel landing? Seems like it would want to swerve. Now, if that swerving tendency is in the same direction as the p-factor/torque/gyroscopic forces (take your pick) make it want to swerve........yee haw!

Eric

[pilot1]

Eric It does get kinda a skidish when the tail comes up. Do you know if its a big job to correct the MLG alignment(Legs)? I dont have a book

Also is toe out worse than toe in

Steve

[inman]

I think I have found a great way to acurately check the main gear toe-in on my 170.

I role it up on grease plates with full tanks and 200 lbs. in the pilot's seat. (my most common situation). Als make sure tire pressure is equal.

Drop a carpenter's plumb-bob from the center of the firewall and mark the floor.

Do the same just forward of the tail wheel to establish a centerline.

Snap a chaulk line on the floor between the marks.

Clamp a cheap laser level to the inside face of each brake rotor with a small spacer so my tire sidewall does not interfere with the level.

Shoot a line on the floor parallel with my chaulk centerline back to my tail cone and mark the floor left and right.

At the tail, measure from the centerline out to the marks from the laser line and compare them to the measurement from the laser lense-to-firewall centerline line.

This gives you a good idea of which way you need to start flipping axle shims to get as close to 0 as possibel. You can also tell how even, side-to-side your legs are to the centerline for arc. I also measure from an axel bolt to the tail cone mark to see if the legs are similar for-and-aft. In use a little dial level on the rotor to try to get close to 0 camber.

I have found that things happen very quick and unpridictably if I have lot's of toe-in and lot's of positive camber. (carry extra underwear)

[GAHorn]

If one has a 2 by 8 board, on it's edge, laid across the hangar floor and resting against the rear of the tires... and if one takes a straight-edge across the brake discs fore/aft (carpenter's square works well) and draws a line across the top of the board on both left/right ends of the board... then move the board to the front of the tires and do the excersize again... then the difference toe in/out will be apparent without much need for sophistication.
If one drawn line is used as a steady reference (say the left side) then the total amount of in/out is readily discernable. If the "average" is adjusted on each side, the airplane should behave very nicely with regard to this matter.
(The actual amount of toe in/out with regard to left right wheels is more important than any need for longitudinal accuracy. This can be easily imagined by considering what happens every time we land with a wind that's not exactly down the centerline of the runway.)