Not for your plane, but in general
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Necessary Tools:
1. Carpenter's square
2. 4 ea. 18"X 18" aluminum plates 0.125" thick or greater.
3. Protractor (with bubble level)
4. Straight edge approx. 10.5 feet long.
5. 6" scale or ruler
6. Level flat area as large as your plane.
7. Several 4x4 wooden blocks 6" long
Basic procedures: Apply a thin layer of grease to one side of two of your aluminum
plates, place the other plates on the greased surface forming a grease sandwich. Place
these under the main wheels of your plane on a smooth level surface, making sure you
have good access to the wing tips. Once this is accomplished, shake the plane by the wing
tip and let it come to rest on its own. This will allow any energy stored in the gear springs
to be dissipated. Now check to see if the plane sits level.
This is accomplished by
measuring the distance to the floor from the inner rearmost portion of the wing tip next to
the aileron (the rear of the tip rib). The reason for checking here, rather than at the outer
part of the tip is I have seen aftermarket tips installed canted off center giving a false
measurement. Cessna recommends no more than 3 inches total difference tip to tip (1.5"
up and 1.5" down from neutral). If you don't meet this, it should be corrected. On aircraft
without the P-Ponk gear strengthening kit this is easy. Simply add or subtract shims
under the gear leg attach points to raise or lower the tips as necessary. Try to use the
minimum necessary to accomplish this. On planes with a P-Ponk kit installed, this is a
little more difficult, and I am currently working on a procedure to accomplish this on
planes so equipped (like our 185). I will report on this in the future.
Once you are satisfied your plane sits level, load it to the weight at which you normally
expect to fly. It is best to use tool boxes, sand bags or 5 gal. cans of water for this purpose
as friends will tend to get bored and wander away before the job is complete. Block your
straight edge up in front of the main tires with it touching the tread just below axle height.
Depending on what you are using as a straight edge, you may want to block it up near the
aircraft centerline to keep it from sagging. Now place your carpenters square against the
rear side of the straight edge outboard of one wheel and slide it in until it touches the tire.
Determine the toe-in by measuring the distance from the square to the wheel rim both in
front of and behind the axle. The measurement ahead of the axle will be greater if you
have toe-in. Subtract the smaller measurement from the larger, the difference is your toe-
in or toe-out for that wheel. The recommended toe-in is 0 inches at operating weight. If
you choose to align the gear with the plane, empty the maximum recommended toe-in
is.12 inches. This will theoretically give you 0 toein at gross weight.
Next, determine camber for this wheel by placing your protractor vertically against the
tire and adjusting the center level, measure the camber in degrees from vertical. At
operating weight, 0 degrees is ideal, when empty 4 to 6 degrees positive camber is
recommended by Cessna. Positive camber is when the top of the tire leans out. Since
most of us will be doing this with planes that already have shim packs installed, this can
be time consuming as you need to measure these settings before proceeding. If your plane
meets this criteria, go flying. If it doesn't, jack it up and remove all shims between axle
and gear leg, bolt it back together and measure again. Determine what, if any, shims you
will need by referring to the shim chart in the Cessna manual for your plane. In the one
covering our 1970 185, it is figure 5-4. I also have an older 1962 manual, in it the shim
chart is figure 5-10. Once you have determined your shim pack, install on the plane, and
remeasure to make sure you got the correction you needed. If it is satisfactory, repeat the
entire process on the other wheel. Cessna recommended a shim pack thickness of not
more than .10 inch in the 1962 manual, but deleted this from the manual covering 1969-
1980 airplanes. My recommendation is use the absolute minimum number of shims
necessary to obtain the desired results. This is also a good opportunity to inspect the
condition of all your axle attach hardware. If it doesn't look perfect, replace it. Nuts and
bolts are cheap compared to the parts they hold up.
The reasons for keeping your gear in proper alignment are to keep tire wear to a
minimum, and to improve ground handling. Too much toe-in or positive camber will
wear your tires on the outside, too much toe-out or negative camber will wear your tires
on the inside. Excessive toe-in tends to cause the plane to be directionally unstable on the
ground. Here is an example: As you are landing a wind gust causes you to swerve to the
right, your gear is toed in excessively, as you swerve right centrifugal force puts more
weight on the left wheel giving it better traction on the pavement. Being toed in the left
wheel is actually aimed to the right of the direction the plane is pointed, thus causing the
turn to want to tighten up even more, and requiring very high rudder input to stop the
turning tendency. If allowed to progress too far, rudder and tailwheel steering alone may
not be enough to counteract the turning tendency, and left brake may be needed to add
some drag to the outside of the turn. If allowed to progress still further, a good hull
coverage policy may be needed to fully recover. How many times have you met a 180 or
185 pilot who tells you what a tricky plane these things are? Chances are this guy is
flying around with his gear out of alignment big time. Now let me tell one "war story"
and you can get out to the hangar and go to work. I aligned the gear on a Cessna 195 one
time for a customer who regularly flew it loaded to gross weight. So I zeroed it out for
these conditions. I then had several opportunities to fly the plane, but always by myself,
without baggage, and usually less than full tanks. The plane had a tendency to hop down
the runway on both takeoff and landing as the wheels were toed in significantly at these
low weights. The wheels would pull in as the plane rolled along loading the gearlegs until
spring load overcame tire friction and unloaded the gear, then it would do it all over
again. I flew this plane once at near gross weight and was amazed at the difference, no
hopping at all and it tracked like it was on rails. Tire wear will tell you quite a bit about
how your gear is aligned and about other things like wheel balance and tire pressure. The
key to success in maintaining your Skywagon is the same as it is for flying it. Always
keep looking for things that are not right and correct them as soon as you notice them,
that way they will never become life-threatening to you or your plane. The protractor
(with bubble level) can be purchased at a hardware store.
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