Toe measurement results...

[Aero_tango]

I`m confused with my toe measurement results...

The Jan-March 2009 BH newsletter explained clearly the procedure for toe measurement:
""The main gear axles should be checked for proper alignment with the plane in the three point position, and with the tread at 68”-70”. Check that both axles (referencing off the brake discs) are square with a centerline dropped with a plumb bob off the engine crankshaft center (or nose of spinner) and the tail post or tail spring bolt center. TOE IN should be 0 to ½ degree. ""

As per the measurement procedure, I used two steel angles clamped to the bottom part of the brake discs and measured the separation of both steel angles in reference to the centerline of the airplane.
Using some basic notion of trigonometry, i then converted the measured distance to angle values.

My first issue was to get the proper tread of 68" to 70". With the engine installed (but no wing) I was only getting around 65".
This is where i decided to replace the two shock struts with scrap piece of steel angles. I drilled one end of each steel angle with 3 holes, to mimic 3 different shock struts extension. I didn't really know what to expect in terms of tread with these 3 set of holes. So i installed the steel angle struts, measured the resulting tread for each set of holes and, of course, measured the toe for each tread.

The results obtained where:

Tread	Left toe	Right toe
71.75"	0.1 deg (out)	0.2 deg (in)
68.5"	0.4 deg (in)	0.9 deg (in)
64.5"	1.0 deg (in)	2.1 deg (in)

Wow...the toe results varies quite a bit depending on how much tread you have. Remember, the spec is TOE IN should be 0 to ½ degree with the tread at 68”-70”
I've also plotted the results (see attached photo) and add a green box, which represent the toe spec. Looking at the plot, only the left wheel is within spec.

Questions are:

1. Should I try to bring the right wheel within spec or leave it as is? It requires about 0.5 deg of correction, which is quite small to achieve with the Heat/bend procedure.
2. From the plotted data, near GW (ie around 72" of tread), toe is 0 and start to be negative (ie Toe Out). Is that a concern?
3. In the same BH newsletter, it also explains how to measure the toe per drawing #23. In this case, the tread is set at 72”. The 2 axles should be in line with each other (zero toe in/ toe out) or at most have ½ degree toe out per side. Well, if I looked at my data, at 71.75" of tread, I have 0.1 deg toe out (left) & 0.2 deg toe in (right). Based on this data and spec, and considering measurement errors, I shouldn't do anything and leave everything as is !!!

Mike

[Battson]

Oh wow - you've gone to a lot of trouble there!

There is only a fraction of a degree difference between the true centreline of the plane (or as best you could measure it) and the "effective centreline" angle created by the gear. I note that you haven't got the plane loaded in the normal way, and you've removed some parts to get the measurements you wanted.

Overall, I don't think this small difference in measurement represents a big problem. After all, we are talking about welded steel, not precision machined parts. Things are never going to be perfect, and everything moves / flexes a lot with the stresses of landing / flight anyway.

I can't recall what my toe-in was, something like 0.8 degrees toe-in each side comes to mind - but that was without the wings hanging on it. Anyway, the plane handles great on the ground. Like every taildragger, you need to watch what you are doing at all times...

[jaredyates]

One way to get the desired width measurement is to remove the shock struts and lift the airplane up on wooden supports. It needs to be in a level flight attitude, so the tail is going to need some kind of support anyway.