Tolerances - and the old Quick link aileron bellcrank chesnut
One thing that really bugs me occasionally are no mention of tolerances. One
particular problem I have had this weekend was the quick connect bellcrank
installation.
The actual installation of the CS14P/S brackets I did a couple of weeks ago
lining the 1/4 inch studding up with the holes in the spar. Taking great care I
positioned the brackets in place and all seemed well.
Since then the fuel tank has been installed and the brackets replaced on their
flox/redux pads.
The bellcrank bolts were reduxed home and the bellcranks fitted ready for the
trial fit of the Tufnol pads.
Having positioned the wings back onto the cockpit module I could not figure out
why the bellcrank pivots do not align exactly with each other. The starboard one
was pretty close - probably 1/32 inch out (acceptable? within allowable
tolerances?), but the port one was a good 1/16th inch out - perhaps more, I
would think out of tolerance but who knows?
I have repositioned the quick connect bracket on the port side to correct the
misalignment.
I can only assume that my holes in the spar were not exactly at 90 deg to the
spar and that the port side accentuated the problem as the pivot bolt is so much
longer. The hole must only be a smidgen out - but over 3 inches of bolt length
it amounts to what appears to be visually at least quite a bit out.
The question is - how much out of alignment is acceptable. As the module is
still yet to be positioned in the fuselage and the wing incidence set the
alignment might all might move again.
Anyone had a similar problem? OK, I know people have fitted dummy spars etc.but
that still would not have helped in this case.
Question remains - what sort of tolerance is acceptable here? Ideally, alignment
should be spot on but unless the pivot holes are factory drilled I challenge
anyone to drill a 1 inch deep hole exactly 90 deg in all planes by eye.
Any thoughts from builders past this stage would be appreciated.
Martin Tuck
#152
Wichita, Kansas
U.S.A
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