I have been asked off-Forum about what recommendation Neville gave me
recently on fixing the problem of trim tab link rod TS05 hitting bellcrank
TS03 (or hitting first the tips of the lower plastic fork link). As I
understood from Neville that this was a frequent problem, not caused by
inaccurate building but probably by different limit settings in the servo
motors, it may be experienced in the future by those not yet having reached
Ch. 19.
Graham has already mentioned the basic fix in his response several days ago:
quote
In the early days we had to shorten the two plastic fork ends by about 3mm,
1/8" to avoid this problem. The brass screwed rod was also shortened and
the forks were butted together end to end. if you are a Classic builder I
guess the mod is still required.
unquote
I would like to emphasize that this shortening of the fork ends must NOT be
done prior to installing the servo motor, in an attempt to avoid the problem
ever occuring, but only AFTER the servo has been installed in accordance
with the Building Manual, if it then is realized that the bellcrank and
T-tube, or T-tube and lower fork tips, are touching. Otherwise, nothing is
achieved by the shortening of the forks (which purpose is to lift the aft
end of the bellcrank).
Further: Shorten the length of the forks only as much as required.
Neville's recommendation was 3 mm off each fork, i.e. total 6 mm. In my
case, 3 mm TOTAL was sufficient. Reason to minimize is that you must also
extend the slot for the friction damper upwards to let the servo reach its
internal stop, and this may leave little material above the slot if the
forks are cut off too much.
Another hint (I realized it the hard way!): The rivets shown in fig. 9 of
Ch. 19 should not be placed horizontal and vertical, but at + - 45 degr., in
order to avoid a rivet head protruding into the underside of the bellcrank.
Regards,
Svein
A225 (now in Norway)
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