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Jabiru J450 Constructors Manual
General>Aircraft grade bolts and lock nuts
Tuesday, April 6, 2010
18 of 343
Determining and checking bolt lengths
A bolt must be long enough to ensure that no more than one thread will be inside the bolt hole
when the bolt is fitted. This
grip length
should be equal to the material thickness that is being
held by the bolt.
What this means is that
the
correct bolt length must be used in every case
, and if a nut
cannot be tightened to safety then measures must be taken to correct the length, either by
packing with washers (an absolute maximum of 3 flat washers may be used for packing,
starting with the required washer under the nut, then one washer under the head of the bolt
and finally, if needed, another washer under the nut) or using a different length bolt.
Lock nuts
All bolted components on your Jabiru aircraft are held in place with lock nuts, either a
Nyloc
type fibre lock nut for most uses or a steel lock nut for hot areas such as in the engine bay.
It is important to understand the procedure for tightening Aircraft lock nuts: each nut must be
fitted with a flat washer under it and “
tightened to safety
”, which is defined as having a
minimum of 1½ threads and a maximum of 3 threads showing beyond the end of the lock nut.
This is considered
critical
for load-bearing bolts and good practise for all other bolts.
Any less than 1½ threads showing beyond the end of the lock nut means a risk of the nut not
locking correctly while any more than 3 threads showing beyond the end of the lock nut could
mean that the lock nut is bottoming on the thread and there is a risk overstressing the bolt and
nut and/or not gripping the joined material correctly. Examples of each case are shown above.
In general all nuts should be fitted so that they face outward so that they can be easily
inspected. Nuts inside the cabin should face out and towards the pilot if at all possible.
Nuts that have been tightened to safety should be marked with a dab of
TorqueSeal
.
!!WRONG!!
Less than 1½
Correct
!!WRONG!!
More than 3