AIR TRACTOR AT-502A, Секция обслуживания

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Air Tractor, Inc. Maintenance Page 21
AT-502A/502B/504 March 14, 2018
Stabilizer Struts
The stabilizer struts attach to the fuselage frame with a AN6C11A bolt and to the stabilizer eyebolts
with AN6-11A bolts. There are p/n 30256-1 stainless terminals with AN316C8 check nuts at each strut end to
allow for adjustment.
The struts are constructed of 2.36 x 1.00 x .049 4130N streamlined tubing and may be repaired if
necessary. They are oiled internally through the threaded fittings on the ends, and should be re-oiled if
repaired. They are grit-blasted, primed, and finished with yellow Polyurethane paint. At various intervals, the
struts should be re-sand-blasted and finished as called out above. Be sure to remove the terminals and plug
the open holes before sand-blasting. Oil inside with linseed oil after painting.
WARNING: The forward gusset on the inboard end of the struts will
erode from having dry fertilizer particles strike the lower aft portion of
the fuselage structure. Substantial strength reduction of the strut to
fuselage connection will occur when the gusset is severely eroded.
Consult Service Letter #198 for appropriate action.
Stabilizer Rigging
To rig the stabilizers, the elevators must be removed. The factory practice is to adjust the terminal in
the forward strut so that approximately the same amount of threads is showing on both R/H and L/H struts.
The struts are pinned to the fuselage fittings and the stabilizers are pinned to the fuselage attach fittings
(Don’t forget the washers under each bolt head) but no nuts yet. Have someone hold up the stabilizer tips
when they are being attached. Then attach the struts to the forward eyebolts only. Sight down the stabilizer
hinge line to see that the hinges on both sides of the aircraft line up within .03". Adjust each strut length the
same amount until the hinges are in line. Then stand directly behind the aircraft on the exact fuselage
centerline and raise or lower your line of sight until the same part of each stabilizer falls in the line of sight
with a reference point on the wings. It is likely that the terminal on one strut will have to be lengthened a
certain number of turns and the opposite strut shortened the same number of turns so that the stabilizers line
up with the wings.
Then adjust the terminal at the rear eyebolt on each side so that the bolts can be inserted without
causing a twist in the stabilizers. All bolts are now in place and it is necessary to re-check the hinge
alignment from side to side, and re-check the stabilizer position with the wings. If all is still in order, install the
washers and nuts on all ten attach bolts (five each side). Torque the AN4 bolts to 100 inch-pounds on the nut
and torque the AN6 bolts to 300 inch-pounds on the nut. Tighten the check nuts at the end of each terminal
to 290 inch-pounds torque. Insert a piece of safety wire in the small inspection hole at each terminal location
to be sure the terminal is screwed into the strut fitting far enough.
Re-check nut installation on the stabilizer to frame location and install the gap covers with the 90008-1
screws. If the rubber channel is loose on the gap cover, re-attach with 3-M 8001 adhesive before the gap
cover is installed.
VERTICAL FIN
The cantilever vertical fin is attached to the fuselage frame at the front spar location with two
NAS1306-13 bolts and AN365-624 nuts. It has been found that these two bolts tend to loosen in service. No
doubt buffeting from the propeller slipstream during run-up and stresses from turns tend to produce constant
loads from side to side that tend to loosen the nuts.