Preparing The Angle Gearbox (Not Included In The Basic Kit) - GRAUPNER NH90 Bedienungsanleitung

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NH90
1.6.2 Tail rotor drive system

1.6.2.1 Preparing the angle gearbox (not included in the basic kit)

Slide a ballrace 4607.137 onto each of the two bevel gears 4619.21 as far as it will go, pushing
on the inner ring of the race only!
Fit a spacer sleeve 4619.22 on each bevel gear as shown, followed by a second ballrace, also
pushed on as far as it will go. Press the steel inserts into the bevel gears, lining up the threaded
holes with the holes in the bevel gears, so that the M4 grubscrews can be fitted; make sure that
the shaft bore is entirely unobstructed. The drawing shows the completed bevel gearbox;
however, the bevel gear assemblies should not be fitted in the housing at this stage, as the
drive shafts first have to be cut to length.
1.6.2.2 Checking and shortening the tail rotor drive shaft
Slip the quick-release sleeve 4618.58 onto the tail rotor drive shaft and fit the front, pre-formed
end inside the sleeve; follow this with the retaining collet 56.0 and retaining screw, which is left
loose for the moment. Cut down the shaft to a length of 905 mm. Cut two rings about 3 mm wide
from fuel tubing (supplied with the mechanics) and push them onto both ends of the Teflon shaft
bush. Slip the tubular bush onto the shaft, then push one of the two bevel gears (angle gearbox)
onto the rear end of the shaft, allowing it to project by 1-2 mm on the inside (at the gear end);
temporarily tighten the grubscrews.
Fit the 180 mm length of 2 mm Ø spring steel rod into the other bevel gear, again allowing it to
project on the inside by 1-2 mm. Grind a flat on one side of the steel rod at the point at which
the grubscrews engage, using a grinding stone or small cut-off disc. Apply thread-lock fluid to
one grubscrew and tighten it carefully, checking that it engages fully on the ground flat, then
repeat the process with the grubscrew on the opposite side.
Now place both bevel gears in the gearbox housing as shown in the drawing, and temporarily
screw the two half-shells together.
Fit the tail rotor drive shaft in the fuselage from the rear, retaining sleeve first, so that the short
shaft can be fitted through the tail rotor opening at top rear. Engage the pre-formed end of the
drive shaft in the yoke 4618.57 of the quick-release coupling, and slide the retaining sleeve into
place to complete the connection.
Screw the angle gearbox to the fuselage shell using four countersunk M2 screws, and check
that the short shaft (from the tail rotor) projects through the tail rotor opening without any hint of
stress (although it will not be central). The shaft which runs forward to the quick-release coup-
ling of the main mechanics should be deployed in a broad, smooth curve. It is essential that the
shaft should not be too long; there must be definite axial clearance (1-2 mm) in the yoke of the
quick-release coupling. Length check: when the angle gearbox is screwed in place, the shaft
must still have at least 1 mm clearance in the front coupling yoke (see drawing).
Install the tail rotor, sliding the short drive shaft into the coupling as far as it will go. This shaft is
still overlength, so you must measure the distance from the underside of the tail rotor to the
support surface on the vertical stabiliser. The drive shaft can then be shortened by the measu-
red amount (+ 1 mm clearance). When you are satisfied, remove the whole assembly (angle
gearbox and both shafts), cut the short shaft to the correct length, then grind a flat on the shaft
where one of the tail rotor grubscrews engages.
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