Starlet 50
7
1. Assembling the main mechanics
The mechanical system of the STARLET 50 is based primarily on parts moulded in glass-fibre
reinforced nylon, a material which offers significant advantages for use in model helicopters
compared with aluminium, including high mass constancy combined with light weight, freedom
from fatigue effects, low noise, and the ability to absorb vibration generated by the motor. The
design of this type of mechanical system imparts a generous degree of robustness and rigidity;
in a „hard landing" the ideal situation is that the parts either survive undamaged (and can
therefore be re-used immediately) or alternatively fail completely, in which case there is no
doubt about whether they have to be replaced. Aluminium chassis components tend to bend or
become distorted, and this kind of subtle damage may not even be noticed; however, in the long
term it causes damage to other components, has a negative effect on the model’s flying
characteristics, and can even have a serious effect on the safety of the whole system. The type
of construction used in the Starlet 50 is simply not subject to this kind of damage.
Glass-filled nylon components therefore have many advantages, and the only drawbacks are
their greater complexity, and therefore higher cost of manufacture, and the requirement they
place on the builder to assemble and adjust the parts with greater care and a conscientious ap-
proach; you may also find that some parts need to be trimmed slightly in order to obtain a per-
fect fit. Provided that you invest a little extra care in constructing your machine, you will be re-
warded by a model in which rates of wear are low, and which lasts much longer than conven-
tional model helicopters.
Shafts, bearings, fits
Virtually all the rotating parts of the mechanics are ballraced. Wherever ballraces are used, it is
very important that the shaft is a tight fit in the inner ring of the bearing. This ensures that it
cannot rotate inside the ring; if this happens, the inner ring heats up (causing a blu-ish or yellow-
ish discoloration), and the bearing is damaged and becomes unserviceable. In the worst case
the bearing can become so hot that it melts the nylon bearing seat, and this destroys the correct
location of the shaft relative to other components. Please note that this kind of damage is simply
a result of an incorrectly fitted bearing, and is not an indication that the bearing support material
is not up to the job.
A loosely fitted bearing can also cause another problem: the shaft starts to move axially inside
the inner bearing ring, and the shaft wears in that area and its diameter is reduced. If there are
gears mounted on that shaft, they now lose their correct meshing clearance, leading in turn to
increased rates of wear, and eventual failure of the parts.
In order to prevent the problems described above, the fits between shafts and ballraces in the
Graupner/Heim system are maintained on the „close" side of normal, and now and then this can
result in too tight a fit if manufacturing tolerances accumulate in the same direction. This
manifests itself in a bearing which cannot be fitted onto the corresponding shaft. If this should
happen, just reduce the diameter of the shaft slightly by rubbing it down using fine wet-and-dry
paper (600 - 1200 grit), until the bearing can be pushed into place using no more than moderate
force. If manufacturing tolerances accumulate in the other direction, i.e. the fit is uncomfortably
free or too loose, the solution is to fix the bearing to the shaft using LOCTITE 603 bearing
retainer fluid, which guarantees a firm seating. If you use this fluid, please note that its cure time
varies according to the fit; the closer the fit, the faster the cure. Under certain circumstances you
may have only a few seconds to locate the bearing correctly on the shaft before it is fixed
permanently.
If a shaft is supported in two or more bearings, it is important to ensure that the location of the
bearings does not place axial stress on them. There are two ways of achieving this: you can
either take the trouble to position the two bearings really accurately on the shaft, or use a com-
bination of a fixed and sliding fit: one bearing is pressed or glued to the shaft to locate it per-
manently, the other is left as a sliding fit, i.e. it can be moved axially along the shaft using
moderate force; in this case the second bearing will find its own optimum position once the
system has been installed.
In general terms you can assume that the danger of bearings slipping on the shaft varies with
shaft diameter and rotational speed: the smaller the shaft, and the higher the speed, the greater
the danger.
The danger of stress in multiple bearings is greater when the difference between the internal
and external diameters of the bearings is small.
If you are aiming to achieve maximum possible operational security and reliability, all these
factors have to be considered in each individual case. The building instructions for the Starlet 50
state which connections should be made using thread-lock fluid and/or bearing retainer fluid.
