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Instructions Titan ZG 45PCI-HV
14
Propeller fixing
Caution:
With a fairly thin propeller it is possible for the prop bolt to come against
the end of the crankshaft, thereby preventing the propeller from being tightly fixed.
You see, there are two propeller fixing bolts of different lengths with each engine. The
longer bolt is to allow for our Titan spinner backplate of 5 mm. There is a threaded
hole in this longer bolt to take the spinner fixing screw.
Experience has shown that, without doubt, the safest method is to fix the propeller
onto the ZG 45PCI-HV with a single large bolt and a wide flange on the prop hub. As
long as the bolt is tightened down enough, the prop will not come loose. Should the
propeller come loose by normal starting, then the prop bolt was not tightened down
sufficiently, or the propeller has shrunk under pressure from the tightening down. But
again, nothing dangerous will happen, you will not be able to overlook the loose bolt!
It is a real danger for persons and property to fix the propeller to the ZG 45PCI-HV with
a multiple screw hub system. The problem is, that you will not notice if the screws are
not tightened down sufficiently to provide enough friction between the propeller
and the hub to prevent any movement at all between the two. The continuous firing
stroke impulses from the engine can very quickly lead to metal fatigue in these fixing
screws, should they not be tight enough. This fatigue will cause the screws to shear,
allowing the propeller to fly off. This is not something I have dreamt up, it is something
I have seen happen with multiple screw hubs.
For the single prop bolt it is not possible to come loose while the engine is running,
as every firing stroke impulse only serves to tighten the bolt more. But should the
ZG 45PCI-HV be adapted for glow fuel and the timing be incorrect, it is then possible
for the engine to start pinking (knocking) and, like the well known four stroke problem,
this can lead to a prop being thrown.
Please do not fit a steel pin through the propeller and hub, the reason being the dowel
holds the prop in place although the bolt may be loose. You may not notice this loose-
ness, then suddenly the prop is split in two by the dowel. You can count yourself lucky
with a near miss when this happens.
Should there not be enough resistance to movement between a smooth aluminium
spinner back plate and the prop hub, the answer is to put a disc of 320 grit wet or dry
paper between the hub and the back plate, the grit side against the back plate.
When you have understood what I am saying about propeller fixing bolts, and see
that the friction between propeller and hub is the only means to give a safe fixing,
you do not then have to envy your club friends, when they must bore a chain of holes
around the hub of each new propeller, only to try to compensate for a too small and
smooth prop hub surface.
