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Instructions Titan ZG 45PCI-HV
15
Changing the propeller hub
We have 3 different lengths of
propeller hubs. To remove and
refit the two socket head screws,
securing the propeller hub only
requires a propeller to be firmly
fixed to the hub to act as a lever.
Carburettor linkage
Do not remove or disengage the spiral return spring on the throttle lever arm. All play
in the throttle linkage will be taken up with the return spring and this spring is also
preventing end play and premature wear on the throttle flap. Further, in the unlikely
event of the throttle pushrod either breaking, or becoming unhooked, the spring will
throttle the engine. Do not worry that the throttle spring will absorb too much servo
power. The loading on the servo caused by this spring is relatively small in comparison
to the loading on the other servos in flight .
If necessary, the throttle lever can easily be modified by cutting a horn from sheet
Tufnol and using the existing hole in the steel lever, fixing the Tufnol horn onto it with
a M2 screw and nut, then securing the whole with Araldite Epoxy. Keep the weight of
this new horn as low as possible so as to keep the vibration-induced loading on the
throttle-shaft bearing surfaces within reasonable limits. The throttle pushrod can be
run from the servo to the throttle arm by way of a 90 degree bellcrank fixed to the
firewall. A simpler and better alternative is a Bowden cable formed into a wide bend.
The key to a reliable and low idle:
The Bowden cable between the servo and throt-
tle lever has to be connected in such a way, that the return spring causes the throttle
lever to press against the Bowden cable and not pull on it! Let me explain why this
is so important: Engine vibration induces swinging of the bend in the Bowden cable,
this wants to throw the cable outwards, similar to a skipping rope. If the return spring
on the throttle lever pulls the cable inwards against this movement, it can cause the
tickover speed to fluctuate considerably. On higher rpm there will be almost no swing
and the spring is able to keep the cable inwards, but on lower rpm, often at about 2000
rpm, the cable may get into resonance and the swinging becomes stronger and will
throw the cable outwards. This raises the rpm, as the cable now pulls on the throttle
lever and opens the throttle. To compensate for this, you will be forced to throttle the
engine down even more. At lets say 1800 rpm the cable will fall out of resonance and
the spring will gain the upper hand again, closing the throttle completely and causing
the engine to stop immediately.
When the servo is pushing against the spring, the centrifugal force and the spring are
working in the same direction, the engine will then react smoothly and accurately to
the throttle stick - always and at every rpm!
