Here is the stub off an F&P shaft
I made to plug the hole and provide a fulcrum with a
centre of gravity adjustment.
The main thing to note if you make your
own, is that for consistency, the thread must be firm
and the string must be tight through the string hole.
- Pick a dead calm day or go indoors
where no draughts.
- Fit the plug to the prop.
- Lower the C of G (centre of gravity)
for a dead action.
- Add weight for a horizontal balance.
- Raise the C of G and adjust with
weight as required.
- Repeat this step until a very sensitive
action is achieved.
Never fear, most will go to far to a
neutral or accelerating action and get odd and confusing
readings. Just go back a little.
Well that's how I do mine. Hope you
Let me see if I got that
- what you call the 'fulcrum' is the
top end of the threaded rod, where the string exits?
- the balancing 'action' positions
are adjusted by screwing the threaded rod in and out
(up or down actually) on the splined stub?
- your propellor hangs backside up
and the washers (or lack of them) are your balancing
Did I get it? Very clever, your method
"Your spot on working out what
I didn't say. It's a YES to each question though the
backside facing upward is because the CofG is closer
to that face on this prop.
If the blades protruded forward and
the C of G was to be near or even further forward than
the front of the hub, then that face would need to be
uppermost. In such cases the threaded rod can protrude
past the splined stub to position the fulcrum in correct
relation to the C of G even if the C of G appears to
be in no-mans-land.
Don Brown has made the following notes...
"The sensitivity of the balancing arrangement will be affected by the length and weight of the bolt or threaded section used for balancing.
Unnecessary length (and hence weight) lowers the centre of gravity of the combination of the blades and the bolt. This makes it more difficult to approach the toppling point, where the centre of gravity of the blades plus bolt is above the point at which the suspension line enters the bolt.
Just before, or at, the toppling point is where the balance will be most sensitive.
This consideration is of particular importance for small and/or extremely light blade sets, especially when the weight of the bolt becomes a significant percentage of the weight of the blades.
The basic message is that, for maximum sensitivity, keep the bolt short and light."
Good point, thanks Don.