wooden propeller tracking

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Altsel
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Joined: Tue Aug 25, 2015 5:20 pm

wooden propeller tracking

Post by Altsel » Fri Aug 02, 2019 9:43 am

Does anybody have a simple guide to tracking a wooden prop?
My Hercules prop on a D112 needs adjustment and a simple guide would be appreciated - thanks

Tony
Anthony Myers
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tnowak
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Re: wooden propeller tracking

Post by tnowak » Mon Aug 05, 2019 7:48 am

I think you need to speak to Rupert Wasey at Hercules propellers about your issue.
I will probably be proved wrong but I don't believe any adjustment for tracking is possible or permissable when the prop is on the engine.
How far out is the tracking?

Tony N
Tony Nowak
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dmcnicholl
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Joined: Sun Feb 14, 2010 8:25 pm

Re: wooden propeller tracking

Post by dmcnicholl » Mon Aug 05, 2019 8:19 am

Tony (Altsel), it seems a reasonably straightforward process and as no one else has responded this is how I do mine.

My prop is a wooden, fixed pitch, two blade with 6 No. M8 bolts. Manufacturer torque limits are stated as 15-17 Nm. You will have appropriate manufacturer values for your prop.

Things to consider:-
  • With the prop mounted on the hub and the bolts started these should run up fairly easily by hand to finger-tight so that when you come to use the torque wrench the wrench responds to the tightening and not any stiction of the bolts binding in the prop.

  • When torqueing to a setting, whether intermediate or final, rotation of the wrench should be smooth and continuous to the ‘click’. Don't stop-start in small arcs as each 'start' will take extra break-out torque that may give a false result.

  • Raise the tail on to a sawhorse or similar to make the prop disc vertical.
  • You will need some sort of tracking gauge. I use a piece of wire, actually a bicycle spoke, clamped to some sort of support which can be positioned immediately adjacent to, but not touching, a blade L/E tip when the blade is horizontal.

  • When turning the blades over to check each against the gauge I always turn my engine backwards so I cannot get caught out by a ‘live’ mag, but equipment attached to your engine (vacuum pump) may make that inadvisable.

Start with a low torque wrench setting. I will work up to my lower limit of 15Nm so will start at 8 or maybe 10Nm. With the blades horizontal and with my gauge in the 9 o’clock position I will start at 9 o’clock bolt then do its opposite at 3 o’clock. Next the opposing pair at 11 and 5 finishing with 1 and 7. It could equally be the other way round, you choose but work systematically.

Reset the wrench to an intermediate figure, for me 12 or 13Nm then go round again in the same order. Depending on your prop and torque limits you might use an additional intermediate setting.

Finally set the wrench to the target, in my case 15Nm and go again.

Now turn each blade past the gauge and visually check that the same point on each blade passes the gauge. Usually that’s all I need to do and even if there is a millimeter or two variation that’s probably good enough.

However if I do need or want coarser correction, having used the lower toque limit as a start I still have some range to work with, up to 17Nm, if I need to pull one blade back a little.
If I’m doing that I will set the wrench just shy of the upper limit and use the wrench in small increments on the appropriate bolts but I don’t want to hear the ‘click’. Instead work visually with small angle turns.
If, for example, I know the thread pitch of my bolts is 1mm a turn of, say, 20 degrees will take it in 0.055 of a mm. But remember working close to the hub the movement at the tip will be magnified so gently does it.
If doing this I will have the blade to be pulled back set beside the gauge and will work the 9 o’clock bolt by a small amount then the 11 o’clock and 7 o’clock bolts by slightly lesser amounts. After every adjustment the tracking of both blades is checked against the gauge.

If you have resort to this last tactic you should reset the wrench to the the original lower limit and revisit the bolts at 1 and 5 o'clock, then recheck the tracking.

Do not exceed the manufacturer's upper torque limit.

If that's not enough then TonyN's advice is probably apt.
Donald McNicholl
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Bill McCarthy
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Location: Caithness

Re: wooden propeller tracking

Post by Bill McCarthy » Tue Aug 06, 2019 10:28 am

If I might add - it it absolutely essential to get your torque wrench calibrated before use. Even a new one can be “out” by more than 10%. In addition, if you use lubricant on the hub bolt threads, this can lead to over-torquing, especially on fine threads.
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fury290
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Joined: Wed Feb 06, 2019 10:28 am

Re: wooden propeller tracking

Post by fury290 » Tue Aug 06, 2019 3:03 pm

Just to add to the general topic, wooden prop torques should be regularly checked throughout the year particularly when temperature and humidity changes with the seasons. A prop torqued in damp weather can lose a large amount of size when checked on a hot dry day (and of course the other way round). I would also recommend leaving several days between torqueing initially and finally, the difference can be considerable.


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Edward King
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