G-UFOX - Propeller (Stuff We Have Learnt)


The spinner backplate/flange needs to be drilled with the six holes for the prop mounting bolts. These must be aligned so that the prop blades are aligned with the spinner.

Lay the flange horizontal on a bench with the prop loose assembled on top. Put the spinner on top and align the notches of the spinner and its flange. You can then align the prop blades with the apertures in the spinner by eye. Carefully remove the spinner without disturbing the prop and then mark the position of the mounting holes onto the flange. You can then use the aluminium spacer to fine align the holes for drilling.

Assemble the prop blades into the hub with the bolts fitted with the heads to the front and nuts towards the the engine. Ensure you put the main bolts in FIRST in the same orientation. Each blade must be pulled outwards radially. You don't need to tighten fully until you adjust the blade pitch. The main bolts have plain washers between the bolt head and the front of the prop. We did try extra washers here for balancing, but later used weights on the flange. The special washers with the radial serrations go between the gearbox flange and the nuts, with the serrations toward the nuts.

The pitch of the blades is set using a special protractor with a spirit level mounted in it. Roger has one made by DUC that you may be able to borrow. Use masking tape and mark the distance from the blade tip (200mm) with a line. Set the plane attitude so that the prop boss is vertical (or otherwise subtract the angle from the setting angle). Clamp the gauge onto the back of the blade with the correct pitch set and check the blade is horizontal. Gently wriggle the blade around until the bubble is level (you will probably have to loosen the main bolts to achieve this) and then tighten the bolts. Do all blades and then re-check them. You can also check the tracking at the same time using a fixed pointer. Of course, once you have done the static engine speed test, you may need to change the pitch to get the correct speed. It is apparently about 200rpm per degree.

If you ask Roger very nicely, you may be able to use his prop balancer - it is the right tool for the job and can balance the prop, spinner, flange and spacer as a complete unit. The prop assembly gets bolted to the balancers flange. Ensure that the bearing is horizontal. The bearings are heated with a heat gun to reduce the grease friction. An electric drill it attached to the mechanisms extra shaft and will vibrate a bearing and effectively kill the stiction, so that gravity will pull the heaviest part of the rig downwards. Experiment by starting at a few different starting positions in case you happen to get the heaviest part at top dead centre (when it wouldn't move). The balance can be nulled by attaching some self adhesive weights onto the rear of the spinner flange. Don't remove the backing tape yet - just stick them on with masking tape, so that you can move them around until you get them perfect - it will take several goes. Then drill, stick and pop rivet them into the flange. It might be worth drilling the weights before you start. It sounds like a faff but is WELL worth the effort.


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