Prop & Spinner Mount Issues

[Capt Kremen]

This is a two part issue regarding securing a prop and spinner to an electric motor.

Example Motor : Ripmax 'Quantum 40' fitted with supplied prop mount i.e. prop mount is bolted to motor and motor shaft protrudes unused the other end.

Issue 1: The prop mount has a small but noticeable curve where it changes from the threaded spindle to the bolted on flat back.

If you attempt to fit a aluminium back-plated spinner, it will not sit flush with the prop mount back. Typical 'APC E' props are relieved at the back allowing direct (no spinner) attachment flush.

Suggestions for how to avoid this issue. (I do not have access to a lathe to remove the offending 'curve'.

Issue 2: Having fitted a spinner and prop with a nice close gap between the backplate and model nose section, how to sufficiently tighten the prop nut? The backplate rotates and slips before sufficient torque can be applied to secure the whole assembly.

I wondered whether creating a thin metal tool, similar to a bicycle bottom crank spanner, might be inserted to purchase on the 'half moon' indentation on the prop mount(?)

Neither of these issues are 'show-stoppers' but I'm curious, others must surely have noticed and encountered similar. (Yes, I do use better quality motors and prop drivers too that do not suffer from such irritants)

Your ideas welcome. Thanks in advance.

Rough Diagram, (Not to Scale), attached:

Edited By Capt Kremen on 01/02/2021 16:45:24

[Bob Cotsford]

Here's my approach for Turnigy and similar motors with smooth prop drivers:

I use a countersink bit to bevel the edge of the spinner backplate bore to accommodate the stress relief radius on the prop drive, alternately it's soft aluminium so can be scraped to fit using a stanley knife. As for the slipping issue, there are two ways that I've found to work. One is to make washers from course wet'n'dry or fine emery paper which go between the backplate and driver, the other is to roughen the face of a prop driver using a course Permagrit block or file.

Both methods will provide enough grip between driver and backplate to allow you to tighten the prop just by restraining one blade.

I do like the idea of a thin steel C spanner to engage the driver cut-outs though!

Edited By Bob Cotsford on 01/02/2021 16:46:49

[john stones 1 - Moderator]

Usually found pulling the prop on one side, gets the job done, a tool would be great though, always been too lazy to make one.

[Ron Gray]

What Bob says!

[dan h]

Number 1 the same as Bob.

Number 2 I have cut a slot in the end for a flat head screw driver to fit and hold the shaft whilst doing the nut up provided it is a normal nut and not a domed type one. Never had a problem getting the nut on and off with this slot in the end

[Martin McIntosh]

Had exactly the same issue trying to fit alloy spinners to NTM prop drive motor shafts. The curvature was particularly pronounced and the only solution was to remove it in a lathe since the spinners required the usual inserts.

Beats me as to why these distributors do not match their products with each other; the same can be said for HK retracts and oleos. Try buying an oleo to fit the retract pins. If only these people would go that extra mile.

[Trevor]

I've had both of these problems more than once. If your spinner backplate uses a brass insert, you might be able to replace it with a nylon insert, e.g. from an APCe propeller. With luck, this won't take up the full depth of the spinner backplate so will clear the radius on the prop driver.

Apiece of thin double-sided tape (not the padded foam sort!) behind the spinner backplate is often enough to help with tightening the prop nut. Alternatively, if the prop driver shaft protrudes beyond the nut, you can drill a hole through it and use a tommy bar to stop the shaft from turning.

Edited By Trevor on 02/02/2021 08:32:07

[Gordon Whitehead 1]

I learned about 20 years ago that the foolproof way to prevent prop slip when tightening up and slackening the prop nut is to cut two discs of 250 grit wet-and-dry paper the same diameter as the prop driver and evo-stik (or similar) them together back-to-back with the grit outwards of course. Bore a hole in the centre for the propshaft using a sharpened piece of brass tubing or old 35mHz antenna tube, or if you have no tube, use a scalpel blade to cut out the hole as it doesn't have to be accurate and can even be square. If you're fitting only the prop (or edf rotor) use one of these double-sided non-slip washers between prop and prop driver. If you're fitting a spinner too, make two of these washers and fit one between spinner and prop driver, and one behind the prop.

Then make a few spares for the rest of your leccy planes.

Another couple of tips are:  if the propshaft adapter is aluminium, replacing aluminium prop nuts with steel prop nuts will prevent the nut from "picking up" on the adapter threads;  a tiny drop of 3-in-one oil on the threads eases tightening and slackening the nut, the friction washer preventing any prop slip.

Gordon

 

Edited By Gordon Whitehead 1 on 02/02/2021 15:20:49

[Capt Kremen]

Thanks Gordon.

Often the simplest and easiest cures are the best.

(Incidentally, you are part responsible for my early ventures into proportional R/C. Whilst serving in a 'Blue Suit', I recall West Drayton sports field and the 'Fly Baby', 'Turbulent' etc. Then Bldg 123 gym hall for indoor flying. Spent the rest of my civvy working career there too. Happy days, many thanks).

[Gordon Whitehead 1]

Thanks for re-kindling old memories Capt K. They were really good times despite the lack of bells and whistles on our radio gear.

Gordon