Prop adapters

[Basil]

Can someone advise me if there is a way to extend the length of a prop shaft to enable say a cowl to be added in front of the motor.

I currently have a motor fitted witha radial, screw on, 5mm prop adapter. Can I purchase an adapter that can be attatched to the current shaft so as to extend it's length?

Or is there a better way.

Thank you in advance Bas

[Shaun Walsh]

Posted by Basil on 29/12/2020 14:22:04:

Can someone advise me if there is a way to extend the length of a prop shaft to enable say a cowl to be added in front of the motor.

I currently have a motor fitted witha radial, screw on, 5mm prop adapter. Can I purchase an adapter that can be attatched to the current shaft so as to extend it's length?

Or is there a better way.

Thank you in advance Bas

Hi Basil

Can you clarify:

What motor is it.

By how much do you wish to extend the shaft?

[cymaz]

Any chance of adding motor mount extensions?

[Geoff S]

I wouldn't think extending a motor shaft was a good idea. As it will be unsupported and further from the bearings there's a potential for vibration and subsequent failure. I'm not a mechanical engineer but it just doesn't feel like the right way to solve your problem.

A better solution is to move the whole motor forward either by spacers or, as I've done many times, longer bolts with lock nuts. Or you could add a motor box attached to the firewall. I use high tensile cap head bolts - mostly 4mm - which allows for fine adjustment to get the prop driver with minimum clearance.

Geoff

[John Lee]

As others have said extending the shaft can cause problems. The only model I've successfully used an extended shaft on was the Multiplex Xeno. This had a coupling, carbon fibre shaft and a supporting ball race. It can be done but would require some engineering. The following diagram should give you the idea.

[Shaun Walsh]

Posted by cymaz on 29/12/2020 14:29:24:

Any chance of adding motor mount extensions?

Agreed, extending the motor mount is much better than extending the prop driver.

[Basil]

Morning Gentlemen, I have a model that could do with having a spare 1/4" in front of the motor in order to make it look correct. I am unable to move the motor forward, so the only way to 'gain' some room is by moving the prop forward.

I raised this question as I had seen on the net, 4Max as an instance reference to prop extenders, that if I understood it correctly, did as their name suggests, and therfore the use was suitable. The reason I asked advise is that my thoughts were, in line with many of you, re susspected shaft loads.

If the extenders are for such use, and are unsuitable, why are they on offer.

We are of course talking Electric.

Bas

[Andy48]

I can think of many examples of things on sale that are not only unsuitable but illegal and dangerous.

[Martin Harris - Moderator]

1/4" is probably quite reasonable. A spacer and, if the shaft thread is too short, sleeve nut in an oversized prop hub bore might do the job - easy enough if you (or a mate) have access to a lathe and basic engineering tools.

Edited By Martin Harris - Moderator on 31/12/2020 11:16:30

[leccyflyer]

Prop adaptors to attach to a motor shaft come in all sort of lengths, as do radial mount prop adaptors fixed directly to the motor case. Careful selection of one of these ought to be able to sift the prop forward by 1/4 in and would not generally be considered as motor shaft extensions. It's just a case of finding the right one and it can be quite a quest, as retailers rarely include all the required information.

Way back in the day a number of models - rear mounted pushers for instance - did have extended shafts, including carbon fibre rods, running in bearings or guides, to give a mid-mounted motor, saving the weight of a motor mounted in the tail. IIRC Tim Hooper definitely had one such modification featured in the magazines.

Edited By leccyflyer on 31/12/2020 11:19:37

[kc]

Basil, you need to tell us more about your motor. You stated " radial, screw on, 5mm prop adapter. " There are collet type adaptors too which fit on the motor shaft and they can project further. It all depends on which way around the motor has the shaft - opposite end to the rotating magnet part or same end as magnets. Maybe swapping motor for a different type would work using a differnt adaptor type.

It is also common for the collet type adaptors to come in cheap lightweight versions or more chunky ones of the same shaft size. The chunky ones come out longer in most cases. Might solve the problem.

[Bob Cotsford]

I would always pack the motor mounts out to bring the prop forward, if it's only 1/4" then longer mounting bolts and a stack of washers or a couple of nuts will do the trick, any more and I'd go for tubular spacers. Of course it all depends on the size of motor but a 5mm shaft suggests a medium-large setup.

[Piers Bowlan]

Just cut a square piece of ply, 1/4 in thick to bring the motor forward, use longer bolts if necessary. Extending the motor shaft will create many more problems than it will fix.

[leccyflyer]

Gents - the OP has said that he cannot move the motor forward, so spacers and stand-offs aren't a solution to the problem as presented.

I've certainly used prop adaptors with far more than 1/4" difference in where the face of the prop driver/back of the prop sits. It's just a case of finding the right one. You can never have too many prop adaptors IMHO.

[Basil]

Hi, just to recap. The motor CAN NOT be moved forward. If it could I would not have this problem

In addition it is almost impossible to get at the mounting screws/bolts.

. Bas

Edited By Basil on 31/12/2020 15:48:57

[Doctor Chinnery]

I think the only way you're wish is going to come true is to get someone with a lathe to turn you an extended prop' adaptor out of alloy bar stock - I would guess there are loads of tool makers in the West Midlands who have made a living producing one-offs. Just a case of who and how much.

The only potential problem I can see is the likelihood for the whole thing, mount and all, to tear itself off the firewall if the prop' is only slightly out of balance. - the further the prop is from the front of the motor the greater the mechanical advantage multiplying the self destructive loads on the mounting system.

[leccyflyer]

We have no idea what size of prop adaptor Basil has tried so far to give him the requirement to move the prop 1/4" forward. Does you mean that you want the rear of the prop 1/4" beyond the current motor shaft length? Or 1/2" beyond that? Or more? These could all easily be within the range of commercially available prop adaptors.

Any chance of uploading a sketch showing where the front of the motor is and where the rear of the prop needs to be?

[kc]

A spacer could be made out of a spare identical prop adaptor ( with the shaft cut of ) and fitted with longer screws to move the prop out 5 or 6 mm.

Most of us would find it easier to shorten the cowl a tiny bit than turn an adaptor from scratch. If all possible swopping of adaptors & motors are exhausted then look again to see what could be altered on the cowl.........

[Basil]

Gentlemen, thank you to all of you that have contributed to this thread. I think the easiest way is to live with it as it is. Many thanks.

Bas