Props for OS 15LA

[Tim Donald]

I'm looking for a prop for an OS 15 LA in the recommended 8x4 size.   The problem is that APC props seem to be for prop shafts from 6mm and the OS15 is 5mm (or just under according to my calipers).  Can anybody recommend a prop or a solution please?  Other manufacturers don't seem to say the prop shaft size (Master etc.)  Can I get some sort of adapter ring like the electric props sometimes come with?

 

[Engine Doctor]

That often happens. I get around it by finding a piece of brass tubing that fits the prop shaft on the engine then drill the prop for a tight fit for the brass tube a bush the prop

Rebalanced the prop after fitting brass Bush. 

[Jon H]

My 15fp has a master 8x4 on it and i dont remember drilling out of faffing with it. Admittedly its been on the engine for 20 years so i could have forgotten about it, but i dont think so. 

[Tim Donald]

Thanks again both.  Yes Master seem to have a smaller pre drilled hole that is smaller so I will go with them.  Same problem with spinners now as most seem to have a 6mm hole.  JP seem to come with adapters,  one of which is 5mm - seems about the only option there too.

[john stones 1 - Moderator]

Decent spinners usually come with a variety of adaptors, the Ali ones do, Irvine ?

[Outrunner]

All the APC props I have came with a selection of adaptors, you choose the one that is a good fit on the engine, never had one not fit yet.

[dave windymiller]

Only electric APC props have adaptors!   

[Outrunner]

1 hour ago, dave windymiller said:

Only electric APC props have adaptors!   

Ah ha, learn something every day!

[Christopher Wolfe]

I have used a layer of one or more short pieces of heat shrink tubing to increase the diameter of a prop shaft to suit a hole in a prop.

 

Shrink it in place with a heat gun until the prop is a snug fit.

[PatMc]

29 minutes ago, Christopher Wolfe said:

I have used a layer of one or more short pieces of heat shrink tubing to increase the diameter of a prop shaft to suit a hole in a prop.

 

Shrink it in place with a heat gun until the prop is a snug fit.

I used to do the same & previously something similar with a few turns of insulating tape.

[leccyflyer]

Have used both of those methods successfully to get a snug fit for a prop.

[Nigel R]

I'd guess the little OS will use a UNF thread much like their bigger glow engines... 7/32" maybe?  APC IC props are usually imperial drillings - 1/4"? 

 

Must admit I'd just wind some tape round the shaft until the thing was snug. It's all held in place by the prop nut anyway.

[Andy Stephenson]

Graupner props have a recess larger than the bore so I've often used a piece of fuel tubing or an O ring stretched over the shaft, in fact anything that can hold the prop concentric until it's fully tightened will work.

[J D 8]

   Do not know what type of aircraft you are fitting your 15 to, but if a small and a bit fast then a 7x6 may suit best as in my O/D Fun fly. Fitted with OS MAX15 in pic but has flown with LA15 [ Met the trunk of a very large oak at high speed and drove the crank out of the backplate.  Aircraft nose destroyed but new one grafted on.

[Tim Donald]

It's to go in a 1m delta wing so you may be right.  Just going on the recommended one for running it in then I will experiment a bit (if I manage to avoid oak trees 😂)

 

[Martin Harris - Moderator]

10 hours ago, Nigel R said:

I'd guess the little OS will use a UNF thread much like their bigger glow engines... 7/32" maybe?  APC IC props are usually imperial drillings - 1/4"? 

 

Must admit I'd just wind some tape round the shaft until the thing was snug. It's all held in place by the prop nut anyway.

I've just learnt something.  I always thought these engines used M5 threads for their prop nuts but according to info on the web they are 10-32 UNF - which makes more sense for OS which have traditionally used UNF threads for most, if not all their larger engines.  M5 nuts will fit on 10-32 UNF threads but not vice versa as although dimensionally very close, the M5 is slightly larger diameter.

 

10-32 = 5.08mm diameter

10-32 pitch is 32 tpi and M5 is 31.75 tpi

 

I've used a variety of methods to adapt available propellers to smaller shafts ranging from tape, cardboard and metal shim to machined adapter rings depending on circumstances.  As Nigel says, the important thing is to ensure location while tightening.

[Robin Colbourne]

10 hours ago, Nigel R said:

I'd guess the little OS will use a UNF thread much like their bigger glow engines... 7/32" maybe?  APC IC props are usually imperial drillings - 1/4"? 

 

Must admit I'd just wind some tape round the shaft until the thing was snug. It's all held in place by the prop nut anyway.

Nigel, The OS instruction sheet for the 15LA says the thread is M5 (look at the bit in the middle of the second sheet at the bottom, where it lists the optional spinner nut).  OS15LA & OS25LA Instruction Sheet

Regarding spinners, the old black KeilKraft spinners with moulded screw thread between the front and back halves have a smaller hole than current spinners.  You maybe lucky enough to find one on Ebay, or an older club member may have one in the back of a drawer.
 

Edited November 18, 2022 by Robin Colbourne

[Martin Harris - Moderator]

The plot thickens.  That may be where I got my original impression they were M5 - and it is from the horse's mouth!

[Nigel R]

Always believe the manufacturer and not some mug punter on a forum! Every days a school day. 

[Engine Doctor]

The older OS 15's had the UNF crank thread and was probably given in good faith ?