I am about to purchase an OS 15LA for an electric to glow conversion plane and came up with this problem.

The crankshaft thread size for it is 5mm.
But the only prop i found on TH ,
with center hole 5mm for fitting the 15LA was some MA's.
All APC's and TF props i found have center hole more than 5mm,app. 5.5mm.

So what can i do?
Anyone that encounter the same problem?

Kostas

I had the same problem with my Saito FA-90TS twin. The center hole of the intended APC 14x6 prop was too big.

I solved this using some scotch tape to increase the diameter of the crankshaft (see (blurry) photo).

Just make sure that the tape is not wrinkled around the crankshaft and that it is of the correct width (too wide and it may interfere with the locknut; too narrow and the propeller may not be well supported).

Radial.

Ouau,
thank's for ur fast reply.
But how can we be sure that the prop is in the place it should? i mean outline of the imaginative center on the crankshaft?
Because if it doesn't line up PERFECTLY
it will vibrate the hell out of it and may damage even the crankshaft.......

Let's see - OS is probably the most popular brand of .15 with the most units sold. Even my old HB .15 and TT .15 size engines have a 5mm crankshaft. What was APC thinking that day?


Ed Cregger

Brodak Maufacturing sells a very nicly machined aluminum spinner. I have one in front of me now. It came with a collar for the prop nut. The projection on the prop side of the prop nut is about 5.5 mm in diameter, with the adapter collar it allows the use of a prop with an 8 mm hole in it. I have a dial vernier caliper and in inches the dimensions are: prop nut .236" and with the adapter collar it's .314". Now if I can get this 1" spinner to work on a Cox .049 prop and hub you should have no problem. I actually had to drill out the Cox prop hub to a depth of 1/8" with a 15/64" drill bit. The spinners aren't cheap however, $15.00, but I think worth it.

Good luck,
Bill

Well, all I can tell you is that I did not pay attention to this particular aspect. I just made sure that the tape is flat, put the prop on it, tightened it and started the engine (of course I had balanced the prop before mounting it on the engine). Even at 9000 rpm the engine is silky smooth.
In addition, I have removed and reinstalled the prop several times (without making sure to put it back on in the exact same position), and I have never noticed more or less vibration, meaning that absolute precision is not needed when mounting a propeller this way.

Radial.

I've used the scotch tape trick too. It works just fine, if you make sure not to wrinkle it and be sure it's a tight fit. I've used enough tape that I have to spin the prop as I install it, bascially forcing it over the tape. The tape is pretty solid. Obviously a hard sleeve would be better, but the tape worked for me too..

I wonder if anyone makes a screw on adapter?

Jack

This is an everyday issue with us 1/2A fliers. Common remedies are a short length of fuel tubing or aluminum tubing. Aluminum tubing can be split down the side so it can expand a bit to fit over the crank. The best fix are the aluminum inserts turned on a lathe.

David

....put the Master Airscrew prop on the engine.

FBD.

I think that Dubro spinners come with collar sets too.

Thank u all for your kind replies.

I will either buy MA props to fit my engine
or
i have a friend with a mini cnc so maybe we can make a small alluminum tube.

Thank's again all of u!

Kostas

Keep in mind that with APC props, the hole in the centre is stepped or 'counterbored'. The hole on the rear side of the hub is larger than the one on the front side of the hub. The larger diameter is the 'true' centre of the prop, while the smaller diameter is just a hole near the centre of the prop. If your going to make collars, be sure that they fit the larger diameter of the stepped hole.

An excellent point.


Ed Cregger

As others here have said, just buy a Master Airscrew prop. But you may need a 5mm drill bit to ream it out.

Buy an APC lekky prop - the kind that comes in a bag - they have spacers with 'em.

Oh , didn't know that,longdan!

Thank's!

I'd be worried about one of those thin bladed 'lekky props on a glow engine - maybe get one just to get the spacers, but use the electric prop for something else...