Hey all.

Ok, as you can see in the pic I don't have a whole lot of thread to screw the prop nut onto.
I don't think this looks very safe as the nut in the pic is done up as far as it can go.
As this is my first .15 size engine I'm not sure if it's because the APC prop has such a thick hub, or if there is another reason.
The engine is an ASP, or Magnum, don't think there is much diff nowadays.

Anyhow, your help would be appreciated.
Thanks in advance.

Is that the stock washer? Maybe replace it with something thinner? That pitch looks like it's giving the prop a pretty thick hub.

somegeek

I used to have a spinner adapter nut that had a necked down section that actually protruded into the washer till it was flush on the backside of the washer, and had threads all the way. I believe it was a tru-turn adapter, you might look for something similar for your engine - that way you've got more threads engaged.

A .15 should be running a 7x6 to 8x4 range of sizes so for starters you need a bigger prop.

And you're right. That's not enough threads engaged for safety or for wear and tear on the crankshaft threading. How the hell they figure we're going to mount a prop and spinner on there with so short a length I'll never know.

You'll want to find a prop brand with a thinner hub or get one of the nuts that extends down into a washer with a larger hole so that more threads are in engagement. Generally the rock bottom minimum number of turns of full engagement is considered to be 3. But not for big loads. This isn't a big load however wear comes into the picture as well. The threads in a nut with only three turns of engagement is going to wear out sooner from being put on and taken off numerous times.

Would one of them big round nose nuts work without a washer?
Not a home depot axlenut, but a hobby round prop nut... like a weighted nut but not so interested in the weight.

they make those safety nuts in aluminum as well, and they are very nice

http://www3.towerhobbies.com/cgi-bin...3p?&C=QKC&P=ML
the big acorn looking ones.

Looks like the prop is an 8-5 in the 2nd pic. We use spinner shaped prop nuts on Q500 engines without washers all the time with no problems, maybe that would be an option as someone mentioned above. That would give you another thread or two.

And finding a prop with a thinner hub would be good, too. Too bad Rev-Up is out of business, they made good props.

You're right. It looked like a 6 to me. So shift back to a 7x6 or down to an 8x4 and that should give you an extra thread or two. And a thinner steel washer will finish it off and let you get the full nut into engagement.

From what I found on TruTurn's website, the Magnum 15 has a 5mm x 0.8 threaded shaft. I don't know this for a fact, just what I found.

You might take a look at something like this:

http://www.truturn.com/cgi-bin/store...exact_match=on

I would check the back side of the prop first, I've had several APC props that needed deburring on the back side. This never does seem flat either, I have no idea as to why they make it this way.....?
Traditional props always have a flat back side as far as I know.

So flatten the back and add a thinner washer, that might be enough. And don't forget to balance it, the holes are often off center and it looks like your's is as well...

even a 8x4 is to big of a prop for a stock engine. i would go with an 8x3 if the plane is heavy or run a 7x4 an 8x5 is way to big. i know guys that run 8x5's on their OS .25 ax/fx

I've read that APC holes are drilled by them as required to center the hole where the prop will be balanced... don't know if this is true.

somegeek

Thanks for the replies guys.
I've tried to hunt down thinner hub props, but they are much of a muchness really.
Fizzwater is right about te measurements, it's a M5 size prop shaft, that makes things a touch more difficult as I have tried to find prop nuts etc in that size and there is no luck over here, seems Australia doesn't deal much with 1/2A stuff.

Anyone know who sells the cone shaped nuts that will sit inside the prop washer that Fizzwater spoke of??

Seems odd that there is so little prop shaft.

5.0-0.8 is an almost universal size for bicycles that are sold in proper bike shops. Just drop into any of them and you can find yourself an assortment of new prop nuts. One item in particular is the outer nut for V brake style brake pads. It is a chromed cone shaped outer with a 5 mm hex in the end. here's a picture of what I'm on about. It's the outer tapered fitting on the posts.

They should have lots of these left over from old pads coming off. A smile and a bit of intrest in their wares and you'll likely get a couple for free if they have any sort of customer relations skills at all.

8-4's are fine on a .15, but are the most load I would put on one. They run at decent if not excessive rpm and none of mine have ever showed signs of overheating or distress, plus performance is good in larger/draggier/heavier aircraft. I am not one to put excessive loads on an engine btw. But on something smaller and zippy let it spin - 7-4, 7-5 perhaps.

[quote
I've read that APC holes are drilled by them as required to center the hole where the prop will be balanced... don't know if this is true.
somegeek
[/quote]

I do - it is false. I called them to ask about a batch of pylon props I received with very badly located through-holes, i.e. off-center enough I could spot it at arm's length. They do not balance props before shipping, nor do they drill the hole at the CG. The recesses in the hub are molded and absolutely on center. But the holes are post-drilled, and APC admitted to me on the telephone that the process is subject to error.

To perfectly center an APC prop a bushing is needed, but one that centers in the molded recess in the rear of the hub, NOT one that derives it's indexing from the drilled hole, or else you are back where you started. Or else you need to balance them by centering the balancer shaft on the through-hole, not pinned by the cones - no guarantee the cones are concentric with the through-hole.

I admit I am a fanatic about balancing - many of them run reasonably true off the shelf ( "reasonably" and "many" are the key words here, they are much different than "very" and "always"! ). Thousands of people use them that way. Then again my engines run really smoothly and don't shake the crap out of the airplane and everything attached to or contained within it.

MJD

I just came back in from the shop for a moment. I checked these brake pad posts and they are 6mm. Still, 5.0 x 0.8 IS a common bicycle size and any decent bike shop will have a few nuts of that size laying around. Very possibly a cap nut or two.

I do - it is false. I called them to ask about a batch of pylon props I received with very badly located through-holes, i.e. off-center enough I could spot it at arm's length. They do not balance props before shipping, nor do they drill the hole at the CG. The recesses in the hub are molded and absolutely on center. But the holes are post-drilled, and APC admitted to me on the telephone that the process is subject to error.

To perfectly center an APC prop a bushing is needed, but one that centers in the molded recess in the rear of the hub, NOT one that derives it's indexing from the drilled hole, or else you are back where you started. Or else you need to balance them by centering the balancer shaft on the through-hole, not pinned by the cones - no guarantee the cones are concentric with the through-hole.

I admit I am a fanatic about balancing - many of them run reasonably true off the shelf ( "reasonably" and "many" are the key words here, they are much different than "very" and "always"! ). Thousands of people use them that way. Then again my engines run really smoothly and don't shake the crap out of the airplane and everything attached to or contained within it.

MJD
[/quote]

Good info!

I did notice that the electric props have the inserts for smaller shafts and ensure things are centered as well.

somegeek

Bruce, your right about the 6mm pads, just got back from the bike shop and all they had was 6mm. Might try the other shop.
I did manage to get a thinner washer though.
The existing prop washer is around 2.5mm thick and the new washer is 1mm even, so that will help, that and a drop of loctite I think.
Not the best idea I know, but better than a prop coming loose at 10,000 RPM.

This whole experience is not much fun at all
The Sunday maiden isn't looking good[]

Can you maiden it with a 8x4 or other prop, with a thiner hub?
Save the 8x5 for another day.... who knows, you might like the 8x4. Last .15 I had was an AP, it ran slightly less bad with a 8x4 than other with props.

It should be easier to come up with a 8x4 prop than finding just the right combo of stuff to make the 8x5 happen in time for maiden.

We don't have a large selection of props where I live, so I have to make do with the 8x5 for now, I'll just be gentle with it. And finding a prop with a thinner hub will tak time, as I have to do it over the phone then order it.[]
Did you run an ASP .15??
What was it like??

If you have access to a drill press and an end mill bit, you can remove some thickness from the props' hub. The earlier posters are right, that isn't a .15 sized prop, more for a .25 in a small plane..

Well gonna have to order a couple of props me thinks.
I did manage to find an 8x6 APC to compare with the 8x5 APC, and the hub on the 8x6 is thinner![X(]

The 8x6 fits no worries, with enough thread to properly attach the nut on.

Well, off to order props, thanks for all your help guys, muchly appreciated

Depending on the airplane, you could always trim the 8-6 down to around 7" or so as a stop-gap measure.

Krener-
Not an ASP, the AP.15
And it did what I bought it for, a cheap rear exhaust engine to fit in a cowl. It was pretty much lacking in the horsepower department, but fortunatly that wasnt what I needed it for.