Prop Tip Mod
 

I have a 15 x 6 apc that I had to take 1/2" off the ends of to clean up a chip out. I wanted to keep as much as the prop as I could so, I changed the shape. The leading edge now is larger diameter than trailing edge. Will this be o.k.? Stupid question...Why is it alway the other way? What am I giving up. Please see uploaded picture. The top prop is 18 x 6 not modified and the bottom prop is my hack job.

RE: Prop Tip Mod
 

It should be OK. An unmodified tip is better, especially on the APC type, but what you have will work.

RE: Prop Tip Mod
 

Steve:

It's not a good idea to clean up the damage from a prop strike, sir.

If you want to experiment with an undamaged prop that's one thing, but there could well be concealed damage to the blade that will cause its later failure in service.

It is your airplane and your engine, but it could be someone else's eye if the engine throws a blade while running. I'd cut both blades to nubs and use it only as a dummy prop when doing engine work, New 18" props are not expensive.

Bill.

RE: Prop Tip Mod
 

Thanks for the info. I do not intend to be careless and did not think that the rest of the prop would have suffered damage. If this was a wood prop or a master airscrew plastic do you trash the prop if the tip is compromised or is it just the APC?

Thanks,

Steve

RE: Prop Tip Mod
 

Steve:

I have to be honest and say my trashing the prop would depend a lot on how hard the prop hit. If it was just a buzzing from a slight contact I'd probably clean the tips as you did, but if it hit hard enough to stop the engine it's trash time whether it's an APC, MAS, or Zinger.

I will also admit a wooden prop wont crack without external evidence, if there were none it would be re used after a tip reshaping.

Bill.

RE: Prop Tip Mod
 

While I appreciate what Bill is saying it comes down to how it got scuffed in the first place. A model that noses over at idle and lower ground speeds and gently brushes the tip a number of times and gets a bit worn as a result can easily be saved. But a single strike that causes this level of damage is often reason to get a new prop. In particular if the engine was running above idle.

One thing I've noticed about APC's over the years is that as they suffer from impact or wear they generate whitish spider webb'y areas or single white'ish lines that can be seen in the grey surface. If you see any signs of that then it's time to retire it to paint stirring. I would check carefully around the tips for any signs of these white marks.

And with ANY APC I always make it a point to check the hub and blade roots at the beginning of the day. I've had multi year old props develop these white marks in normal use as well but it does take a few years.

And if this was a wood prop then I would suggest a new one immediatley. Wood props tend to develop splits along the grain and sudden stops are a prime way of doing just that, even at idle.

I ran a glow type 10x6 on a gear drive electric model that belly landed all the time. I would try to level the prop but it was not always successful. After a season the blades were very spider webbed from catching and bending but since it was operating at such a lower RPM (~5000) it didn't worry me but I DID make it a point to test it by test flexing it a bit now and then just in case.

So use a little judgement but if in doubt then I would get a new prop. An 18x6 is not an engine and prop combo to be trifled with.

RE: Prop Tip Mod
 

I have never see a prop explode that was used after a prop strike if the prop was still intact. Show me one and I will beleive that I should throw away a prop that is not damamged, spider cracks and all.

RE: Prop Tip Mod
 

TD:

If you will excuse me, sir, I would much rather not show you an exploding prop, thank you.

I shouldn't think you'd want to have one explode either. Those spider webbing marks are sign of excessive flex, leading to a fatigue failure.

It's a lot cheaper to throw one away than to have some one hurt.

Using a questionable prop is a good example of "Penny wise and pound foolish."

Bill.

RE: Prop Tip Mod
 

I totally agree Bill. Taildragger, we did have a guy's APC fail as a result of those spider web marks. I saw them and mentioned my concerns and he poo poo'd it as well saying it had been like that for quite a while. When I saw him next time he mentioned that it broke a blade right at the marks a couple of weeks later in a simple tip over at low throttle. I know it's only one but how much is an eye or more worth?

RE: Prop Tip Mod
 

I had an APC 12x6 explode on my test stand. The prop had previously been mounted on a plane, but due to a prop strike on landing it shed the tip on one blade. I just cut it down to an 11x6 and only used it to run on engines on the stand. I was running an SC .52 at WOT, when it went bang a piece 2 1/2x5/8" pierced my shed wall (metal shed). I have my stand bolted to a black&decker work bench, the force and sudden imbalance almost topled the work bench. Now I only need to see 1 tiny dink in a prop and it goes in the bin.
Once bitten twice shy ;)...

RE: Prop Tip Mod
 

I personally don't see why the maxim of "better safe than sorry" is not adopted considering the cost of props in proportion to the cost of modelling gear in general. Even if you could get away with not losing any money (because of insurance) if you or someone was injured by an "exploding prop", could you live with yourself if your prop hurt someone else when you knew it was damaged but you flew it anyway?

You are going to think I'm stupid but I flew a 40 powered plane a few months back with a perfectly good prop but a plastic spinner with a bit of a crack in it. I thought it would be fine - was too lazy to drive to the model shop to get a new one, so I took off, and Bang, the spinner hit the prop as half of it exploded and made a sound like a good shot with a baseball bat. This was full power - prop was a 10 6, engine was an OS 40. Luckily the plane was 20 feet up and away from the pits - if that had happened on the runway as it was on take off run and someone had got in the way then it might have been nasty.

So lesson learned - safety considerations are no place for optimism.

RE: Prop Tip Mod
 

The only one of three things that I always check on a plane, the Prop, the engine mount and the wing spar/ mount... Otherwise let safety hang to the wind... like the guy at the field who decided to fly his plane backwards... guess what!? He started his engine backwards tooo... HAHA quickest crash u ever saw... less than 10 feet off ground and cartwheeled into the ground..
Maybe he was high on something... who knows

BFOOTE

RE: Prop Tip Mod
 

I had a spinner explode on me once while testing an engine in my garage. The spinner was brand new and had come with an ARF I was building. I concluded that the spinner backplate must have either had a hairline crack or been molded poorly as the backplate was the only piece broken. Since then I have only used aluminum backplate spinners as I feel they are much safer. The way I look at it, if you are going to skimp on something why risk hurting yourself or someone else while doing it.

RE: Prop Tip Mod
 

It definitely pays carefully inspect props and spinners from time to time. I have had high-time wood props chuck a blade, but the vibration resulting from a relatively lightweight wood blade usually doesn't do all that much damage. Two plastic prop blade-chucking episodes nearly wrecked my model each time - servos were all out of their grommets, horizontal tail came unglued, etc., resulting in barely-controlled crash landings, and neither prop had experienced any previous damage.

While I was helping another modeler tune his engine, his plastic spinner flew off, bounced off the ground, and hit me just over an eye, producing a nasty cut. It could have been much worse - and I was, as always, standing well out of line with the arc of rotation.