Whitish marks near prop hub APC 16x4w

[rcflyer]

I am running an APC 16x4W prop on my Saito 125. I am seeing some kind of faint and fine whitish marks near the prop hub but it is not a crack (see attached photo). Is this of any concern? The prop has been well balanced. There was no accidents with the prop as well.

[SHANERC]

Make sure your spinner isnt touching or rubbing and that it is good and tight

[rcflyer]

The prop is not touching the spinner and no incidents of backfire. Anyone with a 16x4w seen this marks?

[SHANERC]

Is that plastic fibers on the prop & spinner?

[2walla]

I have seen those marks before, I used to run the oddball sized 11.75x 4.25? props on a jet50 on a fun fly. It was turning up about 17k on the ground and you could hear it pick up a couple of thousand when it unloaded in the air. The white marks would appear after about 20 flights. It can be a precursor to failure of the prop. It is turning white because the resin in the prop is separating from the fibers in the prop. Take a broken apc prop and put in in a vise and bend it back and forth a few times, you can see the area you are bending it start to do the same thing.
There were some failures of larger apc props due to them failing near the hub-thats why they don't make the larger diamater props anymore. They ran the engineering numbers for the loads on the prop it shouldn't have been happening, but it was... So APC did the right and quit making the ones that they were having trouble with. They believed it was a funky harmonic casuing the trouble. Maybe you should reprop to a different size, or try a different spinner to see if it stops occouring-ie change the resonant frequency of the system. How many rpm is that 125 turning that prop?

[BreadBowl]

You need to replace that prop now. Do not run it again, it will shed that blade.

If I'm seeing correctly, there is a wide faded white line, but of more concern to me is the small bright white jagged marks. That is indicative that your prop has seen some sort of stress.

APC had a problem with some of their four-bladed props shedding blades, and they remedied it by adding a fillet to the base of the blades. That could be a bad prop, or a bad prop design. In any case, it's no longer safe to run.

[rcflyer]

2walla and breadbowl, thanks for your heads up. This prop has only undergone four 10-min flights. I have not seen this type of defect occuring in my 14x4w after almost 60 flights on a saito 82. APC should put up an advisory on this issue with the 16x4w.

Is there a good alternative 3D prop for the saito 125 out there?

[SENEKAfive]

yea as bread said you really should change it ASAP. The white marks occur on plastic when its bent im assuming its the same on a resin prop so your prop must be bending, This occurs regularly, on a P-47 the prop bends as much as 6 inches. I would recomend a wood prop or something of a stronger nature.

[RCAddiction]

You would be well-advised to contact APC and let them know what you've found. It is possible that they had an improperly molded batch of props which were prone to those incipient stress fractures. Chances are good that they would appreciate your call and photo. Your phone call might help prevent someone else from getting seriously injured.

[flyin4fun]

I use a APC 16x4w on my funtana 100x, OS FS 120III , never had a problem, 100"s of flights, still the original prop, looks like new, I checked it when this post was started.
Let APC know, could be a bad batch.

Doug

[3D1]

get a wood prop they weigh half as much and I like them better for 3D.

[rcflyer]

A member of my club called me to let me know that he experienced a 16x4w shedding a blade in flight last year. The ensuing rotary imbalance caused the firewall to be ripped off. Although the plane was almost totalled, he was glad it didn't happen on the ground where injury could have happened.

[Vic3D]

I have high respect for APC props. If one of those blades comes loose, it will cut through anything.

[nesikachad]

I say pull the prop and mail it back to APC. Give them the opportunity to backwards engineer it.

Include your date of purchase and vendor too if possible.

I also advocate wood props for 3D. Engines just seem to have more snap with the reduced rotating mass. Important for something that is operating in a broad rpm range.

[rcflyer]

A quick update. I received a confirmation from Fred Burgdorf that APC will be beefing up the root and hub areas of the 16x4w fairly soon. Looking forward to it.