Cox prop failures.

nitroairplane Sat Apr 21, 2012 8:30 am

Hello guys today I tested some props on an engine I soon hope to fly to see what was best for the plane it would be in.
I started with a 6x3 then went down to 4.5x2 but this prop just flew apart into 3 pieces.
1/2 the blade fell off in 2 seperate pieces.
First the tip came off throwing it off balance ten the rest of that blade came
Off.
Only doing 15K RPM too.
It was a near new cox Grey prop stored correctly.
Anyone else had this with cox props not like dodgy K sun props?
I have had it before but never cox props or props I have had from new.
Cox prop failures. Kgb8v

SuperDave Sat Apr 21, 2012 8:47 am

Such has not been my experience with Cox props that I have had since new but I also know that exposure to UV rays can be destructive to plastic props. I'm thinking at some time in your prop's history sunlight might have gotten to them.

If you were not injured you are very fortunate. I keep my plastic props in a separate bag from my wooden props and keep them out of direct exposure to the sun when stored.

nitroairplane Sat Apr 21, 2012 9:02 am

Mine are kept in a cupboard away from any form of light. I was thankfully standing behind the engine.

SuperDave Sat Apr 21, 2012 9:21 am

Indra:

The laws of nature are self-enforcing. Centifugal force to be specific.

ahrma_581 Sat Apr 21, 2012 10:07 am

Since it was stored correctly, we can discount accidental exposure to solvents.

Notice any nicks along LE/TE when you were balancing it? Or ripply imperfections in the molded surface? (Probably too late to see anything on the broken blade, but the remaining blade may have something noticeable.) Any nicks or imperfections in the surface are stress raisers and give cracks a place to start.

nitroairplane Sat Apr 21, 2012 10:14 am

It's pristine but the brOken blade did have a swirl in it but that's not where it broke.
I suppose maybe tere was a sub standard material used.
If so everyone with grey props should check that they don't have any from the same batch.
If it has of swirls watch it.

SuperDave Sat Apr 21, 2012 10:51 am

For general information:

Gray Cox plastic props are intended for use in competitive events and are stiffer than black plastic Cox props. Their stiffness ensures a truer pitch when stressed as in extreme manuvers.

Black plastic Cox props are more flexible and are intended for general useage where prop strikes are more common.

Cox International Sat Apr 21, 2012 12:18 pm

Was this a prop you purchased from us? If so please email nichole@coxengines.ca and she will send replacements.

Our grey 4.5x2 props (intended for 020 engines) were moulded about a year ago and I have never heard of one failing. Their life span should be a decade+. However, there is always a possibility of a defect in the odd one.

The props were made with the OEM Cox mould, by the same company that made them for Cox and using exactly the same material. The only difference is that the material now has a darker dye.

nitroairplane Sat Apr 21, 2012 12:22 pm

Cox International wrote:Was this a prop you purchased from us? If so please email nichole@coxengines.ca and she will send replacements.

Our grey 4.5x2 props (intended for 020 engines) were moulded about a year ago and I have never heard of one failing. Their life span should be a decade+. However, there is always a possibility of a defect in the odd one.

The props were made with the OEM Cox mould, by the same company that made them for Cox and using exactly the same material. The only difference is that the material now has a darker dye.

I am pretty sure I did not get them from you unless at some point you were selling new old stock.
It is a different colour to the ones I have from you and Matt.
Bernie you sell some of the toughest and best props on the market IMO I forgot to mention to you how much I love the new Yellow ones, they are great.
I now run them on most of my 0.020-0.061 engines.
They are what I eventually decided on for this coming model too.

Cox International Sat Apr 21, 2012 12:38 pm

To the best of my knowledge we never got our hands on any NOS 4.5x2 grey props. We initially got a case of the black ones from the OEM moulder (production overrun) and later decided to make some in grey from the same mould.

The yellow 5x3 Safety Tip ones are now our best-selling prop. They are "unfortunately" virtually indestructable. I say "unfortunately" as their longevity is not very conducive to repeat sales. Props need to break so that we can sell more of them Rolling Eyes

Our yellow 4.5X4 are just as tough and are mainly purchased by modellers wishing top flight speeds (small diameter - high pitch - high RPM).

nitroairplane Sat Apr 21, 2012 2:12 pm

I have a few 4.5x4 (none of your yellow ones though)
They do not really go with the kind of planes I fly, a bit too harsh.
One thing I did notice with the yellow ones is the blades occasionally tend to pull forwards, The still fly very well on the engines I used.

Cox International Sat Apr 21, 2012 2:30 pm

Correct, the blades on the yellow ones flex more. That is what makes them so hard to break. For those that want inflexible blades, the grey competition series would be better.

nitroairplane Sat Apr 21, 2012 2:33 pm

Cox International wrote:Correct, the blades on the yellow ones flex more. That is what makes them so hard to break. For those that want inflexible blades, the grey competition series would be better.

I still like the yellow ones.
Another thing I noticed though was that the grey ones are thicker than the yellow.(the hub is)

Ivanhoe Sat Apr 21, 2012 4:20 pm

nitroairplane wrote:Mine are kept in a cupboard away from any form of light. I was thankfully standing behind the engine.

First law of running engines....NEVER stand in line with the prop, even the best ones can have a hidden flaw!

Indra, have you checked your PMs lately?

nitroairplane Sat Apr 21, 2012 4:57 pm

Ivanhoe wrote:
nitroairplane wrote:Mine are kept in a cupboard away from any form of light. I was thankfully standing behind the engine.

First law of running engines....NEVER stand in line with the prop, even the best ones can have a hidden flaw!

Indra, have you checked your PMs lately?

That's damn good advice Smile

Yea Wilf I have,
I have not gene receiving many PM's that people say they sent me and my email alerts say I have.
Were you trying to contact me?

Ivanhoe Sat Apr 21, 2012 5:16 pm

nitroairplane wrote:
Ivanhoe wrote:
nitroairplane wrote:Mine are kept in a cupboard away from any form of light. I was thankfully standing behind the engine.

First law of running engines....NEVER stand in line with the prop, even the best ones can have a hidden flaw!

Indra, have you checked your PMs lately?

That's damn good advice
Yea Wilf I have,
I have not gene receiving many PM's that people say they sent me and my email alerts say I have.
Were you trying to contact me?

Yes, I was asking about the Anderson spitzy you mentioned when I was discussing abused engines

nitroairplane Sat Apr 21, 2012 5:47 pm

Oh it didn't get to me.
We're you offering to buy it?
They are quite rare and old.

engine049 Sun Apr 22, 2012 1:50 am

Was it Genuine cox or a Current production item?

nitroairplane Sun Apr 22, 2012 1:50 am

engine049 wrote:Was it Genuine cox or a Current production item?

Genuine cox item.

engine049 Sun Apr 22, 2012 2:06 am

Hmm. must have been a fluke. Cox makes some tough stuff. Bernie makes some bombdiggatey props. I have a few of the new production props I bought from B. Works amazingly

Cox International Sun Apr 22, 2012 12:05 pm

nitroairplane wrote:
Cox International wrote:Correct, the blades on the yellow ones flex more. That is what makes them so hard to break. For those that want inflexible blades, the grey competition series would be better.
I still like the yellow ones.
Another thing I noticed though was that the grey ones are thicker than the yellow.(the hub is)

The yellow and grey ones were made on the same mould, hence there should not be any difference between same-size props. However, there may be differences in hub size between different prop sizes.

Cox International Sun Apr 22, 2012 12:09 pm

engine049 wrote:Hmm. must have been a fluke. Cox makes some tough stuff. Bernie makes some bombdiggatey props. I have a few of the new production props I bought from B. Works amazingly

At the risk of sounding repetitive but our props are made on original Cox moulds, with the original Cox material, in the original Cox factory (in California) and even by the original owners of the Cox factory. There are no differences except that the grey material now has a darker dye.

And, of course, the addition of yellow props.

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