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Old 06-22-2017, 01:12 PM
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I doubt it was heat treated...no value with Ti,, but maybe not stress relieved and needed it?

Not buying the vibration/crystallization theory.
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Old 06-22-2017, 01:22 PM
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Quote:
Originally Posted by Flybye Steve View Post
It broke right where the 1/4" dia. axle meets the larger dia. hub. I think I still have one around and I'll see if I can't post a picture.

I had one recently sheer at that same area. Kinda sucked landing a 38% on one wheel
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Old 06-22-2017, 06:56 PM
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I had a couple do the same thing. Same spot..
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Old 06-22-2017, 10:18 PM
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The problem I had with mine is that two axles bent...and I *think* that was from the plane riding in my trailer.

Also, I stripped the threads on one...like wore them down with a regular lock nut.

Also, when put to a grinder, they don't spark bright blue-white. All of the above is why I started the thread.

To be fair, I'm not a materials engineer and admit I know almost nothing about Ti...just found it odd that they bent and stripped so easily. This can very easily be user error on my part...which is why I tried to ask politely. I'm not mad or anything, was just curious.
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Old 06-23-2017, 09:20 AM
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Ti alloy 6AL-4V is certainly heat treatable. Feel free to look it up:

You can look up the properties of almost any alloy here:
http://www.grantadesign.com/userarea/mil/mil5.htm
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Old 06-23-2017, 09:30 AM
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when turning to a shoulder, i.e.. 1/4 axle to the 7/16 threaded gear mount, a "hard" 90 degree transition can cause a stress point prone to failure. Is there a slight radius at that point to relieve potential stress? Doesn't need much to ease failure potential, especially with materials that may be brittle.
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Old 06-23-2017, 09:39 AM
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Quote:
Originally Posted by flyerman View Post
when turning to a shoulder, i.e.. 1/4 axle to the 7/16 threaded gear mount, a "hard" 90 degree transition can cause a stress point prone to failure. Is there a slight radius at that point to relieve potential stress? Doesn't need much to ease failure potential, especially with materials that may be brittle.
No, it looks like there is a hard 90 degree cut, does not look like it's radiused.

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Old 06-23-2017, 10:48 AM
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Yep, a radius would be a big help.
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Old 06-23-2017, 11:14 AM
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I'll share the pics of where mine broke. You can see in the good one there is a bit of a shoulder (radius) and mine broke right below that shoulder.


In all fairness these had been in use for 4 seasons.
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Old 06-23-2017, 11:32 AM
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Most all materials will fail at stress points- cracks in panels will run forever unless stop drilled to ease the stress point for example. Way back titanium had its problems- SR71 fabrication, but most of that has been ironed out with better technology, fabrication technique and new tooling. Without going into a big titanium treatise, I always leave a very small radius at a shoulder unless the specs state otherwise, and you go by the specs.
White Rose has much more expertise than I and years of production with their design protocols, so I'm sure the failures will be addressed. Many factors contribute to end point failure- metal processing, fabrication, handling, temperature, tooling, etc.- so random failures, like intermittent electrical problems, may be difficult to resolve.
Check out NASA's Normalization of Deviance reports developed after the Challenger tragedy. Many small, isolated deviations came together as a whole at that point in time. Interesting reading.
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Old 06-23-2017, 11:47 AM
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Quote:
Originally Posted by sthudson View Post
I'll share the pics of where mine broke. You can see in the good one there is a bit of a shoulder (radius) and mine broke right below that shoulder.


In all fairness these had been in use for 4 seasons.
From photo it looks like a crack developed at some early point leading to final separation after lift off. Stays together with positive weight bearing and finally goes south when airborne after periods of pos/neg G.
That's a good photo clue for the WR guys. The more info they have the better. Beats looking for a needle in a haystack.
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Old 06-23-2017, 06:15 PM
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No simple answer

I do not have an explanation for these failures but to say they have been few considering that we are past six hundred pairs sold. As someone pointed out, this is the location of the stress riser and they will break at the step every time. The axles pictured were made several years ago when we were having them electroless nickle plated. We no longer do that because the EPA required new chemical usage which drove the price into Lockeed country. I don't think the plating has anything to do with the failures. We have increased the fillet radius with each run because we knew this was happening on occasion. It's currently .04 and is already causing some problems with bushings dragging against the radius until the bushing material wears away some accommodation.

If we get reports that the newer run is still breaking we will have to go with a much larger radius and include a washer/spacer with a large chamfer on one of the ID sides to accommodate the large chamfer. Of course, these will probably have to be custom made which will not improve the pricing.

I would like to know if these failures were largely confined to 40 plus % airplanes. Obviously, the heavier the airplane the higher the loads on the axles. Ti is not steel, we can make steel axles for the heavier planes but it will not save that much per pair (maybe $15.00) and will increase the weight significantly.
As a side note, Ti likes to gall so put a little Vaseline on the threads when you wind on the nut.

I know this will not retrieve any wheels lost in the woods but I do apologize for the problems some of you have had with the axles. We are aware and have been trying to solve it. We will never solve it completely.
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Old 06-24-2017, 12:52 AM
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Quote:
Originally Posted by Vern Smith View Post
... Ti is not steel, we can make steel axles for the heavier planes but it will not save that much per pair (maybe $15.00) and will increase the weight significantly.
I appreciate your candor in discussing this issue. I'm in the manufacturing business also and I know there are always issues with any complex product.

Steel axles seem like a valid alternative. Are you actually going to offer steel axles made to fit your wheels? I would be very interested. Can you estimate the weight penalty?
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Old 06-24-2017, 08:02 AM
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Quote:
Originally Posted by TnAeroNut View Post
I appreciate your candor in discussing this issue. I'm in the manufacturing business also and I know there are always issues with any complex product.

Steel axles seem like a valid alternative. Are you actually going to offer steel axles made to fit your wheels? I would be very interested. Can you estimate the weight penalty?
I'm thinking steel would be fine, for me anyway. Not being a weight Nazi, I really don't care about eliminating every last Gram. In my mind, keeping my expensive wheels attached to the airframe, and not having to one-wheel-land my 37.5% Yak holds top priority.
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Old 06-24-2017, 10:28 AM
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Axle failures

Hey Vern, that is a great response. It's refreshing to hear one of our vendors own up to
issues with their products. In the long haul I believe your customers will respect your position and the fact that you continue to strive for perfection.
I found one of my broken axles and it looks just like the one shown above.
In the overall scheme of things, I'm wondering
how much effect the difference between steel
and Ti axles really matters on a 40-42% plane.
This becomes a more serious question when you consider the possible damage that can occur to your plane from an axle failure.
The design of your axle is a good one Vern.
You may want to consider offering the steel version for the giant scale planes.
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