Wincharger Blades - Failure Test Photos

[Dave B]

  Dave Moller of Royal Fabrication who is carving the Wincharger replacement and custom blades decided to sacrifice a 6' Poplar Laminated Blade today for failure testing.

  The purpose of the test was to determine the maximum flex of the blade by securing the root and adding weight to the tip until failure. The specifics of this test as well as more photos and data analysis of the performance of these blades will soon be posted on Dave's updated website at royalfabrication.com

  He set up the jig and documented the weights he added while I measured the deflection, took the photos and waited for the big bang. The photos speak for themselves and we both felt this to be very useful information to share for future design consideration as well as an appreciation for the strength of wood as a blade material.

  Updated blade performance and specifications soon to be posted on Dave's website at royalfabrication.com    Thanks for running this test today Dave, great information.  Dave B.

[Warrior]

Hello, Dave.

Excellent post!!! Those blades are incredibly strong! I wonder if they'll ever flex as much in a real life situation.

Good Work!

[feral air]

I wonder if this kind of test could be repeated for every blade to ensure a more consistent set? Maybe load each blade with 100lbs and group 'em accordingly? Maybe it doesn't vary enough to matter though, I dunno...

If I was in the market I would pay a little more to know that all the blades I'm buying have the same flex characteristics. I'm a sucker for marketing though....do you hear a "cha-ching" on your end?

Cool post, thanks for sharing! take it easy

[Slingshot]

Interesting results!  It appears in the photos that the root of the blade is supported for a considerably greater length than is normally achieved with most hub designs.  If this is true, then might the location of failure be different in the real world?

[paradigmdesign]

One thing that I noticed is that most of the flexing is between the root and about 35-45% of the span.  I wonder if you either made the inboard section thicker, or made the outboard section a little thinner if you wouldn't get a more uniform flex, and allow the blades to bleed off some more stress from gusts etc. instead of having to absorb it.  Not that a 248lb load limit is bad for a 6 foot blade, considering I have seen 15' blades tested, and broken with 350lbs(granted it was fatigue loading, not static).  

Nice blades and good post!

[paradigmdesign]

[MattM]

Your picture shows a more realistic test than one where all the weight is on the tip.  That same 250 pound weight threshold at the tip could mean it supports four times that at the mid point.  Spreading the weight across the blade could balloon that figure to 1500 pounds if the weight is spread along the entire blade.  Realistically a 2x6 in perfect shape should support 900 pounds across a 4' span per most building codes; the proof is 900 pounds out from a 4' fulcrum so even that leaves a lot of safety factor in the figure.  I can't remember offhand if the figure drops by a factor of four or eight every time the distance is doubled, but it becomes significant as you move out from the fulcrum.

[Sly]

Comments,

That's a shame I need three of those!!! Just kidding I'm curious how dry was the wood? I would think this would also influence the amount of flex tolerated before the failure. Mind you I'm just an electrician!!

sly

[Dave B]

  Obviously there are hundreds of ways to conduct a test and then analyse the results. We wanted to test and then present the results of the extreme condition shown. We are glad to see that most realize this is not a real world run condition as we are using the tip as a point source for the loading.

  I suppose from a marketing standpoint even more people may have been impressed if we had distributed hundreds of pounds more across the blade length with (wow) even less flexing indicated. For those who like to crunch numbers it doesn't take too much calculating from the results of this (face or thrust) test to back figure the incredible stresses required to reach a similar structural failure in the more realistic run conditions.

  By the way, this blade is 2x6 only at the root of which 10" was secured. Take a look at the Gottingen 222 profile to see what we are actually bending here. We know there will be a lot of coulda, shoulda, woulda comments from a test like this and we welcome all replies.

  The test shows we hung 258 LBS. off the tip of the blade and it's maximum deflection over 5' was 17" before it broke. That's it. Thank you for your comments.  Dave M. & Dave B.  

[pyrocasto]

Being wood there are lots of variables to how strong a blade is. I think tests like these show that even to the extreme these blades will hold up to some serious winds though.

Things that will affect the strength: wood specie, the makeup of the tree and the grain variations, and also moisture. As you can see though you are still going to end up with a flippin strong blade that will usually be destroyed by hitting the tower or something of the sort before the wind breaks it.

[Old F]

This also shows you should not under estimate  the flex

As I remember in the early day there were more than few pix of what happens when you don't give enough room between  tower a blade tips.

 An if you are hand carving blades destructive  testing is not high on the to do list for them

Old F

[paradigmdesign]

Just so I am clear, I was not criticizing your blade, or the way you were testing it.  I was just posted the picture to show what I considered a more "uniform" flex.  BTW, tip deflection/loading IS a "real world" way to test turbine blades, especially for fatigue loading(where the blade is flexed back and forth).

[Royalwdg]

We did this test pretty much to see where it was going to fail. You can push on a blade and say that it feels strong or weak. that does not say much, I need numbers. So we have some data. Of course this is not a simulation of a blade at work. a blade secured at the hub is a catilever beam fixed at one end with an evenly distibuted load. we crunched some numbers with the beam equations and found that it took a moment of rotation torque of 1250 ft-lbs to make this fail with a concentrated load at the tip. When you plug that into the evenly distributed load formula it gives you an idea what it would take to make it fail that way. I came up with 100 lbs on every foot of length.

This blade that we broke was 6' long. I think we are safe. Thanks for all the comments.

Dave Moller