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Author Topic: 6 ft Propeller Fabrication  (Read 7963 times)
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Mike
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Mike Texas USA


« on: March 04, 2015, 01:17:37 PM »

I thought I would break in this topic and share some on my latest restoration project.

Needing a few props for various wind charger projects, I finally decided to venture into the craft of workworking.  I know several folks that make their own props using shape templates and hand tools or a duplicator.  I dont think I have the skill or the patience to go down that path plus for some of my projects, I need to be able to create a prop without having an original prop to replicate from.  

I decided to take a slightly different route (and learning curve) and used equipment a little more modern than what was available to the Albers brothers.  I used 3D modeling software (Autodesk Inventor) and a CNC router (Shopbot) at Tech Shop, a community workshop extension of the local Lowes store.  Lowes has 8 Tech Shops around the country and I am fortunate to live near the only one in Texas.  For me, access to the modeling software alone is worth the membership fee.  Keeping the sawdust out of my garage is also a bonus.  

I started with the Gottingen 222 airfoil shape and tweaked it to fit into a 3.5 X .8 cross section (blade hub dimensions for a 6' prop) at a 7 degree pitch.   I have Jim Davis to thank for introducing me to the Gottingen airfoil and the test data and history behind it.  Wincharger changed their props to the Gottingen airfoil in the early 1940s.   As for material, I bought clear Douglas Fir 2x6s from a fine lumber store and milled them to 1 thick.

Below are a few pics that include a perspective view of the 6 prop model, the CNC router in action and my first prop next to a later NOS Wincharger prop.  After a little more sanding, Ill give it a few coats of polyurethane and copper leading edges.  Some folks use a 3M tape specifically designed for leading edges of wings and props.   The copper becomes pitted and distorted over time which results in turbulence and lower efficiency.  Im opting for the original look over performance.
 
Other than a few minor adjustments to the 3D model and router programming, Im pretty happy with my first prop.  This one will go on my Heavy Duty 12V Wincharger for some endurance testing.  Having the modeling and fabrication steps figured out, I should be able to adapt the process to make any size wind charger prop I need.  Ill be glad to share my prop models and techniques with anyone wanting to make a prop using a CNC router.    
« Last Edit: March 04, 2015, 03:18:21 PM by Mike » Logged
Mike
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Mike Texas USA


« Reply #1 on: April 03, 2015, 08:22:31 PM »

I've completed three, 6ft props.  #1 is on my 12V Wincharger running nicely (www.youtube.com/watch?v=OQijXqdYZ4A  

Prop #2 was junked because I made a bad router setup change.  I attempted to use the router to completely cutout the blade, leaving discrete tabs for support.  I've found that the blade needs full support around the perimeter or there's too much vibration and it tears up the delicate trailing edge.  Using a table saw to cut the prop out from the surrounding material seems to work the best.  #3 turned out the best so far and is shown in the pic below with several other wind charger blades.

Prop #3 required a 1000 in-gr balance adjustment that far exceeds the steel tear drop shape you generally see 6-10 inches from the center of rotation.  I use a simple knife edge in the geometric center to check prop balance.  My prop geometry is symmetrical within .01" so I'm suspecting the Douglas Fir material may have density variations that is causing the imbalance.  I corrected with 30 grams of 1/4" rod in the end of the blade and cross drilled and installed a retainer pin.  I've seen a few 6V and 32V blades with steel bars offset from center for what I'm assuming is for a coarse balance corrections.  David Ballinger has seen a steel pin installed in the leading edge of a 6' blade which was covered by copper.  Both the steel bar and a leading edge rod would work fine for coarse balance and the tear drop steel for trim balance.

These are tough little machines that can handle some rough running but I like mine running smooth.  The balance will likely change with time and weathering and I'll learn to live it or take the time to rebalance.  
« Last Edit: April 03, 2015, 08:36:10 PM by Mike » Logged
Charleypete1957
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« Reply #2 on: February 03, 2017, 08:20:49 AM »

Mike,

You bring back lots of memories with this post.  When I was 17, a friend and I found an old Wincharger blade with governor assembly in the top of a barn.  We recognized it immediately, and began to fabricate a wind machine with an old automotive generator.  We had no welding skills or equipment, but my grandfather had a cheap gas welding outfit that we used to attach the blade to the front of our generator with.  We mounted it atop a long piece of windmill pipe, with a piece of greased wood for a swivel bearing.  Our clumsy welding attempts resulted in the destruction of that fine old blade when it came loose in a strong wind and hit the pole.  Well, we already had the bug and that wasn't going to stop us. 

Now it's a few months later, I'm in a shop welding class by now, and we've talked a local truck shop into letting us use their welding machine.  With scrounged materials, an old motorcycle engine gear set and an automotive alternator we set about building a new and improved wind machine.  We knew the alternator had to spin a lot faster, so we put the biggest gear we had on a piece of pipe for a shaft, and the smallest gear we had on the front of the alternator and mounted it all together on a piece of scrap steel plate.  We used bearings from a swamp cooler on the pipe shaft, grinding it down to where the bearings fit snugly.  Using the remains of the original Wincharger blade as a pattern, we found a new 2X4 in my grandfather's shop and created a new blade with a table saw and a wood rasp. 

That little machine sure did go!  We never made much power as we were using an alternator and it just couldn't spin fast enough even with gear reduction.  But it started and ran in the smallest breeze.  It was pretty durable too.  One day a spring front rolled in and the wind blew 60-70 mph for hours, and that little machine roared like an airplane trying to take off, but held together.

I eventually went off to the Navy right after graduation, but my buddy played with that machine for a couple of more years.  We both learned lots of practical experience with that little project.  It sparked my interest in wind power generation that remains today.  I'm sure my propeller-carving days aren't yet over, as I have a massive old truck generator I just acquired last summer that's just begging to have a prop attached to it.  When that happens I'll document it all here. 
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Mike
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Mike Texas USA


« Reply #3 on: February 03, 2017, 09:52:56 PM »

Great story Charlie.  What is it about things that spin that we find so entriging?  Maybe it should be added to our hunting and gathering job description.  Thanks for sharing.

"The answer is blowing in the wind"

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Charleypete1957
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« Reply #4 on: February 12, 2017, 11:27:16 AM »

Mike,
Those are some really good-looking blades you've made. They look factory good!  I have a question you may be able to answer. You made these of Douglas fir, and I've seen in the literature that most blades were. I know that Sitka spruce is often used in homebuilt aircraft for its good strength to weight ratio. Is fir stronger than the spruce?  I don't guess we really need exceptionally light wood in our Wincharger blades, so I'm assuming that the Douglas fir is a stronger wood. Any thoughts on this?
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Charleypete1957
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« Reply #5 on: February 12, 2017, 12:39:04 PM »

Mike,

I thought I'd do a little research on my question about Douglas fir vs Sitka spruce.  On the forum at woodenboat.com, those guys prefer Douglas fir because it's stronger, heavier and "somewhat more rot resistant" than the Sitka spruce.  That last quality may be very important to builders of wincharger blades in wet/humid climates.

On stickbow.com, the guys on that forum prefer the fir because it's more durable, it's heavier and it takes stains better than the Sitka spruce, as all this applies to building bows and arrows.

At ibis.experimentals.de they home-build experimental aircraft.  If weight is not TOO much of an issue, they prefer the Douglas fir because it is "somewhat heavier than Sitka spruce, and quite a bit stronger."  The Sitka spruce is given preference if the final project weight will significantly impact fuel carrying capacity. 

The house builders at arboristsite.com prefer the Douglas fir because it has a superior span rating than the Sitka spruce or other firs.

So there it is in a nutshell:  Douglas fir is heavier, therefore it's stronger than Sitka spruce.  As we're not particularly concerned about making blades that are very light, it seems that the Douglas fir is the wood of choice for blades.  Also, it is a very "stable" wood, given that it doesn't tend to twist as much as some other woods of comparable weight and strength. 

On a little different note, I was driving around this morning and spotted an old Parris-Dunn stub tower and tail fin that somebody had put a fan on the front of for a front yard windspinner.  I'll try to get a pic for this forum.  Have a great weekend!
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Mike
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Mike Texas USA


« Reply #6 on: February 12, 2017, 03:08:58 PM »

Below is a table of mechanical properties for Sitka Spruce and Douglas fir.  Douglas Fir is denser than Sitka but strength and stiffness will depend on what part of the country its from.  I'm not sure where my boards come from; I'll ask next time.  I can tell you vertical grain Douglas Fir is not cheap in central Texas.  I pay almost $50 per prop just for material.  
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Charleypete1957
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« Reply #7 on: February 14, 2017, 09:17:06 PM »

Mike,

Your chart is much more informative and formal than my little foray into the whys and hows of the two woods.  With it you can get a great idea of how any of the woods will perform.  Great find!
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Albino Storm
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« Reply #8 on: February 18, 2017, 01:22:58 PM »

Great looking props, Mike. :-)

Do you plan to make and sell any?

It seems like a good used prop is near impossible to find. 
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Mike
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Mike Texas USA


« Reply #9 on: February 18, 2017, 08:44:25 PM »

I have made extras and sold a few.  Making another batch is on my todo in the next couple of months list. I'll let you know when I have some available.  I have a bathroom renovation to knock out near term.  For my purposes, my prop manufacturing method is very practical.  It's flexible for making any shape and size prop that I can conceive and draw but it obviously doesn't lend itself to larger production runs.  I also don't particularly like the repetition of making them or what I have to charge to pay for expenses.  It would be really nice if someone would develop or find Wincharger's tooling and make a production run.  Maybe supply Wincharger enthusiasts' needs for say the next 10 years.  Problem is it's hard to justify the investment to (re)develop the tooling when the world wide demand for 6' vintage Wincharger props might be a dozen a year.
Keep your eye out, every now and then a stash of NOS props pops up.  I recently learned of a dozen 6 footers, still in the boxes, found in the attic of an old hardware store.  Unfortunately the owner has sentimental attachment with the old inventory so for now they will remain unavailable. 

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GregW
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« Reply #10 on: February 19, 2017, 01:12:22 AM »

I have a propeller I bought for my WinCharger from a guy in Washington state that I would be willing to part with.
71.5 inches long

11/16 thick

1 1/8 diameter hole

6 inch long scratch (might be crack but cannot see it in center hole)

Will need to have holes drilled for your application. Will need to be balanced.

PM me if interested.

Thanks,
Greg
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Albino Storm
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« Reply #11 on: February 19, 2017, 02:32:54 AM »

pm sent
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Albino Storm
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« Reply #12 on: February 19, 2017, 02:34:50 AM »

Thanks Mike, I'll continue to watch ebay.
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Albino Storm
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« Reply #13 on: February 22, 2017, 02:45:45 PM »

Thanks Greg!
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