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Building a Prop

DanH

DanH

Legacy Member
Mentor
My RV8 work has been on hold the last few weeks; needed to finish up a propeller project and get the sawdust cleared from the shop so I can start painting. Thought ya'll might enjoy a look.

This is a prop for a 315 hp fixed pitch M14 radial. It is going on a custom biplane, a half-done project I'll jump back into after the RV-8 is flying. The prop is seven feet long with a chord over 8 inches.



Design is by Don Bates, via his Prop Optimizer Pro software. The code needed a modification to adjust for the reduced free-stream velocity in front of the radial cowl, which got Don interested, and one thing led to another.....nice fellow. Software output is (among other things) a set of airfoil coordinates for 20 or so blade stations. I plotted them in AutoCad and printed them full size, then made hard Formica templates.

Material is sugar maple, in 1/4" laminations. The glued blanks were the size of a railroad tie and about 100 lbs each. I made careful cuts with a circular saw and knocked out a lot of the excess wood with a chisel:



Since I needed to make two props (have a buddy with an identical engine), I decided to do them with a propeller duplicator rather than entirely by hand. First step was carving a master blade; my own craftsmanship guru, 84 year-old Raymond Griffin attacked that project while I built the duplicator. Here's the master in the machine with a prop in process. Yes, that is a knee-deep pile of wood chips against the wall:



The duplicator gets the profile within a 1/16" or so. The rest is done by hand on a template table. Each template includes a reference mark that matches with a line on the table; just keep sanding as necessary:



I know it would look good varnished, but I may do a flox insert in the leading edge and glass the whole thing. For now I'm just gonna store it away and get back to RV work.
 
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Jeeeez Dan! You are one hard core DIY'er. Did you also raise the sugar maple trees from sapplings?! Very impressive and interesting process. Congrats.
 
Guys,
This doesn't even surprise me. I've seen Dan's work first hand and I've said it before on this very forum, Dan is a CRAFTSMAN! Nice work Dan.
 
beautiful!

Dan, that's a stunningly beautiful result! Congratulations!

A nice short chord at the tips. I'd be interested in Paul Lipps' opinion on the design.

Andrew

RV-8 empennage at 30%
 
Mike,
<< have you done a torsional vibration study on these props yet????>>

Actually, yes, in a manner of speaking. Propellers have a great many vibratory mode shapes. One reason I decided to design and build my own was the TLAR-designed prop I commissioned from a popular vendor. It fluttered (and failed some crappy glue joints too) in the test cell in Romania:



Flutter onset was at 1850-1900 RPM, which nicely matches the radial's intersection of F1 and 9th order.

Compare the blade shape you see above with the new prop. Prop Optimizer Pro does structural calculations as well as aerodynamic design. I don't expect any trouble with this one, but we'll see.

There was also a good bit of number crunching for hub design. Notice I did not use the classic "Air Corps" splined hub common to lower RPM radials; they have a history of propeller hub tension failure with overspeed. And I owe Steve Boser at Sensenich a big "thank you" for some frictional torque capacity spreadsheets.

Education and recreation, right?
 
Amazing Dan!

Now I want to see the home-made smelter you're going to use to turn Bauxite ore into the aluminum sheets for your RV....;)

Paul
 
Bill,
From the software documentation:

Prop Optimizer PRO uses the classical Goldstein-Theodorsen vortex theory to calculate propeller aerodynamics.

The program uses the NACA 16xxx series airfoil. It is based on a uniform loading mean camber line. This provides the maximum lift with the least camber which helps raise the Mach number for drag divergence and reduce shock noise. The thickness profile provided has a 60% aft minimum press location to help reduce profile drag. This is ideal for a propeller airfoil but not suitable for wings due to the high pitching moment caused by the more aft loading.

I'm not savvy enough in aerodynamics to offer worthwhile personal comment.
 
Speechless

Dan,

What you've created is simply amazing! Unfortunately, there isn't a 'jaw dropping' icon here. I guess this is the closest one: :eek:

Thank you for showing your talents and sharing your knowledge and expertise with the group.

/\/elson
 
One question Dan, do you make bird houses too? ;)

That is amazing. Is that duplicator machine thingy homemade?
 
Steve,
<<How in the world do you clamp such an enormous glue-up??>>

For the master half-blade, I picked up some nice boards outside Atlanta at a specialty millworks supply and Raymond clamped them with a simple fixture. No big deal, just a flat 2 x 10, a bunch of crossbars, and a lot of threaded rod.

I priced maple too, and was planning on the same thing (just longer) for the prop blanks. Then I got thinking about a prop I'd seen at S&F made from 1/16" maple veneer. Very pretty! So I made a few calls and found out most of the prop vendors just order laminated veneer blanks pre-glued.

I ordered two from a company in Michigan recommended by a prop guy I trust, at $450 each. The millworks said no problem, made them, and shipped them to me. When I cut into them I found some open glue joints. Uh oh!

It was simple enough to track down. The veneers are fed through a glue spreading machine. As they come out, the workers stack them on the clamp table. The catch was the thickness of these blanks, and the fact that they made them in July. I needed 104 laminations, and the glue machine only runs at one speed. It wasn't running fast enough to kick out 104 layers before the glue started setting in the July heat. They had never tried to lay up a veneer prop blank this thick in the summertime; not many crazies building props with 6.375" hubs.

The millworks owner was square about it, and I agreed to drop the veneer order and let them plane 1/4" laminations instead. "Only" needed 26 of those, so no more problem with glue machine speed. They replaced the bad blanks, no charge.

As I didn't wind up with the sexy veneer blanks, they probably cost us a bit more than just laminating boards myself. What the heck, it's only money <g>
 
Prop

Hey there #1. You are the quintessential man. Really proud of you. Say hi to Miss Patti for me.

Rhonda
 
Larry,
<<Is that duplicator machine thingy homemade?>>

Yes...a little welding and machining. Anybody want to buy it? I'm probably going to put it on Ebay.
 
WOW!

I'm speechless. I love this kind of thing!

I really appreciate that some of this 'lost art' stuff isn't lost in the modern CNC kit-builder world. This kind of 'problem solving' is inspirational.
I'll remember this post when I am frustrated about how to solve a particular challenge on my -8 construction.

Patience (no shortcuts and pay attention to the details), patience, and more patience.

Kudos to you Dan for keepin' it real!
 
When people learn that I'm building an airplane, I tend to correct them and point out that I feel like I'm an airplane builder in the same way that someone who buys their furniture at IKEA is a furniture builder.

The breadth and depth of your knowledge and talents is amazing. Thanks for sharing!
 
Ya'll are entirely too kind. I appreciate the compliments; thank you very much.

A little perspective; years ago, most homebuilders had to carve a prop so it's nothing new or exotic. Like those guys, I didn't have a choice; there really wasn't anyplace to buy one. And I think you might be surprised how many other builders with similar experiences lurk on this very forum. I recall threads about "other projects" and "other airplanes"; there is some very cool stuff going on out there.

Just for fun, here's a photo of the thing that turns the airscrew:
 
Good wood

Dan, cool woodworking project!

For some reason my mind flashed back to a state fair long ago. I chatted with a guy who carved big (6' +) wooden bears. One of his tools was this 4.5" angle grinder attachment that looked like a 4.5" circle of chain saw chain. He said it was very controllable. I've seen 'em for sale, but never needed one. Might be a faster way to rough in the prop, compared to hammer and chisel. However, the chisel doesn't remove as much meat from your hand when you're careless!

It sure is a pretty piece of work. I'd have a tough time with the decision to clear coat vs wrap with glas myself!

Congrats,
T.J.
 
Postscript.

I just came up from the shop. Tonight's project was to dig out my old pendulum prop balancer and check static balance before I went any further.

Straight from the template table, end-to-end balance was out by 1.3 grams......a single AN4-960 washer laid on the tip.

Unbelievable. I'm a happy camper.
 
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Balancer

Dan,
Is the static balancer you are using an item that can be purchased somewhere? Did you make it yourself? I have searched around for such a tool but have not found anything on-line or at ACS, etc. What are prop makers using for basic static balancing?

Nice going on your prop project. I am a wood worker more that a rivet bucker so maple on the nose looks good to me.
 
<<Is the static balancer you are using an item that can be purchased somewhere?>>

Well, not this brand:



I love old aviation tools and make a point of giving them a good home. This Flottrop balancer was purchased new by my local FBO in 1957. I've rebuilt it, and I'll pass it on someday.

Operating principle is simple. You mount the prop on cones, centering the balancer, then adjust the acme nuts to raise or lower the CG of the prop as compared to the pivot in the center of the balancer shaft. Sensitivity increases as you raise the prop in relation to the pivot. "Real sensitive" has the prop CG about 1/4" lower than the pivot. Add or subtract weight as necessary so the brass disk on the cable is perfectly centered on the shaft.

Out of balance:



In balance:



Here's the guts of the assembly:



And the whole kit:

 
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Any dynamic balance guys here? I'd love to have a real-world check.

I spent some time carefully checking static balance ths evening. Converting to a term I think is universal in the balancing business, I have unbalances of:

61.5 gram-inches spanwise (ie, 1.5 grams @ 41 inch radius)

92 gram-inches transverse (across the hub, 35 grams @ 2.625" radius)

Are these low values in the balancing world? I see references to maximums of up to 400 gram-inches in dynamic balance literature, but what values do you commonly find when you're out there balancing in the field?
 
Hand Made!

I love it, old school, with hand tools Dan? Wow! It's not like you put it in some CNC machine, you did it the way they did it way back when, with a saw and chisel! :eek: Neat looking prop and airfoil. Nice radial. The fit and finish is nice.

For any that want to get into it, you could get one of these Prop Duplicators:
http://www.wood-carver.com/gemini.html

The gemini site also has articles and http://www.wood-carver.com/store.html like glue for blanks.

Here is a software program for props
http://user.tninet.se/~trz012v/JCPropellerDesign/PropellerDesign.htm

Never got into wood working except in middle school wood shop. I got an "A". I loved it. I like Norm on PBS New Yankee wood working shop. He has a special tool for every operation. If you think building RV's requires special tools, we have nothing on wood workers.
 
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gmcjetpilot said:
I love it, old school, with hand tools Dan? Wow! It's not like you put it in some CNC machine, you did it the way they did it way back when, with a saw and chisel! :eek: Neat looking prop and airfoil. Nice radial. The fit and finish is nice.

For any that want to get into it, you could get one of these Prop Duplicators:
http://www.wood-carver.com/gemini.html
Click to expand...

Well, to be fair, a chisel yes, but a power saw, sanders, etc. And I am gonna build a CNC propeller machine eventually, given the ready availability of prop software that outputs XYZ blade coordinates. After all, this is 2008.

My duplicator is similar to a Pro model Gemini, but with increased arm stiffness....and it can be purchased for less since I'm now done with it.
 
New RV prop maker DanH ! ? ! ?

DanH said:
Well, to be fair, a chisel yes, but a power saw, sanders, etc. And I am gonna build a CNC propeller machine eventually, given the ready availability of prop software that outputs XYZ blade coordinates. After all, this is 2008.

My duplicator is similar to a Pro model Gemini, but with increased arm stiffness....and it can be purchased for less since I'm now done with it.
Click to expand...
Nice are you going to start making props for RV's? Hummmmmm, inquiring minds want to know? :rolleyes: Why not you got the mad skills, tools and aero knowlege, plus a RV test bed.....

PS Yep saw the power sander & saw; I'm sure they had those in the old days, just steam or mule driven. :D
 
I've listed the propeller duplicator on Barnstormers, so ya'll spread the word if you know someone who might like one. Look under "Propellers". Thanks.
 
Hi Dan

Ain't woodworkin' fun, challenging, and very rewarding?
You bring back the days I was living outside Louisville KY and an active member and cabinetmaker in Kyanna woodworking guild which encompassed northern KY annd southern Indiana. A dumb question, does the sugar maple need some protection from absorbing moisture (and therefor warping) from not
being sealed?
 
Jerry,
My understanding is that all wood, given time, sealed or not, absorbs moisture until it reaches an equilibrium with it's environment. ANC-18 structural values are based on 15% moisture content (continental US) and 20% (tropical, 90% relative humidity for long periods of time).....point being, structural wood has significant moisture content under normal conditions.

I think the real purpose of "sealing" wood to moisture stability. Although overall moisture content may drift up and down over time, it is not 10% in the heat of the afternoon, 25% in the night dew, and 50% when left in an all-day rain. Nor is it 20% on one face and 10% on the opposite face, a warp for sure.
 
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