Building a Prop
 

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.

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.

Dan, have you done a torsional vibration study on these props yet????:eek:

Awesome work Dan!:cool:

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?

Very impressive :)

Good Lord Dan! That is freakin' amazing!! Nice work man!!

:cool::cool::cool:

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