The National Air and Space Museum in Washington DC (and the one at Dulles) is my favorite museum in the world (the National Museum of the USAF and the Imperial War Museum- Duxford are close seconds). I could spend hours upon hours drifting through the exhibits- and I have. I saw the propellers Orville and Wilbur designed and hand carved in the Smithsonian and I thought, well if they could do it, certainly I can with all the modern amenities afforded to me that they had to figure out without Google. (Did you know the Wright brother's prop was only 5% less efficient than props used today? Woah!)
Close by, this little exhibit showed how props were carved from this:
Into functional aviation art:
I found old blueprints at woodenpropeller.com for a multi layered prop like the one pictured above and traced them into AutoCAD to give me a crisp line drawing to scale the prop as large as I needed it. The prop I'll be building is going to be 72 inches in diameter, but the drawings are scalable so you can make the prop small enough for a model airplane if you really wanted to. It may require some manipulation of the PDFs but it can be done. Typical propellers used during and prior to WWI were 8' or longer. As engine speeds increased, the length of the propeller decreased, so post-war props were typically between 6'-8'.
What you'll need
- Planer (or have the sawmill do it)
- Jigsaw/band saw
- Clamps- lots of them. 6 good ones at a minimum.
- Drill press
- 2" hole saw
- 5/8" drill bit
- Chisels (maybe)
- Full scale print outs of the prop sections. Take the drawings to FedEx Office or a similar print shop and have them printed. Get a few copies while you're at it just in case.
- Lumber (4) 3/8"x8"x96" planks. Make sure the boards are a minimum of 8 in. wide, not just a nominal 8 in. or the design won't fit on four boards. For a layered look like the prop above, chose wood with different shades. I'm thinking about using locally sourced Red Oak and Ash. In the early days of aviation, Mahogany (most likely a carry over from the furniture industry) and Walnut were the most commonly used materials. Towards the middle of WWI, the use of Oak took over as it was considered to have better properties. Whatever species you choose, hand pick boards that aren't warped or have knots.
- Wood glue
- (8) AN5-34 Drilled Bolts (optional) Another option is to pick up regular 5/8"x3.5" bolts and drill the heads with a 1/16th carbide drill bit (not as easy as it sounds).
- (8) AN310-5 Castle Nuts (optional)
- .032 Safety wire (optional)
- Sandpaper 100, 150, 220 grit, and dry/wet 400 grit
- Orange Shellac from ColorFX to make the wood appear aged (optional)
- Wood Sealer
- Wipe-on, Satin Polyurethane
- Finishing details- i.e. manufacturer decals, impression stamps, paint for the tips, metal tip reinforcement. I haven't decided how detailed I want to get on this one.
PDF files are designed to be scaled to ANSI E-size paper 34x44" to yield a prop 72" in diameter.
This project has been one in my docket for the last year or so. Unfortunately, I'm limited to an outdoor workshop that has a limited season of usage due to the unpleasant weather we get here in Texas. But I think I can squeeze it into my schedule. Stay tuned for the build.
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