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Sunday, June 24, 2007

Make your own Propeller

Why?

Why bother with carving a propeller when you can buy a plastic one cheaply? Surely a balsa prop would break easier than a plastic one, I hear you say. Perhaps that is true, but I was surprised by the robustness and lightness of my first self-made prop. Less weight spinning around means easier trimming, not to mention a lighter model.

How?

I followed the inspirational instructions provided by Dannysoar here. I did not have a block, so laminated bits of 6mm balsa that were lying around with PVA glue. One piece was a "dog" because it was so heavy. It is almost as dense as spruce and I could not find any use for it in my models. So I used that piece as the topmost sheet, that is, to be the front or the leading edge of the prop. Also, I was careful about aligning the grain of each sheet so that one piece was not running opposite. This prevents "snagging" during the carving. I sawed the block into triangles, marked and glued it (photo above) this time with epoxy. Then started carving with a normal craft scalpel. Balsa cuts easily and it was really quick.


The photo on the right shows the initial carving. Basically, you carry on, try to keep it even, then shape the tips. Every now and then, put a piece of wire through the hole and check the balance of the prop. Remove material from the heavier side. Carefully glue some tubing in the hole, check balance, sand and smooth it off. You will need some form of free-wheeling device. I used a simple Z bend clutch - called a Garami. This prop was for my Cloud Tramp. It flies much better than it did with the plastic prop.




The photos below and on the left show details of the Garami freewheel clutch and the finished prop installed on my Cloud Tramp. As a final job, I superglued thin cotton thread to the LE for protection. So I've found a use for that heavy balsa after all! Even though this laminated prop had lots of glue in it and the heavy bit of balsa, it was still 20% lighter than the plastic prop. Wood is a difficult material to beat...






It is a very satisfying thing to do and much easier than I expected. Since the pitch of the wooden prop is higher, the duration of the power run is longer.

I think it also looks prettier.

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