Thrust value and tractor propeller for a Hirth F-33

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Apr 19, 2021
Grapeview WA. USA.
Henri Mignet drew at least three detailed propeller carving plans-- I know because I have paper copies. I suspect he drew more than three.

One is for a 1.6 meter (~63") long prop cut from a monolithic 70 mm (~2.75") tall x 125 mm (~5") wide blank. It was meant to be used on 20-ish horsepower converted motorcycle engines that maxed out at 4000-ish rpm.

His 1933 plan said that a 64+" x 3+" x 5+" straight, square block of aged hardwood would be easy to find... at a reasonable cost... Were but if that was true today. I note his postwar propeller carving plans call for laminating the blanks.

A second is for a 1.5 meter (~59") long cut from a laminated four part 70 mm (~2.75") tall x 125 mm (~5") wide blank. It was to be used on 40 horsepower Continentals.

A third was designed for 85 horsepower Continentals and is 1.75 meters (~69") long, being cut from a laminated five part 90 mm (~3.5") tall x 150 mm (~6") wide blank.

He used cascamite, a powdered, gap filling, urea-fomaldahyde glue... popular in 1948, 1958, and still used in boat construction today to laminate the wood. It is dissolved in water or mineral spirits, spread, and clamped. Googling around I find that many people use this product to laminate wood that will be in wet conditions (like boat hulls). He also bent and riveted thin aluminum sheet to the leading edge.

Absolutely good to use urea aldehyde glue. Casco and Weldwood glues give as good or better service as most modern epoxy. I have built laminated masts for high performance sail boats for many years and have personally seen more failures using polymer compounds than with the more traditional materials. The best epoxy that I have used is West Systems 5 resin mixed with their # 404 adhesive filler. it's just about fool proof when used with their mixing pumps.