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   Post on Scimitar Propellers in Avidfoxflyers General Hangar

   By zadwit, posted 10 Dec 2018

   In the late 70s in Fairbanks, Doug Fowler built a KR-1 only he modified it a lot. LOnger wing, GA-W-1 Airfoil, different canopy , A-65 continental engine. He made his own wood prop. IT worked pretty well. He made several more props, each one a Scimitar prop and the last one he made was pretty radical Scimitar prop. He gained 15 mph in cruise with the last prop he made. Now the dangers of Scimitar dates back to WWI, the trailing edge of the blades is under a lot of tension and can crack. Doug made his prop out of thin laminations of wood, spruce I think and then after the blades were shaped, applied 8 to 12 layers of .8oz. fibreglass cloth, each later squeezed out to remove excess resin. He could make the blades thinner by l adding the fibreglas cloth.
   The last prop was 68" I think and was a radical scimitar shape. It has a fair amout of pitch but when the engine rpm increased, the blade twisted towards a flatter pitch due to centrifugal twisting moment and centrifugal force. In WWI some of the early props flutters and self destructed so the amount of sweep was limited. Anyway as Dougs plane increase in speed, the airload on the prop decrease and he could reduce RPM and the blade naturally twisted in a coarse pitch direction...pretty neat. ALso the sweep of the blade delayed onset of mach compressible airflow so the blade had less drag at higher RPMs. Photos of these props are shown so you can get the idea of how it works...