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Old 03-20-2018, 09:04 PM   #9 (permalink)
freebeard
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Extend two opposite prop shafts. New props with larger overlapping disks and a Prandtl-D profile — deep pitch at the hubs that washes out at the tips. This eliminates air rolling over the tips and thus the efficiency. With the washout the props are less likely to interfere.

https://duckduckgo.com/?t=palemoon&q...-D+wing&ia=web
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