From: David Lednicer <dave@amiwest.com>
Newsgroups: rec.aviation.rotorcraft
Subject: Re: Symmetrical vs unsymmetrical airfoils ?
Date: Tue, 25 Jan 2000 09:02:23 +0000

Hennie wrote:
>     Why do some helicopters (the most) use symmetrical airfoil on the
> rotor blades
> and some unsymmetrical airfoils?
> What is the pro's and cons?

	You mostly see the symmetrical airfoils on older helicopters.
Symmetrical airfoils produce little or no pitching moment, hence the
blades don't get torsional windup from the airfoil properties.
Additionally, the pitch control link loads are lower.  As designers
learned how to stiffen blades torsionally and how to deal with the
control link loads, cambered airfoils came into use.  For more info on
which blades have which airfoils, see my "Incomplete Guide to Airfoil
Usage" at:

http://amber.aae.uiuc.edu/~m-selig/ads/aircraft.html

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