Jeff Spitzer wrote:
snips..

True.  But the blade lift *adds* to the axial tensile stress at the L.E.
and T.E. for a positively cambered airfoil.  Because the lifting forces
come and go with blanking issues and because near the root  torque bending
(pulsed) has the same effect, fatigue issues exist as I stated.  The
helicopter blades you cite either use a flapping hinge or a special bending
beam to eliminate bending in the blade.  As in all structural designs, if
you make it stiff it must be proportionally strong...sometimes making it
not stiff requires less strength.  I'm sure a G.A. prop could be designed
with flapping hinges but I doubt that you would like the coning angle.

Jeff Spitzer

Cut slots in the flap section with a hack saw and fill them with RTV.
That will transfer max stress up to the main part thicker of the blade
which can be reinforced with another couple of layers of carbon cloth.

Carbon cloth composite is inherently crack stop. Unlike metal blades.

Paul Lamar
 
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