Optimized composite flexbeam for helicopter tail rotors

An optimized composite flexbeam (10) for a helicopter tail rotor assembly (2), the optimized composite flexbeam (10) having a plurality of adjoining regions including a hub attachment region (HAR), a blade attachment region (BAR), and an outboard transition region (OTR) adjoining the blade attachment region (BAR), the optimized composite flexbeam (10) further comprising:

• an inboard transition region (ITR) adjoining the hub attachment region (HAR) and having a combination of unidirectional and off-axis composite materials (U, O) defining a total material composition and a percent %O of off-axis composite material (O) relative thereto, said inboard transition region (ITR) further including:
• a first transition subregion (ITR-1) defined by a thickness transition;
• and
• a second transition subregion (ITR-2) defined by a width and thickness transition and defining a width conic, said second transition subregion (ITR-2) defining a critical width transition subregion (CR.sub.wt);
• said width conic defining conic slope angles .theta..sub.WC ;
• said critical width transition subregion (CR.sub.wt) corresponding to conic slope angles .theta..sub.WC between 0 degrees to about 10 degrees;
• said percent %O of off-axis composite material (O) defined by an optimized curve (100), said optimized curve (100) in said critical transition subregion subregion (CR.sub.wt) being defined by the expression:
• ##EQU2## wherein C is a constant between about 14.4 to about 21.6, and k is a constant equal to 1.0 degrees.sup.-1 ;
• a pitch region (PR) adjoining the inboard and outboard transition regions (ITR, OTR) and defining a flapwise bending neutral axis (X.sub.A), said pitch region (PR) including:
• a core laminate (50) of unidirectional fiberglass material (U.sub.F), said core laminate (50) defining lateral surfaces (50.sub.L) and mating surfaces (50.sub.M), said lateral surfaces (50.sub.L) defining a pitch region width dimension (W.sub.PR) therebetween;
• face laminates (52) of unidirectional graphite material (U.sub.G), said face laminates (52) being bonded to said mating surfaces (50.sub.M) of said core laminate (50), said face laminates (52), furthermore, defining face surfaces (52.sub.F), said face surfaces (52.sub.F) defining a pitch region thickness (T.sub.PR) dimension therebetween;
• said pitch region width and thickness dimensions (W.sub.PR,T.sub.PR) defining an aspect ratio, said aspect ratio being greater than or equal to 10;
• said core and face laminates (50, 52), furthermore, defining chamfered edge configuration (CH.sub.E) having chamfered edge surfaces (54.sub.S), each said chamfered edge surface (54.sub.S) defining a critical acute angle .alpha. with respect to said flapwise bending neutral axis (X.sub.A), and, furthermore, defining a lateral edge (54.sub.E) disposed a vertical distance X from said flapwise bending neutral axis (X.sub.A);
• said critical acute angle .alpha. being between about 14 degrees to about 22 degrees;
• said vertical distance X being about 12.5% to about 37.5% of said pitch region thickness dimension (T.sub.PR).