Abstract: A bearingless rotor system includes a flexbeam assembly having a first beam and a second beam arranged in a back-to-back orientation with a pitch shaft channeled therebetween. The beams morph into a rotor blade spar at an outboard rotor blade station. The outboard section of the flexbeam assembly receives the full pitch input from the pitch shaft while the most inboard section of the flexbeam assembly is essentially fixed in pitch by a blade attachment to a rotor hub assembly. The flexbeam assembly twist versus span is essentially linear from the most inboard to the most outboard rotor blade stations. The outboard rotor blade station, being attached to the outboard section of the flexbeam assembly, thereby also defines the pitch input equivalent from the outboard rotor blade station to the rotor blade tip.

Abstract: A bearingless rotor system includes a flexbeam assembly having a first beam and a second beam arranged in a back-to-back orientation with a pitch shaft channeled therebetween. The beams morph into a rotor blade spar at an outboard rotor blade station. The outboard section of the flexbeam assembly receives the full pitch input from the pitch shaft while the most inboard section of the flexbeam assembly is essentially fixed in pitch by a blade attachment to a rotor hub assembly. The flexbeam assembly twist versus span is essentially linear from the most inboard to the most outboard rotor blade stations. The outboard rotor blade station, being attached to the outboard section of the flexbeam assembly, thereby also defines the pitch input equivalent from the outboard rotor blade station to the rotor blade tip.

Abstract: A main rotor blade exhibiting a unique planform shape in which the blade chord increases from the root end of the blade inboard region to the outer main region of the blade, where the blade chord achieves a maximum chord at a spanwise location within the main region, then decreases toward a distal tip end. The leading edge preferably is generally straight while the trailing edge is contoured to define the chord. Another characteristic feature of the rotor blade design is the location of the blade-feathering axis in which the feathering axis is located at a mid chord position over some inboard length of the rotor blade then transitions to a quarter chord location. Another characteristic feature is an airfoil distribution along the blade span that transitions from a blunt trailing edge to a sharp trailing edge airfoil suited for mid-range Mach number operation. The tip region preferably utilizes a transonic flow airfoil.

Abstract: A main rotor blade exhibiting a unique planform shape in which the blade chord increases from the root end of the blade inboard region to the outer main region of the blade, where the blade chord achieves a maximum chord at a spanwise location within the main region, then decreases toward a distal tip end. The leading edge preferably is generally straight while the trailing edge is contoured to define the chord. Another characteristic feature of the rotor blade design is the location of the blade-feathering axis in which the feathering axis is located at a mid chord position over some inboard length of the rotor blade then transitions to a quarter chord location. Another characteristic feature is an airfoil distribution along the blade span that transitions from a blunt trailing edge to a sharp trailing edge airfoil suited for mid-range Mach number operation. The tip region preferably utilizes a transonic flow airfoil.

Abstract: A mounting assembly (50) for mechanically interconnecting a helicopter rotor blade (12) to a rotor hub assembly (10) and for mechanically interconnecting the rotor blade (12) to a damper assembly (52) and a pitch control input assembly (54). The rotor hub assembly (10) includes a hub plate (16) having a hub plate aperture (22) for mounting a rotor assembly yoke (24). The rotor assembly yoke (24) includes upper and lower radially extending arms (28a, 28b) which are disposed above and below the hub plate (16) and which include a set of mounting apertures (29) formed through the proximal end thereof. The mounting assembly (50) includes upper and lower clevis arms (60a, 60b) formed at the root end (56) of the rotor blade (12), a horn/damper fitting (64) interposed between the upper and lower clevis arms (60a, 60b), and upper and lower spacer plates (90a, 90b) disposed between the clevis arms (60a, 60b) and the radially extending arms (28a, 28b) of the rotor assembly yoke (24).

Abstract: A flexbeam for a soft inplane bearingless main rotor assembly has six spanwise regions: a hub attachment region; a first tapered region; a second tapered region; a pitch region; a tapered outboard transition region; and a main rotor blade, torque tube attachment region. One described embodiment of the flexbeam is fabricated from continuous unidirectional fiberglass plies having a 0.degree. fiber orientation, unidirectional fiberglass plies of varying lengths having a 0.degree. fiber orientation, and graphite cross plies having .+-.45.degree. fiber orientations. The pitch region is formed solely by the continuous fiberglass plies which define a rectangular cross section therefor. The second tapered region is formed solely by the continuous fiberglass plies and the fiberglass plies of varying lengths. The ends of the fiberglass plies terminate in a distributed arrangement in the second tapered region to define the taper thereof.

Abstract: A rotor blade subassembly for a rotor assembly having ducted, coaxial counter-rotating rotors includes a flexbeam, an integrated torque tube/spar member, and an aerodynamic fairing or rotor blade. The flexbeam is a laminated composite structure that reacts centrifugal loads and a majority of the bending loads of the rotor assembly. The flexbeam has a spanwise predetermined linear twist so that the pretwisted flexbeam is unstrained during specified forward flight conditions. The integrated torque tube/spar member is formed as a continuous, filament wound tubular composite structure having high torsional and bending stiffness that provides a continuous torsional load path and facilitates load coupling between the rotor blade and the pretwisted flexbeam. The spar segment of the functions as the primary structural member of the rotor blade subassembly and, is operative to react all bending, torsional, shear, and centrifugal dynamic loads of the rotor assembly.

Abstract: A snubber assembly for a rotor assembly having ducted, coaxial counter-rotating rotors that is design optimized to facilitate utilization of a self-aligning bearing and for installation inboard of the corresponding flexbeam-to-rotor hub attachment joint, thereby enhancing accessibility and reducing maintenance costs. The rotor hub of the rotor assembly is design optimized for securing the snubber assembly in combination therewith and includes a plurality of arms, each arm forming an outboard clevis for attaching the rotor assembly flexbeam to the rotor hub. Inboard of the clevis, each rotor hub arm includes an outboard internal bulkhead having a bolt hole therethrough and an inboard internal bulkhead having a bolt hole therethrough. The inboard and outboard internal bulkheads in combination define a bearing cavity and an internal cavity for securing the snubber assembly in combination with the rotor hub.

Abstract: An integrated spline/cone seat subassembly for a rotor assembly that is design optimized to minimize the radial dimensions of the rotor shafts, the rotor shaft bearings, the transmission housing, and the swashplate subassemblies thereof. The integrated subassembly includes a rotor hub having a shaft aperture with a plurality of hub splines extend radially inwardly therefrom. The lower portion of each hub spline has an outwardly tapered portion that makes a predetermined angle with respect to the hub centerline. The integrated subassembly further includes a rotor shaft having a primary shaft portion of a first diameter, an end shaft portion having an intermediate second diameter less than the first diameter, and a conic transition portion that makes a predetermined angle with respect to the rotor shaft axis. The end shaft portion has a plurality of shaft splines extending radially outwardly therefrom that defines a third diameter that is equal to the first diameter.

Abstract: A circulation control aircraft rotor blade having a spanwise Coanda surface 16 and a plurality of spanwise extending flexible composite material panels 18 cooperating with the surface to define slots for the discharge of compressed air from within the blade with each panel having first flexure means 60 associated with screw adjustments 36 for establishing a slot opening preload and second flexure means 62 associated with screw adjustments 38 for establishing a slot maximum opening.

Abstract: Inadvertent slot opening in a circulation controlled rotor due to plenum valve leakage is averted by venting duct pressure below a control minimum. A vent valve is disclosed.

Abstract: A plenum for a circulation control rotor aircraft which surrounds the rotor drive shaft (18) and is so constructed that the top (32), outer (38) and bottom (36) walls through compressed air is admitted are fixed to aircraft structure and the inner wall (34) through which air passes to rotor blades (14) rotates with the drive shaft and rotor blades.

Abstract: X-wing aircraft employ a rigid rotor-wing utilizing symmetrical circulation irfoils. The rotor is driven mechanically, and lift is achieved by modulation of air circulation about the base airfoils. This is accomplished by blowing compressed air through trailing edge openings in the rotor blades, and controlling the amount of air being ejected through those openings. By cyclically modulating the amount of ejected airflow, cyclic lift control is obtained. Likewise, by collectively controlling the ejected airflow collective lift control is obtained. One reason for the lack of popularity of circulation control rotor systems is concern over a loss or air pressure resulting from a damaged rotor blade. The damage to a rotor blade, such as ballistic damage, can cause the entire plenum pressure to be vented through that damaged blade. The result is a loss of pneumatic control, not only of that blade, but control of all rotor blades.

Abstract: A helicopter rotor system using composite flexbeams for connecting a rotor blade to the rotor hub, each flexbeam being of C-section and having a web section made up of 0.degree. and .+-.45.degree. plies and top and bottom flanges made up of low angle plies in the direction of their length with their ends being connected by an arc of plies so that the top and bottom flange plies are continuous with an attachment fitting encased at the ends of the flexbeams.

Abstract: In a helicopter rotor, a blade control linkage is externally supported on the rotor hub and connected to the root end of a torque tube to provide torsion inputs to the blade by twisting the flexible spar member, which is enveloped by the torque tube and joined to the torque tube at a predetermined blade radial location. The linkage forms a parallelogram with the torque tube, and short vertical ball joint mounted links incline in two directions to accommodate blade lead/lag and flapping motions without introducing pitch coupling.

Abstract: A torsionally compliant helicopter rotor blade with maximum blade torsional flexibility at the blade tip portion and so shaped at the blade root portion that the locus of shear centers and the locus of centers of lift are substantially coincident, and so shaped at the tip portion so that the locus of shear centers is selectively forward of the locus of centers of lift to establish an aerodynamic restoring moment in response to blade tip torsional excursions, thereby improving blade torsional stability.

Abstract: A helicopter rotor having opposed blades interconnected by a common flexible spar which passes across the rotor axis is connected to the drive shaft by clamped hub plates. A spanwise extending torque tube having a pitch horn at its inner end forms a rigid connection with the spar and blade at its outboard end. A centering bearing assembly is positioned at the inner end of the torque tube and spar to react control loads, centralize the torque tube about the spar, and provide pitch, flap, and lead-lag decoupling.