Abstract: A method and apparatus for determining the airspeed of a rotary wing aircraft having a sustaining rotor with a plurality of radially extending rotor blades for rotation about a substantially vertical axis comprises the steps of measuring an airflow sideslip angle established during rotation of each rotor blade by the vector of a radial flow component due to the relative wind vector and the rotational velocity perpendicular to a blade feathering axis, producing a signal representative of the sideslip angle, comparing the signal in a processor containing information on a known relationship between the sideslip angle and airspeed, providing an output signal representative of the airspeed and wind direction to a display which may display both the airspeed and wind direction.

Abstract: This invention provides a static vent unit e.g. for use on the side of an aircraft and which in operation is subjected to airflow from any direction within a wide airflow incidence range comprises a generally flat plate having an outer surface for fitment generally to flush to an outer surface of the aircraft, a vent port through the plate for connection during operation to a static vent line in the aircraft, and a bulge on the plate outer surface surrounding at least part of a circumference of the vent port and having in cross section a convex curved upper surface extending radially inwardly from an outer edge on the plate to an inner edger on the plate adjacent the circumference of the vent port and adapted during operation to promote attachment of an airflow from within at least part of the airflow incidence range to its surface and direct the airflow into the vicinity of the vent port to provide a compensating increase in ambient pressure at the vent port.

Abstract: A static vent unit particularly for use in the side of a helicopter fuselage includes a support plate having a vent port and a strake extending generally horizontally below the vent port with an upper surface facing the vent port and generally perpendicular to the support plate surface, and airflow deflection means located below the strake to deflect airflow away from the strake when the unit is operating in an airflow from below the strake.

Abstract: A circulation control aerofoil having an internal chamber for receiving during operation air for exhaust through a circulation control air exhaust slot defined by spaced-apart slot lips is provided with a plurality of actuators of electrically deformable material adapted during operation to cause local bending of the aerofoil structure to which they are attached to selectively adjust the width of the air exhaust slot. The actuators may be piezo-electric actuators.

Abstract: A rotary blade includes a fixed boundary layer control device extending spanwise on a lower surface adjacent the trailing edge to improve the lift/thrust characteristics of the blade especially at positive incidence angles. It was discovered that expected detrimental effects at zero/negative incidence did not materialize and the reasons are identified. Such blades are particularly useful for helicopter sustaining and anti-torque rotors.

Abstract: A bearing assembly for a rotating shaft includes a plurality of frangible bolts located concentrically of an axis of rotation for attaching a bearing housing radial flange portion to a support structure, each having a frangible portion located between axially spaced-apart radial flanges whereby the bearing housing flange portion is spaced-apart axially from the support structure.

Abstract: An electrically conductive ribbon is wound into contact with the screen of each of a plurality of individual conductors in a multicore cable and is passed through a continuous boundary aperture in the tubular body portion of a backshell which is rotated to wind the ribbon about the cable until the ribbon tightly fills the space between the ribbon wound portion of the cable and the internal surface of the body portion to anchor the cable to the tubular body portion. The free end of the ribbon is then severed substantially flush with the external surface of the tubular body portion.

Abstract: A force-generating actuator connected at or across points of a structure capable of relative motion at an exciting frequency is operated to input a predetermined load into the structure and the response of the structure is measured for analysis. In one form of the invention the actuator is one of a plurality of actuators of an active vibration control system which is isolated and operated independently in a shake test mode. Advantageously, especially in a helicopter application, the remaining actuators can continue to be operated to reduce background vibration.

Abstract: This invention monitors data produced by a vibration reducing system relating to the vibration of a structure, compares the data against a predetermined value and provides a warning if the predetermined value is exceeded to provide an integrated vibration reducing and structural health monitoring system.

Abstract: A strut assembly includes an axially elastically deformable tube assembly comprising a plurality of nested concentric tubes arranged in series and an axially extensible actuator attached between the ends of the tube assembly so that reciprocal extensions of the actuator cause elastic longitudinal displacements of the strut assembly. The tubes are rigidly fixed to one another.

Abstract: A strut assembly includes an axially elastically extensible tube having attachment means at each end and an axially extensible actuator attached within the tube and between its ends so that reciprocal axial extensions of the actuator cause elastic longitudinal displacements of the strut assembly. Such a strut assembly is particularly useful for transmitting operational loads between parts of a structure and for inputting periodic loads into one of the parts as part of an active vibration control system.

Abstract: In a helicopter rotor blade having a root end for attachment to a rotor head, a central portion of constant chord dimension and a tip portion having a chord dimension greater than that of the central portion, an outboard region of the central portion has a negative basic pitching moment coefficient, an inboard region of the central portion has a basic pitching moment coefficient more positive than that of the outboard region and the tip portion has a positive basic pitching moment coefficient.

Abstract: An active vibration control system for reducing vibration of a structure includes a first control loop comprising sensors for sensing forces in a primary vibratory load path and providing signals to a control unit incorporating time domain control logic for providing first actuator demand signals, a second control loop comprising sensors for sensing secondary vibration forces and providing signals to a control unit incorporating frequency domain control logic for providing second actuator demand signals, and a summing device for summing the first and second actuator demand signals and providing resultant signals for operating a plurality of actuators for inputting controlled vibration response forces into the structure to reduce vibration.

Abstract: A compound helicopter includes a main sustaining rotor for hover and low speed flight, a propeller for providing propulsion in high speed flight and an engine. Engine output power is controlled so as to ensure efficient use of available power in both modes of operation. A preferred form of control includes a variable area exhaust nozzle from a gas turbine engine which has the advantage also in providing an augmenting jet thrust during high speed flight.

Abstract: Flow separation behind the notch region of a swept tip of a helicopter rotor blade is reduced by features of the geometry and aerodynamic characteristics of the notch region itself. In particular it has been found beneficial for a forwardly swept leading edge portion to extend at an angle between 30 degrees and 55 degrees from a reference line parallel to a blade pitch change axis and the leading edge of the aerofoil in the notch region incorporates blade droop.

Abstract: A rotor for rotation about an axis includes a driving member rotationally fixed to a drive shaft and having a plurality of equi-spaced drive pins extending radially of the axis of rotation and in a plane of rotation perpendicular to the axis, and located in an elastomeric bearing assembly attached to a gimbal housing connected to a spherical elastomeric thrust bearing having a geometral center located at an intersection of the axis of rotation and the plane of rotation whereby in operation the rotor can be tilted in any direction about the center.

Abstract: A flexible beam type helicopter rotor includes restraining means outboard of a snubber means and connected between the flexible beam and a torque tube to increase the stiffness of the rotor in the lead/lag plane as applied pitch is increased.

Abstract: A transmission shaft having a shear neck portion adapted to attract failure of the shaft in the event of an overload includes an annular retainer to retain debris resulting from a failure of the shaft.

Abstract: A method for detecting a crack in the main load bearing spar of a hilicopter rotor blade consists of attaching a capillary tube along an external surface of the spar and connecting the interior of the tube to a supply of colored liquid contained in a reservoir at a root end of the blade, whereby a crack in the spar causes a corresponding crack in the capillary tube resulting in visible leakage of the colored liquid.

Abstract: The swept extreme tip edge of a helicopter rotor blade incorporates blade droop to reduce aerodynamic pitching moments caused by spanwise flow encountered in the fore and aft sectors of a rotor rotational disc during forward flight of a helicopter on which the blade is fitted.