Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Tined or irregular periphery
Utility Patent
1998-04-29
2001-01-02
Verdier, Christopher (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Tined or irregular periphery
C416S22300B, C416S237000, C416S23100A, C416S235000, C415S119000
Utility Patent
active
06168383
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotor blade for a rotary-wing aircraft, designed to suppress BVI (Blade Vortex Interaction) noise which is generated by an interaction of a succeeding rotor blade with tip vortices generated by the tip of a preceding rotor blade.
2. Description of the Related Art
When a rotary-wing aircraft, such as a helicopter, lands, a succeeding rotor blade of a rotary wing interacts with tip vortices generated by the tip of a preceding rotor blade to generate a BVI noise. It is known that the intensity of the BVI noise generated by the rotary-wing aircraft is dependent on the plane shape of a tip part of the rotor blade that generates the tip vortices.
Referring to
FIG. 16
, a rotary wing
20
included in a rotary-wing aircraft comprises a plurality of rotor blades
21
each having a substantially rectangular shape, and rotates about a rotational axis. When the rotary wing
20
of the rotary-wing aircraft rotates in the direction of the arrow D while the rotary-wing aircraft is advancing in the direction of the arrow F, tip trailing edge vortices
22
are generated by the preceding rotor blade
21
a
. When the rotary-wing aircraft descends for landing, the tip trailing edge vortices
22
generated by the preceding rotor blade
21
a
descend with a delay. Therefore, the succeeding rotor blade
21
b
interacts with the tip trailing edge vortices
22
to generate BVI noise. Since tip trailing edge vortices
22
generated by the rotor blades do not start descending at the instant the vortices are generated, the rotor blades are affected by the downwash of the vortices caused by themselves or the downwash of the vortices caused by the preceding rotor blade
21
a
when the rotary-wing aircraft hovers. The dynamic pressure of air acting on the rotor blade reaches a maximum value at the tip of the rotor blade, and the hovering performance of the rotary-wing aircraft is dependent on the plane shape of a tip part of the rotor blade.
A supersonic flow region is created around the leading edge of the rotor blade in a forward turning motion due to the sum of the tangential velocity of the rotor blade and a component of the velocity of the forward motion of the rotary-wing aircraft in a direction tangent to the path of the rotor blade while the rotary-wing aircraft is in high-speed forward flight. Consequently, power loss at the tip of the rotor blade increases to a maximum and a large aerodynamic pitching moment is produced at the tip of the rotor blade. Therefore, the performance of the rotary-wing aircraft and the aerodynamic balance of the rotor blade are dependent on the plane shape of the tip part of the rotor blade. Moreover, impulsive HSI (High Speed Impulsive) noise is generated due to the compression of air particularly by a tip part of the rotor blade in a forward turning motion while the rotary-wing aircraft is in high-speed forward flight. Thus, the intensity of the HSI noise generated by the rotary-wing aircraft is dependent on the plane shape of the tip part of the rotor blades. Many studies of the plane shape of the tip part of rotor blades have been made to design a rotor blade capable of exhibiting high performance, of reducing noise and of securing appropriate aerodynamic balance.
A rotor blade for a rotary wing disclosed in JP 56-167599A has a tip part having a sweepback angle, a taper and an anhedral angle selectively determined to improve the performance of the rotor blade during hovering. In this prior art rotor blade, the sweepback angle reduces air velocity toward the tip to reduce the load on the tip and the intensity of tip trailing edge vortices which are generated during hovering, and the taper reduces chord length toward the tip of the rotor blade. As a result, the chord length decreases from the root toward the tip of the rotor blade so that the chord length of the tip is about half that of the root to reduce the area of a tip part of the rotor blade for the further reduction of the load on the tip and the intensity of tip trailing edge vortices during hovering. Thus, the anhedral angle warps down a tip part of a length corresponding to 4% of the radius of the rotary wing to shift the tip trailing edge vortices generated by the preceding rotor blade to a position apart from the succeeding rotor blade.
A rotor blade disclosed in JP 3-66198B has a tip part in which the respective sweepback angles of the leading edge and the trailing edge are determined so that the leading edge and the trailing edge of the tip part extend outward at different angles, respectively, to reduce the intensity of impulse waves due to the compression of air and to reduce the HSI noise during the forward flight of the rotary-wing aircraft.
A rotor blade disclosed in JP 64-16498A has a tip part inclined at a dihedral angle, and a part adjacent to the tip part inclined at an anhedral angle to improve the hovering performance of the rotary-wing aircraft and to suppress the torsional distortion of the rotor blade during high-speed forward flight.
A rotor blade disclosed in JP 64-22693A, similarly to that disclosed in JP 3-66198B, has a tip part in which the respective sweepback angles of the leading edge and the trailing edge are determined so that the leading edge and the trailing edge of the tip part extend outward at different angles, respectively, to improve the flight performance of the rotary-wing aircraft.
A rotor blade disclosed in JP 2-60898A has a swept-back tip part capable of reducing or removing aerodynamic pitching moment. This rotor blade has a root part attached to a rotor head, a main part extending from the root part and having a blade profile of a predetermined chord length, a swept-back tip part determining blade width and extending from the outer end of the main part, and a droop for changing the distribution of bound vortices of air currents in the direction of the width of the blade over the edge of the tip part to reduce the aerodynamic pitching moment of the rotor blade.
A rotary wing employed in a rotary-wing aircraft disclosed in JP 4-176795A reduces resistance and improves flight efficiency by the effect of sweepback angle, suppresses separation by the double delta effect of two swept-back parts, delays the stalling of a rotor blade in backward turning motion for the further stabilization of high-speed flight.
A rotor blade disclosed in JP 4-262994A has a mean chord length greater than 50% of the chord length of its main part, and is provided with a tip blade of a span length greater than 50% of the chord length of the main part to generate two tip vortices of substantially the same intensity to suppress acoustic shocks and BVI noise.
FIG. 17
shows an end part
30
of this rotor blade in a plan view. The end part
30
of this rotor blade has a tip part
32
having a leading edge
31
and a trailing edge
33
determining the chord length of the tip part
32
perpendicular to a reference axis, and a tip blade
34
extending from the tip part
32
. As shown in
FIG. 18
, vortices generated by this rotor blade is divided into vortices
34
a
shed from the tip blade
34
and vortices
35
a
shed from the tip
35
of the tip part
32
and, consequently, BVI noise is suppressed. Thus tip blade
34
of the rotor blade disclosed in JP 4-262994A has a span length greater than 50% of the chord length of the main part of the rotor blade to generate the two vortices of substantially the same intensity so that the two vortices remain separated from each other for the longest possible distance as indicated in FIG.
19
. Therefore, the tip blade has an elongate shape and hence contrivance is necessary to strengthen the joint of the root of the tip blade
34
and the tip of the main part
32
particularly.
SUMMARY OF THE INVENTION
The present invention has been made in view of that respects and it is therefore an object of the present invention to provide a rotor blade for a rotary-wing aircraft, based on a new principle and incorporating new contrivance to reduce noise resulting from the interaction
Barton Rhonda
Fuji Jukogyo Kabushiki Kaisha
Smith , Gambrell & Russell, LLP
Verdier Christopher
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