Patent Application
20060067822
The present invention relates to a blade fold system for a helicopter, and more particularly to a rotor blade positioning system which positions each rotor blade prior to blade folding while minimizing applied strain to elastomeric bearings within the rotor head.
While the flight capabilities of helicopters makes them effective vehicles for a wide variety of missions, operation of helicopters in certain circumstances may be limited by the overall structural envelopes thereof. The large radial dimensions of helicopter rotor assemblies results in helicopters having relatively large structural envelopes, which may limit their utility in some circumstances.
Helicopters, particularly military helicopters utilized for maritime flight operations, may be required to conduct operations from ships for extended periods of time. Shipboard space is generally at a premium, and the large structural envelopes of helicopters means that stowage during periods of non-use requires a relatively significant allocation of such limited space. Furthermore, strategic and tactical considerations in the military utilization of helicopters has led to a requirement for helicopters having main rotor assemblies that may be readily reconfigured for rapid deployment, routine transport, and/or stowage through reduction in structural envelopes.
Several options are available to reduce the structural envelopes of helicopters to facilitate rapid deployment, routine transport, stowage, and/or to reduce the vulnerability thereof to environmental conditions. One option is to design the main rotor assemblies thereof so that the main rotor blades may be folded about the main rotor hub assembly. Main rotor blade folding operations are typically implemented automatically.
One helicopter with an automatic blade folding system is the CH-53E. The CH-53E is currently the world's largest shipboard compatible helicopter. A significant consideration in the design of the CH-53E is shipboard compatibility. The CH-53E in a stored configuration effectively defines the maximum structural envelope which will fit on the elevators and in the hangar deck of United States Marine Corps Amphibious Assault Ships.
Prior to folding blades on any helicopter the blades must be located and locked in a pre-set blade fold position such that a blade hinge axis is oriented to allow folding of each blade to its proper folded position. On aircraft such as CH-53E, blade positioning is accomplished using a series of hydraulic actuators and stops. The current CH-53E rotor head utilizes a hydraulic actuated piston incorporated into the damper as a pitch lock. Accumulator pressure drives the damper to hold the blade in the pre-set blade fold position in which the yoke is driven to full lag or lead position. The swashplate is then located in a pre-set position such that each blade is at the correct pitch angle for the blade pitch locks to engage. Since pitch motion occurs between the sleeve and the spindle, a hydraulic actuated pin on the sleeve engages a lug on the spindle to lock the spindle and sleeve together to prevent pitch motion. These components function independently as the current CH-53E rotor head employs separate conventional bearings for pitch, flap, and lead/lag blade motions.
Elastomeric rotor heads with elastomeric bearings provide numerous advantages over conventional rotor head assemblies which utilize separate bearings for pitch, flap, and lead/lag blade motions. Elastomeric rotor heads provide such significant advantages, that current aircraft such as the CH-53E may be modernized to include an elastomeric rotor head.
Current blade folding systems are not transferable to an elastomeric rotor head as the elastomeric bearings and visco-elastic damper are essentially springs which are always biased toward a predetermined position. Deflection away from the predetermined position strains the elastomeric bearings and visco-elastic damper. Significant deflection over prolonged timer periods, such as during a blade fold position, may eventually damage the elastomeric rotor head system.
Accordingly, it is desirable to provide a blade folding system for an elastomeric rotor head system which positions each rotor blade prior to blade folding while minimizing applied strain to elastomeric bearings within the rotor head.
The rotor blade folding system according to the present invention generally includes a blade lock assembly, a rotary actuator and a blade fold controller to selectively position each rotor blade assembly in a particular predetermined folded position. The blade lock assembly positions each yoke in a predetermined lead/lag and pitch position and a predetermined rotor blade fold angle.
In operation, an electric motor drives a planetary gear train to sequentially extend a lag lock pin into a tapered lag lock bushing formed in the yoke to locate the yoke in a predetermined lead/lag fold position. The lag lock pin continues to extend along a lag lock pin axis until fully seated within a lag lock bushing. Once the lag lock pin is fully seated, one planetary gear train gear is locked to drive a pitch lock pin along a pitch lock axis into a pitch lock bushing mounted within the yoke to locate the yoke in a predetermined pitch fold position. Once each yoke is locked in the blade fold position, the blade fold controller drives the rotary actuator to rotate each rotor blade to a predetermined blade fold angle.
To unfold the blades, the blade fold controller reverses the rotary actuator to return the rotor blade to a flight position and reverses the electric motor to retract the pins such that the yoke returns to a flight configuration defined by the elastomeric bearings.
The present invention therefore provides a blade folding system for an elastomeric rotor head system which positions each rotor blade prior to blade folding while minimizing applied stress to elastomeric bearings within the rotor head.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:
Referring to
A rotor blade folding system 44 generally includes the pitch lock assembly 42, the rotary actuator 32, a retractable blade retaining pin 33 and a blade fold controller 47 (illustrated schematically) to selectively position each rotor blade assembly 24 in a particular folded position to minimize the aircraft structural envelope (
Referring to
Referring to
In operation, the electric motor 46 drives the output shaft 62 which is meshing engagement with the planet gears 60. The planet carrier 56 remains rotationally stationary due to a detent pin 61 engaged therewith. The detent pin 61 is preferably a solenoid-actuated pin controlled by the blade lock controller 47. It should be understood that other anti-rotation devices may also be used to provide the selective output with which to drive the pins 50, 52. The planet gears 60 rotates the ring gear 58 which drives a lag pin jack screw 66 to extend the lag lock pin 50 along a lag lock pin axis L. The lag lock pin 50 extends into a tapered lag lock bushing 68 formed in the yoke 36. The lag lock pin 50 continues to extend along the lag lock pin axis L until fully seated within the lag lock bushing 68 (
Referring to
Each rotor blade assembly 24 may be positioned in pitch by articulating the swashplate prior to seating the pitch lock pin 52 along the pitch lock axis P into a pitch lock bushing 72. That is, the pitch lock pin 52 does not specifically pitch the rotor blade assembly 24 during seating but lock the yoke 36 in the blade fold position which the yoke has previously been articulated to by the swashplate. When the swashplate is positioned properly, all the blades 28 are at the correct pitch angle for the blade pitch lock assembly 42 to engage. Separately, the blade fold pivot axis B (
Once both pins 50, 52 are fully seated, the blade fold controller 47 stops the electric motor 46 through communication with a sensor such as a limit switch or the like such that each yoke 36 is positioned for blade 28 fold. Once each yoke 36 is positioned for blade 28 fold, the controller 47 drives the rotary actuator 32 to rotate each rotor blade 28 to a predetermined blade fold angle about the blade fold pivot axis B (
To unfold the blades, the blade fold controller 47 reverses the rotary actuator 32 to unfold the rotor blades 28 (∝ to zero) then retracts the pins 50, 52, such that the yoke 36 returns to a flight configuration defined by the elastomeric bearing 38 neutral position.
It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting.
Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention.
The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.
