Technical Field

The present application relates in general to the field of rotor blades for rotorcraft; but more particularly, a method and apparatus for the folding of rotor blades during flight.

Description of the Prior Art

Tiltrotor aircraft are hybrids between traditional helicopters and traditional propeller driven aircraft. Typical tiltrotor aircraft have nacelles with rotor systems that are capable of rotating relative to the aircraft fuselage. Tiltrotor aircraft are capable of converting from a helicopter mode, in which the aircraft can take-off, hover, and land like a helicopter; to an airplane mode, in which the aircraft can fly forward like a fixed- wing airplane. During airplane mode of the tiltrotor, forward speed and range is limited by certain fundamental limitations of the rotor systems.

Brief Description of the Drawings The novel features believed characteristic of the method and apparatus of the present application are set forth in the appended claims. However, the method and apparatus itself, as well as, a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, wherein: Figure 1 is a perspective view a rotorcraft according to the preferred embodiment of the present application in a helicopter mode;

Figure 2 is a perspective view a rotorcraft according to the preferred embodiment of the present application in an airplane mode; Figure 3 is a perspective view a rotorcraft according to the preferred embodiment of the present application in a folded mode;

Figure 4 is a perspective view of the rotor assembly from the rotorcraft according to the preferred embodiment, while in a folded mode; Figure 5 is a perspective view of the rotor assembly from the rotorcraft according to the preferred embodiment, while in a helicopter mode;

Figure 6 is a perspective view of the rotor assembly from the rotorcraft according to the preferred embodiment, while in an airplane mode; and

Figures 7A-7H are perspective views progressively detailing the spiral fold path according to the preferred embodiment of the present application.

While the method and apparatus of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the method and apparatus to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present application as defined by the appended claims.

Description of the Preferred Embodiment

Illustrative embodiments of the method and apparatus of the present application are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present application, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as "above," "below," "upper," "lower," or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction.

The present application represents a unique method and apparatus for the folding of rotor blades during an aircraft flight so as to allow the aircraft to fly further and faster. When the rotor blades are folded into a stowed position, the tiltrotor relies upon jet thrust of the engine for propulsion during forward flight.

Referring to Figure 1 , a tiltrotor aircraft 101 is depicted in a helicopter mode with nacelles 105a and 105b in an approximately vertical position. A nacelle 105a is configured to rotate a rotor system assembly 1 15a between a helicopter mode position and an airplane mode position. Similarly, a nacelle 105b is configured to rotate a rotor system assembly 1 15b between a helicopter mode position and an airplane mode position. While in helicopter mode, rotor blades 109a and 109b are selectively operably with nacelles 105a and 105b, respectively, in order to provide vertical lift to aircraft 101. Rotor assemblies 115a and 115b are configured to selectively control the pitch of rotor blades 109b and 109a, collectively and cyclically, in or order to provide yaw, pitch, and roll control to aircraft 101 in helicopter mode. An engine 103 provides power to the aircraft 101. A driveshaft 119 provides a means for power transfer between engine 103 and rotor assemblies 115a and 1 15b. A clutch 1 13 is configured to selectively disengaging and engaging rotational power between engine 103 and driveshaft 119. A rotor break 1 1 1 is configured to selectively slow and stop rotation of drive shaft 119 after clutch has disengaged power from engine 103 to driveshaft 119. A wing 107 is connected to a fuselage 1 17 so as to provide lift during forward flight. It should be appreciated that though engine 103 is shown in fuselage 1 7 other engine configurations may be used. For example, engine 03 can be located in other areas of fuselage 117, as well as on or near wing 107. It should also be appreciated that even though aircraft 101 is depicted with three rotor blades per rotor assembly, greater or fewer rotor blades can be employed. For example, it is fully contemplated that the method and apparatus of the present application may use four rotor blades 109a and 109b in rotor assemblies 115a and 115b, respectively. A computer 135 is schematically shown in fuselage 1 17, but it should be appreciated the computer 135 may take a number of forms and exist in a variety of locations within aircraft 101. Computer 135 is configured to control systems within aircraft 101 , including the operation of folding rotor blades 109a and 109b in a spiral fold path.

Referring to Figure 2, tiltrotor aircraft 101 is depicted in an airplane mode with nacelles 105a and 105b in an approximately horizontal position. While in airplane mode, rotor blades 109a and 109b are selectively operably with nacelles 105a and 105b, respectively, in order to provide forward thrust to aircraft 101. Rotor assemblies 1 15a and 1 5b are configured to selectively provide control inputs on aircraft 101 while in airplane mode. For example, rotor assemblies 1 15a and 115b can provide yaw control by selectively adjusting the pitch of rotor blades 109a differently from rotor blades 109b. It should be appreciated that other aerodynamic control features on wing 107 provide different and redundant control features on aircraft 101.

Referring to Figure 3, tiltrotor aircraft 101 is depicted in a folded mode with rotor blades 109a and 109b folded in a stowed position against nacelles 105a and 105b, respectively. Aircraft 101 in a folded mode is able to fly more efficiently than when in an airplane mode. For example, in a folded mode, aircraft 101 is able to flying faster, farther, and smother than when aircraft 101 relies upon rotor blades 109a and 109b for propulsive force. When aircraft 101 is in a folded mode, propulsive force is provided from thrust of engine 103. It should be appreciated that rotor assemblies 1 15a and 1 15b are essentially symmetric versions of each other. As such, features discussed herein regarding rotor assembly 1 15b also symmetrically exist on rotor assembly 115a. It should be appreciated that rotor assemblies 115a and 1 15b function similarly in regards to the translating of aircraft 101 from helicopter mode, airplane mode, and folded mode, as discussed herein.

Referring to Figure 4, rotor assembly 115b is shown in further detail, while aircraft 101 is in folded mode. A swashplate 123 is configured to selectively adjust the pitch of rotor blades 109b. Swashplate 123 can tilt in a cyclic mode so as to differentially change the pitch of one or more rotor blades 109b. Similarly, swashplate 123 can be selectively actuated in a collective mode so as to uniformly change the pitch of rotor blades 109b. A pitch link 125 is operably connected to a grip pin 127 of each rotor blade 109b. Each grip pin 127 is configured to be selectively rotated by swashplate 123, via pitch link 125, about a grip pin axis 129. A blade fold actuator 121 is located in each grip pin 127. Each blade fold actuator is preferably an electric actuator, but may also be other actuators, such as hydraulic, piezoelectric, motor, or any mechanism suitable to provide rotational force. Additionally, even though a blade fold actuator 121 is depicted as being located within each grip pin 127, it should be appreciated that each blade fold actuator 121 can be located exterior to each grip pin 127. Each blade fold actuator 121 is operably associated with each rotor blade 109b so as to selectively rotate each rotor blade along a blade fold axis 131. An inflatable airbag 139 may be positioned on the skin of nacelle 105b so as to be selectively inflated upon folding of rotor blades 109b. Rotor assembly 105b is configured to rotate around rotor mast axis 137. Referring now to Figure 5, rotor assembly 115b is shown in further detail, while aircraft 101 is in helicopter mode. Each pitch link 125 is operably associated with each rotor blade 109b. Swashplate 123 is configured to receive collective and cyclic inputs so as to selectively control the pitch of each rotor blade 109b. Nacelle 105b is configured to be actuated between a helicopter mode and an airplane mode via a nacelle actuator 133.

Referring now to Figure 6, rotor assembly 115b is shown in further detail, while aircraft 101 is in airplane mode. Each pitch link 125 is operably associated with each rotor blade 109b. Swashplate 123 is configured to receive collective and cyclic inputs so as to selectively control the pitch of each rotor blade 109b.

Referring now to Figures 7A through 7H, the system for changing the position of rotor blades 109b from an airplane mode to a folded mode is described. Rotational power from engine 103 is decoupled from driveshaft 119 via clutch 1 13 (shown in Figures 1 -3). Rotor blades 109b are feathered parallel to the direction of airflow during flight such that aerodynamic drag is reduced during the folding process. Rotor blades 109b are feathered by actuation of swashplate 123 in a manner so as to collectively adjust the pitch of each rotor blade 109b into feathered position. Rotational velocity of rotor blades 109b is decreased, aided by rotor brake 1 1 1 , until rotor blades 109b reach a known index position. The preferred known index position, as shown in Figures 7A through 7H, is a rotor blade position wherein rotor blades do not foul with any wing structure. Additionally, the known index position coincides with predetermined locations for other features to be used in the rotor blade folding process, as discussed herein. Once rotor blades 109b are in the known index position, the rotor blades are locked in place so rotor blades 109b do not continue to rotate about rotor mast axis 137. Still referring to Figures 7A through 7H, actuation of blade fold actuators 121 and swashplate 123 occurs in a predefined sequence, so as to facilitate the folding of rotor blades 109b in a specified spiral path. Specified spiral path is the folding sequence wherein rotor blades 109b are maintained edgewise into the airstream as much as possible throughout the folding process, i.e. feathered. By keeping rotor blades 109b primarily edgewise into the airstream, aerodynamic loading and drag on rotor blades 109b is minimized. Typically, rotor blades are designed to exhibit maximum strength while experience centrifugal loading. As such, rotor blades are typically unable to withstand as much bending forces while in a static position. Therefore, folding rotor blades 109b in the spiral load path allows rotor blades 09b to fold while minimizing aerodynamic loading.

Still referring to Figures 7A through 7H, the folding of rotor blades 109b in a spiral fold path involves simultaneous actuation of blade fold actuators 121 so that rotor blades fold about blade fold axis 131 , while rotor blades 109b are feathered edgewise into the free airstream. During the folding of rotor blades 109b about blade fold axis 131 , rotor blades 109b are also actuated about grip pin axis 129 by swashplate 123 so that rotor blades 109b are positioned approximately near nacelle 105b. Preferably, rotating of rotor blades 109b about blade fold axis 131 , by actuation of blade fold actuator 121 , occurs at a linear rate. In contrast, most of the actuation of swashplate 123, so as to rotate rotor blades 109b about grip pin axis 129, occurs towards the end of the spiral path. As a result, rotor blades 109b remain feathered edgewise into the free airstream for as long as possible during the process. Rotor blades 09b contact hard stops located within rotor assembly 1 15b when rotor blades 109b are fully folded. With rotor blades 109b in the fully folded position, airbags 139 may be deployed from the skin of nacelle 105b, under each rotor blade 09b. Airbags 139 act as a buffer in order to minimize contact between rotor blades 109b and nacelle 105b, as well as tailor aerodynamic airflow around rotor blades 109b while in the folded position. While rotor blades 109b are in the folded position, blade fold actuators 121 are locked in position. While rotor blades 109b are in the folded position, aircraft 101 can fly further and faster by relying upon thrust propulsion from engine 103, instead of propulsion from rotor blades 109b. Aircraft 101 can convert from folded mode back to airplane mode by reversing the process described herein for converting from airplane mode to folded mode. The process for converting from airplane mode to folded mode takes approximately 6-8 seconds. However, it should be appreciated that the process can be configured to take to less or more time, depending upon the application.

The method and apparatus of the present application provides significant advantages, including: (1 ) providing a method for folding the rotor blades so as to allow an aircraft to rely upon jet thrust propulsion during a folded mode; (2) reducing the drag upon the rotor blades during the folding process by feathering the rotor blades substantially edgewise into the airstream while folding; and (3) employing inflatable air bags while rotor blades are in the folded position so as to tailor airflow around the folded rotor blades. It is apparent that a method and apparatus with significant advantages has been described and illustrated. Although the method and apparatus of the present application is shown in a limited number of forms, it is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof.