Fluid reaction surfaces (i.e. – impellers) – With means moving working fluid deflecting working member...
Utility Patent
1999-03-01
2001-01-02
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
With means moving working fluid deflecting working member...
C244S215000, C244S217000, C244S09000B
Utility Patent
active
06168379
ABSTRACT:
PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 198 08 196.0, filed on Feb. 27, 1998, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to a helicopter rotor blade particularly having a movable flap along at least a trailing edge of an air-foil profiled portion of the blade.
BACKGROUND INFORMATION
It is generally known to equip helicopter rotor blades with movable flaps or control surfaces, respectively along the trailing edge or the trailing portion of the airfoil profile section. Such flaps or control surfaces serve to control the helicopter. Namely, these flaps can be tilted up or down relative to the main airfoil body of the rotor blade, to achieve an aerodynamic control effect in addition to or separately from the overall pitch control of each blade. In one known arrangement of such flaps on rotor blades, the flaps are pivotally connected by mechanical bearings to the main body of the rotor blade, and are mechanically actuated by a cam plate or swash plate. In this context, the cam plate or swash plate can actuate the flaps of the several rotor blades of a helicopter rotor collectively or also cyclically at a frequency of about 7 Hz, for example.
A more recent conventional rotor blade includes flaps connected to the trailing portion of the airfoil profile by a pivot joint or the like, and these flaps are electrically actuated rather than mechanically actuated by cam or swash plate as described above. Such flaps serve to increase the rotor power and lift generating capacity while simultaneously reducing the extent of vibrations. Due to the electrical actuation of the flaps at a relatively high frequency, e.g. about 35 Hz or higher, the flaps influence the dynamic response and behavior of the rotor blades. Thereby the respective rotor blade is deformed due to the arising aerodynamic forces, in such a manner that the vibration characteristic of the rotor blade is improved.
It is a serious disadvantage of the conventional arrangements, that the bearings suffer very rapid wear due to the alternating movement of the flaps at a relatively high frequency. As a result, the inspection and maintenance intervals are rather short, and the bearings must be replaced frequently. Moreover, the bearings are subjected to high loads due to the various forces arising on the rotor blades due to the effect of the flaps. Such high forces can also result in sudden failures of the bearings, in addition to the rapid wear mentioned above.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to provide a helicopter rotor blade including a movable control flap, with a durable and reliable bearing connection of the flap to the main airfoil body of the blade, so as to reduce the occurrence of wear and to avoid or minimize the damage of the bearing connection arising from the high loads. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present description.
The above objects have been achieved in a helicopter rotor blade according to the invention, including a main airfoil body, a movable control surface or flap, a flexible junction element that movably and flexibly connects the flap to the main airfoil body, and an actuator connected to the flap in order to move the flap to selected positions or deflection angles relative to the main airfoil body. The flexible junction element includes a flexible bending portion at which the junction element flexibly bends when an actuating force is applied to the flap, so as to allow the deflection or movement of the flap relative to the main airfoil body.
The inventive arrangement provides a durable and wear-resistant flexibly movable connection of the flap relative to the main airfoil body of the rotor blade. Moreover, this flexible connection or junction of the flap to the main airfoil body provided by the flexible junction element is also capable of withstanding the high loads that arise, and allows the necessary flap movements at high frequencies without suffering substantial wear. For this reason, the inspection and maintenance intervals can be considerably extended in comparison to the prior art.
The flexible junction element is preferably made of a fiber-reinforced synthetic or plastic composite material, in which the fibers may be glass fibers, for example. The fibers in the composite material achieve an especially high strength with a low weight, i.e. a high strength to weight ratio. The use of glass fibers in this context makes it possible to achieve a particularly high elasticity or insensitivity to strain as well as a high durability and high fatigue strength of the flexible junction element. In order to achieve the flexible bending at a desired location, the junction element preferably includes a flexible bending portion having a reduced thickness as compared to the other portions of the junction element adjoining the flexible bending portion. With this arrangement, the flexible bending will preferentially occur about a virtual axis in the thinner flexible portion.
The fibers of the fiber reinforced composite material of the junction element are preferably oriented to run in the direction of the junction between the main body of the rotor blade and the flap. Moreover, the mutual spacing between the fibers is advantageously reduced in the flexible portion as compared to the rest of the junction element. In other words, the fibers are preferably continuous through the junction element and especially through the flexible bending portion thereof, while comprising a higher fiber density and a reduced proportion of the synthetic matrix material in the flexible bending portion as compared to the remainder of the junction element.
The main airfoil body of the rotor blade is preferably constructed with top and bottom skins or walls over a skeleton of spars and ribbing or over a cellular or foam core or the like or even enclosing a hollow core therein. With such a construction, a flexible junction element preferably connects the top skin of the main airfoil body with the upper part of the flap, and/or a flexible junction element connects the bottom skin of the main airfoil body with a lower part of the flap. In this manner, a particularly good aerodynamic surface contour of the overall rotor blade is achieved.
To further improve the configuration in this regard, the upper part and the lower part of the flap are preferably pressed together in sliding contact with each other in a trailing edge region of the flap. Thereby the upper part and lower part of the flap slidingly move relative to each other along an interposed sliding contact surface when the flap is deflected. The sliding contact surface preferably comprises a layer of polytetrafluoroethylene and/or fluorinated ethylene propylene, for example which is commercially available under the name “Teflon”.
With such an arrangement, it is possible to securely and directly connect the upper part of the flap to the top skin of the main airfoil body, and simultaneously securely connect the lower part of the flap to the bottom skin of the main airfoil body, by means of respective flexible junction elements. When the flap is deflected, this arrangement avoids the formation of a gap between the flap and the main airfoil body, so that a smooth, closed aerodynamic transition is formed by the respective flexible junction elements. The occurrence of wearing abrasion along the sliding contact surface is also avoided.
Advantageously in this arrangement, the upper part and the lower part of the flap are pre-stressed to press against each other along the sliding contact surface. Thereby, it is necessary to actuate only one of the parts of the flap to move the entire flap in each respective direction, because the actuated part of the flap will push against and correspondingly move the other part of the flap.
It is preferred that the flexible junction element and the respective part
Eurocopter Deutschland GmbH
Fasse W. F.
Fasse W. G.
Look Edward K.
McDowell Liam
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