Aeronautics and astronautics – Aircraft sustentation – Sustaining airfoils
Reexamination Certificate
2000-09-11
2002-04-16
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Aircraft sustentation
Sustaining airfoils
C244S219000, C244S075100
Reexamination Certificate
active
06371415
ABSTRACT:
PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 200 04 499.0, filed on Mar. 14, 2000, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to aerodynamic components in general and particularly to helicopter rotor blades having a leading edge flap that is driven by a piezoelectric actuator.
BACKGROUND INFORMATION
In rigid wing aircraft, three spatially separated systems are conventionally used to control the lift, the propulsion, and the steering. Contrary thereto, in a helicopter the main rotor substantially assumes itself the above-mentioned control functions to assure a controlled flight. As a result, the design and construction of a helicopter rotor blade requires numerous compromises due to the non-stationary events that occur during flight of a helicopter. Thus, it is in the nature of a helicopter blade that its aerodynamics are not optimal in certain sections or areas along the blade if the rotor blade construction is fixed. For example, one aspect that is not optimal is the possible dynamic stall when the rotor blade is rotated in the reverse direction.
When a helicopter travels in the forward direction, the rotor blades are exposed along their leading edge to higher flow-on velocities than are effective on the trailing edge due to the vectorial superposition of the flight velocity and the rotational velocity. In order to assure a symmetrical distribution of the lift, the angle of attack of the profile of the rotor blades is cyclically varied for each full revolution of the blade. The faster the helicopter moves in the forward direction, the more angling must be applied to the blade profile along the trailing edge. However, at a certain point such steep angling leads to dynamic stall along locally limited areas of the rotor blade.
On the one hand, the dynamic stall may cause strong vibrations. On the other hand, the dynamic stall limits the performance of the helicopter. Moreover, the flight comfort is noticeably reduced for the pilot and the passengers by the noise caused by the blades and by the vibrations in the passenger cell. Moreover, such vibrations lead to a premature tiring of people and to fatigue failures in the materials of which the helicopter components are made. As a result, an increased inspection and maintenance effort and expense is unavoidable.
The problem can be alleviated by a continuous adaptation of the aerodynamic profile of the rotor blades to the continuously varying aerodynamic operating conditions, for example by means of a shape variable profile geometry. Such a shape variable profile geometry can significantly improve the performance, safety and comfort of helicopters. Starting from different structural possibilities of dynamic lift aids, it is known that a dynamic variation of the leading edge of the flow profile is aerodynamically very effective. For example, high suction peaks along the leading edge of the blade can be reduced by lifting and lowering of a leading edge flap also referred to as nose flap secured to the leading edge of the blade. Such lifting and lowering of the nose flap delays the dynamic stall or flow separation and reduces the hysteresis loops in the course of the aerodynamic coefficients. Additionally, a discrete nose flap makes it possible to provide the required energy for overcoming the aerodynamic forces and moments required for a continuous variation of the contour by an elastic deformation or to provide a larger motion range for these contour deformations.
U.S. Pat. No. 5,409,183 (Gonzales) discloses a helicopter rotor blade with leading edge servo-flaps for pitch positioning the rotor blade. The rotor blade is equipped with a flap that extends in front of the leading edge of the blade because the flap is mounted on two brackets (42) secured to the fixed rotor blade (28). The flap is tiltable or movable about an axis (40) by a hydraulic actuator (44) through a linkage and bellcrank mechanism (46, 48). Such a system has the drawback that the relatively complicated mechanical linkage mechanism does not provide the required high adjustment speeds in response to the control signals. Additionally, the linkage requires a plurality of pivot joints which makes it prone to a high repair requirement. Moreover, such a linkage displaces with its own weight the center of gravity distribution in the rotor blade, thereby causing unfavorable center of gravity conditions.
An article entitled “Development of High Performing Piezoelectric Actuators For Transport Systems”, published at a “Actuator 98” meeting on Jun. 17 to 19, 1998 in Bremen, Federal Republic of Germany, describes a helicopter rotor blade having a journalled servo-flap functioning as a trailing edge flap which is adjusted by piezoelectric actuators. These piezo-actuators are distributed in the rotor blade in the longitudinal direction thereof, that is in the span-width direction of the blade. Arranging the piezo-actuators in the span-width direction for driving a leading edge flap would take up a substantial proportion of the available span-width or blade length. Additionally, such a longitudinal distribution of the piezoelectric actuators along the leading edge of the rotor blade would adversely influence the center of gravity distribution in the rotor blade. A pair of piezo-actuators disposed or displaced in the span-width direction furthermore would not be able to apply to the leading edge flap the forces required due to the high air loads, without twisting the leading edge flap.
U.S. Pat. No. 5,626,312 (Head) discloses a piezoelectric actuator or transducer (1) in the form of a torque rod (15, FIG.
3
). The torque rod (15) is constructed of a plurality of piezoelectric rod elements (8) that are connected at their ends to end plates (4) and (6) to form a squirrel cage that is installed in a helicopter blade (31) in the lengthwise direction for operating a leading edge flap or a trailing edge flap or both, please see
FIGS. 6A and 6B
of Head. Due to the lengthwise orientation of the transducer (1) in the rotor blade a substantial installation space is required. Moreover, a substantial number of rod elements (8) forming the squirrel cage contributes to the weight of the blade.
OBJECTS OF THE INVENTION
In view of the above it is the aim of the invention to achieve the following objects singly or in combination:
to construct an aerodynamic component such as the helicopter rotor blade or a wing or the like having a flow profile with a leading edge flap, in such a way that the flap can be adjusted with a high adjustment speed, with high accuracy, with a rapid response characteristic and without play;
to construct a piezo-actuator for such high speed adjustment which requires an optimally reduced maintenance and repair;
to construct the piezo-actuator in such a way that its piezo-elements can be arranged in the chord direction of the aerodynamic component rather than in the span-width or length direction, to thereby avoid changing the center of gravity characteristics of modern rotor blades;
to provide the above-mentioned high speed adjustments even for extreme flight maneuvers and conditions;
to avoid a plurality of pivoted rod linkage and bellcrank elements as well as torque generating piezoelectric elements that require a substantial installation length;
to construct a piezo-actuator for adjusting a flap on an airfoil with an optimal performance while the actuator has a minimal weight; and
to construct the actuator in such a way that the flap adjustment is accomplished by a push-pull action.
SUMMARY OF THE INVENTION
A component having an aerodynamic flow profile such as a helicopter rotor blade having at least one leading edge flap or nose flap along its leading edge is characterized according to the invention in that each nose flap is driven by a piezo-actuator which comprises two piezo-elements forming a pair. The piezo-elements are arranged one behind the other in the chord direction of the rotor blade. The two piezo-actuator element
Hermle Frank
Jaenker Peter
Lorkowski Thomas
Barefoot Galen L.
Daimler-Chrysler AG
Fasse W. F.
Fasse W. G.
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