Aeronautics and astronautics – Aircraft sustentation – Sustaining airfoils
Reexamination Certificate
2002-03-27
2003-05-20
Swiatek, Robert P. (Department: 3643)
Aeronautics and astronautics
Aircraft sustentation
Sustaining airfoils
C244S075100, C244S212000
Reexamination Certificate
active
06565045
ABSTRACT:
The present invention relates to an aircraft aerodynamic surface such as an airplane wing, a vertical stabilizer, an empennage, a fairing, an engine nacelle pylon, etc., equipped with at least one trailing edge deflector.
Document U.S. Pat. No. 4,867,396 already discloses an aerodynamic surface, more specifically an airplane wing, the lift and drag of which are respectively increased and reduced by virtue of a deflector, known as a microflap, arranged at the trailing edge of said aerodynamic surface, inclined with respect to the pressure face thereof. This deflector is fixed and so is its inclination with respect to said pressure face, it being possible for the angle of inclination between said deflector and the chord of the aerodynamic surface to be chosen from several values, for example 20°. In addition, the chord of said deflector is short by comparison with that of the aerodynamic surface, the ratio of said chords being between 0.5% and 1.5%.
Furthermore, it is known that the wing structures of airplanes may be subjected, to a phenomenon of fluttering, generally known as “buffeting”. This phenomenon is the result of unsteady or turbulent separation of the airflow originating on the reduced-pressure face of the wing structure and, through a coupling effect, giving rise to vibration of the structure. This buffeting may occur at any speed of flight of an airplane and is accentuated at transsonic speeds by the fluctuations of the shock wave brought about by the turbulent separation.
In order to combat buffeting, thought has already turned to the use of the customary trailing edge moving flaps designed for controlling airplanes as described, for example, in Patents FR2,531,676 and U.S. Pat. No. 4,705,902. What happens is that such trailing edge flaps have a reduced-pressure face and a pressure face which respectively extend the reduced-pressure face and the pressure face of the aerodynamic surfaces to the rear of which they are articulated. Thus, when they are turned, they locally modify the curvature of both the reduced-pressure face and the pressure face of said aerodynamic surface.
However, it has been found that when the buffeting was combated using trailing edge flaps, there was a risk of the flow separated from the reduced-pressure face of the aerodynamic surface reattaching to the reduced-pressure face of the turned flap, making the airplane difficult to control. In addition, combating buffeting using trailing edge flaps, the usual and specific function of which is to play a part in controlling the aircraft, is not without difficulties.
Hence, it is an object of the present invention to eliminate, or at the very least to reduce, the buffeting of the aerodynamic surfaces that occurs essentially in transsonic flight while at the same time making it possible to improve the aerodynamic characteristics of these surfaces. To do this, the invention relates to a system with deflector likenable to the one described in document U.S. Pat. No. 4,867,396, briefly analyzed hereinabove, and making it possible to improve said characteristics and to combat buffeting by the static or dynamic turning of said deflector.
To this end, according to the invention, the aircraft aerodynamic surface comprising:
a reduced-pressure face and a pressure face which are connected together, at the front, by a leading edge and, at the rear, by a trailing edge base, the extreme rear section of which forms the trailing edge of said aerodynamic surface; and
at least one deflector intended to improve the aerodynamic performance of said aerodynamic surface, the chord of said deflector being equal to a few hundredths of the chord of said aerodynamic surface and said deflector being arranged to the rear thereof, is noteworthy in that:
said deflector can move and is housed in a recess made in the thickness of the pressure face of said trailing edge base and opening into said trailing edge so that the rear edge of said base consists of a reduced-thickness part of said trailing edge;
said moving deflector is articulated, via its front part, about an axis at least essentially parallel to said trailing edge so as to be able to pivot about said axis of articulation under the action of actuating means; and
said moving deflector can adopt:
either a retracted extreme position, for which said deflector is fully housed in said pressure face recess ensuring the continuity of said pressure face, the rear edge of said deflector then collaborating with said rear edge of said base to form said trailing edge;
or any one of a number of deployed positions, for which said deflector is turned with its rear part projecting from said pressure face recess, thus giving the trailing edge of said aerodynamic surface a parameterizable variable thickness.
Thus, when a short-chord deflector such as this is in the retracted position, no modification is made either to the reduced-pressure face or to the pressure face of the aerodynamic surface, whereas in the turned position, said pressure face alone is modified. When said deflector is in such a turned position, the geometry of the reduced-pressure face of the aerodynamic surface remains unchanged, the aerodynamic performance thereof being improved through the modification to the thickness and the divergence of the trailing edge, something which, incidentally, delays the onset of buffeting.
The deflector or deflectors according to the present invention may be operated mechanically, electrically, pneumatically or hydraulically.
According to a first method of operation, the deflector or deflectors may be placed in a fixed position with an angular turning of adjustable determined value. This then is static turning, similar to that of document U.S. Pat. No. 4,867,396, which creates a difference in pressure at the trailing edge between the pressure face and the reduced-pressure face, which increases the rear load on said aerodynamic surface by modifying the thickness and divergence of the trailing edge. Hence:
for a fixed Mach number and fixed incidence, the turning of the deflector causes the mean position of the aerodynamic shock to move back toward the trailing edge and causes an increase in the rear load, which generates an appreciable increase in the coefficient of lift;
for a given Mach number and a given coefficient of lift (cruising flight), the aerodynamic performance of the aerodynamic surface is enhanced, with a reduction in drag.
As an alternative, the deflector or deflectors may be given a movement about a mean position of turning. This then is dynamic operation which can cause the deflector or deflectors to fluctuate at a frequency of between a few Hz and a few kHz.
The buffeting can thus be controlled, with or without a shock wave, actively, the deflector turn law being deduced directly at every moment from the level of separation or from the position of the shock.
The site of separation and the position of the shock under transsonic conditions are preferably identified using unsteady-state pressure measurements. They may also be obtained by other means, such as friction probes, parietal hot films, etc. Processing these data makes it possible, at any instant, to locate the levels of intensity of the separation or the position of the shock.
As soon as the unsteady-state sensors arranged along the aerodynamic surface detect the onset of instability, the closed-loop active dynamic control comes into effect. Buffeting is thus dealt with as soon as aerodynamic instabilities occur, before it has been able to excite the natural modes of the structure.
In addition to the unsteady-state pressure measurements, the ensuing vibration may be taken into consideration by strain gauges and/or accelerometers and may be introduced into the control law for the deflectors, so as to improve the overall performance.
In order to be active, the deflector of the invention does not need to have a long chord. Significant results have been obtained with deflectors the chord of which is, for example, at most equal to three hundredths of the chord of said aerodynamic surface.
Furthermore, when said deflector is
Caruana Daniel
Correge Michel
Gobert Jean-Louis
Mignosi André
Onera
Stevens Davis Miller & Mosher LLP
Swiatek Robert P.
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