Method for improving roll steering of an aircraft and aircraft using same

A roll steering method subdivides the direction of an aircraft control surface into two elements and, during a roll control operation using ailerons, steers an upper element of the control surface in the roll direction and a lower element in the opposite direction.

FIELD OF THE INVENTION

The present invention relates to a method for improving the roll steering of an aircraft, as well as to an aircraft implementing this method.

BACKGROUND OF THE RELATED ART

It is known that the wings of an aircraft are provided with controllable aerodynamic surfaces—principally ailerons and subsidiarily spoiler flaps—making it possible to steer said aircraft roll-wise about its longitudinal axis. It is also known that, in particular for aircraft of large dimensions, said wings are flexible and deformable so that, in certain flight situations (high speed, high Mach number, high dynamic pressure), the deflection of said aerodynamic roll control surfaces results in the twisting of said wings, thereby causing the latter to take up a local angle of incidence opposing the aerodynamic roll effects of said aerodynamic surfaces and greatly reducing their effectiveness. The roll response of the aircraft does not therefore correspond to the roll instructed by said aerodynamic surfaces.

SUMMARY OF THE INVENTION

The object of the present invention is to remedy this drawback.

Accordingly, according to the invention, the method for improving the roll steering of an aircraft comprising:a fuselage,two wings, symmetric with respect to said fuselage, provided with controllable aerodynamic surfaces able to produce a roll movement for the aircraft, anda vertical fin projecting with respect to the rear part of said fuselage and provided with a rudder extending along the rear edge of said fin and able to turn, with respect to the latter, about an axis of rotation,
is noteworthy in that:said rudder is divided, transversely to said axis of rotation, into at least two rudder elements disposed successively along said axis of rotation and being independently controllable in rotation about the latter; andwhen said wing aerodynamic surfaces are deflected so as to communicate a roll movement to said aircraft in a determined direction:at least one of said rudder elements disposed on the side of the end of said vertical fin opposite to said fuselage is deflected in said determined direction of roll, andsimultaneously, at least one of said rudder elements disposed on the side of the end of said vertical fin neighboring said fuselage is deflected in the opposite direction.

Thus, said rudder elements produce antagonistic lifting forces transverse to said aircraft, which exert on the latter roll moments, likewise antagonistic, with respect to the longitudinal axis of said aircraft. However, on account of the fact that the rudder elements which exert a roll moment in the same direction as the movement due to said aerodynamic surfaces of the wings are further from said axis than said rudder elements which exert a roll moment in the opposite direction, the resultant moment exerted roll-wise by said rudder elements therefore enhances the roll movement produced by said aerodynamic surfaces of the wings.

Preferably, the number, the surface area, the disposition, etc., of said rudder elements is chosen in such a way that the antagonistic yaw effects, produced by said rudder elements deflected in opposite directions, balance one another at least approximately, the resultant yaw effect being practically zero.

In an advantageous mode of implementation of the present invention, said rudder comprises just two rudder elements, namely a lower rudder element and an upper rudder element, and, during a roll movement produced by said aerodynamic surfaces of the wings, said upper rudder element is deflected in the direction of the roll movement and said lower rudder element is deflected in the opposite direction simultaneously. In this case, the surface areas of said lower and upper rudder elements are at least approximately equal and said lower and upper rudder elements are deflected symmetrically about said axis of rotation of the rudder. Thus, no yaw effect results therefrom.

Regardless of the number of said rudder elements, it is preferable for the extra roll control afforded by said rudder elements to take place only when the aircraft is in a flight situation in which said aerodynamic surfaces of the wings exhibit a loss of roll effectiveness. Generally, in such a situation, the speed, the Mach number or the dynamic pressure of the aircraft are very high. So, in order to determine such a situation, it is possible to measure at least one of the three quantities hereinabove in the guise of parameter and to compare the measurement of said parameter with a threshold, for example determined experimentally, beyond which said situation occurs. Thus, as long as the measurement of the parameter is below said threshold, the roll effectiveness of the aerodynamic surfaces of the wings is satisfactory and it is not necessary to involve the rudder elements. On the other hand, when the measurement of the parameter is above said threshold, the roll effectiveness of the aerodynamic surfaces of the wings is no longer satisfactory and the method according to the invention is implemented.

The present invention relates moreover to an aircraft implementing the above-described method of the invention. Such an aircraft, comprising:a fuselage;two wings, symmetric with respect to said fuselage, provided with controllable aerodynamic surfaces able to produce a roll movement for the aircraft;means of roll steering of said aircraft able to control said controllable aerodynamic surfaces;a vertical fin projecting with respect to the rear part of said fuselage and provided with a rudder extending along the rear edge of said fin and able to turn, with respect to the latter, about an axis of rotation; andmeans of yaw steering of said aircraft able to control said rudder,
is noteworthy in that:said rudder consists of at least two rudder elements disposed successively along said axis of rotation;said means of yaw steering are able to produce first individual deflection orders for each of said rudder elements;said means of roll steering are able to produce, in addition to deflection orders for said aerodynamic surfaces, second individual deflection orders for said rudder elements, said second deflection orders being such that the resultant yaw action is at least approximately zero; andmeans of addition are provided for adding, for each of said rudder elements, the second individual deflection order to the corresponding first individual deflection order, when the measurement of a parameter representative of a particular flight situation exceeds a preset threshold.

In a preferred embodiment, said rudder consists of a lower rudder element and of an upper rudder element.

DETAILED DESCRIPTION OF THE INVENTION

The wide-bodied civil aircraft1, shown inFIG. 1, comprises, in a known manner, a fuselage2exhibiting a longitudinal axis L-L and provided with two wings3G and3D symmetric with respect to said fuselage2as well as a vertical fin4, projecting upwards with respect to the rear part2R of the fuselage2. Moreover, likewise in a known manner, on the one hand, said wings3G and3D are each provided with at least one aileron5G or5D, said ailerons5G and5D being symmetric with respect to the fuselage2and being able to produce a roll movement for the aircraft and, on the other hand, the vertical fin4is provided with a rudder6extending along the rear edge7of said fin4and being able to turn, with respect to the latter, about an axis of rotation z-z.

Moreover, said wings3D and3G are respectively provided with spoiler flaps8D and8G, pair-wise symmetric with respect to the fuselage2, said spoiler flaps8D and8G being usable, in a known manner, for the roll control of the aircraft1, to enhance the action of the ailerons5D and5G.

According to a first particular feature of the exemplary implementation of the present invention, represented inFIG. 1, said rudder6is divided, transversely to said axis of rotation z-z, into two rudder elements6S and6I, of aerodynamically equivalent service area, disposed one following the other, so that one,6I, is near the rear part2R of the fuselage2and occupies a lower position, while the other,6S, is near the upper end4S of the vertical fin4, opposite from said rear part2R, and therefore occupies an upper position.

The upper6S and lower6I rudder elements may be controlled jointly in rotation so that the rudder6behaves as if it were monolithic. The rudder elements6S and6I may also be controlled individually and, as the case may be, in opposite directions.

When, as is illustrated inFIG. 2, a roll movement is controlled in a standard fashion with the assistance of said ailerons5G and5D (the action of which is optionally enhanced by the spoiler flaps8G,8D, not represented inFIG. 2), it may happen that in certain flight situations where the speed is high, the deflection of the ailerons5G,5D—and possibly of the spoiler flaps8G,8D—results in the twisting of the wings3G,3D with respect to their point of anchoring in the fuselage2. This results in adoptions of local angle of incidence of said wings, symbolized by the arrows f inFIG. 2, opposing the aerodynamic effects of the ailerons5G,5D and, possibly, of the spoiler flaps8G,8D and greatly reducing the roll effectiveness of said ailerons5G,5D and spoiler flaps8G,8D. The aircraft1therefore no longer has a roll response tailored to the request of the pilot.

To remedy this drawback, according to the invention, at the same time as the ailerons5G,5D (and possibly the spoiler flaps8G,8D) are deflected to obtain a roll movement of the aircraft1about the longitudinal axis L-L, the rudder elements6S and6I are deflected in a symmetric manner with respect to the fin4of the aircraft (seeFIGS. 3 and 4), the upper rudder element6S being deflected in the direction of the roll instructed, while the lower rudder element6I is deflected in the opposite direction.

Under these conditions, the upper and lower rudder elements produce respectively lateral lifting forces FS and FI, of equal moduli, but of opposite directions. In their turn, these forces FS and FI respectively produce, and with respect to the longitudinal axis L-L of the aircraft1, a moment in the direction of the roll movement instructed and a moment antagonistic to said roll movement. Since the lever arm of the force FS is larger than that of the force FI, the moment in the direction of roll is greater than the moment in the antagonistic direction and the resultant moment of these two moments therefore acts in the direction of the roll movement instructed.

Thus, the rudder elements6S and6I assist the ailerons5G,5D (and possibly the spoiler flaps8G,8D) in the achieving of said instructed roll movement.

Moreover, it will be noted that, since the rudder elements6S and6I exhibit almost identical surface areas and are deflected symmetrically with respect to the fin4, their deflections do not cause any yaw effect.

The device for the implementation of the method described above, represented diagrammatically inFIG. 5, comprises:a stick system11, able to produce, among other things, roll control orders for the ailerons5G,5D and, possibly, for the spoiler flaps8G,8D;a rudder bar system12, able to produce control orders for the rudder elements6S and6I;a computer13receiving said control orders originating from the stick system11and from the rudder bar system12and delivering, to its outputs and as a function of the electric flight control laws that it possesses in memory, respectively, a moment order instructed yaw-wise and a moment order instructed roll-wise;a computer14receiving from said computer13the yaw-wise instructed moment order and formulating respective control orders for the rudder elements6S and6I, which orders are addressed to the actuators of the latter, respectively by lines15and16;an adder17interposed on the control line15for the upper rudder element6S;an adder18interposed on the control line16for the lower rudder element6I;a computer19receiving from said computer13the roll-wise instructed moment order and formulating respective roll-wise control orders:for the ailerons5G,5D and possibly for the spoiler flaps8G,8D, said corresponding orders being addressed to the actuators of the latter by a line20,for the upper rudder element6S, said corresponding orders being available on the working contact of a switch21, whose resting contact r is connected to a zero potential and whose common contact c is connected to the adder17by a line22, andfor the lower rudder element6I, said corresponding orders being available on the working contact of a switch23, whose resting contact r is connected to a zero potential and whose common contact c is connected to the adder18by a line24; anda comparator25receiving, from a terminal26, the measurement of a parameter P, such as the speed of the aircraft, the Mach number, the dynamic pressure, etc., and comparing this measurement with a preset threshold Po representative of a flight situation beyond which the roll control by the ailerons5G,5D assisted possibly by the spoiler flaps8G,8D, is no longer satisfactory, said comparator25being able to control said switches21and23by an action line27.

Thus, when the aircraft1is not in a flight situation for which the roll action of the ailerons5G,5D (and possibly that of the spoiler flaps8G,8D) is lessened, the rudder elements6S and6I are controlled by the rudder bar system12, through the computers13and14and the lines15and16.

On the other hand, when such a situation occurs, it is detected by the measurement of the parameter P which becomes greater than the threshold Po and the comparator25toggles the switches21and23, from their resting positions r to their working positions t, so that the roll orders formulated by the computer19respectively for the upper rudder element6S and for the lower rudder element6I are transmitted to the adders17and18, respectively by the lines22and24. In this case, the orders addressed to the rudder elements6S and6I comprise, on the one hand, yaw orders instructed by the rudder bar system12and, on the other hand, roll-assist orders originating from the computer14.