GB2096551A

GB2096551A - A method of optimizing the cruising conditions of aircraft with supercritical wings and an arrangement for carrying out the method

Info

Publication number: GB2096551A
Application number: GB8209016A
Authority: GB
Original assignee: Vereinigte Flugtechnische Werke GmbH; Vereinigte Flugtechnische Werke Fokker GmbH
Current assignee: Vereinigte Flugtechnische Werke GmbH; Vereinigte Flugtechnische Werke Fokker GmbH
Priority date: 1981-04-08
Filing date: 1982-03-26
Publication date: 1982-10-20
Also published as: DE3114143A1; DE3114143C2; FR2503661A1; NL191460B; NL8105237A; FR2503661B1; GB2096551B; NL191460C

Abstract

A method serves to optimize the cruising conditions of aircraft with supercritical wings and consists of detecting current data with regard to altitude, payload and airspeed during cruising flight and of varying the curvature of the wing in a defined manner as a function of these parameters. The curvature can be varied differently in the direction of the wing span and the curvature of the leading and/or trailing edges may be controlled. The flap and spoiler system (2,4,) provided for controlling the altitude of the aircraft is used to carry out the method and additional auxiliary flaps (5) can be provided in order to balance the profile. The flaps are divided into a plurality of segments along the wing, (Figure 7, not shown) as are leading edge flaps (7, 8). <IMAGE>

Description

SPECIFICATION A method of optimizing the cruising conditions of aircraft with supersonic wings and an arrangement for carrying out the method The invention relates to a method of optimizing the cruising conditions of aircraft with supersonic wings, more particularly passenger and cargo aircraft. In addition the invention relates to an arrangement for carrying out this method.

The wings of modern passenger aircraft and civil and millitary cargo aircraft are being equipped in ever increasing numbers with super criticl profiles and these supersonic wings or airfoils are able to improve the economic viability of these aicraft significantly and to expand their capabilities. However the result of this is that in cruising conditions, which differ from the conditions for which the wing was designed, relatively high power losses are apparent. It is not possible to avoid situations which are different from these design conditions, i.e. from the optimum cruising of each aircraft. This is due among other things to different numbers of seats occupied on each flight and differences in distance to be covered and the resultant differences in the values of the current payload, altitude and the speed of the aircraft.

It is an object of the present invention to provide a method in which, in an aircraft of the above type stated at the outset, the optimum cruising range either with respect to as low a fuel consumption as possible or a predetermined duration of flight can be extended still further. At the same time the invention seeks to provide an arrangement which is capable of implementing the method in accordance with the invention at the lowest possible cost but with a high degree of efficiency.

According to a first aspect of the present invention, there is provided a method of optimizing cruising conditions of aircraft with supersonic wings, wherein current parameters relating to altitude, payload and airspeed are detected during flight and the curvature of the wing is adjusted as a function of these parameters.

According to a second aspect of the present invention, there is provided an arrangement for optimizing cruising conditions of an aircraft with supersonic wings, comprising means for varying the curvature of the wing in dependence upon the current altitude, load and airspeed of the aircraft.

Thus the flow of air over the wing is deliberately adjusted in accordance with the respective flying conditions given the desired change in curvature, and therefore lift and drag data are controlled during the flight.

The desired favourable design conditions are maintained by the control measures provided for in the method in accordance with the invention by means of a very much larger Mach No./angle of attack range than would be possible without these control measures.

In addition the shock-induced separation of the boundary layer atthe trailing edge, the buffeting due directly to shock waves and the position of the shock waves can be controlled at high Mach numbers. By changing the curvature on the underside of the wind the lift component on the underside (rear loading) is also controlled.

By varying the curvature of the wing differently in the direction of the wing span, the lift distribution over the wing can be matched optimally in the direction of the wing span to the respective flight conditions. An additional expansion of the economic cruising range in supersonic flow conditions is achieved by superimposing a limited increase in surface area. This increase in wing chord also reduces the relative wing thickness which is decisive for supersonic flow.

Since in further refinement of the method in accordance with the invention it is not only the curvature of the trailing edge of the wing which is changed but also the wing tip curvature, the trimming losses which cannot be avoided and which occur when there is a change in the curvature of the trailing edge are substantially reduced. The desired flow conditions can be mantained over an ever larger Mach number/angle of attack range if controlled in this way.

In a preferred method in accordance with the invention, control of the lift/drag ratio is implemented essentially with the aid of the flap and spoiler system provided for the low speed range of the aircraft, i.e. take off and landing phases and for manoeuvring and there is a consierble economic advantage in this. In order to achieve this, provision is made for the spoilers in a flap and spoiler system to abut the high lift flaps closely, under prestress. As a result the spoilers automatically fo!low the outward movement of the flaps when there is a change in the curvature which is caused by pivoting the high lift flaps and therefore ensure that the contour is balanced. One method of balancing the contour which is particularly favourable in terms of flow, is achieved by the measure envisaged in a further refinement of the invention according to which the spoilers are flexible.

Further measures are suitable for increasing the efficiency of the arrangements according to the invention. For example, on the underside of the wing the contour may be balanced by an additional auxiliary flap covering the clearance which also abuts the high lift flaps closely and under prestress.

Here too the contour balance is optimal if the auxiliary flaps are also flexible. The auxiliary flaps covering the clearance are particularly advantageous if the high lift flaps are formed as Fowler flaps in order to provide simply for increases in the area of the wing. On the one hand the clearance between the trailing edge of the wing and the respective Fowlerflap remains covered even when the flap is extended to a limited extent. On the other hand the auxiliary flaps improve the flow conditions in the clearance and therefore the maximum lift conditions during landing if the Fowler flaps are fully extended. In addition the lift/drag ratio is increased by these auxiliary flaps at takeoff if the flap angle is reduced.

It is possible in simple manner by subdividing the trailing edge flap system into individual segments as proposed to vary the curvature of the wing across the span width. In addition in order to avoid steps, it is particularly advantageous if the individual segments are susceptible to torsion to a limited extent.

Finally, when using the combination proposed in a further refinement of the invention, comprising a leading edge slat flap in each case with an additional flap running towards the underside of the wing tip, there is the possibility of changing the curvature of the wing tip additionally and precisely in simple manner and of achieving an additional lift and a favourable effect on moment distribution as a result of a pressure distribution in the direction of the wing chord which is controlled by the Mach number. At the same time this arrangement makes it possible to improve the lift/drag ratio on take-off additionally and to improve the maximum lift. By dividing up the leading edge flap system into individual segments which are susceptible to torsion, in addition the curvature of the tip can be varied for different regions in the direction of the span width.

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which Figures 1 to 3 show sectional views of the trailing edge region of a supersonic wing in different positions, the wing having a device for carrying out the method in accordance with a first embodiment of the present invention; Figures 4 to 6 show sectional views of the leading edge of a supersonic wing in different positions, the wing having a device in accordance with a second embodiment of the present invention; Figure 7 shows a supersonic wing in plan view, the wing being provided with the arrangement of Figures 1 to 3 and of Figures 4 to 6; Figures 8a and b show schematic views for controlling the wing shown in Figure 7 during cruising flight;; Figure 9 shows a view of the lift/drag ratio as a function of the lift coefficient: and Figure 10 shows a view of the path of the product comprising the Mach number and the lift/drag ratio as a function of the Mach number.

Referring now to the drawings, Figures 1 to 3 show a system of trailing edge flaps of a supersonic wing 1 comprising a so-called Fowler-Tab-flap which serves as a high lift flap. It comprises in detail a pivotable and longiudinally displaceable first flap 2 which is mounted on the wing structure and a tab 3 which is pivotally mounted on the flap 2. Furthermore the system of trailing edge flaps inclues a spoiler 4 pivotally mounted on the wing struture its rear end region abutting the high lift flaps 2 and 3 under preloading or prestress.

Finally the arrangement shown in Figures 1 to 3 has on the underside of the wing an auxiliary flap 5 which is also pivotally mounted on the wing structure with an inwardly directed prestress and which covers the clearance 6 on the underside of the wing, which is formed between the flap 2 and trailing edge of the wing in the flap position shown in Figure 1 in which the high lift flaps 2 and 3 are completely retracted.

Both the spoiler 4 and the auxiliary flap 5 are flexible to limited extent in this embodiment. The outer end regions are so formed that they abut without any break or step on the high lift flaps 2 or 3.

As Figure 2 shows the clearance 6 is still covered by the auxiliary flap 5 when the flap 2 is extended to a limited extent. Figure 3 shows that when flaps 2 and 3 are fully extended the auxiliary flap 5 abuts the inner wall of the clearance 6 and contributes to improving the flow ratios in the clearance. As is apparent from Figures 1 and 2, the spoiler 4 and the auxiliary flap 5 provide an optimum contour balance of the upper and lower side of the wing in each case when the flaps 2 and 3 are pivoted in a positive or negative direction.

In Fifures 4 to 6 the leading edge of the supersonic wing 1 is shown and is provided with an extendable forward or leading wing element 7. The forward wing element 7 is formed as a so-called leading edge slat flap. An additional flap 8 is pivotally mounted on the front end of the flap 7 with one end on the inside of the said flap 7 while the other end of the additional flap 8 abuts the underside of the wing tip with preloading or prestress in the flap position shown in Figure 4. The flap 7 and the additional flap 8, which are flexible to a limited extent in this embodiment are so formed that in the different pivot positions of the flap 7 indicated in Figure 4 they provide complete contour balance in each case both on the upper and lower side of the wing.

The latter applies to a limited extent to the starting position of the flaps 7 and 8 shown in Figure 5 in which the additional flap 8 covers the flap clearance at both back and front. Only in the position shown in Figure 6 is the slat clearance 9 opened. the additional flap 8 contributes to an improvement in the slat profile and to a shaping of the clearance which is more favourable to flow and as a result improves maximum lift. It should also be noted that in Figures 1 to 3 and in Figures 4 to 6 the respective drive elements for the flaps 2,3 or 7 which are already known, are not illustrated for the sake of simplicity.

The supersonic wing 1 is shown in overall plan view in Figure 7 and an engine 10 arranged underneath the wing is also indicated. As is apparent from this illustration the leading edge slat flaps 7 and the high lift flaps 2,3 are sub-divided into individual segments S1 to S4 or F1 to F5. The same is true for the spoilers 4 which are formed from the segments Sp 1 to Sp 8. In addition a curvature flap 11 which covers the clearance is indicated in this fig !re and is arranged in the outer region of the wing 1, in which region spoilers cannot be used and the said flap 11 balances the contour in this region.

In this embodiment, both the segments S1 and S4 and F1 to F5 are susceptible to torsion to a limited extent in each case so that they can swing out to different extents beyond the respective segment span width.

Figures 8a and 8b respectively show a view of the changes in curvature of the trailing edge (Figure 8a) or leading edge (Figues 8b) of the wing, which can be achieved with the arrangement shown in Figure 7, each of these being represented by the path of the respective angle h of outward swing of each respective flap. The solid curve shows the path of the angle in the direction of the span width as long as flap segments which are susceptible to torsion (i.e. which can twist) to a limited extent as described above are used, whereas the broken curves show the same path when conventional flap segments are used.

The use of the arrangement described above in carrying out the method in accordance with the invention is clear from the Figures. In order to optimize the flying conditions of an aircraft moving in the high speed range, i.e. cruising, with supersonic wings equipped in accordance with the above description, current flight data in each case is ascertained with respect to altitude, current pay load and Mach number. According to these current parameters, the lift/drag ratio of the aircraft is affected; the lift drag of the wing being controlled precisely.

This is achieved by varying the wing flow in controlled manner in accordance with the current boundary conditions and in accordance with predetermined criteria with respect to which optimization is to take place. To this end the curvature of the trailing and also leading edge of the wing can be varied on the one hand and on the other hand the area of the wing can be increased. Furthermore, the curvature of the wing can be selected differently in the direction of the wing span. In all cases the changes necessary are computer controlled.

Finally the effect of the above-described method in accordance with the invention with regard to extending the most favourable cruising range is shown in Figures 9 and 10. Figure 9 shows the lift/drag ratio (L/D) - depending on the lift coefficient CL at a constant cruising Mach number on the one hand for an aircraft with uncontrolled fixed-wing geometry (the chain line curve) and on the other hand using the method in accordance with the invention (enveloping curve ofthe hatched region). In the latter case the economic flying range is extended considerably because of the measures carried out in accordance with the invention.

Figure 10 shows the corresponding effect with regard to extending the economic flying range to a higher Mach number region and in this case the product of the Mach number and the lift/drag ratio is plotted against the Mach number. In this case too the chain line curve shows the appropriate path when not using the method in accordance with the invention whereas the solid line curve shows the extension of the limits on the lift and therefore the economic cruising range when the method in accordance with the invention is used.

Finally it should be mentioned that the method described above can of course be used independently of the respective type of trailing edge flap system i.e. it can also be used with single clearance Fowler flaps without tabs, for example, and with multiple clearance Fowlerflaps.

Claims

1. A method of optimizing cruising conditions of aircraft with supersonic wings, wherein current parameters relating to altitude, payload and airspeed are detected during flight and the curvature of the wing is adjusted as a function of these parameters.

2. A method according to claim 1 wherein the curvature of the wing in the direction of the wing span is varied.

3. A method according to claim 1 or 2 wherein the suface area of the wing is also varied.

4. A method according to any preceding claim wherein the curvature of the trailing edge of the wing is varied.

5. A method according to any preceding claim wherein the curvature of the leading edge of the wing is varied.

6. A method according to claims 4 and 5, wherein changes in curvature of the leading edge and trailing edge of the wing are controlled independently.

7. A method according to any preceding claim, wherein the changes in curvature of the wing are effected with the aid of a flap and spoiler system provided for the low speed range or for manoeuvring the aircraft.

8. An arrangement for optimizing cruising conditions of an aircraft with supersonic wings, comprising means for varying the curvature of the wing in dependence upon the current altitude, load and airspeed of the aircraft.

9. An arrangement according to claim 8 wherein said means varies the curvature of the wing in the direction of the wing span.

10. An arrangement according to claim 8 or 9 wherein said means is in the form of a trailing edge flap system comprising high lift flaps and spoilers, the spoilers closely abutting the high lift flaps and being under prestress.

11. An arrangement acccording to claim 10 wherein the spoilers are flexible.

12. An arrangement according to claim 10 or 11 with a clearance between the trailing edge of the wing and the high lift flaps wherein auxiliary flaps which cover the clearance are arranged on the underside of the wing and also closely abut under prestress,the high liftflaps.

13. An arrangement according to claim 12 wherein the auxiliary flaps are flexible.

14. An arrangement according to any one of claims 10 to 13 wherein the high lift flaps are formed as Fowlerfiaps.

15. An arrangement according to any one of claims 10 to 14 wherein the trailing edge fl?p system is subdivided into individual, separately controllable segments.

16. An arranement according to claim 15 wherein the individul segments can twist to a limited extent over the span width of the segment.

17. An arrangement according to any one of claims 10 to 16 in which the wings are also provided with extendable forward wing elements which are formed as leading edge slat flaps, additional flaps being provided which are pivotable at their ends on the underside of the wing, and in which the leading edge slat flaps and the additional flaps abut the structure of the wing under prestress.

18. An arrangement according to claim 17 wherein the area of the slat flaps adjacent the wing tip and the additional flap are flexible.

19. An arrangement according to claim 17 or 18 wherein the leading edge slat flaps and the additional flaps are subdivided into individual segments each of which can twist to a limited extent over the span width of the segment.

20. A method of optimizing cruising conditions of aircraft substantially as hereindescribed with reference to the accompanying drawings.

21. An arrangement for optimizing cruising conditions of an aircraft substantially as herein described with reference to the accompanying drawings.