GB1587482A

GB1587482A - Configuration of an aircraft

Info

Publication number: GB1587482A
Application number: GB18577/78A
Authority: GB
Original assignee: Vereinigte Flugtechnische Werke Fokker GmbH
Current assignee: Vereinigte Flugtechnische Werke Fokker GmbH
Priority date: 1977-07-02
Filing date: 1978-05-09
Publication date: 1981-04-01
Also published as: DE2730032A1; FR2395889A1

Description

(54) A CONFIGURATION OF AN AIRCRAFT (71) We, VEREINIGTE FLUG TECHNISCHE WERKE-FOKKER GMBH of Hunefeldstrasse 1-5, 28 Bremen 1, Federal Republic of Germany, a German Body Corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a configuration of an aircraft, more particularly for fighter aircraft operating in the subsonic, transonic and supersonic range.

The configurations of modern fighter aircraft are determined by the power requirements or the missions which these aircraft have to fulfil. Formation of the wing with certain lift, drag and torque characteristics constitutes an essential means of solving the requirements set. Basically there are two types of wing as alternatives, i.e. on the one hand the delta wing, which is characterised by a small spread and a large leading edge sweepback, and the trapezoidal wing, which is characterised by relatively large spread and a smaller leading edge sweepback. The angle pv is to be understood as the leading edge sweepback, this angle being formed from the leading edge of the wing and from a line parallel to the transverse axis of the aircraft in the X-Y plane.By spread or spread ratio is meant the quotient of the square of the width of span and the wing surface b2/F. In order to further distinguish these two types of wing, trapezoidal and delta, the tapering must be introduced which arises as the ratio between 'the outer and inner wing chords A ii a/i.1. In the theoretical delta wing, this tapering is equal to zero and in the trapezoidal wing on the other hand it takes on finite values.Trapezoidal and delta wings are distinguished besides these and other features by a different flow with the highly incident wing: thus the trapezoidal wing only permits relatively small angles of incidence before rhe pow is disturbed, while the delta wings per- mits fairly large angles of- incidence because of a controlled dispersion of flow on its highly sweeping leading edge with a stabilized turbulent flow. In order to extend this advantage of the delta wing to the trapezoidal wing, a small delta wing has been arranged in front of the trapezoidal wing having a smaller leading edge sweepback, and this small delta wing is a so-called strake.This strake produces its own stable turbulence system in the region of large angles of incident, which system is superimposed on the flow system of the trapezoidal wing and thus contributes among other things to improved lift characteristics. These wing configurations, characterised by the combination of a trapezoidal wing with a strake have become known from the fighter aircraft F16 and YF 17.

The disadvantages of this known configuration lies in the fact that it can only solve certain requirements unsatisfactorily, such as small weight of the wing structure, good fast flight properties (low drag with low lift co efficients), low sensitivity to gusts in high flight (small changes in the lift coefficient) over the angle of incidence and good "high lift properties.

The invention seeks to create an aircraft configuration, more particularly for high power fighter aircraft, which avoids or reduces the disadvantages of the known configurations which have been mentioned. In particular, the invention seeks to implement two requirements which, according to the previous level of knowledge, were mutually exclusive (fast flight power and manoeuvering flight power) in one aircraft.

According to the invention, there is provided an aircraft configuration comprising a wing assemble including a delta wing i.e. a wing of relatively small spread ratio and relatively large leading edge sweepback and so-called strake i.e. small triangular wing of relatively, very small spread ratio and relatively very large leading edge sweepback in combination therewith and a separate altitude control surface.

Preferably the delta wing has a leading edge sweepback pv~50 and a spread ratio A; = 25, and the strake has a leading edge sweepback Pv~75 By combining these two features, not only are the advantages of these features retained, i.e. of the strake and of the delta wing, but they are strengthened. In summary this means that the combination in accordance with the invention achieves a considerable improvement as compared to the known configurations in the high lift characteristics. It has not been considered possible to combine a strake with a delta wing in the part since their turbulance systems were considered to be incompatible and this is why the strake was only combined with a trapezoidal wing.However contrary to this technical prejudice, the two turbulance systems of the strake and of the main or delta wing are complementary in an advantageous manner: with small angles of incidence, the leading edge turbulance of the main wing is effective initially while, with larger angles of incidence, the strake turbulance begins to "pull". While with these high angles of incidence in the region between 20 and 300.

The external region of the delta wing no longer produces any lift, the very pronounced stabilised strake turbulence in the internal wing region prevents this stagnant region of the external region from extending further towards the inside of the wing and thus causing a reduction in lift. The latter is the case for example with the delta wing without a strake.Besides these advantages in terms of 'flow technology, which constitutes essentially a gain in lift (improved manoeuvring flight power) the specific features of the pure delta wing (without a strake) are retained: good fast 'flight properties caused by a negligible drag and a small induced drag at small CA values, a low sensitivity to gusts, a small wing thickness a large wing root chord and a small wing structure weight connected therewith as well as favourable facilities for installation of trailing edge flaps.

The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Figure 1 shows a side view of an aircraft in accordance with the invention; Figure 2 shows a plan view of the aircraft of Figure 1, and Figure 3 shows a perspective view of the aircraft of Figures 1 and 2.

The essential features of the configuration according to the invention can be recognised in Figure 2: the wing assembly 1 comprises a delta wing 2 and a strake 3 arranged in front of the delta wing. The leading edge sweepback of the delta wing 2 is stated as the angle pv between the leading edge 4 and a reference line perpendicular to the longitudinal axis 6 of the aircraft. Furthermore the width of span b and the area of the delta wing 2 are stated for the purpose of determining the span ratio A. This triangular area FD is formed by the two leading edges 4 and the trailing edge of the delta wing 2 or its extensions, drawn in broken lines. The strake 3 has an essentially large sweepback with its leading edge 5 than the delta wing 2 with its leading edge 4; furthermore the strake 3 has a smaller spread ratio than the delta wing 2.The area Fs of the strake is formed by the two area parts which in turn are formed by the leading edge 5, the extension of the leading edge 4 and the intersection line 8 between the strake 3 and the fuselage 6 of the aircraft. Moreover, this aircraft, shaped in accordance with the invention, has two engines 9 and 10 as well as the bi-lateral control surface assembly 1"1 and the height control surface assembly 12.

Further details of the fighter aircraft in accordance with the invention can be gathered from Figures 1 and 3. Thus the perspective view in Figure 3 shows more particularly that the strake 3 forms a unit in terms of surface with the delta wing 2. This embodiment represents a fixed wing configuration -- the wing assembly 1 in accordance with the inven tion, comprising the strake 3 and delta wing 2, can be used however for other configura tions while having the same advantages.

In conclusion it should be stated that the configuration in accordance with the invention has overcome the technical prejudice of the experts who did not consider that a strake could be combined with a delta wing because the two different turbulence systems of the strake and the delta wing would have an un favourable effect rather than a favourable effect. In wind tunnel testing with a model in accordance with the invention, it could be proved however that this delta-strake configuration provided considerable and surprising advantages. Thus there is an increase in the maximum lift coefficient in the first Dlace connected with steeper angles of incidence from which it is possible to recover and noncritical stalling characteristics. Both turbulence systems, on the one hand at the leading edge 5 of the strake 3 and on the other hand at the leading edge 4 of the delta wing 2 are not only able to function adjacent each other but even support each other in their effect. It is possible to refer to a true functional blending of the features of the strake 3 and the delta wing 2 to this extent, this blending leading to an unexpected result i.e.

to an increase in power of this fighter aircraft.

Moreover the specific characteristics of the delta wing are obtained and are still completely usable.

WHAT WE CLAIM IS: 1. An aircraft configuration comprising a wing assembly including a delta wing i.e. a wing of relatively small spread ratio and relatively large leading edge sweepback and a

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Claims

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By combining these two features, not only are the advantages of these features retained, i.e. of the strake and of the delta wing, but they are strengthened. In summary this means that the combination in accordance with the invention achieves a considerable improvement as compared to the known configurations in the high lift characteristics. It has not been considered possible to combine a strake with a delta wing in the part since their turbulance systems were considered to be incompatible and this is why the strake was only combined with a trapezoidal wing.However contrary to this technical prejudice, the two turbulance systems of the strake and of the main or delta wing are complementary in an advantageous manner: with small angles of incidence, the leading edge turbulance of the main wing is effective initially while, with larger angles of incidence, the strake turbulance begins to "pull". While with these high angles of incidence in the region between 20 and 300.

The external region of the delta wing no longer produces any lift, the very pronounced stabilised strake turbulence in the internal wing region prevents this stagnant region of the external region from extending further towards the inside of the wing and thus causing a reduction in lift. The latter is the case for example with the delta wing without a strake.Besides these advantages in terms of 'flow technology, which constitutes essentially a gain in lift (improved manoeuvring flight power) the specific features of the pure delta wing (without a strake) are retained: good fast 'flight properties caused by a negligible drag and a small induced drag at small CA values, a low sensitivity to gusts, a small wing thickness a large wing root chord and a small wing structure weight connected therewith as well as favourable facilities for installation of trailing edge flaps.

The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Figure 1 shows a side view of an aircraft in accordance with the invention; Figure 2 shows a plan view of the aircraft of Figure 1, and Figure 3 shows a perspective view of the aircraft of Figures 1 and 2.

The essential features of the configuration according to the invention can be recognised in Figure 2: the wing assembly 1 comprises a delta wing 2 and a strake 3 arranged in front of the delta wing. The leading edge sweepback of the delta wing 2 is stated as the angle pv between the leading edge 4 and a reference line perpendicular to the longitudinal axis 6 of the aircraft. Furthermore the width of span b and the area of the delta wing 2 are stated for the purpose of determining the span ratio A. This triangular area FD is formed by the two leading edges 4 and the trailing edge of the delta wing 2 or its extensions, drawn in broken lines. The strake 3 has an essentially large sweepback with its leading edge 5 than the delta wing 2 with its leading edge 4; furthermore the strake 3 has a smaller spread ratio than the delta wing 2.The area Fs of the strake is formed by the two area parts which in turn are formed by the leading edge 5, the extension of the leading edge 4 and the intersection line 8 between the strake 3 and the fuselage 6 of the aircraft. Moreover, this aircraft, shaped in accordance with the invention, has two engines 9 and 10 as well as the bi-lateral control surface assembly 1"1 and the height control surface assembly 12.

Further details of the fighter aircraft in accordance with the invention can be gathered from Figures 1 and 3. Thus the perspective view in Figure 3 shows more particularly that the strake 3 forms a unit in terms of surface with the delta wing 2. This embodiment represents a fixed wing configuration -- the wing assembly 1 in accordance with the inven tion, comprising the strake 3 and delta wing 2, can be used however for other configura tions while having the same advantages.

In conclusion it should be stated that the configuration in accordance with the invention has overcome the technical prejudice of the experts who did not consider that a strake could be combined with a delta wing because the two different turbulence systems of the strake and the delta wing would have an un favourable effect rather than a favourable effect. In wind tunnel testing with a model in accordance with the invention, it could be proved however that this delta-strake configuration provided considerable and surprising advantages. Thus there is an increase in the maximum lift coefficient in the first Dlace connected with steeper angles of incidence from which it is possible to recover and noncritical stalling characteristics.Both turbulence systems, on the one hand at the leading edge 5 of the strake 3 and on the other hand at the leading edge 4 of the delta wing 2 are not only able to function adjacent each other but even support each other in their effect. It is possible to refer to a true functional blending of the features of the strake 3 and the delta wing 2 to this extent, this blending leading to an unexpected result i.e.

to an increase in power of this fighter aircraft.

Moreover the specific characteristics of the delta wing are obtained and are still completely usable.

WHAT WE CLAIM IS: 1. An aircraft configuration comprising a wing assembly including a delta wing i.e. a wing of relatively small spread ratio and relatively large leading edge sweepback and a

so-called strake i.e. small triangular wing of relatively very small spread ratio and relatively very large leading edge sweepback in combination therewith and a separate altitude control surface.
2. An aircraft configuration according to claim 1, wherein the delta wing has a leading edge sweepback pv~50 and a spread ratio 't > 2.5.
3. An aircraft configuration according to claim 1, or 2, wherein the strake has a leading edge sweepback pv750.
4. An aircraft configuration according to claim 1, 2, or 3 wherein the proportion of the net area of the strake is approximately 15% of the gross area of the delta wing.
5. An aircraft configuration substantially as described herein with reference to the drawings.