GB2085820A - Aircraft with variable strakes - Google Patents

Abstract

An aircraft having strakes 13 has the strake area variable (for control at high angle of attack) either overall or by disposition (by, for example, increasing a strake's span and decreasing its chord). As shown, each strake has a fixed portion 13a and a movable portion 13b which may retract into the fuselage 11 or the fixed portion 13a, or may be moved to overlie or underlie the fixed portion. The strakes may be adjusted symmetrically for pitch control, or asymmetrically for roll, yaw, and side force control in addition to pitch. Parts 13b can be automatically locked during flight at low angles of attack. <IMAGE>

Description

SPECIFICATION Combat aircraft The present invention relates to combat aircraft.

Combat aircraft are required to have a high top speed, and also to be highly manoeuvrable. Other design factors, such as the desire for economical fuel consumption, conflict with these requirements and frequently lead to aircraft instabilities and control difficulties which prevent the full aircraft performance potential from being exploited. Also, with some aircraft, the margin between controllable and uncontrollable flight regimes is so fine that artificial limitations have to be applied to control inputs.

One device commonly used to improve the performance, and stability and control of aircraft is the strake - a chordwise forward extension of the root of the wing. Strakes, at high angles of attack, generate vortices which interact with the flow over a substantial area of the aircraft wings and this has generally been found to extend the usable lifting range of the wings However, effectiveness of the control surfaces is adversely affected by operating at high angles of attack, so the potential for improved performance is offset by difficulty of control and reduced manoeuvrability. The effectiveness of the aircraft as a weapons launching system is thereby reduced.

According to the present invention an aircraft has variable area strakes.

The strake area can be varied overall or by disposition (for example by reducing the chord and increasing the span) or both.

When the strake areas are varied symmetrically (so that the strake areas on each side of the aircraft fuselage are always equal) pitching moments are induced on the aircraft. When the strake areas are varied antisymmetrically, rolling and yawing moments are induced on the aircraft. Variation of the strake areas therefore serves to augment or replace the operation of conventional longitudinal and lateral controls, particularly at large angles of attack.

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, Figures land 2, which are plan views of an aircraft.

An aircraft 10 has a fuselage 11, wings 12 and strakes 13 extending forward of the wings.

Each strake 13 is in two parts, a first part 13a fixed relative to the fuselage and a second part 13b movable relative to the fuselage, as indicated by the dotted line in Figure 2.

In operation the second parts 13b are moved to vary the areas of strakes 13. When the strakes 13 have equal areas (as illustrated in Figures 1 and 2) variation of the areas results in a pitching moment being induced on the aircraft 10. When the strakes 13 have different areas (for example one strake 13 being as shown in Figure 1 and the other as shown in Figure 2) rolling and yawing moments and a side force will be induced on the aircraft 10, in addition to a pitching moment resulting from the nett change in combined strake area. The sizes of the applied moments and forces can be varied by variation of the strake 13 areas.

The moments and force variations caused by changes in strake 13 areas can be expected to be greatest at high angles of attack where the strakes generate vortices which strongly interact with the flow over the wings 12, the rear of the fuselage 11, fin and tailplane. It is in this flight regime that the effects are most useful, as under these conditions conventional controls such as, for example, all moving tail plane 14 and ailerons, have their effectiveness greatly reduced.

The second parts 13b of the strakes have been illustrated as fully extended (Figure 1) or fully retracted (Figure 2) but it will be realised that adjustment between these two limits is possible.

Parts 13b may be retracted into the fuselage 11 or into the first parts 13a of the strakes 13, or may be moved to underlie or overlie parts 13a. Movement of parts 136 two vary the areas of strake 13 may be controlled by the aircraft longitudinal and lateral control initiators. In many embodiments of the invention strake 13 area variation might be required only when flying at high angles of attack, in which case an angle of attack sensor on the aircraft 10 may be used to lock the parts 13b in a predetermined position when flying at low angles of attack.

Whilst the invention has been described and illustrated in Figures 1 and 2 as utilising variation in over-all strake 13 areas, it also encompasses changes in strake 13 area disposition for example increases in strake 13 span accompanied by decreases in chord length. Alternatively, a combination of these two factors can be used.

Mechanical arrangements for moving parts 13b will be apparent to one skilled in the art and are therefore not described here. Operating loads will be relatively light and actuation rates can therefore be large. The invention is not limited to strakes 13 as herein illustrated and described with reference to Figures 1 and 2 but can be used with other strake configurations.

1. An aircraft having variable area strakes.

2. An aircraft as claimed in claim 1 wherein the strake area is varied overall.

3. An aircraft as claimed in claim 1 wherein the strake area is varied by disposition.

4. An aircraft as claimed in claim 3 wherein the strake area is varied by reducing a strake chord length and increasing its span.

5. An aircraft as claimed in any one of claims 1 to 4 wherein the area of strake on either side of a fuselage are varied symmetrically.

6. An aircraft as claimed in any one of claims 1 to 4 wherein the area of strake on either side of a fuselage are varied asymmetrically.

7. An aircraft substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Combat aircraft The present invention relates to combat aircraft. Combat aircraft are required to have a high top speed, and also to be highly manoeuvrable. Other design factors, such as the desire for economical fuel consumption, conflict with these requirements and frequently lead to aircraft instabilities and control difficulties which prevent the full aircraft performance potential from being exploited. Also, with some aircraft, the margin between controllable and uncontrollable flight regimes is so fine that artificial limitations have to be applied to control inputs. One device commonly used to improve the performance, and stability and control of aircraft is the strake - a chordwise forward extension of the root of the wing. Strakes, at high angles of attack, generate vortices which interact with the flow over a substantial area of the aircraft wings and this has generally been found to extend the usable lifting range of the wings However, effectiveness of the control surfaces is adversely affected by operating at high angles of attack, so the potential for improved performance is offset by difficulty of control and reduced manoeuvrability. The effectiveness of the aircraft as a weapons launching system is thereby reduced. According to the present invention an aircraft has variable area strakes. The strake area can be varied overall or by disposition (for example by reducing the chord and increasing the span) or both. When the strake areas are varied symmetrically (so that the strake areas on each side of the aircraft fuselage are always equal) pitching moments are induced on the aircraft. When the strake areas are varied antisymmetrically, rolling and yawing moments are induced on the aircraft. Variation of the strake areas therefore serves to augment or replace the operation of conventional longitudinal and lateral controls, particularly at large angles of attack. One embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, Figures land 2, which are plan views of an aircraft. An aircraft 10 has a fuselage 11, wings 12 and strakes 13 extending forward of the wings. Each strake 13 is in two parts, a first part 13a fixed relative to the fuselage and a second part 13b movable relative to the fuselage, as indicated by the dotted line in Figure 2. In operation the second parts 13b are moved to vary the areas of strakes 13. When the strakes 13 have equal areas (as illustrated in Figures 1 and 2) variation of the areas results in a pitching moment being induced on the aircraft 10. When the strakes 13 have different areas (for example one strake 13 being as shown in Figure 1 and the other as shown in Figure 2) rolling and yawing moments and a side force will be induced on the aircraft 10, in addition to a pitching moment resulting from the nett change in combined strake area. The sizes of the applied moments and forces can be varied by variation of the strake 13 areas. The moments and force variations caused by changes in strake 13 areas can be expected to be greatest at high angles of attack where the strakes generate vortices which strongly interact with the flow over the wings 12, the rear of the fuselage 11, fin and tailplane. It is in this flight regime that the effects are most useful, as under these conditions conventional controls such as, for example, all moving tail plane 14 and ailerons, have their effectiveness greatly reduced. The second parts 13b of the strakes have been illustrated as fully extended (Figure 1) or fully retracted (Figure 2) but it will be realised that adjustment between these two limits is possible. Parts 13b may be retracted into the fuselage 11 or into the first parts 13a of the strakes 13, or may be moved to underlie or overlie parts 13a. Movement of parts 136 two vary the areas of strake 13 may be controlled by the aircraft longitudinal and lateral control initiators. In many embodiments of the invention strake 13 area variation might be required only when flying at high angles of attack, in which case an angle of attack sensor on the aircraft 10 may be used to lock the parts 13b in a predetermined position when flying at low angles of attack. Whilst the invention has been described and illustrated in Figures 1 and 2 as utilising variation in over-all strake 13 areas, it also encompasses changes in strake 13 area disposition for example increases in strake 13 span accompanied by decreases in chord length. Alternatively, a combination of these two factors can be used. Mechanical arrangements for moving parts 13b will be apparent to one skilled in the art and are therefore not described here. Operating loads will be relatively light and actuation rates can therefore be large. The invention is not limited to strakes 13 as herein illustrated and described with reference to Figures 1 and 2 but can be used with other strake configurations. CLAIMS

1. An aircraft having variable area strakes.

2. An aircraft as claimed in claim 1 wherein the strake area is varied overall.

3. An aircraft as claimed in claim 1 wherein the strake area is varied by disposition.

4. An aircraft as claimed in claim 3 wherein the strake area is varied by reducing a strake chord length and increasing its span.

5. An aircraft as claimed in any one of claims 1 to 4 wherein the area of strake on either side of a fuselage are varied symmetrically.

6. An aircraft as claimed in any one of claims 1 to 4 wherein the area of strake on either side of a fuselage are varied asymmetrically.

7. An aircraft substantially as herein described with reference to the accompanying drawings.