A Drogue Assembly for In-Flight Refuelling

This invention relates to a drogue assembly for in-flight refuelling. Drogues are used to stabilise refuelling hose trailing from a tanker aircraft in a generally horizontal attitude. They provide drag for a refuelling coupling at the trailing end of the refuelling hose which is to be coupled for in-flight refuelling with a probe from a following aircraft which is to be refuelled. This drag resists the forward movement of the probe. However, the resistance due to drag should not be so great that the probe may be damaged by impact with the drogue in flight. Also the higher the drag, the greater the power that will be necessary to wind in the refuelling hose after in-flight refuelling has been completed.

It is desirable to be able to use the same in-flight refuelling equipment to refuel either a low speed or high speed aircraft. For example, a helicopter may cruise at about 100 to 130 Knots Equivalent Airspeed (KEAS) whereas jet aircraft refuelling speeds are commonly in excess of 180 KEAS, and may be up to 325 KEAS. This is difficult if the equipment has a drogue parachute because drag load on the parachute varies proportionally to the square of the airspeed. In addition, at high airspeed there is a requirement (ie stipulated in NATO STANNAG 3447) that receiver aircraft must have a certain geometry around the probe. This geometry only allows the use of a small drogue, which would not produce sufficient drag at low speeds.

US-A-6,145,788 discloses a drogue assembly for in-flight refuelling including a drogue parachute which comprises a circumferential array of triangular support arms which carry a canopy which extends circumferentially around their shorter sides at the distal ends. At least alternate ones of the support arms carry leaf springs which extend into pockets formed in the canopy. The leaf springs act on the canopy in opposition to air pressure loading on it in flight so that it tends to increase the chord angle of the canopy and thus the effective area

presented to the airflow. Hence the effective area of the drogue parachute in flight is varied automatically above a certain predetermined minimum so it is reduced as air speed is increased and vice versa.

This configuration has proved suitable for drag coefficient changes approaching a factor of 2. However, for the range of speeds referred to above, changes of above a factor of 3 must be dealt with. It has been necessary therefore to use different drogues having different sizes in order to operate over this range of airspeeds.

An object of this invention is to provide a compact drogue assembly which minimises the range of drag loads established when conducting in-flight refuelling over a broad range of different air speeds.

According to this invention there is provided a drogue assembly for inflight refuelling comprising a reception coupling member having an aperture for receiving a refuelling probe along an axis thereof, and a drogue parachute arranged around the coupling, the parachute comprising at least one circumferential array of support arms carrying a first canopy and a second canopy arranged around the first canopy, the second canopy having a configuration which is arranged to change under air pressure loading on the canopy in flight such that the second canopy folds inwardly towards the first canopy and the effective area of the second canopy is thereby reduced.

Thus the effective area which the second canopy presents to the airstream is varied automatically so that it reduces as air speed increases, and vice versa, which facilitates providing a drag force which remains substantially stable at low speeds. Preferably, the configuration of a first of the canopies is also arranged to change, but over a range of airspeeds higher than that causing the configuration of the second canopy to change. This allows the working range of airspeeds to be maximised.

The first canopy may comprise a first drogue parachute arrangement of a known type as described above, for example a small high speed drogue. In this case, the second canopy may be mounted to the coupling member on a second

array of support arrays positioned upstream of the first parachute, so as to form a second parachute arranged around the outside of the first parachute, and foldable towards it. Thus in the folded condition, the second parachute may overlie the outside surface of the first parachute, so as not to significantly increase the size or envelope of the drogue at high speeds.

Alternatively, the first and second canopies may be mounted on the same array of support arms. In this case, the first canopy may extend inwardly of the support arms in the conventional manner, and the second canopy may extend outwardly of the support arms, so as to be arranged around the first canopy. The canopies may each comprise sheet material mounted adjacent the tips of the support arms, and extending therebetween. Each canopy is conveniently an annular strip of sheet material mounted to the support arms at circumferentially spaced intervals, for example by means of radially extending leaf springs.

The support arms may be biased outwardly by biasing means, which may for example comprise a spring attached between the base of each support arm and the coupling member. The arms may each be pivotally mounted to the coupling member at a position adjacent the base, so that the arms rock around the pivotal mounting.

The invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a perspective view from the behind of a drogue assembly according to the invention;

Figure 2 is a schematic side cross-sectional view of the drogue assembly of Figure 1 with the second canopy parachute in a deployed condition; Figure 3 is schematic cross-sectional side view of the drogue assembly of

Figure 2 with the second canopy parachute in the folded condition;

Figure 4 shows schematic partial front view of a second drogue according to another embodiment of the invention, in the folded conditions;

Figure 5 shows the canopy section of the drogue of Figure 4 in the unfolded

condition; and

Figure 6 is a schematic side view of a drogue assembly according to another embodiment of the invention.

Referring to Figures 1 and 2, the drogue assembly includes a reception coupling unit 2 which is substantially cylindrical in form and which is arranged to receive a refuelling probe of a following aircraft at an open end 4 thereof. At the opposite or upstream end 6 a hose 8 for carrying the fuel and delivering it to the probe is connected to the coupling unit 2. A fixed drogue parachute 10 of a known type is arranged around the periphery of the opening 4 in the coupling unit 2 in a known manner. The known drogue parachute assembly in this example comprises a plurality of circumferentially arranged support arms 12 having a triangular shape, and carrying a first canopy 14 between the short sides at the tips of the support arms 12. The canopy 14 may present a fixed effective area to the airflow to provide drag in flight, or it may be mounted on leaf springs so as to provide a variable area, as is known in the art.

The drogue assembly further includes a foldable parachute 16. The foldable parachute 16 also comprises a circumferential array of support arms 18 which carry a second canopy 20. The second canopy 20 comprises an annular strip of sheet material connected to the tip portion 21 of each support arm 18 at circumferentially spaced intervals. The support arms 18 are mounted to the reception coupling 2 upstream of the fixed drogue parachute 10, so as to be arranged around the fixed parachute 10, and axially spaced therefrom. Each of the support arms 18 extends through an aperture 19 in the coupling unit 2. In the deployed condition as shown in Figure 2, the second canopy 20 presents a certain effective area to the air flow in flight to provide additional drag for the coupling unit 2.

As also shown in Figure 2 and 3, each support arm 18 is pivotably mounted within the coupling unit 2 at a pivotal mount 22 adjacent the base of the arm 18. The base of each support arm 18 comprises a short leg 24 extending beyond the pivotable mount 22, at the end of which is connected one end of a

spring 26. The opposite end of the spring 26 is attached to the coupling unit at a position axially spaced in a downstream direction from the pivotable mount 22. Thus the biasing effect of each spring 26 tends to pull the end of the leg 24 axially downstream with respect to the coupling unit 2, so as to tend to cause the support arm 18 to rock around the mount 22 such that the tip 21 moves in an upstream direction. Thus the arms 18 flare outwardly from the coupling 2, and the second canopy 20 presents a relatively large effective area to the airflow.

In use of the drogue assembly at low speeds, the foldable parachute will maintain the deployed position described above, as the air load on the second canopy 20 will be insufficient to cause the arms 18 to move against the bias of the springs 26. However, as the speed of flight, and thus of movement of the coupling unit 2 increases, for example above around 130 KEAS, the air pressure loading on the second canopy 20 tends to push the tips 21 of support arms 18 in a downstream direction. Thus the arms 18 rock around the pivot mounts 22 against the bias of the springs 26, extending the springs and folding the parachute 16 inwardly towards the fixed drogue parachute 10. With the springs 26 extended, as seen in Figure 3, and the foldable drogue parachute 16 folded inwardly, the second canopy 20 makes a shallower angle to the unit 2, presenting a smaller effective area to the air flow, and reducing the drag. Furthermore, in the folded condition, the overall diameter of the drogue is reduced. Therefore at high air speeds, the drogue assembly has an envelope similar to the envelope of a known drogue parachute alone. A high speed aircraft which has been designed for coupling with a standard drogue may have a structural exclusion area sized for a standard fixed drogue assembly. Since at such speeds the foldable drogue assembly of this invention is in a folded condition, the exclusion area should be sufficient to accommodate the assembly of the invention.

Referring now to Figures 4 and 5, the foldable drogue may be arranged such that only alternate support arms 30 are biased outwardly, with the remainder 32 being simply pivotally mounted. The second canopy has alternating radially

extending stiffened sections 34, 36 and flexible sections 38. The stiffened sections 34, 36 are attached to each support arm 30, 32, with the flexible sections 38 between the arms 30, 32. In this arrangement, the boundary 40 between each adjacent section forms a fold line when the canopy is folded. Thus the canopy tends to adopt a shape in which the biased arms 30 flare further outwardly than the unbiased arms 32. Therefore, when the canopy folds against the bias, the unbiased arms 32 lead, such that the stiffened sections 36 attached thereto overlap the remaining stiffened sections 34, with the flexible sections 38 stretched in between. This arrangement avoids the canopy fabric being loose in the folded condition of the drogue, and therefore prevents the fabric from flapping which could potentially damage the canopy.

Figure 6 shows an alternative embodiment of the invention, in which the second canopy 42 is mounted on the same set of support arms 12 as the first canopy 14. The canopy 42 comprises an annular strip of sheet material similar to that of the first canopy 14, but it extends outwardly from the support arms so as to surround the first canopy 14. The second canopy 42 is mounted so as to be able to flex towards the direction of the air flow into the position showing in broken lines, such that it is folded in towards the first canopy. For example it may be mounted on a set of leaf springs inserted into pockets of the canopy in the conventional manner. With this arrangement, the second canopy 42 exerts a load on the support arms 12 tending to push them inwardly in the presence of an air flow. Therefore the support arms are biased outwardly by means of an array of springs 44 connected between the coupling unit 2 and at least some of the support arms 12, at a position near the base thereof. In use, at low airspeeds (for example below 100 keas) the first and second canopies 14, 42 are in the positions shown in solid lines in Figure 6. In this position the canopies present a high effective area to the air flow. As the airspeed increases, the first and second canopies 14, 42 move towards the positions shown in broken lines. The canopies may reach these positions for example at airspeeds of approximately 200 keas. It can be seen that each canopy presents a smaller

effective area to the air flow in these positions, thus automatically providing a substantially constant drag load on the drogue. Also, in the folded position, the second canopy is closed towards the envelope of the first canopy.