EXHAUSTING OF HOT GASES FROM WITHIN AN AIRCRAFT

Abstract

An aircraft may have one or more electrically powered thrust-generating engines and a combustion engine forming part of a power generator system for powering the electric engine and/or recharging a battery system that powers the electric engine. An exhaust pipe leads via an interior space within the aircraft from the exhaust of the combustion engine, or other source of hot gases, to an exhaust outlet. The direction of the exhaust pipe at the outlet is transverse to the longitudinal axis of the aircraft. A fairing immediately upstream of the outlet has a trailing edge, for example with a sawtooth profile, which creates turbulence and/or chaotic airflow over and downstream of the outlet, and thus mixes the freestream air and the hot gases from inside the aircraft more efficiently.

Claims

1. An aircraft structure comprising an outer surface that in use is on an exterior of an aircraft, the aircraft having a longitudinal axis, wherein: the outer surface accommodates an exhaust outlet configured to allow hot gases to flow from within the aircraft to the exterior of the aircraft, a direction of flow of gases immediately before exiting via the exhaust outlet being transverse to the longitudinal axis of the aircraft; the outer surface extends downstream of the exhaust outlet; and the aircraft structure comprises a fairing located immediately upstream of the exhaust outlet having a shape that creates turbulence and/or chaotic airflow over and downstream of the exhaust outlet.

2. The aircraft structure according to claim 1, wherein the aircraft structure comprises an exhaust duct that terminates at the exhaust outlet and extends from inside the aircraft from a supply of hot gases.

3. The aircraft structure according to claim 2, wherein a direction of the exhaust duct is transverse to the longitudinal axis in a region directly adjacent to the exhaust outlet.

4. The aircraft structure according to claim 3, wherein the direction of the exhaust duct in the region directly adjacent to the exhaust outlet is different from a direction of the exhaust duct in a region upstream of the outlet.

5. The aircraft structure according to claim 1, wherein the fairing has a length and a width, the width being along a widthwise direction which is perpendicular to the longitudinal axis of the aircraft, and the fairing has a shape which creates a series of airflow detachment regions distributed across the widthwise direction such that airflow over the fairing detaches from the fairing and causes a disturbed airflow at the airflow detachment regions, there being two or more upstream airflow detachment regions which are interleaved between, and upstream of, respective downstream airflow detachment regions.

6. The aircraft structure according to claim 1, wherein the fairing has a trailing edge which has a sawtooth profile.

7. An aircraft comprising the aircraft structure according to claim 1.

8. The aircraft according to claim 7, wherein: the aircraft is configured for flight in which thrust is generated at least in part by one or more electrically powered engines; and the aircraft comprises: one or more rechargeable energy cells for producing electric energy for powering the one or more electrically powered engines; and one or more combustion engines for recharging the one or more rechargeable energy cells; the exhaust outlet being configured to allow hot gases to flow from an exhaust of the combustion engine to the exterior of the aircraft.

9. The aircraft according to claim 8, wherein at least one of the one or more combustion engines additionally performs a function of an auxiliary power unit of the aircraft.

10. The aircraft according to claim 8, wherein a further combustion engine is supplied to perform the function of an auxiliary power unit of the aircraft.

11. The aircraft according to claim 7, wherein the aircraft includes one or more combustion engines for directly generating thrust.

12. The aircraft according to claim 8, wherein the one or more combustion engines for recharging the one or more rechargeable energy cells have a power rating of 500 kVA or more.

13. The aircraft according to claim 8, wherein the one or more combustion engines for recharging the one or more rechargeable energy cells are located in a fuselage of the aircraft, and spaced apart from a tail of the aircraft.

14. A method of exhausting hot gas from within an aircraft comprising: exhausting hot gas from within the aircraft via an outlet, a direction of flow of gas immediately before exiting the aircraft via the outlet being perpendicular to the longitudinal axis of the aircraft within +/−30 degrees, the outlet being accommodated within an exterior surface of the aircraft which extends for at least 1 meter downstream of the outlet; a fairing, at least part of which is located upstream of the outlet, creating turbulent airflow over and/or downstream of the outlet to mix the freestream air and the hot gas more rapidly than without the fairing.

15. An aircraft configured for flight in which thrust is generated at least in part by one or more electrically powered engines, wherein the aircraft comprises: one or more rechargeable energy cells for producing electric energy for powering the one or more electrically powered engines; a combustion engine for recharging the one or more rechargeable energy cells; an exterior surface in which an outlet is located; an exhaust duct leading via an interior space within the aircraft from the exhaust of the combustion engine and terminating at the outlet, a direction of the exhaust duct, in a region directly adjacent to the exhaust outlet, being transverse to a longitudinal axis of the aircraft; and and a fairing located immediately upstream of the outlet having a trailing edge with a sawtooth profile.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Embodiments of the disclosure herein will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0021] FIG. 1 is a side view of an aircraft according to a first embodiment of the disclosure herein;

[0022] FIG. 2 is a plan view of the aircraft of FIG. 1;

[0023] FIG. 3 is a further simplified side view of the aircraft of FIG. 1 showing the location of an exhaust outlet and associated fairing;

[0024] FIG. 4 is a further simplified plan view of the aircraft of FIG. 1 showing the location of the exhaust outlet and associated fairing also shown in FIG. 3;

[0025] FIG. 5 is a perspective view of part of the aircraft of FIG. 1 with an enlarged view of the exhaust outlet and associated fairing;

[0026] FIG. 6 is a schematic view from the side of the exhaust outlet and associated fairing showing schematically airflows in use; and

[0027] FIG. 7 is a flowchart of a method of exhausting hot gas from within an aircraft using the apparatus of the first embodiment.

DETAILED DESCRIPTION

[0028] FIG. 1 shows a side view of an aircraft 10 in accordance with an embodiment of the disclosure herein. FIG. 2 is a plan view showing the outline of the aircraft 10 of FIG. 1. The aircraft 10 has two wings 12 and a tail plane/empennage 14.

[0029] The aircraft 10 has four wing-mounted engines 16 in the form of three conventional jet engines 16j and a single electrically powered engine 16e. The aircraft 10 is in the form of a demonstrator aircraft designed to test the feasibility of an electric aircraft, namely an aircraft for which the thrust is provided at least in part by one or more electric motors. In this embodiment, only a single engine 16e is electric, the other three being jet engines 16j. It will be appreciated however that the concept embodied by the aircraft of FIGS. 1 and 2 could be extended to an aircraft with two, three or all four engines being electric engines. The aircraft 10 also includes an auxiliary power unit (APU) 30 which is located at the very rear of the aircraft.

[0030] The electric motor 16e is powered by a high-power battery pack 18, which is mounted within the fuselage 22 of the aircraft. The battery pack 18 is connected to an on-board power generator system 20, for the purpose of extending the life of the battery during a single operation of the aircraft (i.e. from take-off to landing inclusive, and associated taxiing manoeuvres) and for directly powering the electric motor 16e. The battery pack is configured to be capable of storing at least 10 MW-hours of electrical charge. The power generator system 20 comprises a gas turbine combustion engine which is able to deliver 2.5 MW of power which is converted to electricity by a generator. The power generator system 20 weighs about 2,500 Kg and is about 3.5 meter long (in the direction of the central longitudinal axis 24 of the aircraft) and about 1 meter in height and width.

[0031] The power generator system 20 is also mounted within the fuselage 22 of the aircraft and is fed with jet fuel stored in one of more fuel tanks and air fed via an intake system (not shown in the drawings). The size and weight of the power generator system 20 is such that it needs to be mounted within the fuselage and in a position set apart from the bulkhead (not shown separately in the Figures) that separates the empennage 14 and the fuselage 22. It is therefore the case that the power generator system 20 is located in the fuselage and spaced apart, in the longitudinal direction, from the extreme aft end of the tail of the aircraft. It is also the case that the center of mass of the power generator system 20 is spaced apart, in the longitudinal direction, from the fore end of the empennage 14. As such, consideration needs to be given to how best to exhaust the hot exhaust gases that are exhausted from the combustion engine of the power generator 20 in use, it not being feasible to vent exhaust gases from the extreme rear of the aircraft.

[0032] In the configuration of the present embodiment, the free space within the fuselage means that exhaust gases need to be exhausted from the fuselage in a direction that is close to perpendicular both to the external surface of the aircraft surrounding the exhaust outlet and to the longitudinal axis of the aircraft. It might be thought that exhausting hot gases in this direction would assist with reducing the amount of undesirable contact of undiluted hot gases with the aircraft structure immediately downstream of the exhaust outlet. However, the local free-stream flow around the aircraft when airborne tends to entrain any such hot gases introduced to the free-stream flow close to the aircraft body.

[0033] According to the present embodiment, and as shown in FIGS. 3 to 6, a fairing 40 is provided immediately upstream of the exhaust outlet 50 to promote better mixing of the hot exhaust gases and the free-stream air so as to reduce undesirable heating of the external aircraft structure immediately downstream of the exhaust outlet by the exhaust gases. The fairing 40 is static, has a rigid and fixed shape and is mounted at a fixed location on the aircraft 10. The fairing has a length aligned with the longitudinal axis 24 of the aircraft and a width aligned with a widthwise direction W. The shape of the fairing 40 includes a shallow convexly shaped ramp profile 42 that ramps up and flares out (increases in size in the widthwise direction W) in a downstream direction DD, before terminating in a saw-tooth profile 44. The saw tooth profile 44 has a slanted concave arrangement of thirteen teeth that are positioned next to each other in the widthwise direction. The arrangement of teeth is concave in that the first and last end teeth 44e in the arrangement are closest to the aircraft external surface 60 and the middle teeth 44m are furthest away from the external surface 60 (and are therefore the upmost teeth). The arrangement of teeth is slanted in that the first and last teeth 44e in the arrangement are further downstream than the middle teeth 44m.

[0034] The shape of the fairing 40 is designed so as to create a turbulent and chaotic airflow over and downstream of the outlet, which increases the mixing of, and dispersion of, hot exhaust gases within the free-stream air. With reference to FIG. 6, each of the teeth of the saw tooth profile defined an airflow detachment region 48 (only some of which being labeled) that are arranged in a series in the widthwise direction. The airflow upstream of the fairing (region R1) is relatively smooth (laminar flow). The airflow over the fairing (region R2) detaches from the fairing and causes a disturbed airflow (region R3) at and downstream of the airflow detachment regions. The pointed free ends the teeth on the fairing 40 may be considered as downstream detachment regions and the junction between adjacent teeth as upstream airflow detachment regions, such that there is an alternating series of downstream airflow detachment regions and upstream airflow detachment regions on the downstream end of the fairing. There may thus be multiple single upstream airflow detachment regions each of which are interleaved between, and upstream of, a pair of respective downstream airflow detachment regions. Such an arrangement promotes turbulence and chaotic airflows over and downstream of the outlet (i.e. within region R3 in FIG. 6). Thus, the hot air flow (dashed arrows 54) emerging from the exhaust outlet 50 mixes with the free-stream air better.

[0035] The shape of the fairing is also designed to have minimal effects on drag, although it is acknowledged that its introduction on the fuselage outer surface will increase drag, albeit by a relatively small percentage.

[0036] The shape of the pipe 56 that supplies hot exhaust gases from the power generator system 20 is shown in FIG. 5. It will be seen that the direction (represented by arrow 52) of the axis of the pipe 56 at the region of the outlet 50 is close to being perpendicular to both the local plane of the external surface 60 of the aircraft and perpendicular to the longitudinal axis. In this embodiment a single direction, shown as double-headed arrow 62, is both perpendicular to the plane of the external surface 60 and perpendicular to the longitudinal axis. It will be seen that arrow 52 is in the same general direction as double-headed arrow 62, although not exactly parallel in this case. The pipe 56 has an elbow 58 which causes a change in direction of the exhaust gases from being closer to the longitudinal axis 24 of the aircraft at a location upstream (in the direction of the exhaust gases) to a direction being at a greater angle from the longitudinal axis 24 at a downstream location (i.e. close to the outlet). It will be seen that the direction 52 of the exhaust duct 56 is transverse (and close to exactly perpendicular) to the longitudinal direction 24 at the point at which the pipe 56 terminates at the outlet 50. The pipe 56 has a diameter of about 50 cm so that the area of the outlet is about 0.2 m.sup.2 (and therefore in the range of between 0.05 m.sup.2 and 1.0 m.sup.2).

[0037] The method of operation of aircraft having an exhaust outlet 50 and fairing 40 as shown in FIGS. 1 to 6 will now be described with reference to the flowchart 100 shown in FIG. 7. Hot exhaust gases flow from a source (in this case a combustion engine of an on-board power generator system) via an exhaust pipe (step 110) within an airborne aircraft. Exhaust gas flows from the pipe, out of the aircraft, via the exhaust outlet (step 120). The temperature of the gas is greater than 100 degrees Celsius and about 30 Kg of hot gas is exhausted per second. The outlet is accommodated within an exterior surface of the aircraft which extends for at least 2 meters downstream of the outlet. If the downstream extent of the exterior surface of the aircraft were less than 1 meter then it might make treating the downstream exterior surface of the aircraft with heat protection a more attractive option. The direction of flow of gas immediately before exiting the aircraft via the outlet is perpendicular to the longitudinal axis of the aircraft (within +/−30 degrees). The direction of flow of gas immediately before exiting the aircraft via the outlet is also perpendicular to the plane of the outlet (within +/−30 degrees). The plane of the outlet should in most cases be clear, but if there is doubt over the matter (e.g. the outline of the outlet does not lie on a single plane), the plane can be defined as one which (a) bisects the outline of the outlet so that exactly half the outline is on one side of the plane and (b) has its normal axis parallel to the axis of the exhaust pipe where it crosses the plane. The fairing, being located upstream of the outlet, creates turbulent airflow (step 130), which passes over and downstream of the outlet so as to mix the freestream air and the hot gas more rapidly than would be the case without the fairing (step 140).

[0038] While the disclosure herein has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the disclosure herein lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0039] The aircraft may be a commercial aircraft, not merely a demonstrator aircraft.

[0040] The combustion engine of the on-board power generator system may additionally perform the function of an auxiliary power unit (APU) of the aircraft.

[0041] The power generator system may be provided more as a back-up to the battery pack, and not necessarily operational during a flight. The extent to which of the battery pack and the on-board power generator system is seen as the primary power source for driving the electric motor and which is seen more of a secondary power source (or back-up for example) may be altered as so desired.

[0042] Although the embodiments are described in the context of a fixed-wing aircraft application, there may be potential benefits in relation to various other applications, including but not limited to applications on vehicles such as helicopters, drones, and spacecraft. The source of hot gases need not be the exhaust gases from a combustion engine. The source of hot gases could for example be generated by a heat exchange system within an aircraft.

[0043] The size and power-rating of the on-board power generator system may be scaled upwards or downwards according to the weight and size of the aircraft with which it is to be used.

[0044] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the disclosure herein, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the disclosure herein that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope. Moreover, it is to be understood that such optional integers or features, while of possible benefit in some embodiments of the disclosure herein, may not be desirable, and may therefore be absent, in other embodiments.

[0045] While at least one example embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the example embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a”, “an” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.