Firefighters train to control and extinguish fires in the quickest and safest way possible. As with any profession that is required to work in a hostile and dangerous environment, frequent and realistic training is essential in maintaining the specialist skills needed to fight fires. Usually, firefighters tackle fires in teams and so it is important that each individual firefighter's ability to function as part of a team is also trained and tested frequently.

Fires may occur in many various scenarios, and different types of fire require different strategies to deal with them effectively. Specifically, fires in some situations may require firefighters to adopt a different set of priorities when choosing which part of the fire to extinguish first, for example due to the presence of highly flammable material in close proximity to the fire. In other cases, for example an aircraft undercarriage with tyres that are ablaze, there is an explosion risk that increases if the fire spreads to other parts of the aircraft. In such situations, it is important for the firefighters tackling the fire to know not just how to tackle the fire, but also how to position themselves safely so that if an explosion were to occur, the danger to the fire-fighting team members is minimised. In all cases, it is essential that early indications of danger are picked up and acted upon instinctively, and this can only be accomplished through repetitive simulation training for each scenario.

In an aircraft fire incident, there is invariably some fuel on board the aircraft in its fuel tanks, and probably passengers and crew in the cabin and cockpit. The potential for a rapid escalation in the intensity of the fire, perhaps explosion, and the potential for loss of life is obvious. Matters are worsened by the fact that one of the most common causes of loss of life in aircraft fires is smoke inhalation in the confines of

the cabin, and that fires which reach the cabin can quickly fill the cabin with toxic smoke. Hence the speed at which aircraft fires are controlled is crucial in minimising smoke generation in the cabin so any passengers can have the best possible chance of escaping the stricken aircraft. This is another important reason why aircraft fires especially necessitate the quick and accurate responses that are made possible only by effective practice.

To train effectively, dedicated simulators are required to mimic the conditions present in a real fire so that firefighters are familiar with the scenarios in which they might have to work. For example, knowing how much space there is and the disposition of obstacles in any particular scenario is important in deciding which types of equipment may be employed. Furthermore, being familiar with the surroundings is also of immense benefit to the safety and efficacy of the firefighters; if they are reasonably comfortable with the situation, they can concentrate more on tackling the fire while keeping themselves safe.

A consideration when using a fire-fighting simulator is how accurate the flame appears to the firefighter in comparison with a real fire. Although fires can start in any environment with an ignition source, flammable material and a supply of oxygen, each scenario will usually have a specific flame signature depending upon the type and location of flammable materials that can be expected to be found in that scenario and hence, how those flammable materials will burn. The flame signature will also be affected by the shape of the environment in which the fire establishes itself.

Of the many types of fire that may be associated with aircraft, one of the most difficult to deal with is a fire in or around the aircraft undercarriage. This is due to the difficulty of applying sufficient firefighting media to some parts of the undercarriage such as the brakes which are located within the wheels, the presence of pressurized tyres which may explode given sufficient heating, and the proximity of brake and hydraulic fluid lines which may rupture, ejecting flammable liquid under very high pressure.

A frequent starting point for undercarriage fires is overheating brakes. The brake components on aircraft, especially heavy commercial wide-body airliners, are put under tremendous thermal load when an aircraft lands and applies its brakes.

Furthermore, if an aircraft aborts its take-off while accelerating down the runway, it is preferable to stop the aircraft without overshooting the runway so as to prevent damage to the undercarriage and engines especially. So, in an aborted take-off, the brakes are put under maximum thermal load as maximum braking force is called for.

During severe retardation, as in both the above examples, the brake components such as discs, drums and pads may get so hot that they ignite, leading to a fire taking hold in the brakes. It is common in this instance for one brake to catch fire first, followed by the others, rather than for all the brakes to catch fire at once.

Once the brake components ignite, flames appear inside the wheel rim and if not quickly stopped, the tyre attached to the wheel may also catch fire, producing additional smoke and flames and increasing the risk of explosion as the tyre bursts.

When the fire has become that intense and especially if an explosion has taken place, brake lines and hydraulic lines containing flammable fluid may be breached. Flames then spurt out, travel along the path of the brake and hydraulic lines or extend across exposed pools of fluid to reach other parts of the undercarriage and the aircraft.

Ultimately the fire may rise up the undercarriage'oleo'leg and threaten not just the integrity and strength of the leg itself-perhaps causing the leg to buckle under the weight of the aircraft-but also the integrity of the part of the aircraft to which the leg is attached. By way of example, the leg may depend from a wing, an engine nacelle or the fuselage of an aircraft. This introduces a risk of a major conflagration: it is usual for an aircraft to have fuel tanks in the wing or fuselage above or in the immediate vicinity of the undercarriage housing, and the interior of an engine nacelle is obviously rich in fuel supply lines.

Sometimes, however, firefighters might keep a single'hot brake' (this term indicating an overheated brake on the brink of full ignition, either smouldering or slightly aflame) under observation for a short time without applying extinguishing media that could damage the undercarriage, so as to see if the brake will cool of its own accord. If the brake does cool down, this avoids unnecessary damage to the undercarriage. However, if the hot brake situation develops into a significant brake fire, the firefighters need to intervene quickly and so must ensure that they and their equipment are already disposed in the safest and most effective manner around the affected wheel.

Another cause of undercarriage fires is overheating tyres. In any situation where the brakes are locked and the tyres skid along the ground, for example during braking after an aborted take-off run, the tyres will smoke and if the skid is held long enough, the tyres will ignite due to the high temperatures reached. Tyre fires pose the same problems as brake fires, and are tackled in much the same way although more smoke may be emitted and there is a more immediate danger of the pressurised tyres exploding.

Also, there is always a risk of accidental fuel spillage at airports. As aircraft are refuelled from underground tanks buried under the apron, long hoses lead from the underground fuel tank hydrants to the receiving aircraft. Usually, there is a mobile pumping station in between the underground fuel tanks and the aircraft to meter and filter the fuel. The presence of fuel-laden hoses in a noisy and busy environment such as an airport apron presents significant opportunities for accidents to occur leading to aviation fuel being spilt. Furthermore, the presence of hot jet engine exhausts means ignition sources for the spilt fuel are never far away.

In light of the above, one of the most common scenarios with which airport fire rescue services have to cope are aircraft fires in which the undercarriage is aflame, or is engulfed in flames from a pool of flammable liquid.

In the past, fire training simulators deemed suitable for training firefighters to tackle aircraft undercarriage fires have not been able to replicate the full range of fires that are possible with undercarriage fire incidents. These past simulators attempted to replicate only one of the burning modes, usually just burning brakes, or a conflagration involving the entire undercarriage including the wheel (s) and the leg.

They do not adequately reflect reality as expressed above.

Against this background, the invention resides in an aircraft undercarriage fire simulator comprising: a leg structure representing a landing gear leg ; a wheel/tyre structure representing at least one wheel/tyre combination associated with the leg; burner means associated with each of said structures ; and control means operable to control the burner means to simulate a fire spreading from the wheel/tyre structure to the leg structure.

The wheel/tyre structure may, for example, be attached to the leg structure via a simulated bogie or axle. More than one wheel/tyre structure can be associated with the leg structure.

Preferably, for greater realism, the wheel/tyre structure is subdivided to include a wheel structure and a tyre structure representing a wheel and a tyre respectively, each of the wheel and tyre structures having a respective burner means. In that case, the control means is advantageously operable to control those burner means to simulate a fire spreading from the wheel structure to the tyre structure or to start the simulated fire on the tyre structure.

The burner means of the wheel structure is suitably within the wheel structure, and the burner means of the tyre structure is suitably outside the tyre structure.

In a large-scale simulator, the leg structure can depend from a wing, nacelle or fuselage structure representing a wing, an engine nacelle or the fuselage of an aircraft. In that case, the wing, nacelle or fuselage structure preferably has a burner means and the control means is operable to control that burner means to simulate a fire spreading from the leg structure to the wing, nacelle or fuselage structure.

For realism, the flame intensity or the flame signature produced by the burner means of each structure is variable. Advantageously in this respect, the control means can be operable to increase the flame intensity at one structure before the simulated fire spreads to another structure.

In general, it is much preferred if the control means is operable to increase the severity of the simulated fire incident in response to inadequate fire-fighting efforts sensed by sensor means associated with at least one of the structures. The sensor means may include at least one array of temperature sensors distributed over, around or within any of said structures.

The control means can have a memory for logging temperature readings from the temperature sensors. In this way, the memory can record a fire-fighting profile by taking inputs from the temperature sensors and logging those inputs against the sensor position and the elapsed time. Then, the recorded fire-fighting profile can be compared with a predetermined target fire-fighting profile and the burner means can be controlled in response to that comparison.

The simulator of the invention can also include means for logging the identity of a fire-fighter against the recorded fire-fighting profile. This enables appropriate training feedback to be directed to the appropriate trainee.

Smoke and sound generator means are preferably associated with one or more of the burner means or structures. Also for added realism, means may be provided for ejecting fuel outwardly from any of the structures. This emulates a fracture in a high- pressure line carrying flammable fluid.

Pilot ignition means can be associated with the burner means. Elegantly, the pilot ignition means can be capable of simulating a fire in one of said structures, hence serving a dual function.

The invention also resides in a method of simulating an aircraft undercarriage fire, comprising simulating a fire in or on a wheel/tyre structure representing a wheel/tyre combination, monitoring a fire-fighting response to that fire and, in accordance with the quality of that response, varying the flame intensity or flame signature of the simulated fire and/or extending the simulated fire to a leg structure representing a landing gear leg with which the wheel/tyre structure is associated.

In order that this invention may be more readily understood, reference will now be made by way of example to the accompanying drawings in which: Figure 1 is a schematic perspective view of an undercarriage fire simulator in accordance with the invention; Figure 2 is a part-sectioned front view of an undercarriage fire simulator in accordance with the invention, used as part of a larger aircraft fire simulator; Figure 3 is a part-sectioned side view of the undercarriage fire simulator of Figure 2; Figure 4 is a sectional view on line A-A of Figure 2; and Figure 5 is a sectional view on line B-B of Figure 2.

Referring to Figure 1, an aircraft undercarriage fire simulator 1 comprises a main leg structure 2 representing an oleo leg and a bogie structure 3 attached to the base of the leg structure 2 supporting four wheel/tyre structures 4,5,6 and 7. The leg structure 2 is a tube of painted mild steel (preferably a corrosion-resistant steel such as is supplied under the trade mark Cor-Ten) that is oriented generally vertically and the bogie structure 3 is defined by opposed T-shaped tubular parts that in turn define axles 8 and 9 supporting the wheel/tyre structures in forward (4 and7) and aft (5 and 6) pairs.

A leg burner 10 in the form of a perforated pipe extends along the leg structure 2.

Another similar burner (not shown) can be on the other side of the leg structure 2.

The holes 11 in the leg burner pipe preferably face outwardly as shown so as to project flames away from the leg structure in use, thus emulating rupture of a high- pressure hydraulic line or brake line.

Each wheel/tyre structure also has a respective wheel burner 12 which, in this embodiment, is arranged to emulate a brake fire within a wheel. The wheel burners 12 (only one of which is shown) can again be perforated pipes, albeit generally circular to suit the wheel configuration rather than the straight leg burners. Thus, the holes in the pipe are disposed in angularly spaced relation around the circle.

The wheel burners 12 are connected by a common manifold so that a common fuel supply feeds all of the wheel burners. With suitable valves and control means, it would be possible to select wheel. burners so that one or more of those burners are alight rather than all of them at once.

Each wheel-tyre structure 4,5,6 and7 comprises an array of openings 13 corresponding to the wheel hub of an aircraft wheel, the holes on each wheel burner facing outwardly and thus being arranged to project flames outwardly through a mesh covering each opening.

In the embodiment illustrated in Figure 1, a further oblong burner 15 extends around the base of the leg structure 2 just above the bogie structure 3 to emulate a fire affecting a bogie. Again, the oblong burner 15 is a perforated pipe and in this instance the holes 16 in the pipe face upwardly so as to project flames upwardly from the bogie structure 3 around the leg structure 2.

Each burner 10 and 12 is supplied with LPG fuel from a remote source via supply piping (not shown), so that fuel flowing along the burner pipe exits from the holes in the pipe 11 and 16 and, with suitable ignition means such as a pilot light (not shown), burns to simulate a fire that envelops or emanates from the structure concerned.

Whilst it would be possible to supply all of the burners from a common manifold, the invention contemplates individual control of each burner in the sense that at least some burners can be used independently of the other burners. It is further contemplated that the flame intensity and flame signature produced by each burner can be varied to emulate the appearance and progression of a real undercarriage fire.

Variation of flame intensity can be achieved by varying the fuel flow rate into the burner concerned. Variation of flame signature can be achieved by altering the configuration of the burner. For example, the burner can be subdivided into a diffuser portion that produces a diffuse flame, and a nozzle portion that ejects a jet of flame.

With suitable valve means to switch from one portion to another, the flame signature can be varied as desired.

It is particularly contemplated that a burner pipe may be surrounded or partially shrouded by a vaporisation channel that receives fuel emanating from the holes in the burner pipe, diffuses the fuel and allows it to exit from. the channel through one or more elongate slots extending along the channel or defined between the channel and the pipe. In this way, the flame signature adopts a continuous sheet-like appearance for added realism and controllability, although local spurts of flame may also be encouraged by interrupting the vaporisation channel and allowing fuel to gush from a hole in the burner pipe and directly to atmosphere.

Referring now to Figures 2 to 5, these show a practical embodiment of the invention that has many features in common with the embodiment shown in Figure 1.

Accordingly, like numerals are used for like parts. However, there are dissimilarities too, notably the lack of an oblong burner above the bogie structure and the addition of tyre burners 20 to emulate burning tyres, together with a water drench facility 21 to keep the leg structure 2 cool.

More specifically, the embodiment of Figures 2 to 5 is shown as part of a larger aircraft mock-up that comprises a fuselage structure 22 and a broken wing structure 23, the fracture 24 in the wing being above the leg structure 2. Additional burners (not shown) may be associated with that simulated fracture to emulate a fuel tank fire issuing from the wing tanks of an aircraft.

Figures 2 and 3 show how the leg structure 2 is anchored to the wing structure at the top and also bolted to the ground at the bottom. This limits the freedom of the leg structure 2 to expand when heated and so introduces a risk of buckling in use of the simulator 1. That risk is minimised by water drench pipes that surround the leg structure 2 at upper and lower levels and spray water through inwardly-facing nozzles 25 onto the leg structure 2. Provided that the water does not boil away when it hits the leg structure 2, this ensures that the leg structure 2 is kept below 100°C.

The nozzles of the water drench pipes should achieve a wide flat spray pattern with uniform distribution of water over the leg structure 2. Nozzles sold under the trade mark Delavan, type AN80, are an example that produce spray angles between 130° and 150°. An exemplary water flow rate is 10.6 litres/min/m2.

It will be evident from the front view of Figure 2 that the upper and lower levels of the water drench pipes have a common supply 26 that extends from the fuselage structure 22 out to the leg structure 2 of the undercarriage simulator 1.

Figures 2 and 3 also show how the perforated tyre burner pipes 30 arch over the upper outer surface of each wheel/tyre structure 4,5,6 and 7. The tyre burner pipes 30 are supplied with fuel by a fuel supply pipe 31 that depends from the wing structure parallel to the leg structure 2 but on the side opposed to the leg burner pipe 10, so that the leg structure 2 shields the fuel supply pipe 31 from flames emanating from the leg burner pipe 10.

Figures 4 and 5 show how the wheel burners (Figure 4) and tyre burners (Figure 5) are interconnected for the supply of fuel. A beneficial feature of this embodiment is that the wheel burner circuit 28 doubles as pilot burner pipework that ignites fuel flowing in the tyre burner circuit 29. In this respect, it will be noted that Figure 5 shows spur pipes 32 extending from the tyre burner circuit into each wheel/tyre structure, in close proximity to the associated wheel burners 12. Similarly, the leg burner pipework includes a spur pipe 33 (shown in Figure 2) that extends laterally from the base of the leg burner pipe 10 into close proximity to a tyre burner 30 arching above a wheel/tyre structure. Thus, when fuel is introduced into the tyre burner circuit 29 when the wheel burners 12 are alight, the tyre burners 30 ignite via the spur pipes 32 and when fuel is introduced into the leg burner pipework 10 when the tyre burners 30 are alight, the leg burner 10 ignites via the lateral spur pipe 33.

It will therefore be apparent that the simulator 1 of the invention emulates reality in that a wheel or brake fire can progress into a tyre fire and then into a leg fire in which wheels, tyres and leg are all ablaze. This progression is achieved simply by supplying fuel to the tyre burner circuit 29 and then to the leg burner pipework 10 when the successive stages of the incident are to be simulated.

The operation of the simulator 1 is controlled by a control means (not shown) that can govern the simulation of a fire incident automatically (either following a pre-set plan or in response to sensed criteria) or under manual control. For example, the control means may be operable to increase the flame intensity at one structure before the simulated fire spreads to another structure. This reflects reality in which, say, a

small brake fire grows before spreading to the tyre and from there, with a tyre explosion or with increasing flame intensity, to the leg.

With suitable feedback provisions, the control means can be operable to increase the severity of the simulated fire incident if the efforts to control and extinguish the fire are deemed inadequate. In the preferred embodiments described, that feedback is achieved by sensor arrays associated with the structures, notably temperature sensors (not shown) distributed over, around or within the structures. By logging temperature readings from the temperature sensors and knowing the position of each sensor, a fire-fighting profile can be built up as time elapses. In this way, the control means can know if fire-fighting media has been applied to a critical location quickly enough to lower its temperature below ignition point, or if a'hot spot'has been missed that could initiate the next stage of a developing conflagration.

A predetermined target fire-fighting profile can be stored and used by the control means, or by a controlling human operator, to judge whether the recorded fire- fighting profile is adequate. If it is not adequate, thus indicating that a real fire would not have been brought under control, the burners can be controlled to increase the flame intensity at a given structure and/or to spread the fire to the next structure.

Further to improve training feedback, the identity of a firefighter can be logged against the recorded fire-fighting profile. In this way, a good trainee can be identified and praised and a less competent trainee can be given feedback as to how to improve his or her fire-fighting techniques the next time.

Many variations are possible within the inventive concept. For example, fuels other than LPG, such as kerosene, can be used ; however, LPG fuels are much preferred for their clean burning.

More or fewer burners can be employed. For example, a fire can start at a tyre structure and from there progress to the leg structure 2, without necessarily involving a wheel or brake fire as such. It is also possible for a fire to progress from the leg

structure 2 to another structure beside or above the leg, which in the embodiment of Figures 2 to 5 is a wing structure. In that case, the wing structure can have a further burner that simulates a spreading fire. Similar considerations apply to other structures adjacent to or adjoining the undercarriage, such as an engine nacelle or a fuselage.

Smoke and/or sound generators can be employed to add realism. A sound generator can emulate the sound of a fire incident and in particular can emulate an explosion when flame spreads from one structure to another.

In view of these and other variations within the inventive concept, reference should be made to the appended claims and other conceptual statements herein rather than to the foregoing specific description in determining the scope of the invention.