A fuel tank is a container in which liquid fuel is stored; it is placed directly on board the aircraft. From the fuel tanks there are fuel wires to the power plant, which ensures its supply with fuel. Tanks for supplying fuel to heating systems can also be placed on board the aircraft.

Turboprop and turbojet aircraft engines use aviation kerosene with additional additives in their work. Light-engine aviation, equipped with piston power plants, uses high-octane gasoline as fuel.

Fuel tank in an airplane wing

In modern aircraft construction, caisson tanks are used; they look like sealed cavities. They are mainly installed in the wings, stabilizer and keel. These are soft tanks made of rubber materials, which allows them to maintain their integrity during overloads and shocks. In addition, such material is very reliable and effectively occupies the allotted space.

Sometimes tanks-compartments are used, which perform both the role of a fuel tank and the role of a power element. To prevent spillage of fuel from the caisson tanks, fighter jets use a sponge filler similar to foam rubber.

Large airliners, which are designed for long-haul flights, have several fuel tanks, which are additionally equipped with pumps. All fuel tanks are interconnected by a system of fuel wires, which allow you to use fuel from any tank or to transfer it. The transfer of fuel from one tank to another is possible due to the implementation of a more efficient centering of the aircraft. Fuel from service tanks is pumped into spare tanks according to the developed program of fuel consumption in flight.

Fuel tanks made from standard aluminum canisters

It should be noted that the process of refueling the aircraft tanks also takes place in accordance with the balance plan. Fuel is supplied to the tanks of the apparatus under pressure from a special tanker through the neck, after which it is distributed between the tanks.

Each fuel tank in an aircraft has a so-called drain port through which all fuel can be drained. After each refueling, this neck is opened, which allows you to drain the condensate or water that has settled at the bottom of the tank. Naturally, there should not be any impurities in the tank, otherwise this may cause engine failure and an accident.

Aircraft also have systems for emergency fuel dumping right in the air. This system is necessary when performing emergency landings, immediately after takeoff, since the allowable landing weight of the aircraft is much less than the takeoff weight.

Fuel tank in side member

Combat aircraft that need to carry out combat operations at a great distance from the base can be equipped with additional hanging tanks. They are streamlined to improve overall aerodynamics and are hung from the fuselage or wing of the aircraft. After the development of all fuel, they are reset. Also, such devices are used for ferrying aircraft to other airfields of deployment; they are usually installed in the middle of the hull.

Outboard fuel tanks

Fuel tank safety

Combat aircraft and some passenger vehicles use inert gas to fill their tanks, which is supplied as fuel is used up. Carbon dioxide or nitrogen is used as the gas. This helps to prevent a fire on board or an explosion of the fuel tank due to mechanical damage. A similar scheme for filling the fuel tank with gases was used back in World War II, only the cooled exhaust from the engine manifold was used as gas.

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The aircraft fuel system is designed to accommodate fuel and its uninterrupted supply to the engines in the required quantity and with sufficient pressure at all specified flight modes and altitudes.

The fuel system of a modern aircraft includes the following main elements:

tanks or compartments of the aircraft, in which the fuel supply necessary for the flight is located;

power control taps (tank switching); cranes for emergency shutdown of fuel supply to engines (fire-fighting cranes);

cocks for draining fuel sediment from different points of the system; fuel filters;

pumps supplying fuel to engines and pumping fuel from one tank to another;

devices for monitoring the amount of fuel, its consumption and pressure; pipelines for supplying fuel to engines, connecting tanks to the atmosphere and returning cut-off fuel.

Bucky. On modern aircraft, fuel reserves can reach many tens of tons. When flying over long distances, fuel is placed in a large number of tanks installed in the wing and, less often, in the fuselage.

Currently, three types of fuel tanks are used: rigid, soft and sealed tanks-compartments.

Rigid tanks are made of light aluminum-manganese alloys, which allow deep stamping and knockout, are well welded, have high elasticity and corrosion resistance. To give the tanks the necessary strength and rigidity, they have a frame of longitudinal and transverse partitions and profiles. The transverse baffles simultaneously serve to reduce shocks resulting from the movement of fuel inside the tank during accelerated flight. Small tanks may not have internal baffles.

Currently, soft tanks are widely used. They are easier to use, more durable, have less weight. Soft tanks are made of special rubber or nylon. Thin rubber tanks are glued on blanks made of fabric and one or two layers of rubber made of synthetic polysulfide (thiokol) rubber. Rubber-metal fittings are glued into such tanks: flanges for fuel gauge sensors, fillers, connecting pipes, sockets for fastening locks, etc.

Rubber thin-walled tanks are fastened in containers inside the wing or fuselage.

The tank compartment is a suitably sealed internal volume of a part of the wing. The tank-compartment is sealed with synthetic films. The rivet seam is sealed, for which the rivets are pre-coated with sealant. The final sealing is provided by repeated coating of the entire inner surface with a liquid sealant that cures at room temperature.

Covers of operational hatches of tanks-compartments are fastened on bolts with rubber sealing rings and tight (blind) nuts.

Cranes, installed in the fuel supply system, allow you to control the fuel supply to the engines from the corresponding tanks (or groups of tanks), as well as to turn off the fuel supply to the failed engine. In accordance with the purpose, all valves are divided into shut-off (overlapping) and distribution. According to the method of control, cranes are of direct and remote control. By design, they can be cork, spool, valve, etc.

Remote control of cranes is carried out by means of electromechanisms for closing the crane of the MZK type or by compressed air.

Filters. The need to clean the fuel supplied to the engines from impurities is caused by the presence in carburetors, direct injection units, pumps of gaps ranging in size from tenths to thousandths of a millimeter, which must be protected from solid particles entering them. Although the fuel filled into the tanks is filtered, and the tanks are protected from mechanical impurities, during operation, corrosion products of pipelines and fuel system assemblies may form, pieces of rubber gaskets may enter, etc. The presence of the smallest amounts of water in the fuel sharply increases its corrosive properties and, in addition, can lead to clogging of pipelines in the event of ice formation at low temperatures. Especially dangerous is the precipitation of moisture and the formation of ice in the pipelines of the fuel systems of modern high-altitude aircraft, which can gain high altitude in a short time, as a result of which the formation of condensate is sharply accelerated.

Mesh metal, silk, slotted, metal-ceramic, paper and mechanical filter devices are used in aircraft fuel systems.

Fuel system pumps serve to supply fuel to the engines in flight at all altitudes, at any evolution, and from all tanks or groups of tanks.

According to their purpose, pumps are divided into booster and pumping pumps, and according to the type of drive - driven by an aircraft engine and with an autonomous drive, as a rule, from an electric motor. Of the wide variety of different designs and types of pumps, the most widely used rotary or centrifugal pumps of low pressure, piston and gear - high pressure.

Modern aircraft typically have two booster pumps, one electrically driven in the fuel service tank or at the beginning of the fuel supply pipeline, and the other, driven by the aircraft engine, at the end of the pipeline in front of the supply (high pressure) pump. Such an installation of pumps ensures reliable fuel supply to the engines.

Transfer pumps are designed to transfer fuel from those tanks from which it should be produced in the first place, to consumable tanks, that is, to tanks from which fuel is sent directly to the engines. The production of fuel from different tanks or groups of them is dictated by the need to maintain a strictly defined centering of the aircraft during the entire flight and to ensure the necessary unloading of the wing.

The pipelines of the fuel system, which provide fuel supply to the engines, communication of tanks with the atmosphere, refueling under pressure, are most often made of aluminum alloy and hoses with fittings. The most common pipeline connections are: durite (flexible) on tie-down collars and nipple (rigid).

Recently, flexible metal sleeves have been widely used, which resist vibration loads well, are convenient for installation, and are relatively light.

On fig. 115 is a diagram of the aircraft fuel system.

The production of fuel from the tanks is carried out using aircraft booster pumps, the pressure at the outlet of which must be greater than the minimum allowable (usually about 0.3 kg / cm 2). A non-return valve is usually installed behind the boost pump, which prevents the fuel from flowing back.

The fire valve closes the fuel supply line when the engine is not running and in flight in case of emergency.

On some aircraft, the hydraulic resistance in the line from the tank to the engine pump reaches a large value. This necessitated the inclusion of an additional engine booster pump in the fuel line, which provides the necessary pressure at the main engine pump.

If it is planned to cool the oil of the engine lubrication system with fuel, then a fuel-oil cooler is installed in the fuel system.

As the fuel runs out of the tank, the pressure in the latter will decrease, which can lead to tank collapse. To prevent this, the fuel tanks communicate with the atmosphere through drainage pipes.

On airplanes flying at altitudes exceeding 15,000-20,000 m, there is a threat of release of a significant amount of fuel through the drainage. To eliminate this, excess pressure must be created in the tanks. This pressure is created by inert gases - nitrogen, carbon dioxide and others, which at the same time are a means of fighting a fire.

A characteristic feature of the fuel systems of modern aircraft is the large capacity of their tanks. Filling a large amount of fuel through the upper conventional tank necks is a difficult, time-consuming task, which is why the vast majority of modern aircraft have systems for refueling from below under pressure. These systems allow refueling in a very short time.

The refueling system of each aircraft consists of refueling nozzles (one or two), a refueling control panel, pipelines for supplying fuel to refueling tanks or a group of tanks, refueling valves with electric remote control, float safety valves that prevent overfilling of tanks in case of failure of refueling valves.

To increase the flight range of combat aircraft, some types of them can be refueled in the air from a specially equipped tanker aircraft.

The forced landing of a modern transport aircraft immediately after takeoff, i.e., at maximum flight weight, is in some cases unacceptable due to the limited strength of the landing gear. Lightening the landing weight in these emergency cases can be achieved by draining the fuel.

The in-flight emergency fuel jettisoning system must meet the following requirements: the jettisoning of a certain amount of fuel (sufficiently lightening the aircraft) must be done within a limited time of about 10-15 minutes. In this case, the centering of the aircraft should change slightly. Drained fuel must not enter the hot gas zone.

The emergency fuel drain system consists of valves, pipelines and drain control valves.

Used literature: "Fundamentals of Aviation" authors: G.A. Nikitin, E.A. Bakanov

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• I. General information about LA GA fuel systems and requirements for it
• II. Assessment of the technical condition of the aircraft fuel system
• III. Fuel System Maintenance Technology
• 3.1 Inspection and defect detection
• VIII. Calculation of the fuel drain line in flight by gravity

I. General information about LA GA fuel systems and requirements for it

Fuel system aircraft intended for accommodation And storage necessary for fulfillment flight reserve fuel And filing his in working engines in necessary quantity And under required pressure on the all modes flight.

The main requirements for the fuel system:

The fuel system must ensure uninterrupted fuel supply to the engines in all flight modes.

In the event that the booster pump is turned off, the fuel system must provide power to the engines from the MG to the takeoff mode at altitudes up to 2000 m while maintaining the balance and heeling moments within acceptable limits.

The capacity of the fuel tanks must be sufficient to carry out the flight at a given range and must include an emergency (air navigation) reserve for 45 minutes. flight in cruise mode (according to FAR and JAR standards).

Fuel consumption should not significantly affect the balance of the aircraft.

The fuel system must be fire safe.

The fuel system must provide centralized refueling, and must also have facilities for filling under pressure.

The possibility of emergency fuel draining in flight should be provided if the maximum aircraft weight exceeds the allowable one from the landing conditions.

The fuel system must be able to reliably and continuously monitor the sequence and quantity of fuel consumption, both in a single tank and in a group of tanks.

The fuel system is conditionally divided into two systems:

internal, or engine power supply system;

external, or aircraft.

The internal system includes fuel units and pipelines connecting them, installed on the engine and supplied with the D-ZOKU-154 engine.

The aircraft fuel system consists of fuel tanks and the following functional systems:

fuel supply to the main engines;

supplying fuel to the engine of the auxiliary power unit;

fuel pumping;

fuel tank drainage;

refueling;

fuel consumption and measurement automation systems SUIT4-1T;

fuel consumption measurement systems SIRT-1T.

Fuel on the Tu-154 aircraft is placed in five caisson tanks. Three tanks - one tank No. 1 and two tanks No. 2 - are located in the center section and two tanks (tanks No. 3) - in detachable parts of the wing. The space in the center section between the side ribs No. 3 and the first and second spars is used as tank No. 4.

The engines are powered from supply tank No. 1, which is replenished with fuel from tanks No. 2 and 3, as well as from tank No. 4.

Centralized refueling of tanks with fuel is carried out from below, through two receiving necks installed in the toe of the center section of the right wing. In case of failure of the centralized filling under pressure, filling of all tanks (except for the consumable) can be carried out through the upper filling necks of the tanks.

Tu-154 fuel system capacity:

Tank No. 1 (consumable) 3300kg

Tank No. 2 (left, right) 9500kg

Tank No. 3 (left, right) 5425kg

Tank No. 4 (fuselage) 6600kg

Total amount of fuel39750kg (at 0.8g/cm3)

Each fuel tank is a sealed compartment formed by spars, ribs, and upper and lower wing panels.

II. Assessment of the technical condition of the aircraft fuel system

The assessment of the technical condition of the fuel system implies, first of all, obtaining information about possible failures and malfunctions that are possible in this system. The main failures and malfunctions of the fuel system are:

Booster pump failures due to bearing failure.

Failures of electromechanisms of gate valves and taps due to failures of DC electric motors.

Leaks caused by worn O-rings and bushings, as well as external leaks in connections.

Drop and fluctuation of fuel pressure as a result of misalignment and failure of fuel pumps, pressure reducing valves, etc.

Freezing of fuel in pipelines due to flooding of the fuel, as well as failures of the system of radiators, pumps.

For a long time, the "Test" device has been used to monitor the technical condition of the fuel system units, which monitors the condition of the fuel system using a set of parameters:

The time of opening and closing the damper (crane).

The current consumed by the electric motor.

The level of switching noise (sparking), which characterizes the technical condition of the brush-collector device of the electric motor.

To diagnose the bearings of booster pumps of the fuel system, the root-mean-square value of the level of vibration acceleration in the characteristic frequency ranges is used.

The main attention during maintenance of fuel systems should be given to their tightness. First of all, the joints of pipelines and units are checked. It is also necessary to check the intakes of the drainage system.

Failures and damages of fuel system elements are caused by:

design and manufacturing deficiencies;

the manifestation of unfavorable fuel properties, which can have a damaging effect on engine structural elements;

violations of the manufacturability of maintenance and the rules of operation of engine fuel supply systems on the ground and in flight;

mistakes made during aircraft repair.

Typical system failures include:

1)Flowfuelfromcaisson tanksAnddrainvalves.

Leakage of tanks and sludge drain valves is detected by traces of fuel leakage on the lower wing panels, undercarriage niches or under the center section. The main reason for tank leaks is the weakening of the rivet joints of the caisson tank panels, their poor-quality sealing, and the drain valves - the destruction of the sealing rings.

2 ) Failurespumping upAndpumpingpumps.

They are associated with the destruction of the bearing of electric motors (accompanied by noise during their operation, vibration), wear of the pump seal cuffs and, as a result, are accompanied by fuel leakage from the drain fittings of the pumps, wear of the brushes and destruction of the electric motor collector assembly.

3 ) Violationworkcranes (firemen,bandingAndothers.).

It occurs due to wear and destruction of seals, damper drive elements, failure of electrical mechanisms.

4 ) Destructionbuildingsfuelfilters.

It is caused by increased pulsations of fuel in the system.

5 ) Destructionmembranes,oxidationcontactssignaling devicespressure.

6 ) blockagefilteringelementsfuelfilters ice crystals at low outdoor temperatures.

aircraft fuel system tightness

Ice crystals clog the filter of the low pressure line, which leads to a significant increase in the hydraulic resistance of the line and a deterioration in the cavitation characteristics of the main fuel pump. Freezing of water sludge in the cavity of the booster pump can cause freezing of its rotor to the housing and destruction of the pump drive shaft when the engine is started.

7 ) blockagefilteringelementsAndnozzles micro-pollution at high fuel temperatures (above 100-110°C).

At the same time, sulfur compounds, metal oxides, resins and solid carbon particles are released from the fuel in the form of a precipitate, which are formed as a result of the decomposition of thermally unstable fuel fractions. This deposit also causes increased wear of the fuel pumps.

8 ) hitairinsystem.

It leads to a violation of the operating modes of fuel regulators, fluctuations in the rotor speed and engine shutdown, cavitation in pipelines and pumps. Therefore, after a long-term parking of the aircraft, air is removed from the fuel lines through special valves.

9 ) destructionfuelpipelines.

They occur as a result of their oscillations and constitute a significant part of all failures of fatigue origin in gas turbine engines. The destruction of pipelines is observed, as a rule, in places of stress concentration: in the zones of welding and soldering of nipples, along the transition of a cylindrical section of a pipe to a flared conical one, under pipe clamps and in places of their maximum curvature. Cracks along the generatrix of the pipeline arise under the influence of fuel pressure pulsation, and circumferential cracks - as a result of cyclic bending by vibrations transmitted from the engine housing. The reduction in the fatigue strength of pipelines is facilitated by distortions in the shape of their cross section, mounting stresses, surface damage (dents, nicks, risks, etc.). Therefore, high demands are placed on the quality of pipeline installation.

III. Fuel System Maintenance Technology

3.1 Inspection and defect detection

The main maintenance works of the fuel system are: checking the condition of pipelines and system units, checking the operation of booster and transfer pumps, portioner, APU fuel pump; checking the tightness of the power supply system of the main engines and shut-off (fire) cocks; refueling and unloading work

During operation, it is necessary to carefully monitor the tightness and reliability of all pipeline connections. If there are leaks in the connections, replace the sealing rings in them.

When dismantling the connecting metal couplings of pipelines, it is necessary to drain the fuel from the pipeline and unlock the nuts of the coupling. Loosen one nut with a special wrench, and completely unscrew the other. Then slide the sleeve towards the loosened nut. Remove sealing rings. With the O-rings removed, the unscrewed coupling must move freely along the ends of the pipes.

When mounting the coupling, the nuts must be screwed onto the coupling without twisting the sealing rubber rings.

Parts with nicks, scratches and scuffs on the sealing surfaces are not subject to installation on the aircraft.

When connecting pipelines with a coupling, it is necessary to ensure the alignment of the pipelines at the joints. Their misalignment is allowed no more than 1 mm. The gap between the ends of the joined pipelines should be 9 ± 3 mm.

Inspect the fuel and drain lines. There should be no dents, scratches, abrasions on the pipelines. Contact between pipelines and aircraft frame elements is not allowed.

Make sure that there are no fuel leaks in the places where pipelines are laid and attached to the units.

Check the integrity of the metallization jumpers and their fastenings

For fastening pipelines located inside the caisson tanks, to avoid corrosion, use clamps only with galvanized steel tape.

When inspecting the fuel system units, it is necessary to make sure that there are no leaks, smudges, cracks, nicks, damage to the paintwork, loosening of the fastening bolts and misalignment.

When inspecting the float device of the portioner, pay special attention to the condition of the floats and their levers.

When carrying out work, it is necessary to ensure that foreign objects, water, snow, dirt do not get into the caisson tanks, pipelines and units.

To dismantle the ESP-323 and ESP-325 pumps, it is necessary to drain the fuel from the tanks. The dismantling of the ESP-319 pump should be carried out without draining the fuel from the tank. It is forbidden to lift pumps by electrical wires.

When installing the pump, do not damage the protective casing of the electric motor

Before installing the units, it is necessary to check the integrity of the seals, make sure that there are no bites, undercuts, dents, deformations, aging nets on the rubber rings. Rubber sealing rings are allowed to be lubricated with MK-8 oil.

After installing the pumps, check their performance by turning them on manually in the pilot's cabin and listening to them.

After repair and dismantling of pipelines and units of the fuel system, it is necessary to flush the fuel supply pipelines to the engines before starting the engine for the first time by turning on the fuel booster pumps.

At any time of the year, it is necessary to monitor the cleanliness of the air intakes of the fuel tank drainage system.

The filler neck drain pipe must not be clogged, as the condensate in it may freeze, break it, and fuel will flow out of the tank through this break.

Checking the operation of the booster pumps and the tightness of the power supply system of the main engines is carried out by turning on the supply tank pumps in turn.

Illumination of the signal lamps indicates that the pumps and the alarm system are working.

This work, as well as work on checking the functioning of other fuel pumps, electromagnetic valves and systems that require power supply, should be carried out when the gas station systems are turned on. To check the tightness of the power supply system of the main engines, open the shut-off valves and after 5 minutes (at least) of the booster pumps, inspect the fuel lines and make sure they are tight. If there is a leak at the pipeline connections between themselves and the units, replace the sealing rubber rings.

When checking the functioning of transfer pumps, set the transfer pump control switching switch to the "Manual" position. When the transfer pumps are turned on in turn, the signal lamps corresponding to them should light up, which indicates that the pumps and the alarm system are in good condition.

The operability of the portioner is checked with the fuel gauge and automatic fuel consumption automatic control on with automatic control of the transfer pumps (the "Automatic - Manual" switch must be in the "Auto" position). Use the green signal lamps of the transfer pumps of tanks No. 2 and 3 to monitor the operation of the pumps. The extinction of these lamps indicates that the portioner is faulty.

To check the operability of the APU fuel pump and the tightness of the shut-off valves 768600MA of the power lines of the main engines, set the APU start switch to the on position, set the "Start - cold scroll" switch to the "Start" position.

Illumination of the "P fuel" display on the APU launch panel indicates that the pump is in good condition. If, after 5 minutes of pump operation, the signal displays "Fuel P" of the main engines on the engine control instrument panel do not go out, then the shut-off valves are tight.

The handles on the refueling shield in the open or closed position of the refueling valves must be in the same plane; their deviation from the plane of ±2 mm is allowed.

Refueling of the aircraft is carried out in accordance with the flight task using a pressurized refueling system.

The main fuel for aircraft engines and the APU engine is kerosene grades T-1, TS-1, T-7 (TS-1 G), T-7P and mixtures of these grades

When refueling an aircraft, safety precautions must be observed. Before starting work, make sure that the aircraft and the tanker are grounded, stop blocks are installed under the front and rear wheels of the main landing gear, and sp. № 67, a safety rod is installed, the plugs are removed from the drainage system intakes. There must be fire extinguishers in the parking lot. Smoking and lighting matches near the aircraft is prohibited. Maintenance of radio and other electrical equipment and replacement of batteries is prohibited. Fuel drained from tanker sedimentation tanks must not contain water and mechanical impurities. The fuel passport must contain the visa of the responsible person authorizing the refueling.

The amount of refueling fuel is determined in accordance with the mission for the flight and the schedule of its consumption and refueling.

When servicing the aircraft fuel system, special care must be taken to follow the safety instructions.

Works on replacement of aggregates, pipelines and other works related to the possibility of open fuel leakage to the ground or to the aircraft structure must be carried out with the aircraft's electrical network de-energized. It is not allowed to get fuel on the electrical wires and electrical equipment of the aircraft. Work in the fuel caisson tanks must be carried out in overalls, in a mask or gas mask in the presence of a liaison officer for observation.

Overalls should be made of cotton with non-sparking fasteners or buttons. The liaison for observation must see the worker in the tank and the signals given by him during the entire work in order to take action in the event of a call for help. When working inside the tank, remove all unnecessary tools and personal items from pockets; do not take metal items with sharp edges into the tank.

To prevent a fire when refueling an aircraft, it is necessary to reliably ground the aircraft, refueling hoses and tankers. Place chocks under the fuel tanker wheels. It must be remembered that the source of a fire can be discharges of static electricity and sparks that appear as a result of metal objects hitting each other. Therefore, in order to avoid the appearance of discharges of static electricity, it is forbidden to use woolen and textile materials for washing, work.

Open the necks of caisson tanks and other containers with combustible materials with your hands, without hitting them with metal objects in order to prevent the appearance of a spark. It is not allowed to rub and drag any metal objects (ladders, boxes, etc.) near the aircraft or under it with open fuel tanks. It is not allowed to walk in shoes lined with nails and metal plates in the immediate vicinity of open tanks.

3.2 Maintenance of the fuel system

Fuel systems are designed to supply the required amount of fuel to the engines. They are a complex of the system: fuel supply to the engine, drainage of fuel tanks, automatic control of fuel consumption and measurement of its quantity.

Pump uppumps. PNL is checked by pressure (where there are pressure gauges), by ear or by the lighting (extinguishing) of alarm lamps, and also control the condition of their seals. The presence of fuel leakage from the drainage tubes of the booster pumps indicates a violation of the stuffing box seals. The correct operation of various valves (fire, shut-off, cross-feed), booster and transfer pumps, pressure alarms and other fuel system control devices are checked.

Servicefueltanks in operation is reduced to their periodic inspection. Malfunctions of soft fuel tanks are: they leak due to poor-quality gluing of the walls of the tanks; detachment or detachment from the inner layer of linings (fastening tapes) of the liquid ribs;

cracks in the inner layer as a result of natural aging of rubber, as well as destruction in the places of sealing of flanges at filler necks, PNL and inter-tank connections.

Controlinternalsuperficialsofttanks carried out through the mounting hatches. The tanks are first purged for 20-30 minutes. compressed air to reduce the concentration of fuel vapors. They work inside the tanks in special overalls, soft shoes and a gas mask with an elongated hose that leads outside the fuel tank. At negative ambient temperatures, due to a decrease in the elasticity of rubber, the installation and dismantling of soft tanks is carried out after they are preheated with warm air with a temperature not exceeding 40-50 degrees.

Bolt tightening torques are specified in the instructions. Their value depends on the design of the tanks and the diameter of the bolts.

Checking the tank for leaks is done by pouring fuel into the entire group of tanks with holding for 10 hours. If there is no leak, the mounting hatch cover bolts are locked and sealed, the false panel is removed, the removable panel is installed and the aircraft is lowered onto the wheels.

Duplication of PNL is expressed in the installation of two pumps operating in parallel, each of which has a capacity sufficient to independently supply the engines with fuel. When working together, each PNL provides approximately half of the fuel consumption of the engines, which reduces the required cavitation pressure reserve and increases the altitude.

The redundancy of the PNL consists in the fact that when one pump fails, the other is switched on. The latter, to increase the survivability of the fuel system, may have a different type of drive.

3.3 Maintaining the fuel system pipes

Pipelines serve to connect the units of a given line and supply fluid. They are subjected to deformation and vibration as a result of the influence of aircraft and engine parts on them.

The main line of rigid pipelines must have flexible sections to reduce vibration exposure.

Rigidpipelines made of duralumin, aluminum-manganese alloys, brass and steel. The latter is used when there is high pressure in the line (fuel supply to the nozzles). To protect against corrosion, pipelines made of aluminum-manganese alloys are anodized, those made of steel are galvanized.

Flexiblepipelines ( hoses) are used to connect rigid pipelines or in areas where installation is difficult.

When installing pipes, avoid elevations in which air could accumulate, as well as deflections that prevent the production and discharge of fluid from the line.

Small pipe bend radius increases hydraulic resistance and stress concentration.

The pipe is bent so that the bending radius (to the pipe axis) is at least three of its outer diameters. In places where it is impossible to bend the pipeline, put squares.

The wall thickness of the pipeline should not be less than 1 mm for pipes made of aluminum alloys and 0.5 mm for steel pipes. The calculated dimensions of the diameter and wall thickness of the pipe are specified according to the dimensions specified by GOST 1947-56 for pipes made of aluminum and aluminum alloys and GOST 8734-58 for seamless cold-drawn and cold-rolled steel pipes.

flanging. Attention is drawn to the fact that the pipelines are fixed to the structural elements of the airframe with special blocks or clamps with gaskets made of rubber, leather or felt. Poor fastening of pipelines can cause their destruction due to material fatigue or chafing against airframe parts, the passages of pipelines through partitions must be flanged, and the pipes in this area are sheathed in leather (leatherette) or protected from chafing with rubber gaskets.

Mountingwithouttightness. When replacing rigid pipelines, make sure that their length and configuration ensure the installation and connection of pipelines without interference. In the free state, there should be a small (0.5 - 1.0 mm) gap between the ends of the nipple connection. A sign of the correct connection of pipelines is the coincidence of the axis of the nipple with the axis of the fitting, while the flared part of the pipeline is joined to the conical surface of the fitting, and the union nut of the pipeline is screwed onto the fitting by hand by at least 2/3 of the thread length.

eliminationleaks. It is forbidden to eliminate the leakage of liquid in the threaded connection by over tightening the nuts. If, after pulling the nuts, the flow does not stop, then find out the cause of the malfunction and eliminate it. At low ambient temperatures, tightening of joints and rubber joints is carried out only after heating them with warm air. Piping should not have sharp bends or dents that could cause connection misalignment.

Metallization. For good electrical contact of the connected pipelines and protection from the accumulation of static electricity charges in them, the reliability of the contact of the metallization of each durite connection is monitored. To do this, pay attention that on the durite tubes under the clamps there is a strip of aluminum foil, the ends of which must be bent under the durite tube to come into contact with the metal tubes cleaned in these places of the paintwork or anode film.

3.4 Aircraft fuel system leak test

General tests of the fuel system are carried out after refueling the aircraft at the airfield to check the tightness.

After the overhaul, the pipelines of the fuel system are tested with compressed air using stands equipped with pressure gauges and monovacuum gauges. The check is carried out on separate highways. The drainage line is checked with the tanks turned off at a pressure of 1140 mm Hg. Art. within 10 min. The pressure drop in the line should not exceed 3 mm Hg. Art. The power line is tested with the tanks turned off under an air pressure of 2 kgf / cm 2. If within 15 minutes. there will be no pressure drop, the line is tested together with tanks under an excess air pressure of 50 mm Hg. Art. measured with a monovacuum gauge. Air during this test is supplied through the drain pipe of the tanks, while the remaining drain, drain and discharge pipes must be plugged and the shut-off valves closed.

Washing method. To detect leaks (leaks), soaping of joints available for inspection is used. Soap foam is prepared either from a soap root (OST 4303) or from ordinary neutral soap with an alkali content of not more than 0.05% with the addition of gelatin as a foaming agent and glycerin to increase viscosity.

3.5 Checking the hardness of fuel tanks

Typical malfunctions of rigid tanks are: destruction of partitions, corrosion of the inner surface of the bottom, shells and frame of the tank, especially near the heads, rivets and from under the sealing gaskets of the reinforcement. On riveted tanks that do not have longitudinal baffles, cracks are often observed in the lower part of the transverse baffles, and sometimes breaks. They appear due to the large one-sided load created by the fuel when the tanks are tilted.

The above malfunctions lead to a violation of the rigidity of the fuel tanks, and, accordingly, affect the strength of the aircraft wing as a whole.

Corrosion of the inner surfaces of the lower shells of the tanks occurs under the action of moisture released from the fuel to the bottom. The shells of riveted fuel tanks are always wavy. Between the seams of the fastening of the partitions, depressions are formed in which water accumulates. This water cannot be drained through the drain hole of the tank. Corrosion spreads especially intensively if the tanks are stored unfilled for a long time.

Examinationtankon thetightness. After inspection, the tank is checked for leaks. If the tank is stamped and does not have internal partitions, then before testing it must be put on a special device that protects the tank from swelling. Tests are carried out under a pressure of 0.2 kgf / cm 2.

Measuressecurityatexaminationtanks. Inspection of the internal structure of the tank is carried out before steaming with illumination by an explosion-proof low-voltage electric lamp or a flashlight with a long trunk; The lantern lamp must be protected from damage. An explosion-proof lamp is placed in a sealed glass cap with carbon dioxide. If the cap breaks, the gas pressure will decrease and the pneumatic switch will cut off the current.

3.6 Control of flexible fuel tanks

Tank malfunctions. The main malfunctions of soft tanks are cracks at the transition points, and thickening of the walls for fittings and the tank lid. These cracks appear as a result of inaccurate removal of tanks at low temperatures.

Checking the tank for tightness is carried out by pouring fuel into the entire group of tanks with a holding time of 10 hours. If there is no leakage, the mounting hatch cover bolts will be locked and sealed.

Tests of the removed tanks for tightness are carried out in a special container by pouring fuel under a pressure of 0.25 kgf / cm 2, or the repaired area is smeared with soapy foam and an overpressure of 0.2 kgf / cm 2 is created in the tanks for 5-10 minutes. In the event of a leak, air bubbles coming out of the tank will be visible in the soap suds.

3.7 Control of fuel tanks-compartments of the wing

Before testing the tank-compartment for tightness, the riveted seams of the tank are coated with chalk water and dried. The tightness test is carried out by filling the tank-compartment with fuel and holding it under a pressure of 0.1 kgf / cm "for one hour, and without pressure for 3 hours. Leaks are detected by the appearance of spots on the chalk coating.

3.8 Strength testing of pipelines

The strength test is carried out with a 1-2% solution of chromium peak (GOST 2652-48) in pure water under a pressure 1.5 times higher than the working pressure for 3-5 minutes. For stainless steel pipelines, pure water without chromium peak can be used. Tightness is usually checked with compressed air in an aquarium placed in an armored chamber. First for 3 min. an excess pressure of 2-3 kgf / cm 2 is supplied inside the pipeline, then it rises to a value close to the working one, and is also maintained for about 3 minutes. The air used must be relatively dry with a dew point of around -40°C.

After the test, the pipelines are blown with air and dried at a temperature of about +150 C.

Chrompeak potassium technical (potassium dichromate technical) K2Cr207 - potassium salt of bichromic acid - orange-red crystals. They produce (GOST 2652-67) the highest grade with a basic substance content of 99.6%, the 1st grade - 99.3% and the 2nd grade - 99.0%. "

rejectionpipelines. Pipelines are rejected in the presence of the following defects: damage to the flaring; twisting, tears, cracks, differences in wall thickness over 0.1 mm and overall thinning of the walls by more than 0.3 mm; recession of the flare in the nipple; ovality, which is more than 20% of the outer diameter; dents, scratches (more than 0.2 mm deep) and nadir exceeding the allowable; damage to the nipple, cracks, nicks, deformations of the increased gap between the nipple cage and the pipeline; damage to the union nut, cracks, deformations, nicks on the thread.

On pipelines, longitudinal risks are more dangerous, because internal pressure tends to break the pipe along the generatrix, so the allowable depth of longitudinal scratches is 0.1 mm. On pipelines not removed from aircraft, it is allowed to leave 0.5 mm deep dents without straightening.

3.9 Corrosion damage to pipelines

The main types of corrosion damage to pipelines are: corrosion damage to the inner surface of pipelines in the presence of corrosive components and impurities in the working fluid (gas).

Corrosion damage to the outer surface of pipelines is accompanied by the formation of through holes or holes of various depths.

As a rule, areas with a damaged protective coating and places of accumulation of dirt and other corrosive substances serve as centers of corrosion pits. Contaminated areas serve as zones of moisture condensation, which creates favorable conditions for the occurrence of chemical or electrochemical corrosion of the pipeline material.

To prevent corrosion damage to pipelines, the safety of their protective coatings is monitored, as well as to ensure that moisture does not get on the pipelines, especially in the places of their fastening, and under the protective sheathing of the pipelines. To do this, tightly close all hatch covers, carefully cover the aircraft with covers, clean drainage holes in a timely manner, etc.

The protective coatings of pipelines are protected from damage, from the ingress of acids and alkalis on them, and the affected areas of the coating are restored in a timely manner.

Piping defects caused by improper maintenance:

damage to the paintwork of pipelines during their dismantling and installation, as well as during the installation and dismantling of units and parts located near pipelines, due to careless handling of the tool;

sharp bends (breaking) of pipelines made in the process of their disassembly and installation; similar kinks in pipelines are also formed due to the presence of installation stresses in them;

infliction of dents, scratches and other damages on pipelines due to careless handling of the tool in the process of performing installation and dismantling works;

collapse of pipelines due to incorrect selection of flanging blocks (the diameter of the recesses of the blocks is less than the diameter of the pipeline);

twisting of pipelines in the process of tightening the nipple connection, etc.

Most of the listed defects are the result of careless handling of the tool by the maintenance personnel during the assembly and disassembly work. A concomitant factor is the operational imperfection of technological systems, the difficult approach to units or pipeline connections.

Fixing the connection. A number of defects are the result of improper installation and dismantling of pipelines. In particular, a frequent defect is the twisting of pipelines, which occurs when the union nut of the nipple connection is tightened without fixing the unit fitting or adapter with another key.

As a rule, fittings or adapters supplied and fixed in the unit in the period preceding the installation of pipelines receive some loosening during operation and therefore have the ability to turn together with the cap nut, nipple and tube when tightening the nipple connection. Therefore, in all cases, when tightening the nipple connection, fix the fitting with a second key.

Deformation of connection details. In the event of inaccurate fitting of the conical part of the pipeline to the cone of the articulated fitting (misalignment), a leak occurs in the connection, which cannot be eliminated even when you try to additionally tighten the union nut. At the same time, over-tightening of the union nut usually leads to deformation of the connection parts.

VIII. Calculation of the fuel drain line in flight by gravity

Draining fuel in flight is used when it is necessary to quickly reduce the landing weight of the aircraft, or when it is necessary to quickly change the balance. For the Tu-154, the maximum landing weight of which is 78000 kg, and the take-off weight fluctuates around 100-102 tons, this means the need to drain up to 24000 kg of fuel. However, not all fuel can be drained by gravity, but only that part of it, which is located in caisson tanks No. 3 on the right and left (total 10850 kg). Fuel is drained through two drain valves through pipelines with a diameter of D=0.036m.

Determine the time for draining fuel from the tanks:

Fuel grade TS-1.

a) I calculate the volume of fuel in one tank No. 3

V = = 6.497 m 3

b) I will make an equation for determining the time to drain an elementary volume of fuel

dt=

where dV - elementary volume of fuel, Q - fuel consumption through the drain line; c) given that the elementary volume dV = FHdH(the area of ​​the liquid mirror in the tank per layer thickness), I will transform the expression to determine the drain time

dt==

d) assuming that the average height of the fuel caisson No. 3 is H? 0.5 m, we determine the average area of ​​the fuel mirror in the tank

e) integrating expression (3) over the height of the tank, I determine the time for draining the fuel from the tank through the drain pipeline (while setting such values ​​as the area of ​​the drain nozzle f = 0010174 m2 and the coefficient of outflow velocity from the nozzle u = 0.82)

t =

and, taking into account that the fuel is drained by gravity (and in the absence of tank pressurization), I finally determine the time for draining fuel from tanks No. 3:

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Let's take a look at the next vital aircraft system - the fuel system. Its main purpose is to ensure an uninterrupted supply of fuel to aircraft engines. The aircraft fuel system consists of a system for placing fuel on an aircraft, a system for supplying it to the engines, systems for measuring fuel in tanks, and filling systems. All fuel, on modern aircraft, is located, as a rule, in the wing, in several tanks. The number of tanks in can be different from three to eight or more. (See fig. 1,2,3) Figure 1 shows the location of the fuel tanks on the Tu-134 aircraft, where 1,2,3 are left and right tanks, "rb" is a supply tank, "db" is additional tanks.

Fig.1

Figure 2 shows the location of the tanks on the Tu-154 aircraft

Fig.2

Figure 3 shows the location of the tanks on the aircraft of the A-320 family. The drain tank at the ends of the wing is designed to flow fuel from other tanks into it, in case of its thermal expansion, when parked with full tanks, as well as for short-term filling of this tank in case of failure of the filling valves, in order to avoid swelling of the tanks.

Fig.3

There are aircraft in which part of the fuel tanks is located in the tail section of the aircraft, for example, Il-62, Boeing-747.
Fuel tank is a caisson, which is a power element of an aircraft wing. From the inside, the fuel tank is covered over the entire surface with a special sealing compound that prevents fuel leaks through butt technological surfaces. This composition, in a liquid state, is applied to the inner surface of the caisson during its manufacture, then on a special stand, the caisson rotates in all planes, ensuring uniform spreading of the sealing composition over the entire inner surface.
The basic principle of the fuel systems of all aircraft is that each engine is fed from its own tank, the left engine from the left tank or tank groups, middle, from the central tank, right engine from the right group of tanks. If there are only two engines on the plane, then first they are powered from the central tank, and then each from its own.
To ensure an uninterrupted supply of fuel to the engines, all fuel tanks, or groups of tanks, are ringed among themselves by means of special ringing valves "1" (see Fig. 4)

Fig.4

Banding cranes are normally closed, and open only in case of failure of any fuel supply system to any engine, ensuring its uninterrupted operation.
In the fuel line of each engine are installed fine filters"4" (Fig. 4). The filter element is made of a twill weave metal mesh with a weave size of only a few microns. In case of clogging of the fuel filter, a bypass pipeline "5" is provided around it (see fig. 4), through which the fuel will go uncleaned, also ensuring the operation of the engine.
A fire cock "3" (Fig. 4) is installed directly in front of the engine, which is closed in case of a fire on the engine. When the aircraft is parked with the engine off, the fire valve is closed.
Aviation fuel is not ideal pure, although it has a high degree of purification, it contains water soluble in it. Water to fuel comes from the atmosphere, during the contact of the surface of the fuel with the air in the fuel tank. Because the density of water is greater than that of the fuel, the water gradually settles and sinks to the bottom of the tank. Before each new refueling and after its completion, the sediment water from the fuel tanks is drained through special drain cocks. This is a mandatory operation when preparing the aircraft for departure. However, dissolved water is still present in the fuel.
As noted on the page, air temperature at an altitude of 10-11 kilometers is -50 0 C. Fuel at such temperatures does not particularly change its properties, but the water dissolved in it crystallizes and getting on the fuel filters, the water crystals completely clog them. To prevent the negative impact of this phenomenon, there are installed in the fuel supply lines to each engine fuel oil coolers(aggregates) TMR (TMA) "2" (see Fig. 4). The installation of these units kills two birds with one stone, firstly, the fuel is heated in them (there is no water crystallization after passing through the TMP), and secondly, the oil from the engine oil system is cooled. That. we get a double benefit. In addition, in order to prevent crystal formation in winter, special additives are added to the fuel of many aircraft, their use also increases the stability of the fuel system.
Based on the condition for maintaining the centering within the specified limits, fuel generation from the tanks is carried out in a certain sequence. Each aircraft has its own, there are aircraft with a simple production sequence, for example, on the B-737, fuel is first produced from the central tank, and then from the wing tanks. There is no sequence at all on the Yak-42, here the centering does not depend on fuel consumption in any way. But there are cases that are more complicated, as an example I will give the sequence of development on the Tu-134 aircraft (see Fig. 1). When fully refueled, first, fuel is produced from 3 tanks completely (1st turn), then fuel begins to be produced from 1 out tanks until the balance in them is 2200 kg (2nd turn). After the balance of 2200 kg in the 1st tanks, the production switches to the 2nd tanks (3rd stage), after the full production from the 2nd tanks, the production again switches to the 1st tanks (2b stage), here there is a complete depletion of fuel. It should be noted that the sequence of fuel production is fully automated and is only controlled by the aircraft crew, but in case of its failure, the production can be carried out manually, but in compliance with the same sequence. That. Each aircraft has its own generation system.
To ensure uninterrupted fuel supply to the engines during evolutions, aircraft are equipped with consumable tanks. All fuel supplied to the engines passes through these tanks. Their meaning is that they are always full. During the flight of the aircraft, they are constantly replenished from the fuel tanks with special transfer pumps; booster fuel pumps. To ensure the reliability of the system, on many aircraft the pumps are paired, and sometimes the power supply of such pumps is made from different tires, i.e. has different voltage.
Transfer pumps include in-tank pumps ETsN-91S, ETsN-91B, off-tank agr.

Fig.5

Signaling the operation of all fuel pumps works according to the following principle: in the fuel pipeline, after each pump, a membrane-type sensor is installed. As soon as the pump starts to work, the fuel pressure in the pipeline behind the pump increases, the sensor membrane flexes and closes the alarm circuit contacts. As a result, in the cockpit on the fuel system panel, the light or indicator of the operation of a particular pump lights up, as soon as the fuel in the tank runs out, the pump starts to draw air, the pressure in the pipeline starts to “jump”, as a result, the light on the fuel panel blinks, signaling the end of fuel . It is not recommended to turn on the pumps without fuel, because fuel is at the same time a lubricating element of the rubbing parts of the pump. All booster and transfer pumps are centrifugal type, mounted as close to the bottom of the tank as possible to ensure maximum fuel recovery.

Measuring fuel in tanks happens with the help capacitive sensors. Such a sensor is, in fact, a capacitor, the capacitance of which varies depending on the medium between the plates. A change in the level of the medium leads to a change in its capacity, by measuring this capacity, in fact, we are measuring the level.
In each tank, in different places, there are several capacitive sensors. Since the height of the tank is different in different places, the length of the sensors will also be different (see fig.6). All capacitive sensors are installed in the tanks and adjusted in such a way that during the evolution of the aircraft, the readings of the sensors on the fuel gauge would not change. Moreover, you can measure both the total amount of fuel and the amount of fuel in each tank separately.
Aircraft refueling fuel can be provided centrally, i.e. through the filling hose, all tanks can be filled at once, and in an open way, i.e. through the top filler necks. The disadvantages of open refueling include the fact that it is possible for dirt, debris and precipitation to enter the tank through the neck, as well as a longer refueling time, because the tanks are refueled one at a time. On modern aircraft, open refueling is no longer used.
To ensure the centering of the aircraft when it is parked, centralized refueling is carried out in a strict sequence. For each aircraft, it has its own. The choice of the sequence of refueling tanks depends on the amount of refueling fuel. If the aircraft does not fly to the maximum distance, then there is no need to refuel full tanks, while some tanks may not be refueled at all, for example, on the Tu-134 with a flight duration of 2 hours, the third tanks are not refueled, on the B-737 the central tank remains dry.
Centralized refueling carried out from a special refueling shield. On it, as a rule, the method of refueling is set (in the machine or manually). With the automatic refueling method, the amount of refueling fuel is set on a special adjuster and the central filling valve opens, filling valves each tank can be opened automatically, or can be opened manually. Closing of the filling valves, when the specified amount of fuel is reached, occurs automatically from the filling sensors, which, structurally, are similar to the sensors of the measurement system, i.e. are capacitive.
With manual centralized refueling, it is necessary to constantly control the amount of fuel being filled in order to avoid refilling the fuel tank.
To prevent refilling in automatic mode, several interlocks for closing the filling valves of each tank are used, both from the filling sensors, and the use of a simple float valve.
Applies to all aircraft fuel tank drainage system. Structurally, they are made in different ways, but they all have the same essence, the fuel tanks must be connected to the atmosphere, otherwise, when the fuel is depleted, a vacuum will begin to form in the tank and the fuel will stop flowing to the engines. The drainage system has another function, which is to prevent the tanks from swelling in the parking lot of the aircraft with a full refueling when the air temperature rises. Some planes simply dump the increased fuel into the parking lot.
It should be noted that fuel measurement when refueling an aircraft, it is made in liters, gallons and other volume dimensions. But the measurement of the amount of fuel filled is already made in kilograms or tons. Why this is done is understandable. The weight of the fuel is already a mass characteristic; you cannot measure the take-off weight in liters.
When refueling an aircraft by any means, safety and fire safety rules are always strictly observed. On the territory of the airport, smoking is generally prohibited in the wrong place. Before refueling, the aircraft itself and the tanker that has approached it are grounded with special cables to special grounding wells, each separately, and a special potential equalization cable is laid between the aircraft and the tanker. Only after laying all these cables, you can connect the refueling hose to the refueling nozzle of the aircraft. Well, that's probably all about the fuel system, if you have any questions write to

The fuel system is designed to place fuel on the aircraft and supply it to the engines and auxiliary power unit in all possible operating conditions of the aircraft.

The purpose of the fuel system is to ensure the supply of fuel to the engines in all possible flight modes for a given aircraft (altitude, speed and overloads) in the right amount and with the necessary pressure. In addition, with the help of fuel transfer (forward-backward), you can change the alignment of the aircraft.

The Boeing 767 fuel system includes; three fuel tanks, two expansion tanks, a ventilation system, a fuel supply system for engines and APU, a refueling and draining system, an emergency fuel dump system, and a fuel quantity indication system.

Fuel tanks.

Fuel tanks are located between 3 and 31 ribs, both wings. Tanks of a caisson design. Dry cavities are located in the leading edge of the wing above the pylon to prevent fuel leakage. Ribs 5 and 18 are sealed and have flaps at the bottom of the baffle. These baffles are necessary to evenly distribute the fuel in the fuel tanks and prevent the accumulation of vapors.

Fig2.1..

The main tanks can be heated by heated slats. The fuel tanks have 59 oval access holes located at the bottom of the wing. At the bottom of the tanks there are drain valves to drain the sludge.

Rice. 2.2.

The central tank is located in the center section, between the ribs 3. The central tank is divided into three parts left, right, and central. As with wing tanks, the center tank also has a dry compartment located at the front of the tank. Three sections are interconnected by nozzles for the flow of liquid and vapor. The central tank has two booster pumps installed in the left and right sections. Sludge drain valves are installed at the bottom of each tank.

The power supply system provides a supply of fuel under pressure to the engines and auxiliary power unit. The power supply system is divided into two subsystems. Subsystems operate independently of each other. They have loopback valves for uniform fuel production from tanks and pumping. Usually each engine is powered by its own tank. If the loopback valve is open, then each engine will be powered from any fuel tank. The shut-off valve controls the flow of fuel to the engine.

Fig.2.3.

The pressure in the fuel system is provided by two booster electric pumps 115V. 400Hz. 3 phases installed in one housing. Pumps are located one in each wing tank. Two booster pumps 115V. 400Hz. 3 phases, installed in the central tank, left and right sections. Pump capacity 13,600 kilograms per hour, minimum pressure 15psi. The booster pumps of the central tank feed the left and right subsystems, respectively, and create a pressure higher than the pressure of the booster pumps of the wing tanks. That allows you to first develop the fuel of the central tank.

Automatic jet pumps, installed two in each tank, designed to collect various impurities and water from the bottom of the tanks. They work due to the vacuum created by booster pumps.

Auxiliary power unit power system.

On the left side of the central tank are the components of the Auxiliary Power Unit power system. With the exception of the casing of the nozzle and the receiver.

The components include;

Booster pump DC 28V.

Stop valve,

Pipeline,

isolation valve,

Pipeline casing.

The booster pump is composed of body, receiver, motor, pressure sensor, pressure valve, temperature valve, discharge valve, check valve,

The check valve prevents fuel from flowing in the opposite direction. The pressure valve regulates the pressure of the pump. The fuel passing through the pump cools it and lubricates the moving parts. The electric motor is located on the outside of the tank. The motor rotates at 6600 rpm and generates a pressure of 18 psi. Productivity 3.1 gallons per minute. The temperature fuse prevents the motor from overheating. The fuse will turn off the pump if the temperature exceeds 3508F ±148F (1778C ±88C). The isolation valve is powered by 28V DC. Installed in the central fuel supply line. Prevents the destruction of the elements of the fuel system of the auxiliary installation.

Rice. 2.4. APU power system