Improvement of the Mi-8 helicopter fire protection system

Contents

CONTENTS

INTRODUCTION

MAJOR PART

1 Description of Mi- helicopter fire protection system

2. Main system units: purpose, design, operation, location

3 Failures and faults of fire-fighting system, causes of their occurrence and methods of elimination

4 Proposals for improving the fire protection system

5 Maintenance of the Mi- helicopter fire-fighting system

CONCLUSION

LIST OF SOURCES USED

INTRODUCTION

Mi-8 is a Soviet/Russian multi-purpose helicopter developed by the Design Bureau named after M. L. Mil in the early 1960s. It is the most massive twin-engine helicopter in the world (more than 12 thousand copies were built), and is also included in the list of the most massive helicopters in the history of aviation.

Widely used in more than 50 countries of the world for many civilian and military tasks. Mi8 helicopters, as a rule, have a dual purpose, as indicated in the type certificate; in Russia, military helicopters can be sold only by the state-owned company Rosoboronexport, a member of Rostec Corporation. All other helicopters that are on free sale have only a civilian purpose.

The development of a promising medium-sized multi-purpose helicopter under the designation B8, designed to replace the produced model of the Mi4 helicopter, began at the Mile Design Bureau in the second half of the 1950s. First of all, the new car had to use ergonomics as rationally as possible, so the helicopter layout, which became a car type with a longitudinally elongated fuselage, radically changed. The cockpit was located in the front of the fuselage, the engine (one on the first prototype) was above the fuselage. The rest of the place was occupied by either the cargo cabin or the passenger compartment, depending on the modification of the helicopter.

The first prototype B-8 took off on July 9, 1961, it had one AI24 turboprop engine; the second prototype of the B8A - September 17, 1962, it already had two turbo engines TV2117, which were already installed on production vehicles.

After a number of improvements, the Mi-8 was put into mass production in 1965 and adopted by the Soviet Air Force in 1967 and proved to be such a successful machine that purchases of the Mi-8 for the Russian Air Force are still ongoing

Mi-8 is a multifunctional helicopter, the scope of which is expanded by constant modernization and the ability to equip it with a wide range of additional equipment for various tasks. The helicopter can be used in a wide range of conditions and temperatures (from 50 to + 50 degrees Celsius), easy to operate and maintain.

Mi-8 is equipped with a fire protection system that provides detection and elimination of fire centers in engine compartments, reduction compartment and kerosene heater compartment.

Helicopter fire is a much more likely phenomenon than on an airplane. This is due to the fact that in most cases, as in the case of Mi8, fuel tanks are located under the cockpit, not far from the engine.

The causes of the fire may be:

- helicopter combat damage;

- lightning strike;

- static electricity discharges in the tank;

- emergency landing;

- safety violation during helicopter refuelling;

- equipment failure.

Despite the fact that the Mi-8 fire system has proved to be quite reliable, there are significant shortcomings that, using modern experience, can be eliminated. In this work, an improvement of the fire protection system of the Mi-8 helicopter is proposed.

3 Failures and faults of fire-fighting system, causes of their occurrence and methods of elimination

Failures of the fire system that occur during the operation of the helicopter are in most cases due to its design shortcomings and are directly related to compliance with the requirements of operational documentation. The following approaches are recommended for localization and troubleshooting.

If "Automatic queue cylinders started" or "Manual queue cylinders started" annunciator comes ON when the system is ON, then the alarm of the corresponding queue actuation was switched ON spontaneously. To find out the reason, it is advisable to clarify how the power is supplied to these boards.

The peculiarity of the system lies in the fact that power is supplied to the annunciator through relay contacts, and their "minus" circuit is closed through cartridges installed in the fire extinguishers MPS.

In the serviceable state, the power supply circuit of the control winding of these relays is energized, their contacts are open, and the annunciator is not lit. In cases when one of the relays operates as a result of a failure of the cartridge, its contacts close and the annunciator illuminates, indicating the actuation of the cylinders of the manual or automatic queue.

To eliminate the malfunction, as shown by the experience of operation, it is necessary to ensure reliable contact in the head-shutter SR. For this purpose, it is sometimes enough to tighten the SR nut. If the contact has not recovered after tightening, as evidenced by one of the illuminated annunciators, it is necessary to check the reliability of connection of electrical wires to SCR pins of GZSM. A break is possible at the connection point. If the check of the SR condition indicates that there are no damages here, then the possible cause of the malfunction is the failure of one of the cartridges. In such cases, by sequential verification, it is necessary to localize the defective cartridge and replace it .

If "Valve open" annunciator and annunciator indicating fire in the compartment do not come ON when the fire condition of the fire system is checked at the corresponding position of the "Sensor monitoring" rotary selector switch, the most likely is damage to the thermal battery of one or more sensors.

The alarm check is performed by alternating setting of the rotary switch in the following sequence:

- 1, 2, 3, "Leo. dwig. ";

- 1, 2, 3, "Right. dwig. ";

- 1, 2, 3, 4, "Reducer. compartment ";

- 1, 2, "Compartment KO50."

In case of serviceable sensors and integrity of wiring to them in all 12 positions of the selector switch, which correspond to the groups to be checked, annunciators indicating a fire in a particular compartment come ON and fire protection cranes open. Their opening is evidenced by the glowing scoreboard "Crane open."

The fault of the alarm system is eliminated by replacing the damaged sensor. The easiest way to localize a damaged sensor is to alternately replace them with serviceable ones in the corresponding group.

In addition to the considered reason, as follows from the experience of operation, the failure of the alarm system may be due to the closure of the thermal battery of the sensor on its housing due to moisture ingress. Moisture gets when a helicopter with open hoods is parked during rain or during its washing outside. In such cases, the cause is eliminated by blowing and drying the sensors.

More complex and time-consuming is the process of eliminating the failure of the alarm system in the engine compartment due to shunting of the pins of one of the SR due to moisture ingress into it. Plug connectors are located on the fire partitions of the reduction compartment. Moisture falls, despite the fact that they are sealed and covered with protective covers. On the other hand, when drying SR, its sealing plays a negative role. As a result, the fault cause can not be eliminated without disassembling the block and inserting the SR.

Another, although less likely, but more difficult in terms of localization, cause of failure of the alarm system is the closure of the "mass" of the wiring to the sensors of the engine compartments. The difficulty lies in the fact that the wiring is made with a shielded wire with fluoroplastic insulation and has a large length. To prevent the wiring from closing, it is necessary to monitor its condition and prevent the insulation from breaking.

If a false fire system operation occurs, the most likely cause is damage or failure of the FPSIF FBI actuating unit. To eliminate the cause, the failed MFSPFBI unit must be replaced.

A less likely reason is the installation of DPS sensors in the same circuit as DTBG sensors. Interchangeability of these sensors is not allowed.

False actuation of the system is possible during operation of the KO50 heater with open bonnets during helicopter parking. The fire system of this compartment is activated due to the ingress of exhaust gases from the heater on one of the sensors. To prevent false actuation due to this reason, make sure that the lower hood of the compartment is closed before starting KO50.

If "Crane open" and "Automatic queue cylinders went OFF" annunciators come ON with the fire system ON, and the annunciator indicating fire in any compartment does not illuminate, then the most likely cause is moisture ingress into one of SR electromagnetic cranes 781100. The cranes are installed in the compartment of the main reduction gear box, which does not guarantee them from moisture ingress. Note that the opening of the cranes depends on the availability of power on the winding of their electromagnets 94DN. In cases where there was a closure between the pins "1," "2" and "4" of the plug connector, the nature of the failure is the simultaneous operation of the electromagnet and the automatic queue cylinders with the supply of fire extinguishing composition to the corresponding compartment.

If pins "2" and "4" are closed from the presence of moisture in the plug connector, then the electromagnet will not work and the valve will not open, and the fire-extinguishing composition from the automatic queue cylinders will come only to the main line from the cylinders to the electromagnetic valve unit when opening the fire extinguishers head-gates. As a result, the pressure drop to 4050 kg/cm2 is seen from the pressure gauges of the automatic queue cylinders. In view of the above, it is recommended to proceed only after pressure release from this line. The pressure can be released by manually opening the valve of any compartment.

In both versions of pins closing, to eliminate the cause of the fault, it is necessary to disassemble the plug connector of the supply wire bundle and perform its defect. If there are damages, SR shall be replaced. If moisture enters it, you can limit yourself to drying. Moisture ingress is due to the presence of water drain along the wire bundle towards the crane during the compartment washing. To prevent runoff, it is recommended to change the installation of wire bundles so that water does not flow from the bundle to the plug connector.

If during heating of the compartment of the main reduction gear box from the airfield source there is a spontaneous release of the pressure of one of the cylinders, which is determined by their nanometers, then the cause is the rupture of the safety membrane of the fire extinguisher head-shutter. The rupture is due to an increase in pressure in the cylinder to 200 ± 20 kg/cm2 due to local heating. To prevent release of fire extinguishing agent, it is necessary to observe the rules of heating of the main reduction gear box compartment, which exclude local heating of cylinders.

5 Maintenance of Mi-8 helicopter fire protection system

Maintenance of the helicopter fire system consists in systematic and careful monitoring of the devices operability and their attachment. During maintenance, reliability of attachment, absence of cracks and mechanical damages, tightness of the system are checked. Maintenance is due to the performance of certain scheduled operations to keep all devices in good condition.

By checking the fire-fighting system, reliability of fire extinguishers and fire-fighting valve units attachment, tightness of supply and spraying pipelines are monitored. Pressure of composition in fire extinguishers is determined by pressure gauges. If they are discharged, the extinguishers must be charged.

During inspection of the systems units check their integrity, attachment reliability, correct locking of bolts and nuts. If locking is broken, it is replaced. Do not tear the cotter pins, wire and bend the antennae of the locking plates by turning nuts or bolts, as this can lead to thread disruption or screwing out of the studs. Do not reuse locking wire, cotter pins and locking plates. Lock nuts or bolts with wire so that tightening of nut from wire is directed towards wrapping.

When performing dismantling operations during repair and maintenance it is necessary to observe the following rules: clearances between pipelines and structural elements are not less than 3 mm, clearances between pipelines and sharp edges of the structure are not less than 10 mm, when the pipeline passes through the hole edged with a rubber piston, there remains a gap of not less than 1 mm, carefully check the tightness of fuel and oil connections during testing from ground installations, it is mandatory to check tightening of all screws of tightening clamps.

CONCLUSION

Flight safety depends to a large extent on the efficiency and reliability of the systems used to protect them from fires and explosions.

During operation, the Mi-8 helicopter fire system has proven to be a very reliable system. But like any other system, it is not perfect and requires technical improvements.

Based on the above, a refinement was proposed that will increase reliability in cases of fire hazard.

Rework consists in the introduction of the "AlmazUPM" article into the system, which is a voice warning equipment and is designed to automatically provide crew members with emergency, warning and information messages. It is used for timely involvement of crew members in the beginning fire.

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