The most popular Soviet helicopters are still in service in the Russian Air Force and around the world (export version Mi-17). Numerous modifications of these machines are widely used for both military and civilian purposes. They are still in demand in the global helicopter market, are constantly being improved and will be in use for decades to come.
Multipurpose Mi-4 with one piston engine and a four-bladed main rotor, it proved itself well, but its time was over and at the end of the 50s of the last century the development of second-generation helicopters with turboshaft engines began. In 1961, a new car was shown for the first time in Tushino AT 8 with one turboprop engine above the cabin, but still with a main and tail rotor, a tail boom and a transmission inherited from Mi-4. Only the fuselage and power plant were new. AI-24V.
Two engines were installed on the next prototype TV2-117, a main rotor with five blades and a tail rotor of increased rigidity. This machine received the designation and was tested in the air in September 1962. The designers boldly introduced original technical improvements.
Glue-welded joints and large-sized stampings made of duralumin were widely used, the synchronization and speed of the main rotor were regulated by a new automation system, and the external suspension was radically different from the old one. So in the design bureau of M.L. Mil received a start in life with a new gas turbine helicopter.
The aerodynamic configuration is based on a design with one five-blade main rotor and a tail rotor of three blades. The steel main rotor hub with all-metal blades is located in horizontal and vertical hinges and is controlled by a cyclic pitch handle in the longitudinal control. The main rotor and tail rotor blades are equipped with an electric anti-icing system.
The all-metal semi-monocoque fuselage houses the cockpit at the front. Inside, two pilots sit side by side, and an on-board technician sits slightly behind in the middle on a folding seat. A new autopilot that stabilizes the helicopter in roll, pitch, heading and speed, altitude and hovering altitude is included in the standard equipment.
Two turboshaft gas turbine engines TV2-117A are installed on top of the helicopter body in special engine nacelles; the sides of the nacelles fold down and provide a convenient approach to the power plant for maintenance. The air intake located above the engines serves as an air access channel to the oil radiator fan.
The cargo compartment accommodates 24 people on folding seats; in the sanitary version, 12 stretchers are installed for the wounded. There are load securing points on the floor, and a winch with a lifting capacity of 200 kg is located above the front door. A double-leaf cargo hatch and a ramp are used for loading equipment.
The rear part of the fuselage consists of a tail boom with a tail rotor, a Doppler speed and drift meter, a stabilizer and a support that prevents the tail rotor from touching the ground. The helicopter landing gear consists of three supports, the front control strut is fixed in the air during flight, the supports are not retracted.
Standard electronic equipment includes VHF and HF radios, an automatic radio altimeter, an automatic radio compass and a Doppler speed and drift meter.
Since 1989, they have been equipped with a weather radar in a container located under the fuselage, long-range navigation equipment operating using the LORAN system and equipment that stabilizes the helicopter in hovering mode.
In Afghanistan, Soviet helicopters solved a wide range of tasks - transporting personnel and cargo, evacuating the wounded, providing close fire support and much more. Thousands of Soviet officers and soldiers owe their lives to these machines.
In the Afghan war, helicopter pilots improved their tactics by adopting the “spinner” technique; it was used when attacking in a group, when they approached the target from a dive and covered each other on the way out. The chain of firing points was attacked by the front of the helicopters, forming a ledge relative to the leader. Between the mountains in narrow gorges they attacked one after another with the minimum possible interval.
Having no combat experience and shackled by various instructions and restrictions, the pilots who arrived in Afghanistan quickly learned during combat missions. Only those who quickly mastered maneuvers with high overloads survived: turns with a roll of up to 90 degrees, combat turns in the manner of fighters, dives from which the earth filled the entire view in the cockpit, and slides with negative overloads that were unacceptable for a helicopter in theory.
The pilots said that they learned to really fight in Afghanistan and did not tell the Union about their achievements; instructions and prohibitions at home were still in effect.
In general, in this war the annual losses were 30-35 helicopters, an entire regiment was out of action per year, but a large percentage of losses were among the flight personnel. The main losses occurred during the landing and pick-up of paratroopers on areas under fire - 50% and about 15% when transporting people and cargo.
Analyzing disasters and accidents that occurred outside of combat operations, we can state that the main flight accidents occurred: due to the human factor - 41.5%; aircraft failure – 37.7%; bad weather conditions – 7%; for other reasons – 14%.
Here is the most typical disaster due to the human factor. While flying over the city of Grozny on March 10, 2005 in the Chechen People's Republic, the helicopter caught on a high-voltage power line. 15 people died, one managed to survive.
Here is another similar, but more resonant catastrophe. On April 28, 2002, near the village of Ermaki, in poor visibility conditions, he crashed into a power line. On board was the Governor of the Krasnoyarsk Territory Alexander Lebed and his inner circle. Together with the head of the region, 9 people died.
The case of human negligence is confirmed by the following disaster. During a flight from Surgut to Lyantor on August 30, 2001, a cable that fell out of an open door hit the tail rotor area and was thrown into the main rotor. The car became uncontrollable, overturned and crashed into the swamp. Five people died.
In such cases, as they say, comments are unnecessary.
A helicopter is a very complex aircraft with many moving parts. Designing a helicopter requires great engineering and development. To ensure maximum safety and reliability, helicopters are subject to an extremely strict inspection schedule. Helicopter production levels are low due to their complexity, making the price per helicopter much higher than that of a mass-produced product such as a car.
There are two types of helicopter engines:
They are similar to car engines and small airplane engines. They run on high quality gasoline, which is more filtered and purified than gasoline for cars. This type of fuel is called avgas and is usually 100 octane (low lead content).
This type of engine is usually called a jet engine. It is similar in design to the engines found on commercial airliners, but slightly smaller in size.
The jet engine is usually reserved for medium or large helicopters because it produces a large amount of power and weighs little. Such engines are quite expensive. The turbines use a type of fuel called Jet A, similar to very pure kerosene.
The normal cruising speed of a helicopter varies depending on the available power and rotor system. Typical cruising speed for a two-seat trainer style helicopter is 145-170 km per hour, and for a turbine in a 5-seat helicopter it is 210-230 km per hour. The maximum speed of the Bell 206 helicopter is about 250 km per hour.
Helicopters have the ability to take off and land from a vertical position. Hover over one location or fly at very low speeds, turning 360 degrees while hovering, thereby giving passengers panoramic views of remote or tight areas that fixed-wing aircraft cannot reach.
Helicopters, due to their flexibility, are very often called upon in situations where emergency medical assistance is required, or as part of rescue missions. They are extremely valuable in fighting forest fires, which are sometimes impossible to reach by land.
The cost depends on the helicopter model and your location. The average price for training on a two-seater helicopter is approximately €300 per hour. A training program on a four-seat training helicopter also costs €300 per hour. The Federal Aviation Administration requires a minimum of 40 hours of flight time for a private pilot's license, but it is typically 45-55 hours. Training for a private helicopter license can cost up to €18,000, for a commercial license up to €80,000.
There is a false belief that the main engine blades may suddenly stop rotating. First, the main motor does not stop rotating. Secondly, the helicopter can land safely even if the engine fails.
During a failure, the motor is automatically disconnected from the rotating system. With adequate pilot control, the rotor blades will continue to rotate at normal operating speeds, allowing the pilot to make a fully controlled landing. This procedure is called autorotation. Unlike a conventional airplane, which cannot fly below 50 mph, a helicopter that experiences engine failure is able to land with little or no forward movement and in a relatively small space. Usually a parking lot or a small alley is enough for this.
The helicopter's unique capabilities serve humanity in a variety of ways. One of them is flying very close to the ground. Flight rules allow pilots the flexibility they need to make full use of the aircraft and complete their mission safely. Sometimes the weather is not as good as the forecast said, so for safety reasons and in accordance with regulations, pilots keep their distance from the clouds. Pilots undergo very thorough training on how to safely land from different altitudes and at different speeds. Pilots know what combinations of speed and altitude are safe.
Human perception of the height of various moving objects is very complex. Therefore, there are definitions of the concept “low”. The main thing to know is that helicopters can be flown safely at any altitude above the ground, and pilots consider many factors when choosing an altitude.
Pilots select altitude based on various factors, including weather conditions and the purpose of the flight. At an altitude of several thousand meters, strong winds often blow, while winds near the surface of the earth are not so strong. Most of the airspace allows pilots to choose the most efficient flight routes. Areas near airports where planes fly do not have as much flexibility in routes and altitudes. Pilots in urban environments like New York City often fly at the maximum altitude allowed by Air Traffic Control. The department maintains certain physical separation of aircraft. Very often the helicopters you see are flying at their highest altitude. They have a task and are limited by other factors.
Flying a helicopter is magical because it is a unique type of air transport. Many pilots are asked by their new acquaintances, “is it really so great to fly a helicopter?” A professional pilot will usually answer, “Actually, it's my job to make sure you don't feel nervous.” A professional pilot usually receives indirect compliments when passengers do not even realize that they have already arrived at their destination.
Another fact is that very few people become helicopter pilots and then stop flying. Many pilots who fly for a living retire from one pilot job and move on to another. Others, in good health, continue to fly beyond their company's retirement age because they love their job. Novice pilots learn from their knowledge, experience and endurance.
If you are looking for a machine suitable for the role of a “collective image” of a helicopter of the USSR (and Russia), then, without a doubt, it will be the Mi-8. It has been in production since the 1960s - for more than fifty years. During this time, it became one of the most common helicopters in history and in the world, and among twin-engine machines, the G8 is the most popular.
And as of 2015, the Mi-8 is generally the third most common among aircraft in general. But what’s even more remarkable is that it is still being produced and is not going to give up its positions. Of course, many of the G8’s peers are still in service, but in terms of versatility and relevance it still has no equal.
The date of birth of the Mi-8 is February 20, 1958. On this day, the Council of Ministers adopted a resolution on the experimental construction of a medium helicopter, then called “B-8”. The head of the design bureau, Mikhail Mil, planned to use the experience gained during the creation by creating a replacement for the medium Mi-4.
Replacing the piston engine with two turbines promised not only to improve performance, but also to rationalize the layout of the helicopter.
In those years, American companies also abandoned piston engines, replacing them with gas turbines. The power plant of many piston helicopters (including the Mi-4) was usually bulky star-shaped engines that occupied the entire forward part of the fuselage. This placement forced the pilot's cabin to be moved upstairs, and the space of the cargo compartment to be occupied by drive shafts.
The B-8 was initially designed as a multi-purpose aircraft - both the Air Force and Aeroflot were customers.
Passenger, military transport and armed versions were considered.
The first B-8, which took off in the summer of 1961, was a passenger plane, with a comfortable cabin for 18 people. True, the prototype was single-engine. Development of the twin-engine B-8A started later and it flew only in 1962.
The next experimental vehicles were a military transport for 20 paratroopers, equipped with a heavy machine gun mount, and a helicopter for government transport. The fifth prototype became the reference model, and serial production of the Mi-8 began in 1965.
The Mi-8 helicopter is built according to the classic single-rotor design. The helicopter's fuselage is all-metal, its skin is smooth and functional. In the forward part of the fuselage there is a control cabin with seats for pilots and flight technicians. In the central part there is a cargo compartment (or a passenger cabin, depending on the version). The third part of the fuselage consists of the tail and end booms.
The first Mi-8s were equipped with TV2-117 gas turbine engines with a rated power of 1000 hp. every.
In 1967, development of completely new engines, TV3-117, began on the amphibious version of the Mi-14.
The Mi-8MT helicopter with new engines went into production in 1977. It also featured an auxiliary power unit - a small gas turbine designed to spin up the rotors of the main power unit during startup. Previous models were started either from batteries or from an external starter. If one of the engines fails, the second one automatically switches to high power mode, allowing you to complete the flight.
The Mi-8 turbines rotate the propellers through a transmission of three gearboxes - main, intermediate and tail. The main rotor was initially similar to the Mi-4 propeller - all-metal, with four blades. During the tests it was replaced, the number of blades was increased to five. The chassis is wheeled, non-retractable. The nose wheel is self-orienting. The prototype helicopters had wheel fairings, but they were abandoned on production vehicles.
The fuel tanks are external, suspended on the sides. The capacity of the left tank is 1154 liters, the right one, despite the outwardly longer fairing, is 1044 liters. This is explained by the fact that a kerosene cabin heater is located under the fairing of the right tank. Up to two additional tanks with a capacity of 915 liters each can be installed in the cargo compartment. Starting from the Mi-8 MTV model, fuel tanks are protected.
The helicopters were equipped with an AP-34B autopilot. stabilizing the vehicle in roll and pitch (if necessary, both in direction and height). There is a fire-fighting system that allows you to extinguish fire both in the engines and APU, and in the kerosene heater. The hydraulic system is redundant and powers the control system amplifiers.
The number of modifications of the Mi-8 is huge. These include not only passenger and combat vehicles, but also special ones - from fire-fighting versions to marine amphibians. Let's name the main varieties. The main variants of the first series of helicopters with TV2-117 engines were the passenger Mi-8P, transport Mi-8T and combat Mi-8TV. The helicopter for special transportation, with a “superior comfort” cabin, had the index Mi-8PS.
The Mi-14 amphibian was a highly modified Mi-8 with TV3-117 engines. It became a “bridge” to the next generation of Eights, which were exported under the general name Mi-17. In the USSR they were called Mi-8MT. In the 1980s, a new basic model with an increased altitude was launched into production - the Mi-8 MTV. Its improved version was called Mi-8MTV-1, and the universal air assault helicopter received the designation Mi-8 MTV-2.
For export, the new helicopters were sold as the Mi-171, and the modified model for the domestic market became known as the Mi-8 AMT.
In the mid-90s, Russia developed a G8 with improved aerodynamics - the Mi-8MTV-5. The radar installed in the nose of the helicopter required replacing part of the cockpit glazing with an opaque fairing.
Each generation of Mi-8 also included medical modifications, from the Mi-8MB to the Mi-171VA. A number of options were designed for delivery to a specific customer. The Mi-8VSM, an anti-personnel mine layer, also deserves mention. And under the name Mi-9 hides a flying command post for division commanders.
Initially, only a transport helicopter was developed for the troops, but already in 1968, the military was presented with an armed version of it. And armed very powerfully. Up to six blocks of 57mm unguided rockets, or up to 1500 kg of bombs, were suspended on external consoles. Four Phalanx guided missiles made it possible to fight tanks, and the arsenal was complemented by the installation of a 12.7mm machine gun in the pilot’s cockpit.
In terms of firepower, the Mi-8TV was hardly inferior to the specialized attack aircraft Mi-24, but in terms of security it could not compare with it.
Although the cockpit was additionally protected by armor up to 8 mm thick. A clear disadvantage of the helicopter was its increased weight. Fully loaded with weapons and paratroopers, the vehicle had difficulty taking off, and its flight range decreased.
During the war in Afghanistan, 57mm caliber missiles were replaced with more powerful S-8 80mm caliber analogues. The arsenal was replenished with hanging containers with automatic grenade launchers of 30mm caliber or 23mm cannons.
Let's look at the basic flight performance data of the modern Mi-8 AMT modification and compare it with its competitors. An example will be one of the later modifications of the French Puma - AS.532 and the Sikorsky S-92 helicopter.
| Mi-8 AMT | S-92 | AS.532 | |
|---|---|---|---|
| Length, m | 25,3 | 20,8 | 19,5 |
| Take-off weight, t | 11,1 | 12 | 9,3 |
| Maximum speed, km/h | 250 | 283 | 278 |
| Cruising speed, km/h | 230 | 257 | 257 |
| Ceiling, m | 6300 | 4575 | 4100 |
| Flight range (practical), km | 570 | 999 | 618 |
So, the Mi-8 is larger in size, has a larger ceiling (and a later modification in 2013 rose to a maximum altitude of 9 km), but has a shorter flight range. However, additional tanks can be installed on it.
It is worth noting that the S-92 is a purely civilian vehicle, although it was developed on the basis of the multi-purpose S-70. It may seem strange that the table does not include the obvious rival of the Mi-8 - the Iroquois, or more precisely, helicopters of the Bell 212/412 family. The fact is that, despite their prevalence, these are cars of a lighter class, with obviously smaller dimensions and carrying capacity.
When the “eights” began to replace the Mi-4, it became clear that their predecessors were inferior to them in everything. The Mi-8 was superior to the “four” in speed, capacity, and ease of maintenance. For example, gas turbine engines freed mechanics from the constant struggle with lubricant leakage. But in one thing the old helicopter could not be surpassed for a long time - it was higher altitude. Therefore, until the appearance of the Mi-8MT modification, piston Mi-4s continued to operate in the mountains.
Although the passenger version of the Mi-8 was among those “developed from the start,” few such vehicles were produced during Soviet times.
But in the 21st century, foreign and Russian orders for passenger helicopters greatly helped the factories.
Quite often, “versatility” is understood as the ability of a machine to do everything, but poorly. The range of tasks that the Mi-8 helicopter solved, and successfully, casts doubt on the fairness of this approach. During his half-century career, he transported cargo and passengers, served in the air forces of African countries and in the Russian Ministry of Emergency Situations.
The Eight operated as an air hospital and a flying crane. Mines were laid and trawled from its side. The helicopter served as an attack aircraft and reconnaissance aircraft. Of course, one could write off its prevalence as an inevitable result of the USSR’s sphere of influence, but the Mi-8 was officially exported to Western countries back in Soviet times. And the demand for it did not stop with the collapse of the Soviet Union. All that remains is to recognize the G8 as a real masterpiece of helicopter engineering.
GENERAL CHARACTERISTICS OF THE MI-8T HELICOPTER
1. GENERAL INFORMATION ABOUT THE HELICOPTER
The Mi-8 helicopter is designed to transport various cargoes inside the cargo compartment and on an external sling, mail, passengers, as well as for carrying out construction, installation and other work in hard-to-reach areas.
Rice. 1.1. Mi-8 helicopter (general view)
The helicopter (Fig. 1.1) is designed using a single-rotor design with a five-blade main rotor and a three-blade tail rotor. The helicopter is equipped with two TV2-117A turboprop engines with a take-off power of 1,500 hp. each, which ensures high flight safety, since flight is possible even if one of the engines fails.
The helicopter is operated in two main versions: the passenger Mi-8P and the transport Mi-8T. The passenger version of the helicopter is designed for interregional and local transportation of passengers, luggage, mail and small-sized cargo. It is designed to carry 28 passengers. The transport option provides for the transportation of cargo weighing up to 4000 kg or passengers in the amount of 24 people. At the request of the customer, the passenger cabin of the helicopter can be converted into a cabin with increased comfort for 11 passengers.
The passenger and transport versions of the helicopter can be converted into an ambulance version and into a version for operation with an external sling.
The ambulance version of the helicopter allows you to transport 12 bedridden patients and an accompanying medical worker. In the version for working with external sling, large cargo weighing up to 3000 kg is transported outside the fuselage.
For long-range helicopter flights, it is possible to install one or two additional fuel tanks in the cargo compartment.
Existing versions of the helicopter are equipped with an electric winch, which allows, using an onboard boom, to lift (lower) loads weighing up to 150 kg on board the helicopter, and also, if there is a pulley system, to pull wheeled loads weighing up to 3000 kg into the cargo compartment.
The helicopter crew consists of two pilots and a flight mechanic.
When creating the helicopter, special attention was paid to high reliability, efficiency, ease of maintenance and operation.
Safety of flights on the Mi-8 helicopter is ensured by:
The installation of two TV2-117A(AG) engines on the helicopter, the reliability of the operation of these engines and the VR-8A main gearbox;
The ability to fly in the event of failure of one of the engines, as well as switch to autorotation mode (self-rotation of the main rotor) in the event of failure of both engines;
The presence of compartments that isolate the engines and the main gearbox using fire partitions;
Installation of a reliable fire protection system that ensures extinguishing a fire in the event of its occurrence, both simultaneously in all compartments and in each compartment separately;
Installation of backup units in the main systems and equipment of the helicopter;
Reliable and effective anti-icing devices for main and tail rotor blades, engine air intakes and cockpit windshields, which allows flight in icing conditions;
Installation of equipment that ensures simple and reliable piloting and landing of a helicopter in various meteorological conditions;
Drive of the main units of the systems from the main gearbox, ensuring the operability of the systems in the event of engine failure:
The ability to quickly leave the helicopter after landing by passengers and crew in emergency situations.
2. BASIC HELICOPTER DATA
Flight data
(transport and passenger options)
Take-off weight (normal), kg.................. 11100
Maximum flight speed (instrument), km/h, 250
Static ceiling, m........................ 700
Instrument cruise speed at altitude
500 m, km/h ……………………………………………220
Economic flight speed (instrument), km/h. 120
fuel 1450 kg, km................................ 365
option with fuel filling 2160 kg, km. . .620
Flight range (at an altitude of 500 m) in ferry
option with fuel filling 2870 kg, km... 850
Flight range (at an altitude of 500 m) with refueling
fuel 2025 kg (outboard tanks of increased
capacity), km................................................... ..575
Flight range (at an altitude of 500 m) in ferry
version with fuel filling 2735 kg (outboard tanks
increased capacity), km.... 805
Flight range (at an altitude of 500 m) in ferry
version with fuel refueling 3445 kg (outboard tanks
increased capacity), km.... 1035
Note. Flight range is calculated taking into account 30 minutes of fuel remaining after landing
Geometric data
Helicopter length, m:
without main and tail rotors................... 18.3
with rotating main and tail rotors ...25,244
Helicopter height, m:
without tail rotor................................... 4.73
with rotating tail rotor................ 5.654
Distance from the tip of the main rotor blade to
tail boom when parked, m.................. 0.45
Distance from ground to bottom of fuselage
(clearance), m................................................... ...... 0.445
Horizontal tail area, m 2 ..... 2
Helicopter parking angle................. 3°42"
Fuselage
Cargo compartment length, m:
without cargo doors........................ 5.34
with cargo doors at 1 m from the floor 7.82
Cargo compartment width, m:
on the floor................................................ ... 2.06
for heating ducts........................ 2.14
maximum........................................ 2.25
Cargo compartment height, m.................. 1.8
Distance between power floor beams, m ... 1.52
Escape hatch size, m…………………… 0.7 X1
Loading ramp track, m.............. 1.5±0.2
Passenger cabin length, m............ 6.36
Passenger cabin width (floor), m... 2.05
Passenger cabin height, m 1.8
Seat pitch, m................................................... .... 0.74
Passage width between seats, m... 0.3
Wardrobe dimensions (width, height, depth), m 0.9 X1.8 X 0.7
» sliding door (width, height), m. 0.8 X1.4
» opening, along the rear entrance door in the passenger
option (width, height), m.......... 0.8 X1>3
Size of emergency hatches in passenger compartment
option, m........................................ 0, 46 X0.7
Crew cabin size, m................... 2.15 X2.05 X1.7
Adjustment data
Angle of installation of the main rotor blades (according to the rotor pitch indicator):
minimum................................................. 1°
maximum........................................ 14°±30"
Deflection angle of the trimmer plates of the propeller blades -2 ±3°
» installation of tail rotor blades (at r=0.7) *:
minimum (left pedal all the way) ................... 7"30"±30"
maximum (right pedal all the way)………….. +21°±25"
* r- relative radius
Weight and centering data
Take-off weight, kg:
maximum for transport option…….. 11100
» with a load on an external sling …………… 11100
transport option........................... 4000
on external sling......................... 3000
passenger version (person).......... 28
Empty helicopter weight, kg:
passenger version........................... 7370
transport »................................ 6835
Weight of service load, including:
crew weight, kg................................... 270
» oil, kg................................................... ............. 70
weight of products, kg................................................... 10
» fuel, kg................................................... .......... 1450 - 3445
» commercial load, kg........................ 0 - 4000
Empty helicopter alignment, mm:
transport option........................................ +133
passenger » ..................................... +20
Acceptable alignments for a loaded helicopter, mm:
front................................................... ............. +370
rear................................................... .................... -95
3. AERODYNAMIC AND GEOMETRIC CHARACTERISTICS OF THE HELICOPTER
According to the aerodynamic design, the Mi-8 helicopter is a fuselage with a five-bladed main rotor, three-bladed tail rotor and fixed landing gear.
The main rotor blades are rectangular in plan with a chord equal to 0.52 m. The rectangular plan is considered aerodynamically worse than others, but it is easy to manufacture. The presence of trimmer plates on the blades allows you to change their torque characteristics.
The blade profile is the most important geometric characteristic of the rotor. The helicopter has different profiles along the length of the blade, which significantly improves not only the aerodynamic characteristics of the main rotor, but also the flight properties of the helicopter. From the 1st to the 3rd section, the NACA-230-12 profile is used, and from the 4th to the 22nd - the NACA-230-12M profile (modified) *. The NACA-230-12M airfoil has Mkr = 0.72 at an angle of attack of zero lift. As the angle of attack a° increases (Fig. 1.2), Mcr also decreases at the most favorable angle of attack, at which the lift coefficient C y = 0.6, Mcr = 0.64. In this case, the critical speed in the standard atmosphere above sea level will be:
V KP == a Mkr = 341 0.64 = 218 m/s, where a is the speed of sound.
Consequently, at the ends of the blades it is possible to create a speed of less than 218 m/s, at which shock waves and wave resistance will not appear. At the optimal rotor speed of 192 rpm, the peripheral speed of the blade tips will be:
U = wr = 2 prn / 60 = 213.26 m/s, where w is the angular velocity;
r is the radius of the circle described by the tip of the blade.
Rice. 1.2. Change in the lift coefficient C y from the angles of attack a° and the M number of the NACA-230-12M profile
This shows that the peripheral speed is close to the critical speed, but does not exceed it. The helicopter main rotor blades have a negative geometric twist, varying linearly from 5° at the 4th section to 0° at the 22nd section. In the section between the 1st and 4th sections there is no twist and the installation angle of the blade sections in this section is 5°. Twisting the blade by such a large amount significantly improved its aerodynamic properties and the flight characteristics of the helicopter, and therefore the lift force is more evenly distributed along the length of the blade.
* The compartment from the 3rd to the 4th section is transitional. Main rotor blade profile - see fig. 7.5.
The propeller blades have variable both absolute and relative profile thickness. The relative thickness of the profile c is 13% in the butt, in the area from r =_0.23 to 7 = 0.268 - 12%, and in the area from r = 0.305 to the end of the blade - 11.38%. Reducing the thickness of the blade towards its end improves the aerodynamic properties of the propeller as a whole by increasing the critical speed and Mkr of the end parts of the blade. Reducing the thickness of the blade towards the tip leads to a decrease in drag and a decrease in the required torque.
The main rotor of a helicopter has a relatively large fill factor - 0.0777. This coefficient makes it possible to create greater thrust with a moderate propeller diameter and thereby keep the blades in flight at small installation angles, at which the angles of attack are closer to the most advantageous ones in all flight modes. This made it possible to increase the efficiency of the propeller and delay stalling at higher speeds.
Rice. 1.3. Helicopter rotor polarity in hovering mode: 1 - without ground influence; 2 - with the influence of the earth.
The aerodynamic characteristics of a helicopter main rotor are presented in the form of its polar (Fig. 1.3), which shows the dependence of the thrust coefficient Cp and the torque coefficient tcr on the total pitch of the main rotor<р. По поляре видно, что чем больше общий шаг несущего винта, тем больше коэффициент крутящего момента, а следовательно, больше коэффициент тяги. При наличии «воздушной подушки» тяга несущего винта будет больше, чем без нее при том же шаге винта и коэффициенте крутящего момента.
The tail rotor blades are rectangular in plan with the NACA-230M profile and do not have geometric twist. The presence of a combined horizontal joint of the “cardan” type and a flapping compensator at the tail rotor hub allows for a more even redistribution of the lift force over the surface swept by the propeller in flight.
The helicopter fuselage is aerodynamically asymmetrical. This can be seen from the curves of changes in the coefficients of fuselage lift C 9f and drag coefficient C depending on the angle of attack a f (Fig. 1.4). The lift coefficient of the fuselage is zero at an angle of attack slightly greater than 1, therefore the lift force will be positive at angles of attack greater than G, and negative at angles of attack less than 1. The minimum value of the fuselage drag coefficient C will be at an angle of attack equal to zero. Due to the fact that at angles of attack greater or less than zero the coefficient C f increases, it is advantageous to fly at angles of attack of the fuselage close to zero. For this purpose, a forward tilt angle of 4.5° is provided for the main rotor shaft.
A fuselage without a stabilizer is statically unstable, since an increase in the angle of attack of the fuselage leads to an increase in the coefficient of longitudinal moment, and, consequently, the longitudinal moment acting on pitching up and tending to further increase the angle of attack of the fuselage. The presence of a stabilizer on the tail boom of the fuselage provides longitudinal stability to the latter only at small installation angles from +5 to -5° and in the range of small angles of attack of the fuselage from -15 to + 10°. At large angles of installation of the stabilizer and large angles of attack of the fuselage, which corresponds to flight in autorotation mode, the fuselage is statically unstable. This is explained by the disruption of flow from the stabilizer. Due to the helicopter having good controllability and sufficient control margins in all flight modes, it uses a stabilizer that is not controllable in flight with an installation angle of 6°.
Rice. 1.4. Dependence of the lift coefficient Suf and drag coefficient Схф of the fuselage on the angle of attack a° of the fuselage
In the transverse direction, the fuselage is stable only at large negative angles of attack -20° in the range of gliding angles from -2 to + 6°. This is due to the fact that an increase in the sliding angles leads to an increase in the roll moment coefficient, and consequently, the lateral moment, which tends to further increase the sliding angle.
In terms of direction, the fuselage is unstable at almost all angles of attack at small sliding angles from -10 to +10°; at angles greater than these, the stability characteristics improve. At sliding angles of 10°< b < - 10° фюзеляж нейтрален, а при скольжении больше 20° он приобретает путевую устойчивость.
If we consider the helicopter as a whole, although it has sufficient dynamic stability, it does not cause any great difficulties when piloting even without an autopilot. The Mi-8 helicopter is generally rated with satisfactory stability characteristics, and with the automatic stabilization systems turned on, these characteristics have improved significantly, the helicopter is given dynamic stability in all axes and therefore piloting is significantly easier.
4. HELICOPTER LAYOUT
The Mi-8 helicopter (Fig. 1.5) consists of the following main parts and systems: fuselage, takeoff and landing devices, power plant, transmission, main and tail rotors, helicopter control, hydraulic system, avionics and electronic equipment, cabin heating and ventilation systems , air conditioning systems, air and anti-icing systems, devices for external load suspension, rigging, mooring and household equipment. The helicopter fuselage includes a nose 2 and central 23 parts, a tail 10 and end 12 beams. In the bow, which is the cockpit, there are pilot seats, instrument panels, electric consoles, an AP-34B autopilot, and command control levers. The glazed cockpit provides good visibility; the right 3 and left 24 blisters are equipped with emergency release mechanisms.
In the forward part of the fuselage there are niches for installing containers with batteries, airfield power plug connectors, air pressure receiver tubes, two taxi and landing lights and a hatch with a cover 4 for access to the power plant. The forward part of the fuselage is separated from the central part by connecting frame No. 5N, in the wall of which there is a doorway. A folding flight mechanic's seat is installed in the door opening. At the front, on the wall of frame No. 5N, there are shelves for radio and electrical equipment, at the rear there are containers for two batteries, a box and an electric winch control panel.
In the central part of the fuselage there is a cargo compartment, to enter which there is a sliding door 22 on the left, equipped with an emergency release mechanism. A side boom is attached to the outside of the upper front corner of the sliding door opening. The cargo compartment has folding seats along the right and left sides. On the floor of the cargo compartment there are mooring units and an electric winch. Above the cargo compartment there are engines, a fan, a main gearbox with a swashplate and a main rotor, a hydraulic panel and a consumable fuel tank.
Shock absorbers and struts of the main 6, 20 and front landing gear, outboard fuel tanks 7, 21 are attached to the fuselage components from the outside. A kerosene heater is located in front of the right outboard fuel tank.
The cargo compartment ends in a rear compartment with cargo doors. In the upper part of the rear compartment there is a radio compartment in which panels for radio and electrical equipment are installed. There is a hatch to enter the radio compartment and tail boom from the cargo compartment. Cargo doors cover the opening in the cargo compartment, intended for rolling in and out of wheeled vehicles, loading and unloading large cargo.
In the passenger version, 28 passenger seats are attached to special profiles located along the floor of the central part of the fuselage. On the starboard side in the rear of the cabin there is a wardrobe. The right side panel has six rectangular windows, the left - five. The rear side windows are built into the emergency hatch covers. The cargo doors in the passenger version are shortened, the luggage compartment is located on the inside of the left door, and the boxes for containers with batteries are located in the right door. There is an opening in the cargo doors for the rear entrance door, consisting of a door and a ladder.
Rice. 1.5 Layout diagram of the helicopter.
1-front chassis leg; 2-nose fuselage; 3, 24-sliding blisters; 4-engine exit hatch cover; 5, 21 main landing gear legs; 6-hood heater KO-50; 7, 12-outboard fuel tanks; 8-hoods; 9-gear frame; 10-central part of the fuselage; 11-hatch cover in the right cargo door; 12, 19-load doors; 13-tail boom; 14-stabilizer; 15-end beam; 16-fairing; 17-tail support; 18-ladders; 20-sash flap; 23-sliding door; 25-emergency hatch-window.
The tail boom is attached to the central part of the fuselage, to the nodes of which the tail support and the uncontrolled stabilizer are attached. The tail shaft of the transmission runs inside the tail boom in its upper part. An end beam is attached to the tail boom, inside of which an intermediate gearbox is installed and the end part of the transmission tail shaft passes through. A tail gearbox is attached to the end beam on top, on the shaft of which a tail rotor is mounted.
The helicopter has a non-retractable tricycle landing gear. Each landing gear is equipped with liquid-gas shock absorbers. The wheels of the front strut are self-orienting, the wheels of the main struts are equipped with shoe brakes, for the control of which the helicopter is equipped with an air system.
The power plant includes two TV2-117A engines and systems that ensure their operation.
To transmit power from the engines to the main and tail rotors, as well as to drive a number of units, a transmission is used, consisting of main, intermediate and tail gearboxes, a tail shaft, a fan drive shaft and a main rotor brake. Each engine and main gearbox has its own autonomous oil system, made according to a direct single-circuit closed circuit with forced oil circulation. To cool the engine oil coolers and main gearbox, starter generators, alternators, air compressor and hydraulic pumps, the helicopter is equipped with a cooling system consisting of a high-pressure fan and air ducts.
The engines, main gearbox, fan and panel with hydraulic units are covered by the hood. When the hood covers are open, free access to the units of the power plant, transmission and hydraulic system is provided, while the open hood covers of the engines and main gearbox are working platforms for performing maintenance of helicopter systems.
The helicopter is equipped with means of passive and active fire protection. Longitudinal and transverse fire partitions divide the engine compartment into three compartments: the left engine, the right engine, and the main gearbox. The active fire protection system supplies extinguishing agent from four cylinders to the burning compartment.
The main rotor of a helicopter consists of a hub and five blades. The bushing has horizontal, vertical and axial hinges and is equipped with hydraulic dampers and centrifugal blade overhang limiters. The all-metal construction blades have a visual spar damage alarm system and an electrothermal anti-icing device.
The tail rotor is a pusher, pitch variable in flight. It consists of a cardan-type hub and three all-metal blades equipped with an electrothermal anti-icing device.
The helicopter's dual control consists of longitudinal-transverse control, directional control, combined "Pitch-throttle" control and main rotor brake control. In addition, there is separate control of engine power and engine shutdown. Changing the overall pitch of the main rotor and longitudinal-transverse control of the helicopter are carried out using a swashplate.
To ensure control of the helicopter, the system of longitudinal, transverse, directional control and collective pitch control includes irreversible hydraulic boosters, for powering which the helicopter has a main and backup hydraulic systems.
The four-channel AP-34B autopilot installed on the Mi-8 helicopter ensures stabilization of the helicopter in flight in roll, heading, pitch and altitude.
To maintain normal temperature conditions and clean air in the cabins, the helicopter is equipped with a heating and ventilation system that supplies heated or cold air to the crew and passenger cabins. When operating a helicopter in areas with a hot climate, instead of a kerosene heater, two on-board freon air conditioners can be installed.
The helicopter's anti-icing system protects the main and tail rotor blades, the two front windows of the cockpit and the engine air intakes from icing.
The anti-icing device for the propeller blades and cockpit windows is electrothermal, and the engine air intakes are air-thermal.
The aviation and radio-electronic equipment installed on the helicopter ensures flights day and night in simple and difficult weather conditions.
The first version of the Mi-8 helicopter with a four-blade main rotor was tested in 1962. In October 1963, testing began on the second version with a five-bladed main rotor, which was put into mass production at the end of 1965.
The Mi-8 is equipped with an anti-icing system that operates in both automatic and manual modes. The helicopter's external suspension system allows it to transport cargo weighing up to 3000 kg. If one of the engines fails in flight, the other engine automatically switches to increased power, while horizontal flight is performed without reducing altitude. The Mi-8 is equipped with an autopilot that provides stabilization of roll, pitch and yaw, as well as a constant flight altitude. Navigation and flight instruments and radio equipment that the helicopter is equipped with allow it to fly at any time of the day and in difficult weather conditions.
The helicopter is mainly used in transport (Mi-8T) and passenger versions. In the passenger version, the Mi-8P is equipped to carry 28 passengers. By special order, in Kazan, a version with a luxury cabin can be manufactured, designed for seven passengers. Orders were completed for B. Yeltsin, N. Nazarbayev, M. Gorbachev and others. The military version of the Mi-8T has pylons for mounting weapons (nursing missiles, bombs). The next military modification of the Mi-8TV has reinforced pylons for hanging a large number of weapons, as well as a machine gun mount in the bow of the cabin. By moving the RV to the left side, its effectiveness was increased.
The Mi-8MT is the latest modification of the helicopter, which was the logical conclusion of the transition from a transport to a transport-combat helicopter. More modern TVZ-117 MT engines are installed with an additional AI-9V gas turbine unit and a dust protection device at the entrance to the air intakes. To combat surface-to-air missiles, there are systems for dispersing hot engine gases, shooting false thermal targets and generating pulsed IR signals. In 1979-1988 The Mi-8MT helicopter took part in the military conflict in Afghanistan.
Helicopter modifications:
Mi-8T (Hip-C)- the main military transport modification.
Mi-8TV- modernized version with enhanced weapons.
Mi-8TVK- export version of the Mi-8TV with 6 Malyutka ATGMs.
Mi-9- a flying command helicopter based on the Mi-8T.
Mi-8SMV- electronic warfare and electronic warfare helicopter.
Mi-8PPA- a modernized version of the Mi-8SMV in the role of a communications helicopter and an electronic warfare helicopter.
Mi-8MT- transport and combat helicopter based on the Mi-8TV (1991).
Performance characteristics of the Mi-8 helicopter:
Year of adoption - 1966.
The diameter of the main propeller is 21.29 m.
The diameter of the tail rotor is 3.91 m.
Length - 18.22 m.
Height - 5.65 m.
Weight, kg
- empty - 7260,
- normal takeoff - 11100,
- maximum take-off - 12200.
Internal fuel - 1450 + 1420 kg.
Engine type - 2 GTD Klimov TV2-117A (TV3-117MT).
Power - 2 x 1710 hp. (2 x 3065 hp)
Maximum speed - 260 km/h.
Cruising speed - 225 km/h.
Practical range - 1200 km.
Range - 465 km.
Practical ceiling - 4500 m.
Static ceiling - 1900 m.
Crew - 2-3 people.
Based on site materials
