What is the name of the flying helicopter? Why and how a helicopter flies. Which company's radio-controlled helicopter should I choose?
First of all, it is interesting to know how a helicopter flies? What is special about its design?
It is no less interesting to find out what path this, one of the first, heavier-than-air aircraft, took in its development.
This begs the question:
Why did it take centuries for the idea of a helicopter to be brought to life and a modern aircraft suitable for practical needs to appear?
Can a helicopter be a jet?
Isn’t it interesting to get acquainted with the designs and existing designs of helicopters?
You can ask a thousand questions about a helicopter, each more interesting than the other.
But the most interesting question is about the flight capabilities of a helicopter, which determine its practical value for human creative activity.
When it is necessary to use an airplane to land at some place, they first find out whether there is an airfield there on which the airplane could land and from which it could then take off. If there is no airfield or at least a flat area suitable for landing an aircraft near the intended point, then no matter how much the need for an aircraft may be, the question of its use disappears.
The plane lands at high forward speed and makes a long run along the runway until it comes to a complete stop. The plane can take off from the ground
only when, having previously run up the runway, it develops high speed, and for this the plane needs to make a rather long takeoff run. High-speed aircraft reach speeds of more than 200 km/h to take off from the ground, and in order to reach this speed, the aircraft needs a takeoff run of about one kilometer.
The property of an airplane wing is that it creates sufficient lift for takeoff only if it is flown around by air at high speed. If the speed is low, then the lift force is low. If the speed is zero (i.e. the plane is standing still), then there is no lift. In both cases, the plane cannot take off.
In aviation circles in many countries they are already talking about the so-called airfield problem. In fact, there is something to think about if the development of aviation is proceeding at a rapid pace, and each new airfield means hundreds of hectares of excellent land surface, taken away from agriculture, from meadows and arable land. This is especially true for countries with mountainous terrain, whose territory is small.
However, if an indispensable condition for creating lift on the wing is air flowing around it at high speed, then is it possible to make sure that the plane stands still, and the wing moves relative to the air and creates lift?
It is enough to formulate the problem, and the simplest solution will appear: the wings should rotate in a horizontal plane, while they will describe a circle. The rotation of the wings will force the air to flow around them with sufficient speed even when there is no forward speed of the entire apparatus, that is, when the apparatus is standing or hanging in place. The wings become like the blades of a propeller rotating not in a vertical plane, like an airplane with a piston engine, but in a horizontal one. This is the fundamental solution to the airfield problem.
A helicopter's wings rotate like propeller blades. This is where the name of this class of heavier-than-air aircraft comes from - rotorcraft.
This way you can easily answer the following questions.
What is the takeoff speed of a helicopter? - Zero. The helicopter can take off from a standstill.
What is the take-off run of a helicopter? - Zero. A helicopter does not need a takeoff run.
Are the helicopter's landing speed and flight distance high? - Landing speed and run length are also zero, since the helicopter can descend vertically.
Therefore, there is no need for extensive airfields.
The biggest advantage of a helicopter is that it can be used anywhere. It can “land” on the roof of a high-rise building, on the deck of a sea ship or river steamer, on a raft, on a railway platform, on a mountain plateau, on a clearing in the forest, on a car.
For a helicopter, the surface of the landing site can be uneven, slightly inclined, hilly or bumpy, with stumps or buildings, mobile or stationary - nothing will prevent the helicopter from landing and taking off again.
So, the first decisive factor ensuring the widespread use of a helicopter is the ability to take off vertically, without a run, and land vertically, without a run, which does not exclude the possibility of a helicopter taking off and landing like an airplane, i.e., “like an airplane.”
The second decisive factor is the helicopter’s ability to hover motionless in the air, both above the very surface of the earth or water, and at an altitude of several kilometers.
The speed range of each aircraft for each flight altitude is limited, on the one hand, by the maximum speed, and on the other, by the minimum permissible speed. Since the drag of an aircraft increases with flight speed and the engine cannot produce more power than its maximum power, there is a certain maximum speed for steady level flight. A further increase in the maximum flight speed in this case can only occur due to the descent of the aircraft (loss of altitude). The maximum flight speed of modern aircraft reaches 1000 km/h or more.
The minimum permissible speed of jet aircraft, i.e. the lowest speed at which an aircraft is capable of horizontal and curved flight, is 200-300 km per hour. If the speed is even lower, the plane will begin to lose stability and fall onto the wing, followed by a spin.
Light communication aircraft can fly at a speed of no less than 50-70 km/h; for a helicopter, the minimum speed is zero, and the maximum horizontal flight speed is 150-200 km/h. Moreover, the helicopter can stop in the air, turn in place, fly to the sides and even backwards.
Naturally, such capabilities of a helicopter open up broad prospects for its use in a variety of areas of the national economy, sometimes where it would seem that an aircraft cannot be used.
All these positive aspects of the helicopter should not, however, overshadow its negative qualities.
A helicopter cannot fly at high speeds, it still has insufficient stability, is difficult to control and is more vulnerable to small arms fire than an airplane.
A helicopter is a rotary-wing machine in which lift and thrust are generated by a propeller. The main rotor serves to support and move the helicopter in the air. When rotating in a horizontal plane, the main rotor creates an upward thrust (T) and acts as a lifting force (Y). When the main rotor thrust is greater than the weight of the helicopter (G), the helicopter will take off from the ground without a takeoff run and begin a vertical climb. If the weight of the helicopter and the thrust of the main rotor are equal, the helicopter will hang motionless in the air. For a vertical descent, it is enough to make the main rotor thrust slightly less than the weight of the helicopter. The forward motion of the helicopter (P) is ensured by tilting the plane of rotation of the main rotor using the rotor control system. The inclination of the rotor rotation plane causes a corresponding inclination of the total aerodynamic force, while its vertical component will keep the helicopter in the air, and the horizontal component will cause the helicopter to move forward in the corresponding direction.
Fig 1. Force distribution diagram
Helicopter design
The fuselage is the main part of the helicopter structure, serving to connect all its parts into one whole, as well as to accommodate the crew, passengers, cargo, and equipment. It has a tail and end beams for placing the tail rotor outside the rotation zone of the main rotor, and the wing (on some helicopters, the wing is installed to increase the maximum flight speed due to partial unloading of the main rotor (MI-24)). Power plant (engines)is a source of mechanical energy to drive the main and tail rotors into rotation. It includes engines and systems that ensure their operation (fuel, oil, cooling system, engine starting system, etc.). The main rotor (RO) serves to support and move the helicopter in the air, and consists of blades and a main rotor hub. The tail rotor serves to balance the reaction torque that occurs during rotation of the main rotor and for directional control of the helicopter. The thrust force of the tail rotor creates a moment relative to the helicopter's center of gravity, which balances the reactive moment of the main rotor. To turn the helicopter, it is enough to change the amount of tail rotor thrust. The tail rotor also consists of blades and a bushing. The main rotor is controlled using a special device called a swashplate. The tail rotor is controlled by pedals. Take-off and landing devices serve as a support for the helicopter when parked and provide movement of the helicopter on the ground, takeoff and landing. To soften shocks and shocks, they are equipped with shock absorbers. Take-off and landing devices can be made in the form of a wheeled chassis, floats and skis
Fig.2 Main parts of the helicopter:
1 — fuselage; 2 - aircraft engines; 3 — main rotor (carrying system); 4 — transmission; 5 — tail rotor; 6 - end beam; 7 — stabilizer; 8 — tail boom; 9 — chassis
The principle of creating lift by a propeller and the propeller control system
During vertical flightThe total aerodynamic force of the main rotor will be expressed as the product of the mass of air flowing through the surface swept by the main rotor in one second and the speed of the outgoing jet:
Where πD 2/4 - surface area swept by the main rotor;V—flight speed in m/sec; ρ — air density;u —speed of outgoing jet in m/sec.
In fact, the thrust force of the propeller is equal to the reaction force when accelerating the air flow
In order for a helicopter to move forward, the plane of rotation of the rotor must be skewed, and the change in the plane of rotation is achieved not by tilting the main rotor hub (although the visual effect may be just that), but by changing the position of the blade in different parts of the quadrants of the circumscribed circle.
The rotor blades, describing a full circle around the axis as it rotates, are flown around by the oncoming air flow in different ways. A full circle is 360º. Then we take the rear position of the blade as 0º and then every 90º full revolution. So, a blade in the range from 0º to 180º is an advancing blade, and from 180º to 360º is a retreating blade. The principle of this name, I think, is clear. The advancing blade moves towards the oncoming air flow, and the total speed of its movement relative to this flow increases because the flow itself, in turn, moves towards it. After all, the helicopter is flying forward. Lifting force also increases accordingly.
Fig.3 Change in free-stream velocities during rotor rotation for the MI-1 helicopter (average flight speeds).
The retreating blade has the opposite picture. The speed with which this blade seems to “run away” from it is subtracted from the speed of the oncoming flow. As a result, we have less lift. It turns out there is a serious difference in forces on the right and left sides of the propeller and hence the obvious turning point. In this state of affairs, the helicopter will tend to roll over when attempting to move forward. Such things happened during the first experience of creating rotorcraft.
To prevent this from happening, the designers used one trick. The fact is that the main rotor blades are secured to a sleeve (this is such a massive unit mounted on the output shaft), but not rigidly. They are connected to it using special hinges (or similar devices). There are three types of hinges: horizontal, vertical and axial.
Now let's see what will happen to the blade, which is suspended from the axis of rotation on hinges. So, our blade rotates at a constant speed without any external control inputs.
Rice. 4 Forces acting on a blade suspended from a propeller hub on hinges.
From From 0º to 90º, the speed of flow around the blade increases, which means that the lift force also increases. But! The blade is now suspended on a horizontal hinge. As a result of the excess lifting force, it turns in a horizontal hinge and begins to rise upward (experts say “makes a swing”). At the same time, due to an increase in drag (after all, the flow speed has increased), the blade tilts back, lagging behind the rotation of the propeller axis. This is exactly what the vertical ball-nier serves for.
However, when flapping, it turns out that the air relative to the blade also acquires some downward movement and, thus, the angle of attack relative to the oncoming flow decreases. That is, the growth of excess lift slows down. This slowdown is additionally influenced by the absence of control action. This means that the swashplate rod attached to the blade retains its position unchanged, and the blade, flapping, is forced to rotate in its axial hinge, held by the rod and, thereby, reducing its installation angle or angle of attack in relation to the oncoming flow. (The picture of what is happening is in the figure. Here Y is the lift force, X is the drag force, Vy is the vertical movement of air, α is the angle of attack.)
Fig.5 Picture of changes in the speed and angle of attack of the oncoming flow during rotation of the main rotor blade.
To the point 90º excess lift will continue to increase, but at an increasingly slower rate due to the above. After 90º this force will decrease, but due to its presence the blade will continue to move upward, albeit more and more slowly. It will reach its maximum swing height after slightly exceeding the 180º point. This happens because the blade has a certain weight, and inertia forces also act on it.
With further rotation, the blade becomes retreating, and all the same processes act on it, but in the opposite direction. The magnitude of the lifting force drops and the centrifugal force, together with the weight force, begins to lower it down. However, at the same time, the angles of attack for the oncoming flow increase (now the air is moving upward relative to the blade), and the installation angle of the blade increases due to the immobility of the rods helicopter swashplate . Everything that happens maintains the lift of the retreating blade at the required level. The blade continues to descend and reaches its minimum swing height somewhere after the 0º point, again due to inertial forces.
Thus, when the main rotor rotates, the helicopter blades seem to “waving” or they also say “fluttering”. However, you are unlikely to notice this fluttering with the naked eye, so to speak. The lift of the blades upward (as well as their deflection back in the vertical hinge) is very insignificant. The fact is that the centrifugal force has a very strong stabilizing effect on the blades. The lifting force, for example, is 10 times greater than the weight of the blade, and the centrifugal force is 100 times greater. It is the centrifugal force that turns a seemingly “soft” blade that bends in a stationary position into a hard, durable and perfectly functioning element of a helicopter’s main rotor.
However, despite its insignificance, the vertical deflection of the blades is present, and the main rotor, when rotating, describes a cone, albeit a very gentle one. The base of this cone is propeller rotation plane(see Fig.1.)
To impart forward motion to the helicopter, this plane must be tilted so that the horizontal component of the total aerodynamic force appears, that is, the horizontal thrust of the propeller. In other words, you need to tilt the entire imaginary cone of rotation of the propeller. If the helicopter needs to move forward, then the cone must be tilted forward.
Based on the description of the movement of the blade when the propeller rotates, this means that the blade in the 180º position should fall, and in the 0º (360º) position it should rise. That is, at point 180º the lift force should decrease, and at point 0º (360º) it should increase. And this, in turn, can be done by reducing the installation angle of the blade at the 180º point and increasing it at the 0º (360º) point. Similar things should happen when the helicopter moves in other directions. Only in this case, naturally, similar changes in the position of the blades will occur at other corner points.
It is clear that at intermediate angles of rotation of the propeller between the indicated points, the installation angles of the blade must occupy intermediate positions, that is, the installation angle of the blade changes as it moves in a circle gradually, cyclically. This is called the cyclic installation angle of the blade ( cyclic propeller pitch). I highlight this name because there is also a general pitch of the propeller (the general angle of installation of the blades). It changes simultaneously on all blades by the same amount. This is usually done to increase the overall lift of the rotor.
Such actions are performed helicopter swashplate . It changes the installation angle of the main rotor blades (rotor pitch) by rotating them in the axial hinges by means of rods attached to them. Typically, there are always two control channels: pitch and roll, as well as a channel for changing the overall pitch of the main rotor.
Pitch means the angular position of the aircraft relative to its transverse axis (nose up-down), akren, respectively, relative to its longitudinal axis (tilt left-right).
Structurally helicopter swashplate It is quite complicated, but its structure can be explained using the example of a similar unit of a helicopter model. The model machine, of course, is simpler in design than its older brother, but the principle is absolutely the same.
Rice. 6 Helicopter model swashplate
This is a two-blade helicopter. The angular position of each blade is controlled through rods6. These rods are connected to the so-called inner plate2 (made of white metal). It rotates with the propeller and in steady state is parallel to the plane of rotation of the propeller. But it can change its angular position (tilt), since it is fixed to the axis of the screw through a ball joint3. When changing its inclination (angular position), it affects the rods6, which, in turn, act on the blades, turning them in the axial hinges and thereby changing the cyclic pitch of the propeller.
Inner plate at the same time it is the inner race of the bearing, the outer race of which is the outer plate of the screw1. It does not rotate, but can change its tilt (angular position) under the influence of control via the pitch channel4 and roll channel5. Changing its inclination under the influence of control, the outer plate changes the inclination of the inner plate and, as a result, the inclination of the rotor rotation plane. As a result, the helicopter flies in the right direction.
The overall pitch of the screw is changed by moving the inner plate2 along the screw axis using a mechanism7. In this case, the installation angle changes on both blades at once.
For a better understanding, I’m including a few more illustrations of a swashplate screw hub.
Rice. 7 Screw bushing with swashplate (diagram).
Rice. 8 Rotation of the blade in the vertical hinge of the main rotor hub.
Rice. 9 Main rotor hub of the MI-8 helicopter
The control stick determines the cyclic pitch of the main rotor. With its help, the pilot controls the helicopter in roll and pitch. Working with the control stick while hanging is like balancing on the point of a needle. Almost every action requires corresponding correction by other controls. For example, to increase speed, the pilot pushes the stick away from himself, tilting the car forward. In this case, the vertical component in the propeller thrust vector decreases, and it is necessary to increase the overall pitch (raise the “step-throttle” lever) in order not to lose altitude.
1.Control handle. 2. Step-throttle lever. 3.Pedals. 4. Communication management. 5.Compass.
Step-throttle. By raising the pitch-throttle lever, the pilot increases the overall pitch (angle of attack of the blades) of the main rotor, thereby increasing thrust. In the event of a sharp increase in pitch, the reactive torque of the propeller changes, and the helicopter tends to change course. To stay on the chosen trajectory, the pilot works synchronously with the step-throttle lever and the pedals.
The pedals determine the pitch of the stabilizing (“tail”) rotor. With their help, the pilot controls the course of the car. Sharp pedaling affects the reaction torque of the stabilizing propeller and, despite its insignificant mass, has some effect on pitch. “Experienced trainers sometimes show cadets a trick by fixing the control stick and the “step-throttle” and controlling the altitude and speed of the flight, only slightly waving the tail,” says Sergei Druy, “this is how rumors about “radio-controlled helicopters” and other magic appear.”
6. Variometer (vertical speed indicator). 7. Attitude horizon. 8. Airspeed indicator. 9. Tachometer (on the left is the engine speed indicator, on the right is the propeller). 10.Altimeter. 11. Pressure indicator in the intake manifold (gives an idea of the engine power reserve at a given load and weather conditions). 12. Signal lamps. 13. Air temperature in the intake tract. 14.Clock. 15. Engine instruments (oil pressure and temperature, fuel level, on-board voltage). 16. Lighting control. 17. Clutch power drive switch (transmits torque to the propeller after the engine warms up). 18. Main switch. 19. Ignition switch. 20. Cabin heating. 21. Cabin ventilation. 22. Intercom mixer. 23.Radio station.
Distribution of attention
The most important skill in helicopter control is choosing the correct direction of view. Cadets are taught to take off and land while looking at the ground at a distance of 5-15 m in front of them. It's simple geometry. If you look further, right down to the horizon, you may not notice significant changes in height. Helicopter pilots look directly “under the edge of the cockpit” and notice millimeter changes in height. If the cadet chooses the same direction of gaze, he will see small fluctuations, but will not be able to correct them - he will not have enough skills and fine motor skills that come with experience. Therefore, when training, the trainer suggests that the cadet start by looking at 15 m, and then gradually reduce this distance.
The “valve” on the central tunnel controls the friction of the control handle. With its help, the pilot can increase the resistance on the handle until it is completely locked. This feature helps on long cross-country flights.
The basic direction of view in flight along the route is “hood-horizon”. If the position of the horizon relative to the hood does not change, it means that the helicopter is flying at a given altitude at a constant speed. A “peck” will most likely mean an increase in speed and a loss of altitude; a tilt of the horizon line will mean a change in course. “In good weather, you can fly with the instrument panel taped up,” says Sergei Drui, “but you won’t fly far with the cockpit windows taped up.”
Step or gas?
Most modern helicopters have automation that regulates the fuel supply to the engine to keep the rotor speed within a narrow operating range. By turning the handle of the “step-throttle” lever, the pilot can independently control the fuel supply. During flight, the pilot can feel how the handle itself turns slightly in his hand - this is an automatic operation. It happens that newbies in tension squeeze the handle, preventing the machine from working, and a sound signal is heard warning of a drop in revolutions.
Autorotation
The autorotation mode, in which the propeller with a small angle of attack rotates using the energy of the incoming air flow, allows you, if necessary, to select a landing site and land with the engine turned off. To maintain the mode, the pilot looks at the tachometer. If the propeller speed drops below the operating range, you need to smoothly reduce the overall pitch of the propeller. If the speed increases, the collective pitch needs to be increased. At the same time, the helicopter remains fully controllable in terms of heading, roll and pitch.
How does a helicopter fly?
Aviation - how much fascinating and incredible there is in this word! What are the costs of planes and helicopters alone! Have you ever wondered how a helicopter flies? Well, everything is clear with the plane, the wings allow it to stay in the sky without falling, to fly forward, to the side. “But a helicopter doesn’t have such wings,” you say. And you will be only half right. But more on this.
Helicopter flight principle
Probably everyone has seen the propeller located on the roof of the helicopter. He is the one responsible for lifting the car into the air. A large main rotor consists of blades that, when rotated, lift the helicopter. They perform the function of a wing, like an airplane, only they are smaller in size and there are more of them. When the engine starts, the propeller blades begin to rotate, causing the aircraft to fly into the sky. The force that is applied to each wing-blade adds up to a total force that is applied to the entire machine. It is this aerodynamic force, perpendicular to the plane created by the rotation of all the blades and the propeller as a whole, that helps lift a heavy aircraft into the air. If the rotational force of the propeller is greater than the weight of the entire aircraft, it will take off. If the force is less, the flight will not be completed. But if the force is the same, the helicopter will get stuck in place. You can see more details about how the helicopter flies in the video. You will notice that after the blades pick up speed, the helicopter begins to take off, but not immediately. At first it hangs a little, and after it picks up speed, it takes off.
Fuel for flight
For helicopters, gasoline is mainly used - aviation kerosene. But with the development of technology, they are beginning to look for more suitable and less expensive fuel. For example, methane, or rather, cryogenic fuel, which is made from methane. It is resistant to low temperatures (-170 degrees). This is natural gas that can be safely transported by helicopters. Also, the correct answer to the question of what a helicopter flies on is gas such as butane or propane. Such fuel can be transported at normal temperatures. It is excellent for the engine, does not spoil flight quality, and is considered practically the best fuel for an aircraft.
It is worth saying that fuel for a helicopter can be used in completely different ways, but the quality of the flight will deteriorate. Just like in a car, if you fill it with bad, low-quality gasoline, the car drives poorly, so with helicopters: bad fuel negatively affects the operation of the helicopter.
Second screw
You can often see a helicopter with two rotors, one of which is located on the tail. Thanks to him, he takes off. The tail rotor creates resistance to the main rotor. Its blades do not rotate in unison with the main rotor, but vice versa. Thus, by creating thrust, the second propeller balances the force of the carrier, which makes the helicopter take off, while protecting it from “drifting” to the left or right when the large propeller rotates.
But some helicopters do not have a tail rotor. On models of such an aircraft there is another main rotor. It is located under the upper carrier. Its blades, like those of the tail blade, rotate in the opposite direction. Helicopters with this mechanism take off faster because the propellers have the same force when lifting. Such helicopters take to the air a little faster.
HELICOPTERS
Rice. 1. To explain the principle of helicopter flight
The main rotor (RO) serves to support and move the helicopter in the air.
When rotating in a horizontal plane, the NV creates a thrust (T) directed upward, etc. acts as a creator of lift (Y). When the NV thrust is greater than the weight of the helicopter (G), the helicopter will take off from the ground without a takeoff run and begin a vertical climb. If the weight of the helicopter and the thrust of the NV are equal, the helicopter will hang motionless in the air. For a vertical descent, it is enough to make the NV thrust slightly less than the weight of the helicopter. The force (P) for the forward movement of the helicopter is provided by tilting the plane of rotation of the NV using the rotor control system. The tilt of the NV rotation plane causes a corresponding tilt of the total aerodynamic force, while its vertical component will keep the helicopter in the air, and the horizontal component will cause translational movement of the helicopter in the corresponding direction.
Rice. 2. Main parts of the helicopter:
1 – fuselage; 2 – aircraft engines; 3 – main rotor; 4 – transmission; 5 – tail rotor;
6 – end beam; 7 – stabilizer; 8 – tail boom; 9 – chassis
The fuselage is the main part of the helicopter structure, serving to connect all its parts into one whole, as well as to accommodate the crew, passengers, cargo, and equipment. It has a tail and end booms for placing the tail rotor outside the rotation zone of the NV, and the wing (on some helicopters the wing is installed to increase the maximum flight speed due to partial unloading - (MI-24)). The power plant (engines) is a source of mechanical energy to drive the main and tail rotors. It includes engines and systems that ensure their operation (fuel, oil, cooling system, engine starting system, etc.).
The NV serves to support and move the helicopter in the air, and consists of blades
and NV bushings. The transmission serves to transmit power from the engine to the main and tail rotors. The components of the transmission are shafts, gearboxes and couplings. The tail rotor (RT) (both pulling and pushing) is used to balance the reaction torque that occurs during rotation of the rotor and for directional control of the helicopter. The thrust force of the propeller creates a moment relative to the helicopter's center of gravity, which balances the reactive torque from the propeller. To turn the helicopter, it is enough to change the amount of thrust of the helicopter. The RV also consists of blades and a bushing.
The helicopter control system (CS) consists of hand and foot controls. They include command levers (control stick, step-throttle lever and pedals) and wiring systems to the MV and PV. The NV is controlled using a special device called a swashplate. The RV is controlled by pedals.
Take-off and landing devices (TLU) serve as a support for the helicopter when parked and ensure the helicopter moves on the ground, takeoff and landing. To soften shocks and shocks, they are equipped with shock absorbers. Take-off and landing devices can be made in the form of a wheeled chassis, floats and skis.
Rice. 3. General view of the helicopter design (using the example of the MI-24P combat helicopter).
