The speed during landing and takeoff of an aircraft are parameters calculated individually for each airliner. There is no standard value that all pilots must adhere to, because aircraft have different weights, dimensions, and aerodynamic characteristics. However, the value of speed at is important, and failure to comply with the speed limit can result in tragedy for the crew and passengers.

How is takeoff carried out?

The aerodynamics of any airliner are determined by the configuration of the wing or wings. This configuration is the same for almost all aircraft except for small details. The lower part of the wing is always flat, the upper part is convex. Moreover, it does not depend on this.

The air that passes under the wing when gaining speed does not change its properties. However, the air that passes through the top of the wing at the same time becomes narrower. Consequently, less air flows through the top. This results in a pressure difference under and above the aircraft's wings. As a result, the pressure above the wing decreases, and below the wing it increases. And it is precisely thanks to the pressure difference that a lifting force is generated, which pushes the wing upward, and along with the wing, the aircraft itself. At the moment when the lifting force exceeds the weight of the airliner, the plane lifts off the ground. This happens with an increase in the speed of the liner (as the speed increases, the lift force also increases). The pilot also has the ability to control the flaps on the wing. If you lower the flaps, the lift force under the wing changes vector, and the plane sharply gains altitude.

It is interesting that the smooth horizontal flight of the airliner will be ensured if the lifting force is equal to the weight of the aircraft.

So, lift determines at what speed the plane will leave the ground and begin flight. The weight of the airliner, its aerodynamic characteristics, and the thrust force of the engines also play a role.

during takeoff and landing

In order for a passenger plane to take off, the pilot needs to reach a speed that will provide the required lift. The higher the acceleration speed, the higher the lift will be. Consequently, with a high acceleration speed, the plane will take off faster than if it were moving at a low speed. However, the specific speed value is calculated for each aircraft individually, taking into account its actual weight, load level, weather conditions, runway length, etc.

To broadly generalize, the famous Boeing 737 passenger airliner takes off from the ground when its speed increases to 220 km/h. Another famous and huge Boeing 747 with a lot of weight takes off from the ground at a speed of 270 kilometers per hour. But the smaller Yak-40 airliner is capable of taking off at a speed of 180 kilometers per hour due to its low weight.

Types of takeoff

There are various factors that determine the speed at which an airliner takes off:

1. Weather conditions (wind speed and direction, rain, snow).
2. Runway length.
3. Strip coating.

Depending on the conditions, takeoff can be carried out in different ways:

1. Classic speed dial.
2. Off the brakes.
3. Takeoff using special means.
4. Vertical climb.

The first method (classic) is used most often. When the airfoil is of sufficient length, the aircraft can confidently gain the required speed necessary to provide high lifting force. However, in the case where the length of the runway is limited, the aircraft may not have enough distance to reach the required speed. Therefore, he stands on the brakes for some time, and the engines gradually gain traction. When the thrust becomes high, the brakes are released, and the plane takes off sharply, quickly picking up speed. In this way, it is possible to shorten the take-off distance of the aircraft.

There is no need to talk about vertical takeoff. It is possible if special engines are available. And takeoff using special means is practiced on military aircraft carriers.

What is the speed of the plane when landing?

The airliner does not land on the runway immediately. First of all, the speed of the airliner decreases and the altitude decreases. First, the plane touches the runway with its landing gear wheels, then moves at high speed on the ground, and only then slows down. The moment of contact with the GDP is almost always accompanied by shaking in the cabin, which can cause anxiety among passengers. But there's nothing wrong with that.

The speed when landing an aircraft is practically only slightly lower than when taking off. A large Boeing 747 approaches the runway at an average speed of 260 kilometers per hour. This is the speed the airliner should have in the air. But, again, the specific speed value is calculated individually for all aircraft, taking into account their weight, load, and weather conditions. If the plane is very large and heavy, then the landing speed should be higher, because during landing it is also necessary to “maintain” the required lift force. Already after contact with the airfoil and when moving on the ground, the pilot can brake using the landing gear and flaps on the wings of the aircraft.

Flight speed

The speed at which an airplane lands and takes off is very different from the speed at which an airplane moves at an altitude of 10 km. Most often, airplanes fly at 80% of their maximum speed. Thus, the maximum speed of the popular Airbus A380 is 1020 km/h. In fact, flight at cruising speed is 850-900 km/h. The popular Boeing 747 can fly at a speed of 988 km/h, but in fact its speed is also 850-900 km/h. As you can see, the flight speed is radically different from the speed when the plane lands.

Note that today the Boeing company is developing an airliner that will be able to reach flight speeds at high altitudes of up to 5,000 kilometers per hour.

Finally

Of course, the speed when landing an aircraft is an extremely important parameter, which is calculated strictly for each airliner. But it is impossible to name a specific value at which all planes take off. Even identical models (for example, Boeing 747) will take off and land at different speeds due to various circumstances: workload, amount of fuel loaded, length of the runway, runway coverage, presence or absence of wind, etc.

Now you know what the speed of the plane is when landing and when it takes off. Everyone knows the averages.

The question of what speed a plane develops during takeoff interests many passengers. The opinions of non-professionals always differ - some mistakenly assume that the speed is always the same for all types of a given aircraft, others correctly believe that it is different, but cannot explain why. Let's try to understand this topic.

Takeoff

Take-off is a process that spans the time scale from the start of the aircraft's movement to its complete lift-off from the runway. Takeoff is possible only if one condition is met: the lift force must acquire a value greater than the mass of the object taking off.

Types of takeoff

Various “interfering” factors that have to be overcome to get an airplane into the air (weather conditions, wind direction, limited runway, limited engine power, etc.) have prompted aircraft designers to create many ways to circumvent them. Not only the design of flying vehicles has improved, but also the process of their takeoff. Thus, several types of takeoff were developed:

• Off the brakes. Acceleration of the aircraft begins only after the engines reach the set thrust mode, and until then the aircraft is held in place using the brakes;
• A simple classic take-off, which involves a gradual increase in engine thrust as the aircraft moves along the runway;
• Take-off using aids. Typical for aircraft performing combat service on aircraft carriers. The limited runway distance is compensated by the use of ski-jumps, ejection devices, or even additional rocket engines installed on the aircraft;
• Vertical take-off. Possible if the aircraft has engines with vertical thrust (for example, the domestic Yak-38). Such devices, similar to helicopters, first gain altitude from a standing position vertically or when accelerating from a very short distance, and then smoothly transition to horizontal flight.

Consider, as an example, the takeoff phases of a Boeing 737 turbofan aircraft.

Takeoff of a passenger Boeing 737

Almost every civil aircraft takes off according to the classical scheme, i.e. the engine gains the required thrust directly during the takeoff process. It looks like this:

• The aircraft begins to move after the engine reaches about 800 rpm. The pilot gradually releases the brakes while keeping the control stick neutral. The run starts on three wheels;
• To begin lifting off the ground, the Boeing must acquire a speed of about 180 km/h. When this value is reached, the pilot smoothly pulls the handle, which leads to the deflection of the flaps and, as a consequence, the raising of the nose of the device. Then the plane accelerates on two wheels;
• With its nose raised and on two wheels, the aircraft continues to accelerate until the speed reaches 220 km/h. When this value is reached, the aircraft takes off from the ground.

Profile at mid-span

• Relative thickness (ratio of the maximum distance between the upper and lower arch of the profile to the length of the wing chord) 0.1537
• Relative leading edge radius (ratio of radius to chord length) 0.0392
• Relative curvature (ratio of the maximum distance between the profile centerline and the chord to the length of the chord) 0.0028
• Trailing edge angle 14.2211 degrees

Profile at mid-span

Wing profile closer to the tip

• Relative thickness 0.1256
• Relative leading edge radius 0.0212
• Relative curvature 0.0075
• Trailing edge angle 13.2757 degrees

Wing profile closer to the tip

Wing end profile

• Relative thickness 0.1000
• Relative leading edge radius 0.0100
• Relative curvature 0.0145
• Trailing edge angle 11.2016 degrees

Wing end profile

• Relative thickness 0.1080
• Relative leading edge radius 0.0117
• Relative curvature 0.0158
• Trailing edge angle 11.6657 degrees

Wing parameters

• Wing area 1135 ft² or 105.44 m².
• Wingspan 94’9’’ or 28.88 m (102’5’’ or 31.22 m with winglets)
• Relative wing aspect ratio 9.16
• Root chord 7.32%
• End chord 1.62%
• Wing taper 0.24
• Sweep angle 25 degrees

Auxiliary control includes wing mechanization and an adjustable stabilizer.

The steering surfaces of the main control are deflected by hydraulic actuators, the operation of which is provided by two independent hydraulic systems A and B. Any of them ensures the normal operation of the main control. Steering actuators (hydraulic actuators) are included in the control wiring according to an irreversible scheme, i.e. aerodynamic loads from the steering surfaces are not transmitted to the controls. The forces on the steering wheel and pedals are created by loading mechanisms.

If both hydraulic systems fail, the elevator and ailerons are manually controlled by the pilots, and the rudder is controlled using the standby hydraulic system.

Lateral control

Lateral control

Lateral control is carried out by ailerons and flight spoilers.

If there is hydraulic supply to the aileron steering actuators, the lateral control operates as follows:

• the movement of the steering wheels of the steering wheels is transmitted via cable wiring to the aileron steering actuators and then to the ailerons;
• in addition to the ailerons, the aileron steering actuators move the spring rod (aileron spring cartridge), connected to the spoiler control system and thus set it in motion;
• the movement of the spring rod is transmitted to the spoiler ratio changer. Here the control effect decreases depending on the amount of deflection of the speed brake lever. The more the spoilers are deflected in the air brake mode, the lower the transfer coefficient of the steering wheel's roll movement;
• Then the movement is transmitted to the spoiler control mechanism (spoiler mixer), where it is added to the movement of the spoiler control handle. On a wing with the aileron raised, the spoilers are raised, and on the other wing they are lowered. Thus, the functions of the air brake and lateral control are performed simultaneously. Interceptors are activated when the steering wheel is turned more than 10 degrees;
• Also, along with the entire system, the cable wiring moves from the device for changing the gear ratio to the gearing device (lost motion device) of the steering wheel connection mechanism.

The engagement device connects the right steering wheel with the cable wiring for controlling the spoilers when the misalignment is more than 12 degrees (rotation of the steering wheel).

If there is no hydraulic power supply to the aileron steering drives, they will be deflected by the pilots manually, and when the steering wheel is turned at an angle of more than 12 degrees, the cable wiring of the spoiler control system will be driven. If at the same time the spoiler steering gears work, then the spoilers will work to assist the ailerons.

The same scheme allows the co-pilot to control the roll spoilers when the commander's control wheel or aileron cable wiring is jammed. In this case, he needs to apply a force of about 80-120 pounds (36-54 kg) to overcome the pre-tensioning force of the spring in the aileron transfer mechanism, deflect the steering wheel more than 12 degrees and then the spoilers will come into operation.

When the right steering wheel or spoiler cables are jammed, the commander has the opportunity to control the ailerons, overcoming the spring force in the steering wheel coupling mechanism.

The aileron steering actuator is connected by cable wiring to the left steering column through the loading mechanism (aileron feel and centering unit). This device simulates the aerodynamic load on the ailerons when the steering gear is operating, and also shifts the position of zero forces (trimming effect mechanism). The aileron trim mechanism can only be used when the autopilot is disabled, since the autopilot controls the steering gear directly and will override any movements of the loading mechanism. But when the autopilot is turned off, these forces are immediately transferred to the control wiring, which will lead to an unexpected roll of the aircraft. To reduce the likelihood of unintentional aileron trim, two switches are installed. In this case, trimming will occur only when both switches are pressed simultaneously.

To reduce the effort during manual control (manual reversion), the ailerons have kinematic servo compensators (tabs) and balancing panels (balance panel).

Servo compensators are kinematically connected to the ailerons and deflect in the direction opposite to the aileron deflection. This reduces aileron hinge moment and yoke forces.

Balancing panel

Balancing panels are panels connecting the leading edge of the aileron to the rear spar of the wing using hinged joints. When the aileron deflects, for example, downward, a zone of increased pressure appears on the lower surface of the wing in the aileron zone, and a vacuum appears on the upper surface. This pressure difference spreads into the area between the leading edge of the aileron and the wing and, acting on the trim panel, reduces the aileron hinge moment.

In the absence of hydraulic power, the steering drive operates as a rigid rod. The trimmer effect mechanism does not provide a real reduction in effort. You can trim the forces on the steering column using the rudder or, in extreme cases, by varying the thrust of the engines.

Pitch control

The longitudinal control surfaces are: the elevator, provided by a hydraulic steering drive, and the stabilizer, provided by an electric drive. The pilot's control wheels are connected to the hydraulic elevator drives using cable wiring. In addition, the autopilot and Mach trim system influence the input of the hydraulic drives.

Normal control of the stabilizer is carried out from switches on the helms or by the autopilot. Backup control of the stabilizer is mechanical using the control wheel on the central control panel.

The two halves of the elevator are mechanically connected to each other using a pipe. The elevator hydraulic actuators are powered by hydraulic systems A and B. The supply of hydraulic fluid to the actuators is controlled by switches in the cockpit (Flight Control Switches).

One working hydraulic system is enough for normal operation of the elevator. In case of failure of both hydraulic systems (manual reversion), the elevator is manually deflected from either of the control wheels. To reduce the hinge moment, the elevator is equipped with two aerodynamic servo compensators and six balancing panels.

The presence of balancing panels makes it necessary to set the stabilizer to a full dive (0 units) before de-icing. This installation prevents slush and anti-icing fluid from entering the balance panel vents (see aileron balance panels).

The hinge moment of the elevator, when the hydraulic drive is running, is not transmitted to the steering wheel, and the forces on the steering wheel are created using the spring of the trim effect mechanism (feel and centering unit), to which, in turn, forces are transferred from the hydraulic aerodynamic load simulator (elevator feel computer) .

Trimmer effect mechanism

When the steering wheel is deflected, the centering cam rotates and the spring-loaded roller comes out of its “hole” onto the side surface of the cam. Trying to return under the action of the spring, it creates a force in the control leash, preventing the steering wheel from deflecting. In addition to the spring, the actuator of the aerodynamic load simulator (elevator feel computer) acts on the roller. The higher the speed, the stronger the roller will be pressed against the cam, which will simulate an increase in speed pressure.

A special feature of the two-piston cylinder is that it applies the maximum of two command pressures to the feel and centering unit. This is easy to understand from the drawing, since there is no pressure between the pistons, and the cylinder will only be in the drawn state if the command pressures are the same. If one of the pressures becomes greater, the cylinder will shift towards higher pressure until one of the pistons hits a mechanical barrier, thus eliminating the cylinder with lower pressure from operation.

Aerodynamic load simulator

The elevator feel computer input receives the flight speed (from the air pressure receivers installed on the fin) and the position of the stabilizer.

Under the influence of the difference between total and static pressures, the membrane bends downward, displacing the command pressure spool. The greater the speed, the greater the command pressure.

The change in the position of the stabilizer is transmitted to the stabilizer cam, which acts through a spring on the command pressure spool. The more the stabilizer is deflected to pitch up, the lower the command pressure.

The safety valve is activated when there is excess command pressure.

Thus, the hydraulic pressure from hydraulic systems A and B (210 atm.) is converted into the corresponding command pressure (from 14 to 150 atm.), affecting the feel and centering unit.

If the difference in command pressures becomes more acceptable, the FEEL DIFF PRESS signal is issued to the pilots with the flaps retracted. This situation is possible if one of the hydraulic systems or one of the air pressure receiver branches fails. No action is required from the crew as the system continues to function normally.

Mach Trim System

This system is an integrated function of the Digital Aircraft Control System (DFCS). The MACH TRIM system ensures speed stability at Mach numbers greater than 0.615. As the M number increases, the MACH TRIM ACTUATOR electromechanism shifts the neutral of the trim effect mechanism (feel and centering unit) and the elevator automatically deflects to a pitching position, compensating for the diving moment from the forward shift of the aerodynamic focus. In this case, no movements are transmitted to the steering wheel. Connecting and disconnecting the system occurs automatically as a function of the M number.

The system receives the M number from the Air Data Computer. The system is two-channel. If one channel fails, MACH TRIM FAIL is indicated when Master Caution is pressed and goes out after Reset. In case of a double failure, the system does not work and the signal is not extinguished; it is necessary to maintain the M number of no more than 0.74.

The stabilizer is controlled by trimming electric motors: manual and autopilot, as well as mechanically, using the control wheel. In case of jamming of the electric motor, a clutch is provided that disconnects the transmission from the electric motors when force is applied to the control wheel.

Stabilizer control

The manual trim motor is controlled from push switches on the pilot's controls, and when the flaps are extended, the stabilizer moves at a higher speed than when they are retracted. Pressing these switches disables the autopilot.

Speed ​​Trim System

This system is an integrated feature of the Digital Aircraft Control System (DFCS). The system controls the stabilizer using the autopilot servo to ensure speed stability. It can be triggered shortly after takeoff or during a missed approach. Conditions favoring triggering include light weight, rear alignment and high engine operating conditions.

The speed stability enhancement system operates at speeds of 90 – 250 knots. If the computer detects a change in speed, the system automatically turns on when the autopilot is turned off, the flaps are extended (at 400/500 regardless of the flaps), and the N1 engine speed is more than 60%. In this case, more than 5 seconds must have passed since the previous manual trim and at least 10 seconds after lifting off the runway.

The principle of operation is to shift the stabilizer depending on changes in the speed of the aircraft, so that during acceleration the aircraft tends to lift its nose and vice versa. (When accelerating from 90 to 250 knots, the stabilizer automatically shifts to pitch up by 8 degrees). In addition to changes in speed, the computer takes into account engine speed, vertical speed and approach to stall.

The higher the engine mode, the faster the system will start to operate. The greater the vertical rate of climb, the more the stabilizer works to dive. When approaching stall angles, the system automatically turns off.

The system is two-channel. If one channel fails, the flight is permitted. If you are rejected twice, you cannot fly out. If a double failure occurs in flight, QRH does not require any action, but it would be logical to increase speed control during the approach and missed approach phases.

Track control

The directional control of the aircraft is provided by the rudder. There is no servo compensator on the steering wheel. Steering deflection is provided by one main steering gear and a backup steering gear. The main steering drive operates from hydraulic systems A and B, and the backup one from the third (standby) hydraulic system. The operation of any of the three hydraulic systems fully ensures directional control.

The rudder is trimmed using the knob on the center console by shifting the neutral of the trim mechanism.

On aircraft of the 300-500 series, a modification of the rudder control circuit (RSEP modification) was carried out. RSEP –Rudder System Enhancement Program.

An external sign of this modification is the additional “STBY RUD ON” display in the upper left corner of the FLIGHT CONTROL panel.

Directional control is carried out by pedals. Their movement is transmitted by cable wiring to the pipe, which, rotating, moves the control rods of the main and reserve steering drives. A trimmer effect mechanism is attached to the same pipe.

Wing mechanization

Wing mechanization and control surfaces

Engine transient

The figure shows the nature of the transient processes of the engine with the RMS turned off and running.

Thus, when the RMS is operating, the throttle position is determined by the given N1. Therefore, during takeoff and climb, the engine thrust will remain constant, with the throttle position unchanged.

Features of motor control when the PMC is turned off

When the RMS is turned off, the MEC maintains the specified N2 speed, and as the speed increases during takeoff, the N1 speed will increase. Depending on conditions, the increase in N1 can be up to 7%. Pilots are not required to reduce throttle during takeoff unless engine limits are exceeded.

When selecting the engine mode on takeoff, with the RMS turned off, you cannot use the technology for simulating the outside air temperature (assumed temperature).

During the climb after takeoff, it is necessary to monitor the N1 speed and promptly correct its increase by tidying the throttle.

Automatic traction

Autothrottle is a computer-controlled electromechanical system that controls engine thrust. The machine moves the throttles so as to maintain the given speed N1 or the given flight speed throughout the entire flight from take-off to touching down on the runway. It is designed to work in conjunction with the autopilot and navigation computer (FMS, Flight Management System).

The autothrottle has the following operating modes: takeoff (TAKEOFF); climb (CLIMB); occupying a given altitude (ALT ACQ); cruise flight (CRUISE); decrease (DESCENT); approach (APPROACH); missed approach (GO-AROUND).

The FMC transmits to the autothrottle information about the required operating mode, specified N1 speed, maximum continuous engine speed, maximum speed for climb, cruising and missed approach, as well as other information.

Features of automatic traction control in case of FMC failure

In case of FMC failure, the autothrottle computer calculates its own limit speed N1 and displays the “A/T LIM” signal to the pilots. If the autothrottle is operating in takeoff mode at this moment, it will automatically turn off with an “A/T” failure indication.

The automatically calculated N1 revolutions can be within (+0% -1%) of the FMC climb N1 limits.

In the go-around mode, the automatically calculated N1 revolutions provide a smoother transition from approach to climb and are calculated based on the conditions for ensuring a positive climb gradient.

Features of the automatic traction control when the RMS is not working

When the RMS is not working, the position of the throttle no longer corresponds to the specified speed N1 and, in order to prevent overspeeding, the automatic traction reduces the forward limit of throttle deviation from 60 to 55 degrees.

Flight speed

Speed ​​nomenclature used in Boeing manuals:

• Indicated airspeed (Indicated or IAS) - airspeed indicator reading without corrections.
• Indicated ground speed (Calibrated or CAS). The indicated ground speed is equal to the indicated speed, to which aerodynamic and instrumental corrections have been made.
• Indicated speed (Equivalent or EAS). The indicator speed is equal to the earth's indicator speed, which is corrected for air compressibility.
• True speed (True or TAS). The true speed is equal to the indicated speed, corrected for air density.

Let's start explaining speeds in reverse order. The true speed of an airplane is its speed relative to the air. Airspeed is measured on an airplane using air pressure receivers (APRs). They measure the total pressure of the stagnant flow p* (pitot) and static pressure p(static). Let us assume that the air pressure on an airplane is ideal and does not introduce any errors and that the air is incompressible. Then the device that measures the difference in the resulting pressures will measure the air velocity pressure p * − p = ρ * V 2 / 2 . The velocity head depends on both the true speed V, and on air density ρ. Since the instrument scale is calibrated under terrestrial conditions at standard density, under these conditions the instrument will show the true speed. In all other cases, the device will show an abstract value called indicator speed.

Indicated speed V i plays an important role not only as a quantity necessary for determining airspeed. In horizontal steady flight for a given aircraft mass, it uniquely determines its angle of attack and lift coefficient.

Considering that at flight speeds of more than 100 km/h, air compressibility begins to appear, the real pressure difference measured by the device will be somewhat greater. This value will be called the earth's indicator speed V i 3 (calibrated). Difference V i − V i 3 called the compressibility correction and increases as altitude and flight speed increase.

A flying plane distorts the static pressure around it. Depending on the installation point of the pressure receiver, the device will measure slightly different static pressures. The total pressure is practically not distorted. The correction for the location of the static pressure measurement point is called aerodynamic (correction for static source position). An instrumental correction for the difference between this device and the standard is also possible (for Boeing it is assumed to be zero). Thus, the value shown by a real device connected to a real PVD is called instrument speed (indicated).

The combined speed and M number indicators display the ground indicator (calibrated) speed from the Air data computer. The combined speed and altitude indicator displays the indicated speed, obtained from pressures taken directly from the air pressure pump.

Let's look at typical faults associated with air pressure pumps. Typically, the crew recognizes problems during takeoff or shortly after leaving the ground. In most cases, these are problems associated with freezing of water in pipelines.

If the pitot probes are clogged, the speed indicator will not indicate an increase in speed during the takeoff roll. However, after liftoff, the speed will begin to increase as the static pressure decreases. The altimeters will work almost correctly. With further acceleration, the speed will increase through the correct value and then exceed the limit with a corresponding alarm (overspeed warning). The difficulty of this failure is that for some time the instruments will show almost normal readings, which can create the illusion that normal operation of the system has been restored.

If the static ports are clogged during the takeoff run, the system will operate normally, but during the climb it will show a sharp decrease in speed down to zero. The altimeter readings will remain at the airfield altitude. If pilots try to maintain the required airspeed by reducing pitch while climbing, they usually end up exceeding the maximum speed limit.

In addition to cases of complete blockage, partial blockage or depressurization of pipelines is possible. In this case, recognizing a failure can be much more difficult. The key is to identify systems and instruments that are not affected by the failure and terminate the flight with their help. If there is an angle of attack indication, fly inside the green sector; if not, set the pitch and speed of the N1 engines in accordance with the flight mode according to the Unrelaible airspeed tables in QRH. Get out of the clouds if possible. Ask traffic control for assistance, bearing in mind that they may have incorrect information about your altitude. Do not trust devices whose readings were suspect, but at the moment seem to be working correctly.

As a rule, reliable information in this case: inertial system (position in space and ground speed), engine speed, radio altimeter, stick shaker activation (approaching stall), EGPWS activation (dangerous approach to the ground).

The graph shows the required engine thrust (aircraft drag) in level flight at sea level in a standard atmosphere. Thrust is in thousands of pounds and speed is in knots.

Takeoff

The takeoff trajectory extends from the launch point until the climb reaches 1,500 feet, or the end of flap retraction and airspeed. V FTO (final takeoff speed), which of these points is higher.

The maximum take-off weight of the aircraft is limited by the following conditions:

1. The maximum permissible energy absorbed by the brakes in the event of an aborted takeoff.
2. Minimum permissible climb gradient.
3. The maximum permissible operating time of the engine in take-off mode (5 minutes), in the case of a continued take-off to gain the required altitude and acceleration to remove the mechanization.
4. Available take-off distance.
5. Maximum permissible certified take-off weight.
6. Minimum permissible height of flight over obstacles.
7. Maximum permissible ground speed for lift-off from the runway (based on the strength of the tires). Typically 225 knots, but 195 knots possible. This speed is written directly on the tires.
8. Minimum evolutionary take-off speed; V MCG (minimum control speed on the ground)

Minimum permissible climb gradient

In accordance with airworthiness standards FAR 25 (Federal Aviation Regulations), the gradient is normalized in three segments:

1. With the landing gear extended and the flaps in the takeoff position, the gradient should be greater than zero.
2. After retracting the landing gear, the flaps are in the takeoff position - a minimum gradient of 2.4%. Take-off weight is limited, as a rule, by meeting this requirement.
3. In cruising configuration, the minimum gradient is 1.2%.

Takeoff distance

The available takeoff field length includes the operating length of the runway, taking into account the stopway and clearway.

The available take-off distance cannot be less than any of the three distances:

1. Continued takeoff distances from the start of movement to a screen height of 35 feet and a safe speed V 2 when engine fails at decision speed V 1 .
2. Distances of rejected takeoff, in case of engine failure at V EF. Where V EF(engine failure) - the speed at the moment of engine failure, it is assumed that the pilot will recognize the failure and take the first action to abort takeoff at decision speed V 1 . On a dry runway, the effect of reversing a running engine is not taken into account.
3. Take-off distances with normally operating engines from the start of movement to the climb of a conventional obstacle of 35 feet, multiplied by a factor of 1.15.

The available take-off distance includes the working length of the runway and the length of the end safety strip (Stopway).

The length of the Clearway may be added to the available take-off distance, but not more than half of the airborne portion of the take-off path from the take-off point to a climb of 35 feet and a safe speed.

If we add the length of the landing gear to the length of the runway, we can increase the takeoff weight, and the decision speed will increase, to achieve a climb of 35 feet above the end of the landing gear.

If we use a clearway, we can also increase the take-off weight, but the speed of decision-making will decrease since we need to ensure that the aircraft stops in the event of a rejected takeoff with the increased weight within the operating length of the runway. In the case of a continued takeoff in this case, the aircraft will climb to 35 feet off the runway but over a clearway.

Minimum permissible height of flight over obstacles

The minimum permissible clearance over obstacles on a net takeoff trajectory is 35 feet.

“Clean” is a takeoff trajectory whose climb gradient is reduced by 0.8% compared to the actual gradient for the given conditions.

When constructing a standard exit from the airfield area after takeoff (SID), a minimum gradient of the “clean” trajectory of 2.5% is laid down. Thus, to complete the exit procedure, the aircraft's maximum takeoff weight must provide a climb gradient of 2.5 +0.8 = 3.3%. Some egress patterns may require a higher gradient, necessitating a reduction in take-off weight.

Minimum take-off speed

This is the ground indicator speed during the take-off roll at which, in the event of sudden failure of a critical engine, it is possible to maintain control of the airplane using only the rudder (without the use of nose wheel steering) and maintain enough lateral control to keep the wing in a near-horizontal position. to ensure safe continuation of takeoff. V MCG does not depend on the state of the runway, since its determination does not take into account the reaction of the runway to the aircraft.

The table shows V MCG in take-off units with engines with 22K thrust. Where Actual OAT is the outside air temperature, and Press ALT is the airfield elevation in feet. The note below concerns takeoff with engine bleeds turned off (no engine bleeds takeoff), since engine thrust increases, so does V MCG .

Actual OAT	Press ALT
C	0	2000	4000	6000	8000
40	111	107	103	99	94
30	116	111	107	103	99
20	116	113	111	107	102
10	116	113	111	108	104

For A/C OFF increase V1(MCG) by 2 knots.

A takeoff with a failed engine can only be continued if the engine failure occurs at a speed of at least V MCG .

Takeoff from a wet runway

When calculating the maximum permissible take-off weight, in the case of a continued take-off, a reduced screen height of 15 feet is used, instead of 35 feet for a dry runway. In this regard, it is impossible to include a strip free of obstacles (Clearway) in calculating the take-off distance.

It is very interesting to watch an airplane take off, when a heavy machine turns into a light-winged bird.

The lowest speed at which an aircraft can fly is, as we already know, the minimum speed of horizontal flight. But at this speed the plane is still not stable enough and is poorly controlled. Therefore, the pilot takes off the aircraft from the ground at a slightly higher speed. After liftoff, the pilot continues to accelerate the aircraft, as they say, “holding” the aircraft above the ground until the speed is sufficient for safe ascent.

Thus, the takeoff of an aircraft can be divided into three stages: takeoff, staying above the ground to increase speed, and ascent (Fig. 25, a).

These three stages make up the so-called take-off distance.

Let's see how the pilot takes off, what forces act on the plane during the takeoff, and how acceleration is created). For the sake of simplicity, we will again assume that all the main forces are applied at the center of gravity of the aircraft, that is, their moments are equal to zero (since now we are interested in the forces, not their moments).

Here the plane is standing at the start, ready to fly, and the engine is running at low throttle (Fig. 25, b). The propeller thrust is still insufficient to overcome the friction force of the wheels on the ground. But the pilot gave full throttle, the propeller thrust increased to maximum and the plane began to take off. Excess thrust creates acceleration, and speed increases. To increase speed faster, the pilot slightly deflects the elevator down, so the tail of the aircraft rises and the angle of attack of the wing decreases (Fig. 25, b). As the speed increases, the lifting force of the wing increases, and soon the plane's wheels barely touch the ground. Finally, the lifting force becomes equal to the weight of the aircraft, then a little more, and the machine lifts off the ground (Fig. 25, b). The takeoff run is over - the plane has taken off.

The car flies low for some time, picking up speed. Then the pilot turns the steering stick toward himself and switches the plane to the ascent mode (Fig. 25, a).

When climbing onto an airplane, the same forces act as during horizontal flight, but their interaction is somewhat different (Fig. 26).

The lift of a wing is always perpendicular to the direction of flight. Therefore, during lifting, it is no longer directed vertically and, therefore, cannot completely balance the force of the weight. If we decompose the weight force into two terms of force, as shown in Fig. 26, it becomes clear that the lifting force of the wing can balance only one of them - B. The other component of the weight force - B2 - together with the drag must obviously be balanced by the thrust force of the propeller.

When an airplane gains altitude, the lift on the wing is less than the weight of the airplane. Why, then, does the plane gain altitude? The fact is that the propeller thrust here not only overcomes drag, but also takes on part of the weight of the aircraft, as shown in the figure. In other words, when an airplane rises, the thrust force partially plays the role of a lifting force.

And if the plane could rise vertically upward, then the fixed wing would become completely useless - the machine would be lifted upward solely by the thrust of the propeller. The plane would turn into a helicopter.

When ascending, the aircraft gains a certain altitude every second, which is called the vertical rate of ascent. For example, the vertical speed of a Yak-18 aircraft at the beginning of its ascent is 4 meters per second. But then it decreases.

Why does this happen and what does it lead to?

As you rise to altitude, the air density becomes less and less, so less oxygen needed for fuel combustion enters the engine cylinders, and as a result, the power of the power plant decreases. Consequently, the excess power required for lifting is reduced. And finally, at some altitude there is no longer any excess power, and the plane cannot continue to climb. The altitude at which this occurs is called the "ceiling" of the aircraft.

Humanity has long been interested in the question of how it is that a multi-ton aircraft can easily rise to the skies. How does take-off happen and how do planes fly? When an airliner moves at high speed along the runway, lift is generated at the wings and works from the bottom up.

When an aircraft moves, a pressure difference is generated on the lower and upper sides of the wing, resulting in a lifting force that keeps the aircraft in the air. Those. High air pressure from below pushes the wing upward, while low air pressure from above pulls the wing towards itself. As a result, the wing rises.

For an airliner to take off, it needs a sufficient runway. The lift of the wings increases as the speed increases, which must exceed the takeoff limit. Then pilot increases takeoff angle, taking the helm to himself. The nose of the airliner rises up and the car rises into the air.

Then landing gear and exhaust lights are retracted. In order to reduce the lifting force of the wing, the pilot gradually retracts the mechanization. When the airliner reaches the required level, the pilot sets standard pressure, and engines - nominal mode. To see how the plane takes off, we suggest watching the video at the end of the article.

The aircraft takes off at an angle. From a practical point of view, this can be explained as follows. The elevator is a movable surface, by controlling which you can cause the aircraft to deflect in pitch.

The elevator can control the pitch angle, i.e. change the rate of gain or loss of altitude. This occurs due to changes in the angle of attack and lift force. By increasing the engine speed, the propeller begins to spin faster and lifts the airliner upward. Conversely, by pointing the elevators down, the nose of the aircraft moves down, and the engine speed should be reduced.

Tail section of an airliner equipped with a rudder and brakes on both sides of the wheels.

How airliners fly

When answering the question why planes fly, we should remember the law of physics. The pressure difference affects the lift of the wing.

The flow rate will be greater if the air pressure is low and vice versa.

Therefore, if the speed of an airliner is high, then its wings acquire a lifting force that pushes the aircraft.

The lifting force of an airliner wing is also influenced by several circumstances: angle of attack, speed and density of air flow, area, profile and shape of the wing.

Modern airliners have minimum speed from 180 to 250 km/h, during which the takeoff takes place, plans in the skies and does not fall.

Flight altitude

What is the maximum and safe flight altitude for an aircraft?

Not all ships have the same altitude, the “air ceiling” can fluctuate at altitude from 5000 to 12100 meters. At high altitudes, air density is minimal, and the airliner achieves the lowest air resistance.

The airliner engine requires a fixed volume of air for combustion, because the engine will not create the required thrust. Also, when flying at high altitudes, the aircraft saves fuel up to 80%, in contrast to altitudes up to a kilometer.

What keeps a plane in the air?

To answer why airplanes fly, it is necessary to examine one by one the principles of its movement in the air. A jet airliner with passengers on board reaches several tons, but at the same time, it easily takes off and carries out a thousand-kilometer flight.

The movement in the air is also influenced by the dynamic properties of the device and the design of the units that form the flight configuration.

Forces affecting the movement of an aircraft in the air

The operation of an airliner begins with the engine starting. Small ships run on piston engines that turn propellers, which generate thrust to help propel the aircraft through the air.

Large airliners are powered by jet engines, which emit a lot of air as they operate, and the jet force propels the aircraft forward.

Why does the plane take off and stay in the air for a long time? Because the shape of the wings has a different configuration: round at the top and flat at the bottom, then the air flow on both sides is not the same. The air on top of the wings glides and becomes rarefied, and its pressure is less than the air below the wing. Therefore, due to uneven air pressure and the shape of the wings, a force arises that leads to the aircraft taking off upward.

But in order for an airliner to easily take off from the ground, it needs to take off at high speed along the runway.

It follows from this that in order for an airliner to fly unhindered, it needs moving air, which the wings cut and creates lift.

Airplane takeoff and speed

Many passengers are interested in the question: what speed does the plane reach during takeoff? There is a misconception that the takeoff speed is the same for every aircraft. To answer the question, what is the speed of the aircraft during takeoff, you should pay attention to important factors.

1. An airliner does not have a strictly fixed speed. The lift of an airliner depends on its mass and the length of its wings. Takeoff occurs when a lifting force is created in the oncoming flow, which is much greater than the mass of the aircraft. Therefore, the takeoff and speed of the aircraft depends on wind direction, atmospheric pressure, humidity, precipitation, length and condition of the runway.
2. To create lift and successfully lift off the ground, the aircraft needs reach maximum takeoff speed and sufficient takeoff run. This requires long runways. The larger the aircraft, the longer the runway is required.
3. Each aircraft has its own takeoff speed scale, because they all have their own purpose: passenger, sport, cargo. The lighter the aircraft, the significantly lower the takeoff speed and vice versa.

Boeing 737 passenger jet take off

• The take-off run of an airliner on the runway begins when the engine will reach 800 rpm per minute, the pilot slowly releases the brakes and holds the control lever at a neutral level. The plane then continues on three wheels;
• Before leaving the ground The speed of the airliner should reach 180 km per hour. The pilot then pulls the lever, which causes the flaps to deflect and raise the nose of the aircraft. Further acceleration is carried out on two wheels;
• After, with the bow raised, the airliner accelerates on two wheels to 220 km per hour, and then lifts off the ground.

Therefore, if you want to learn more about how a plane takes off, to what altitude and at what speed, we offer you this information in our article. We hope that you will enjoy your air travel greatly.