The movement process of an aircraft from the starting point to the ground and rising to a certain height is called takeoff.

Aircraft take-off control principle

The reason why the plane glides off the ground is because the lift is increasing until it is greater than the gravity of the plane. However, only when the speed of the aircraft increases to a certain extent can it generate enough lift to support the gravity of the aircraft. It can be seen that the takeoff of the plane is an accelerating process with increasing speed. ; The take-off process of piston-propeller aircraft with small residual tension can generally be divided into four stages: take-off taxiing, off the ground, small angle ascent (or level flight) and ascent. For a propeller plane with enough residual tension, or a jet plane with enough residual thrust, take-off is generally divided into three stages, namely, starting to taxi, leaving the ground and ascending, because this can accelerate and ascend the plane.

(1) The purpose of take-off and taxiing is to increase the speed of the aircraft until the ground speed is obtained. The greater the tension or thrust, the greater the residual tension or thrust, and the faster the growth of the aircraft. When taking off, in order to increase the speed as soon as possible, the throttle should be pushed to the maximum position.

1. Lift the front or rear wheels.

* Why should the plane be too front-wheel at the first three o'clock?

The stopping angle of the plane at the first three o'clock is relatively small. If the aircraft maintains a three-point attitude during the whole take-off and taxiing phase, the angle of attack and lift coefficient are relatively small, and it is necessary to greatly increase the speed to generate enough lift to lift the aircraft off the ground, so the taxiing distance is bound to be very long. Therefore, in order to reduce the speed to the ground and shorten the taxiing distance, when the speed increases to a certain extent, it is necessary to lift the front wheel for two-point taxiing to increase the angle of attack and lift coefficient.

* Time and height of lifting the front wheel.

The timing of lifting the front wheel should not be too early or too late. The front wheel is lifted too early, the speed is still small, the lift and resistance are small, and the pitching moment is also small. In order to connect the front wheels, it is necessary to make the horizontal tail generate a large pitching moment, but under the condition of low speed, the additional aerodynamic force generated by the horizontal tail is also small, so it is necessary to use multiple pull rods to generate enough pitching moment. In this way, with the increase of taxiing speed, the pitching moment will increase rapidly, and pilots have to use a lot of maneuvering to make reciprocating corrections to keep the balance of the front row, which brings difficulties to maneuvering. At the same time, lifting the front wheel is too dry, which increases the aircraft resistance and increases the take-off distance. If the front wheel is lifted too late, it will not only increase the taxiing distance, but also make it difficult for the pilot to correct the height of the front wheel and maintain an appropriate angle of attack with the ground because the time for lifting the front wheel by the tie rod is very short. It is even easy to make the lift suddenly increase a lot, causing the plane to suddenly leave the ground. Vertical speed of front wheels of various aircraft has its specific regulations. The lifting height of the front wheels should be just enough to keep the angle of attack required for the aircraft to leave the ground. If the front wheel is lifted too low, the angle of attack and lift coefficient will be too small, the ground speed will increase, and the taxiing distance will also increase. Although the taxiing distance can be shortened by raising the front wheel too high, the takeoff distance will increase due to the large aircraft resistance, and the angle of attack and lift coefficient will be too large, which will inevitably lead to a large angle of attack and a small ground speed. After leaving the ground, the stability and maneuverability of the aircraft will also be poor. Excessive elevation angle may also cause the tail to wipe the ground. In order to ensure safety and shorten the taxiing distance, the lifting height of the front wheels of various aircraft has its specific regulations. The pilot can judge whether the height of the front wheel is appropriate from the pitch indicator on the plane or from the relationship between the nose and the horizon.

Why did the plane lift its tail wheel after three o'clock?

Compared with the first three-point aircraft, the stop angle of the last three-point aircraft is larger, so the angle of attack in the three-point taxi is larger, which is close to its critical angle of attack. If three-point taxiing is maintained in the whole taxiing stage, the lift coefficient is larger, and the aircraft can generate enough lift to lift the aircraft off the ground at a lower speed. At this time, although the taxiing distance is short, the stability and maneuverability of the aircraft are poor, and it may even stall after leaving the ground at high angle of attack and low speed. Therefore, when the taxiing speed increases to a certain extent at the last three points, the pilot should push the steering column forward and lift the tail to taxi at two points to reduce the angle of attack. Like the first three points, in order to ensure safety and shorten the taxiing distance, the tail must be lifted correctly and timely. Lifting the tail too early or too late, too high or too low will not only increase the taxiing distance and take-off distance, but also endanger flight safety. The tail lifting speed and altitude of various types of aircraft also have their specific regulations.

2. Keep running direction

For propeller aircraft, the main cause of aircraft deflection during take-off and taxiing is the side effect of propeller. During take-off and taxiing, the reaction moment of the propeller tries to tilt the plane in the opposite direction of the propeller rotation, resulting in unequal forces on the ground between the two main wheels, thus making the friction between the two main wheels unequal, and the friction difference between the two main wheels forms a deflection moment on the center of gravity. The propeller slipstream acting on the vertical tail also produces the main deflection moment. When the aircraft lifts the front wheel at the first three points and the tail wheel at the last three points, the precession of the propeller will also deflect the aircraft. The coarser the movements of adding and subtracting the throttle and pushing and pulling the steering rod, the greater the influence of propeller side effects. In order to reduce the side effects of the propeller, the actions of the fuel filler door and the push-pull steering rod should be gentle and appropriate. At the initial stage of taxiing, due to the poor effectiveness of the rudder, the taxiing direction can generally be maintained by front wheel deflection and braking. The rudder should be used in the later stage of taxiing to keep the taxiing direction. With the increase of taxi speed and the improvement of rudder utility, it is necessary to return the rudder to keep the taxi direction.

It is easy to keep the direction of jet plane's take-off and operation, because: firstly, jet plane is the first three planes, which have good directional stability when taxiing. Second, there is no side effect of propeller, so the plane will not deflect when refueling the door and lifting the front wheel.

(2) When the speed increases to a certain extent and the lift is slightly greater than gravity, the plane can leave the ground. The force acting on the plane when it leaves the ground. At this time, the lift is greater than gravity, and the tension or thrust is greater than resistance.

The first three points of the plane leaving the ground are different from the last three points. The first three points of the plane are the upward steering torque generated by the pilot's pull rod, which makes the plane slide at two points. The angle of attack will increase with the increase of taxi speed and pitching moment. Although the pilot keeps pushing forward to maintain the two-point taxiing attitude, the original pitching moment balance is always destroyed with the increase of speed, and the angle of attack will automatically increase when it reaches the ground speed. So the first three planes usually wait for them to leave the ground automatically. The last three points are not the case. When the plane reaches the ground speed, it is generally necessary to take a pole to increase the angle of attack and then leave the ground. This is because during the last three points of taxiing, the pilot kept it by pushing forward and tilting the elevator downward. With the increase of speed, the downward control torque will increase, thus reducing the angle of attack. Although the pilot has been holding the pole to keep sliding at two points, the angle of attack will still decrease when he reaches the ground speed. Therefore, before the plane can leave the ground, it is necessary to increase the backward angle of attack of the stick. After three o'clock, it is very important to grasp the opportunity to leave the ground. Leaving too early or too late is not good for flying. After the wheel leaves the ground, the friction of the wheel disappears, and the plane tends to tilt upward, so it should stop facing forward. For propeller aircraft, the wheel friction torque also disappears, and the aircraft tends to deflect in the direction of propeller rotation, so the rudder should be used to stop it.

(3) For the piston-propeller aircraft with small residual tension caused by flat flight or small angle rise, the aircraft has not reached the required rising speed from the ground, so it needs flat flight or small angle rise to accumulate speed. After the plane leaves the ground, it will meet the pole forward at the height of 12 meters to reduce the angle of arrival, so that the plane can fly horizontally or accelerate at a small angle. When the plane just leaves the ground, it is not advisable to use a large rising angle. Excessive rising angle will affect the growth rate of aircraft and even endanger safety. In order to reduce the resistance and speed up, the landing gear is generally retracted at a height of not less than 5 meters after the plane is in high ground. Don't close the landing gear too early or too late. Too early, the plane clings to the ground. If the plane is prone, it may be grounded again, endangering safety; Too late, the speed is very high, and the landing gear produces great resistance, which makes it difficult to speed up, and may also lead to poor landing gear retraction. It is especially necessary to prevent the occurrence of slope when flying flat or rising at a small angle, because the flying height is low at this time. If the plane has a slope, it will slide down and may hit the ground. Therefore, it is found that the aircraft slope should be corrected in time.

(4) When the speed increases to the specified altitude, the aircraft should be lifted gently to make it rise steadily. When it rises to the specified altitude, the take-off phase is over.

* * * Factors affecting takeoff taxi distance The factors affecting takeoff taxi distance include throttle position, angle of attack from the ground, flap inversion, takeoff weight, airport elevation and temperature, runway surface quality, wind direction and speed, runway slope, etc. These factors usually affect the take-off distance by affecting the ground speed or the average acceleration of take-off taxi.

* Throttle position The greater the throttle, the greater the propeller pull or jet thrust, the faster the aircraft grows and the shorter the takeoff and taxi distance. So usually take off with maximum power or maximum throttle.

* The angle of attack from the ground depends on the height of lifting the front wheel or tail. The attack angle from the ground is large, the speed from the ground is small, and the takeoff and running distance is short. However, the angle of attack from the ground should not be too large. If the angle of attack from the ground is too large, it will only slow down the growth of the aircraft and prolong the taxiing distance because of the large resistance of the aircraft, which will directly endanger the flight safety. Therefore, from the point of view of ensuring flight safety and shortening taxiing distance, it is generally required that all types of aircraft have the most favorable angle of attack from the ground.

* Flap position Lowering the flap can increase the lift coefficient and reduce the ground speed, thus shortening the take-off and taxi distance.

* Take-off weight The increase in take-off weight not only increases the speed of the aircraft off the ground, but also increases the friction of the wheels, making it difficult for the aircraft to accelerate. So the takeoff weight increases and the takeoff distance increases.

* Airport altitude and temperature. The increase of airport altitude or temperature will lead to the decrease of air density. When the top coal caving face is used, the tension or thrust will decrease and the plane will slowly accelerate. On the other hand, as the ground speed increases, the takeoff distance will inevitably increase. Therefore, when taking off at the hot plateau airport, the taxiing distance is obviously increased.

* The running distance varies with the friction coefficient of runway surface quality. If the runway surface is smooth, flat and solid, the friction coefficient is small, the friction force is small, the aircraft speed is fast, and the takeoff and running distance is short. On the contrary, if the runway surface is rough or soft, the distance between takeoff and taxiing will be very long.

* When taking off and taxiing under the wind direction and speed, in order to generate enough lift to make the plane off the ground, the airspeed from the ground is certain whether there is wind or no wind. However, the sliding distance is only related to the ground speed. When coasting against the wind, the ground speed is low, so the coasting distance is shorter than when there is no wind. On the contrary, it is long.

* The slope of the runway will increase or decrease the acceleration of the aircraft.

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The whole process of the plane descending from a certain height, landing, taxiing until it comes to a complete stop is called landing.

Aircraft landing control principle

Contrary to take-off, landing is a movement process in which the altitude of the aircraft decreases and the speed decreases continuously. When the plane lands and descends from a certain height, the engine is idling, that is, it usually descends with a small throttle. When the flying altitude drops to near the ground, the control rod must be pulled back at a certain height to make the plane change from taxiing to drifting. This is called "leveling". After the plane is leveled, the speed of the plane is still relatively high and it cannot be grounded immediately. It is necessary to continue to reduce the speed at a height of 0.5 ~ 1 m from the ground. After leveling, the process of continuing to reduce the speed is leveling. In this process, as the flight speed decreases, the pilot keeps pulling back the steering column to keep the lift equal to gravity. When the plane is 0.15 ~ 0.25m above the ground, the angle of attack required to pull the plane to the ground is slightly less than gravity. After the plane lands gently, it needs to slow down until it stops. This deceleration process is called landing taxiing. As can be seen from the above, the aircraft landing process can generally be divided into five stages: descending stage, leveling stage, drifting stage, grounding stage and landing taxiing stage.

(1) leveling

Flat flight is a curve motion process in which the plane changes from gliding to drifting, that is, the plane changes from gliding to nearly flat flight. In order to complete this process, the pilot needs to pull the rod to increase the angle of attack: the lift is greater than the first component of gravity, and the difference between these two forces is the centripetal force, which pushes the aircraft to make a curved motion upwards and reduces the glide angle. For some aircraft, due to the large pitching moment after the flaps are released, the ejector pin is usually pushed down to maintain the balance of the aircraft during the descent, so it is only necessary to loosen the lever at the beginning of pulling up and then gradually become a pull rod. When the pull rod or loose rod increases the angle of attack, the resistance increases at the same time. Because the sliding angle decreases, the gravity also decreases, so the flight speed with resistance greater than gravity decreases. It can be seen that in the leveling stage, the sliding angle and sliding speed decrease gradually, and the height decreases continuously. The pilot should master the weight and speed of the tie rod according to the situation that the plane leaves the ground and sinks close to the ground, so as to make it conform to the objective reality and achieve correct leveling. If the height is high, the sinking is slow and the depression angle is small, the action of the pull rod will be slower; On the other hand, if the height is low, the sinking is fast and the depression angle is large, the action of the pull rod should be fast.

(2) drift

After the aircraft turns and drifts, under the action of resistance, the speed decreases gradually and the lift decreases continuously. In order to make the aircraft lift approximately equal to the aircraft gravity and make the aircraft slowly sink close to the ground, the pilot should constantly increase the angle of attack through the pull rod to improve the lift. Pull the plane to the ground angle of attack at a height of about 0. 15-0.25m from the ground, and slow down to the ground speed at the same time, so that the plane touches the ground gently.

In the process of drift, the pilot should pull back the tie rod according to the sinking and deceleration of the aircraft. Generally speaking, in the initial stage of drift, fewer tie rods are needed. Because the speed of the aircraft is relatively high at this time, when the speed decreases and the lift decreases, the lift required for drift can be maintained only by slightly increasing the angle of attack of the pull rod. If there are too many tie rods, the lift will suddenly increase and the plane will float.

In the later stage of drift, more tie rods are needed. Because the aircraft speed is low at this time, if the pull rod amount is the same as the previous section, the angle of attack increases the same, and the lift increases slightly, the aircraft will sink quickly; In addition, with the increase of angle of attack, the resistance increases, and the aircraft slows down quickly, which will also make the aircraft sink rapidly. Therefore, only by increasing the angle of attack with more pull rods can the required lift be obtained, so that the plane can slowly sink.

In a word, the timing, weight and speed of the tie rod are determined by the speed and sinking of the plane in horizontal drift. The speed of the plane is high, the sinking is slow, and the action of the pull rod is slower; On the contrary, if the speed is low, the action of the sinking fast pull rod should be accelerated appropriately.

In addition, in order to make the plane land smoothly in the predetermined direction, attention should be paid to keeping the direction with the rudder during the drift process. If there is any inclination, it should be corrected immediately with the coordinated action of joystick and rudder. Therefore, when the angle of attack is high and the speed is low, the effectiveness of aileron is poor. Gu should use the rudder to support the aileron, that is, push the rudder in the opposite direction of inclination to help the aileron correct the inclination of the aircraft.

(3) Grounding

The nose of the plane will automatically descend before touching the ground. This is because the angle of attack will increase during the sinking of the aircraft, and the stable moment of the angle of attack will make the nose bow down. In addition, because the plane is close to the ground, the influence of the ground will increase, the downwash speed will decrease, and the horizontal effective angle of attack will increase, resulting in upward additional lift, and the moment formed on the center of gravity will bend the nose down. Therefore, before grounding, it is necessary to continue to hold the lever backwards to keep the aircraft in the required grounding posture.

In order to reduce the landing speed, increase the resistance during taxiing, and thus shorten the distance of taxiing, it is necessary to have a large angle of attack when landing, so the first three planes are grounded with two main wheels, and the last three planes are usually grounded with three wheels at the same time.

(4) Landing and running

The central problem of landing taxiing is how to slow down and keep the taxiing direction.

After the plane is grounded, in order to slow down as soon as possible and shorten the landing taxiing distance, it is necessary to increase the aircraft resistance during taxiing. The resistance of aircraft taxiing includes aerodynamic resistance, wheel friction, jet thrust and negative tension of propeller. During taxiing, increasing the angle of attack, releasing speed brake (or deceleration rate), using thrust reverser, negative tension of propeller and braking can all increase the aircraft resistance.