Helicopter overweight state ultra-short distance head lowering taxiing takeoff control strategy and calculation method

Abstract

The invention discloses a wheel type undercarriage helicopter overweight state ultra-short distance head lowering taxiing takeoff control strategy and a calculation method, and belongs to the technical field of helicopter flight control and control. The method comprises the steps that 1, helicopter parameters are obtained, and power calculation is carried out; 2, performing power judgment; 3, checking before the helicopter takes off; fourthly, after the helicopter enters the take-off state, the engine operates, the braking state is kept, and the total pitch is increased till the power of the engine reaches 80% or above of the maximum available power; 5, a brake is closed, taxiing is started, in the taxiing process, a control lever is controlled to enable wheels of a rear landing gear of the helicopter to leave the ground, wheels of a front landing gear of the helicopter make contact with the ground, the helicopter lowers the head to accelerate, the safe pitch attitude angle and the distance between rotor blade tips and the ground are kept, and taxiing is conducted to the target takeoff speed; and 6, after the target take-off speed is reached, the total distance is lifted, the residual power is used for the climbing height, the helicopter is made to rapidly rise till the helicopter leaves the ground effect interval, and the short-distance taxiing take-off process is completed at the moment.

Description

Technical Field

[0001] This invention belongs to the field of helicopter flight control technology, and in particular relates to the control strategy and calculation method for ultra-short distance nose-down takeoff of wheeled landing gear helicopters under overweight conditions. Background Technology

[0002] As an aircraft capable of vertical takeoff and landing, the core advantage of helicopters lies in their ability to perform missions in complex environments without conventional runways, making them widely used in rescue, patrol, and transportation. However, this advantage is severely limited in low-air-density environments such as high temperatures and high altitudes, or when under heavy loads. In these situations, the available engine power decreases, while the power required to maintain hover increases, often rendering helicopters unable to take off vertically or utilize ground effect.

[0003] In such critical performance conditions, runway takeoff becomes a crucial and necessary alternative. Compared to vertical takeoff, runway takeoff accumulates airspeed through ground-based movement, allowing the rotor to generate greater lift in the relative airflow, thus significantly reducing the power required before takeoff. This not only compensates for engine power loss and increases maximum takeoff weight, but also improves the inherent safety of the takeoff process and reduces pilot workload by avoiding the complex and risk-concentrated hovering phase.

[0004] Despite the theoretical advantages of runway takeoff, its potential has not been fully realized in practical applications, especially in short-takeoff scenarios demanding extreme performance. Currently, domestic pilots generally adopt a relatively conservative control method when performing such operations, meaning the landing gear remains in contact with the ground and the pitch attitude is basically horizontal; rather than performing the takeoff with the helicopter in a maximum nose-down attitude to reach the target takeoff speed as quickly as possible. This relatively conservative control method makes the takeoff process relatively safe, but it also results in a longer actual takeoff distance. The fundamental reason is that pilots mainly rely on personal experience and qualitative intuition to coordinate and control rotor collective pitch, engine power, and flight attitude, making it difficult to achieve optimal matching of multiple control variables within a very short acceleration time.

[0005] Therefore, a significant gap exists in existing technology: there is an urgent need for a systematic control strategy and calculation method specifically designed for wheeled landing gear helicopters under extreme weight conditions for ultra-short takeoff with nose-down maneuvers. This method aims to optimize the entire process from takeoff to liftoff through explicit logic, transforming the demanding flight techniques of ultra-short takeoff into a repeatable and compliant control method. Thus, while ensuring safety, pilots only need to operate the helicopter according to the calculated key parameters to achieve a sufficiently low nose-down attitude for ultra-short takeoffs, with the rear landing gear remaining off the ground throughout the takeoff, reaching the target takeoff speed as quickly as possible, minimizing takeoff distance, and reducing operational difficulty. This control strategy and calculation method can provide crucial performance support for civilian and military helicopters operating in extreme environments. Summary of the Invention

[0006] The technical problem this invention aims to solve is to overcome the shortcomings of existing ultra-short takeoff (UST) technology for helicopters and provide a control strategy and calculation method for UST takeoff under overload conditions for wheeled landing gear helicopters. This method aims to address the problems of pilots relying solely on experience to perform UST takeoffs in performance-limited scenarios such as high altitudes and heavy loads due to a lack of specific parameter indicators, resulting in excessively long takeoff distances, poor performance consistency, and high safety risks.

[0007] The purpose of this invention is to provide a control strategy and calculation method for ultra-short takeoff with nose-down taxiing in overload conditions for wheeled landing gear helicopters. When the helicopter is at high altitude or under heavy load, based on the helicopter's performance indicators, it is determined whether the helicopter can take off by taxiing, and corresponding key parameters for ultra-short takeoff with nose-down taxiing are given to assist the pilot in performing ultra-short takeoff with nose-down taxiing, shortening the distance required for the helicopter to take off by taxiing and improving takeoff performance.

[0008] To achieve the above objectives, the present invention provides the following solution:

[0009] A helicopter's ultra-short takeoff control strategy and calculation method under overweight conditions, characterized in that the method comprises:

[0010] Step 1: Obtain helicopter parameters and calculate power;

[0011] Step 2: Determine available power With required power Size judgment: If Then proceed to step three; if If the flight mission is cancelled or the takeoff weight is reduced, the flight should return to step one and the required power should be recalculated. ;

[0012] Step 3: Pre-flight checks of the helicopter; once the checks are passed, the helicopter enters takeoff mode.

[0013] Step 4: After the helicopter enters takeoff mode, the engine starts running. At this time, keep the brakes on and increase collective pitch until the engine power reaches more than 80% of the maximum available power.

[0014] Step 5: Close the brakes and begin the takeoff run. During the takeoff run, manipulate the control stick to lift the rear landing gear wheels off the ground and touch the front landing gear wheels to the ground. Pitch down and accelerate, maintaining a safe pitch angle and rotor tip clearance. The helicopter control strategy is to use pitch angle limiting in the longitudinal direction, roll angle maintenance in the lateral direction, and yaw angle maintenance in the yaw direction to safely take off to the target takeoff speed. ;

[0015] Step Six: After reaching the target takeoff speed, increase the collective pitch to climb, using the remaining power to increase the altitude, so that the helicopter can quickly rise until it leaves the ground effect zone. At this point, the short takeoff process is complete.

[0016] Furthermore, step one specifically includes:

[0017] Obtain the altitude of the helicopter Atmospheric temperature Local air quality density Total takeoff weight of helicopter ; Calculate available power With required power ;

[0018] Available power The calculation formula is:

[0019]

[0020] in For engine shaft power, For the efficiency of the transmission system, For installation efficiency (considering intake and exhaust losses). Power loss due to accessories; engine shaft power The corrected power output can be directly obtained from the engine manual by referring to tables based on the current pressure altitude and ambient temperature; transmission system efficiency... The efficiency of power output from the engine, through the transmission system including the main reducer, and finally to drive the rotor, after deducting friction and energy losses, is typically between 0.95 and 0.98; installation efficiency. When the engine is mounted on a helicopter, its intake and exhaust systems, which are not as efficient as those on a test bench due to pressure losses, typically have efficiency values ​​between 0.97 and 0.99; accessory power... The power required to drive the accessories that ensure the normal operation of the helicopter is generally a fixed percentage, approximately 3% to 8% of the shaft power;

[0021] Power required Through dimensionless power coefficient To calculate:

[0022]

[0023] in For power coefficient, Local air quality density, The rotor disk area, The rotor angular velocity (rad / s) Where is the rotor radius (m); for a specific helicopter model, the power factor is... The relationship curves between thrust coefficient and advance ratio were obtained through detailed aerodynamic calculations, wind tunnel tests, and flight tests; these curves can be directly consulted to obtain the required power at different weights, altitudes, and speeds; the required power is determined based on the weight, altitude, and target takeoff speed. The minimum power required.

[0024] Furthermore, in step five:

[0025] The target takeoff speed needs to be calculated separately. With the helicopter engine maintaining maximum power output, the remaining power at different takeoff speeds will be different, resulting in different maximum climb rates that the helicopter can achieve.

[0026] Total distance required for helicopter takeoff It is divided into two parts, one of which is the helicopter ground taxiing distance. Secondly, the forward flight distance of the helicopter from takeoff to reaching altitude without ground effect. ;

[0027]

[0028] The speed-power curve of a helicopter is a saddle-shaped (U-shaped) curve. Therefore, during the acceleration process, there must be a speed point that minimizes the required power, i.e., maximizes the remaining power. If this point is used as the target takeoff speed during the taxiing process, the helicopter can climb at its maximum rate of climb. Relatively short; however, due to the pitch angle limitations during helicopter ground takeoff, there is an upper limit to the maximum ground takeoff acceleration. The higher the target takeoff speed, the greater the acceleration. The longer the length, the better; therefore, the target takeoff speed of a specific helicopter model can be obtained through simulation calculations first. Total distance required for takeoff and landing The relationship curve is used to obtain the optimal target takeoff speed. ;

[0029] The pitch channel control law is ;

[0030] in This is a longitudinal periodic pitch control command. The target pitch angle after amplitude limiting. This is the actual pitch angle. For pitch rate, For proportional gain, This is the differential gain; The range is ( , ), It is the pitch angle of a helicopter when the helicopter pitches down so that the lowest position of the rotor tip is within a certain distance from the ground, with both the roll angle and yaw angle being 0. It can be approximately calculated using the longitudinal and vertical distances between the position of the front landing gear tire axle and the position of the foremost rotor tip. It is the pitch angle of a helicopter when it is stationary on the ground;

[0031] The roll channel control law is ;

[0032] in This is a lateral periodic pitch control command. Set the target roll angle (always 0). This is the actual pitch angle. For the roll rate, For proportional gain, This is the differential gain;

[0033] Yaw channel control law is ;

[0034] in For pedaling commands, The target yaw angle (always 0). This is the actual pitch angle. The yaw rate, For proportional gain, This is the differential gain.

[0035] The advantages of this invention compared to the prior art are as follows:

[0036] This invention enhances the mission flexibility and applicability of helicopters: by implementing this strategy, helicopters are now capable of performing missions in areas previously inaccessible due to harsh environments. This is of vital strategic significance for expanding the commercial applications of civilian helicopters (such as high-altitude material transport and mountain rescue) and improving the forward deployment capabilities of military helicopters.

[0037] This invention achieves a scientific and quantitative approach to takeoff decision-making: transforming traditional qualitative judgments that rely on pilot experience into quantitative decisions based on physical models and real-time data. This fundamentally reduces the significant safety risks associated with blind takeoffs under performance boundary conditions, especially in complex environments such as high altitudes and high temperatures.

[0038] This invention has high engineering applicability: the solution provides a complete closed-loop process from decision-making, preparation, control to takeoff, with clear logic, strong operability, and easy for pilots to understand and accept.

[0039] Specifically, taking the specific embodiment provided by the present invention as an example, compared with the existing conventional takeoff strategy, the total takeoff distance of the ultra-short takeoff strategy is 263.9m, while the total takeoff distance of the conventional takeoff strategy is 428.6m, which shortens the takeoff distance by about 38.43%; the takeoff distance at liftoff is 136.3m, while the takeoff distance of the conventional takeoff strategy is 304.5m, which shortens the takeoff distance by about 55.24%; the effect is significant. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating a short takeoff and landing process for a helicopter using this invention.

[0041] Figure 2 This is a graph showing the longitudinal velocity of a helicopter during ultra-short takeoff as a function of time, as described in an embodiment of the present invention.

[0042] Figure 3 This is a graph showing the change in helicopter power requirement as a function of forward speed in an embodiment of the present invention.

[0043] Figure 4 This is a graph showing the relationship between the helicopter's ultra-short takeoff distance and ground speed in an embodiment of the present invention;

[0044] Figure 5 This is a graph showing the power required for helicopter ultra-short takeoff over time in an embodiment of the present invention.

[0045] Figure 6 This is a graph showing the change in the climb rate of a helicopter during ultra-short takeoff as of time in an embodiment of the present invention.

[0046] Figure 7 This is a graph showing the change in the takeoff altitude of a helicopter over time during a short takeoff run, as described in an embodiment of the present invention.

[0047] Figure 8 This is a graph showing the change in helicopter ultra-short takeoff distance over time in an embodiment of the present invention;

[0048] Figure 9 This is a graph showing the change in the conventional takeoff distance of a helicopter over time in an embodiment of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following examples provide a more detailed description of the invention. It should be noted that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0050] like Figure 1 As shown, the method of the present invention is as follows:

[0051] Step 1: Obtain helicopter parameters and calculate power. Obtain the helicopter's altitude. Atmospheric temperature Local air quality density Total takeoff weight of helicopter ; Calculate available power With required power .

[0052] Available power The calculation formula is:

[0053]

[0054] in For engine shaft power, For the efficiency of the transmission system, For installation efficiency (considering intake and exhaust losses). Power loss due to accessories. Engine shaft power. The corrected power value can be directly obtained from the engine manual by referring to a table based on the current pressure altitude and ambient temperature. Transmission system efficiency. The efficiency of power output from the engine, through the main reduction gear and other transmission systems, to drive the rotor, after deducting friction and energy losses, is typically between 0.95 and 0.98. (Installation efficiency) When the engine is mounted on a helicopter, its intake and exhaust systems, which are not as efficient as those on a test bench due to pressure losses, typically have efficiency values ​​between 0.97 and 0.99. (Accessory power) The power required to drive the accessories that ensure the normal operation of the helicopter is generally a fixed percentage, about 3% to 8% of the shaft power.

[0055] Power required Through dimensionless power coefficient To calculate:

[0056]

[0057] in For power coefficient, Local air quality density, The rotor disk area, The rotor angular velocity (rad / s) Where is the rotor radius (m). For a specific helicopter model, the power factor is... The relationship curves between thrust coefficient and advance ratio were obtained through detailed aerodynamic calculations, wind tunnel tests, and flight tests. These curves can be directly consulted to obtain the required power at different weights, altitudes, and speeds. The required power to be obtained in this invention is determined based on a specific weight, altitude, and target takeoff speed. The minimum power required.

[0058] Step 2: Perform power determination: If Then proceed to step three; if If the flight mission is cancelled or the takeoff weight is reduced, the flight should return to step one and the required power should be recalculated. .

[0059] Step 3: Pre-takeoff inspection of the helicopter. After the inspection is passed, the helicopter enters takeoff mode.

[0060] Step 4: After the helicopter enters takeoff mode, the engine starts running. At this time, keep the brakes on and increase collective pitch until the engine power reaches more than 80% of the maximum available power.

[0061] Step 5: Close the brakes and begin the takeoff run. During the takeoff run, manipulate the control stick to lift the rear landing gear wheels off the ground and touch the front landing gear wheels to the ground. Pitch down and accelerate, maintaining a safe pitch angle and rotor tip clearance. The helicopter control strategy is to use pitch angle limiting in the longitudinal direction, roll angle maintenance in the lateral direction, and yaw angle maintenance in the yaw direction to safely take off to the target takeoff speed. .

[0062] The target takeoff speed needs to be calculated separately. Assuming the helicopter engine maintains maximum power output, different takeoff speeds result in different remaining power, leading to different maximum climb rates. The total distance required for helicopter takeoff is also considered. It is divided into two parts, one of which is the helicopter ground taxiing distance. Secondly, the forward flight distance of the helicopter from takeoff to reaching altitude without ground effect. .

[0063]

[0064] The speed-power curve of a helicopter is a saddle-shaped (U-shaped) curve. Therefore, during the acceleration process, there must be a speed point that minimizes the required power, i.e., maximizes the remaining power. If this point is used as the target takeoff speed during the taxiing process, the helicopter can climb at its maximum rate of climb. Relatively short. However, due to the pitch angle limitations during the helicopter's ground takeoff, there is an upper limit to the maximum ground acceleration; the higher the target's takeoff speed, the greater the acceleration. The longer the length, the better. Therefore, the target takeoff speed of a specific helicopter model can be obtained first through simulation calculations. Total distance required for takeoff and landing The relationship curve is used to obtain the optimal target takeoff speed. .

[0065] The pitch channel control law is ;

[0066] in This is a longitudinal periodic pitch control command. The target pitch angle after amplitude limiting. This is the actual pitch angle. For pitch rate, For proportional gain, This is the differential gain. The range is ( , ), It is the pitch angle of a helicopter when the helicopter's roll angle and yaw angle are both 0, and the helicopter pitches down so that the lowest point of the rotor tip is within a certain distance from the ground (for safety, this angle should be such that the lowest point of the rotor tip is 0.3m to 0.5m from the ground; the specific value can be determined according to the safety range of different helicopter models, the pilot's skill level, and the pilot's experience). It can be approximately calculated using the longitudinal and vertical distances between the position of the front landing gear tire axle and the position of the foremost rotor tip. It is the pitch angle of a helicopter when it is stationary on the ground.

[0067] The roll channel control law is ;

[0068] in This is a lateral periodic pitch control command. Set the target roll angle (always 0). This is the actual pitch angle. For the roll rate, For proportional gain, This is the differential gain.

[0069] Yaw channel control law is ;

[0070] in For pedaling commands, The target yaw angle (always 0). This is the actual pitch angle. The yaw rate, For proportional gain, This is the differential gain.

[0071] Step Six: After reaching the target takeoff speed, increase the collective pitch to climb, using the remaining power to increase the altitude, so that the helicopter can quickly rise until it leaves the ground effect zone. At this point, the short takeoff process is complete.

[0072] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0073] The purpose of this invention is to provide a control strategy and calculation method for ultra-short takeoff (UST) with nose-down maneuvering under overload conditions for wheeled landing gear helicopters. When the helicopter is at high altitude or under heavy load, based on the helicopter's performance indicators, it determines whether it can take off via a runway and provides corresponding key parameters for UST takeoff to assist pilots in performing UST takeoffs, shortening the distance required for takeoff and improving takeoff performance. Specifically, it includes the following steps:

[0074] Step 1: Obtain the altitude of the helicopter Atmospheric temperature Local air quality density Total takeoff weight of helicopter Available power Power required .

[0075] Available power The calculation formula is .

[0076] in For engine shaft power, For the efficiency of the transmission system, For installation efficiency (considering intake and exhaust losses). Power loss due to accessories. Engine shaft power. The corrected power value can be directly obtained from the engine manual by referring to a table based on the current pressure altitude and ambient temperature. Transmission system efficiency. The efficiency of power output from the engine, through the main reduction gear and other transmission systems, to drive the rotor, after deducting friction and energy losses, is typically between 0.95 and 0.98. (Installation efficiency) When the engine is mounted on a helicopter, its intake and exhaust systems, which are not as efficient as those on a test bench due to pressure losses, typically have efficiency values ​​between 0.97 and 0.99. (Accessory power) The power required to drive the accessories that ensure the normal operation of the helicopter is generally a fixed percentage, about 3% to 8% of the shaft power.

[0077] Power required Through dimensionless power coefficient To calculate: .

[0078] in For power coefficient, Local air quality density, The rotor disk area, The rotor angular velocity (rad / s) Where is the rotor radius (m). For a specific helicopter model, the power factor is... The relationship curves between thrust coefficient and advance ratio were obtained through detailed aerodynamic calculations, wind tunnel tests, and flight tests. These curves can be directly consulted to obtain the required power at different weights, altitudes, and speeds. The required power to be obtained in this invention is determined based on a specific weight, altitude, and target takeoff speed. The minimum power required.

[0079] Step 2: Perform power determination: Therefore, proceed to step three; if If the flight mission is cancelled or the takeoff weight is reduced, the flight should return to step one and the required power should be recalculated. .

[0080] Step 3: Pre-takeoff inspection of the helicopter. After the inspection is passed, the helicopter enters takeoff mode.

[0081] Step 4: After the helicopter enters takeoff mode, the engine starts running. At this time, keep the brakes on and increase collective pitch until the engine power reaches more than 80% of the maximum available power.

[0082] Step 5: Close the brakes and begin the takeoff run. In this embodiment, the takeoff run begins after 20 seconds. During the takeoff run, manipulate the control stick to lift the rear landing gear wheels off the ground and the front landing gear wheels touch the ground. Pitch down and accelerate, maintaining a safe pitch angle and rotor tip clearance. The helicopter control strategy is to use pitch angle limiting in the longitudinal direction, roll angle maintenance in the lateral direction, and yaw angle maintenance in the yaw direction until the helicopter safely reaches the target takeoff speed. (See attached longitudinal velocity curve) Figure 2 ).

[0083] The target takeoff speed needs to be calculated separately. Assuming the helicopter engine maintains maximum power output, different takeoff speeds result in different remaining power, leading to different maximum climb rates. The total distance required for helicopter takeoff is also considered. It is divided into two parts, one of which is the helicopter ground taxiing distance. Secondly, the forward flight distance of the helicopter from takeoff to reaching altitude without ground effect. .

[0084]

[0085] The speed-power curve of a helicopter is a saddle-shaped (U-shaped) curve. Therefore, during the acceleration process, there must be a speed point where the required power is minimized, that is, the remaining power is maximized (the speed-power curve of the helicopter in this embodiment is shown in the appendix). Figure 3 If this point is used as the target takeoff speed during the taxiing process, the helicopter can climb at its maximum rate of climb, thus... Relatively short. However, due to the pitch angle limitations during the helicopter's ground takeoff, there is an upper limit to the maximum ground acceleration; the higher the target's takeoff speed, the greater the acceleration. The longer the length, the better. Therefore, the target takeoff speed of a specific helicopter model can be obtained first through simulation calculations. Total distance required for takeoff and landing The relationship curve is used to obtain the optimal target takeoff speed. The optimal target takeoff speed in this embodiment. (See attached speed-run distance curve) Figure 4 ).

[0086] The pitch channel control law is ;

[0087] in This is a longitudinal periodic pitch control command. The target pitch angle after amplitude limiting. This is the actual pitch angle. For pitch rate, For proportional gain, This is the differential gain. The range is ( , ), This is the pitch angle of the helicopter when its roll and yaw angles are both 0, and the helicopter is pitched down with the rotor tips at a certain distance from the ground (for safety, this angle requires the rotor tips to be 0.3m to 0.5m from the ground; the specific value can be determined based on the safety range of different helicopter models, pilot skill level, and pilot experience). It can be approximately calculated using the longitudinal and vertical distances between the front landing gear tire axle and the foremost position of the rotor tips. In this embodiment, the distance from the ground to the lowest rotor tip is taken as 0.3m. (Calculations...) , It is the pitch angle of a helicopter when it is stationary on the ground.

[0088] The roll channel control law is ;

[0089] in This is a lateral periodic pitch control command. Set the target roll angle (always 0). This is the actual pitch angle. For the roll rate, For proportional gain, This is the differential gain.

[0090] Yaw channel control law is ;

[0091] in For pedaling commands, The target yaw angle (always 0). This is the actual pitch angle. The yaw rate, For proportional gain, This is the differential gain.

[0092] Step Six: After reaching the target takeoff speed of 20 m / s, increase collective pitch to climb, using the remaining power for vertical climb (see attached power curve). Figure 5 This allows the helicopter to quickly lift off the ground and ascend at its maximum climb rate of 6 m / s (see appendix for climb rate). Figure 6 ), until completely out of the ground effect zone (30m, see appendix for ground clearance). Figure 7 Thus, the short takeoff run is complete (see appendix for takeoff distance). Figure 8 To demonstrate the advantages of the ultra-short takeoff strategy in this invention compared to the conventional takeoff strategy, a conventional takeoff was performed with the same takeoff speed and climb rate, and the takeoff distance was plotted in the appendix. Figure 9 Used with attachment Figure 8 A comparison was made. Compared with the existing conventional takeoff strategy, the total takeoff distance for the ultra-short distance takeoff strategy is 285.6m (see appendix). Figure 8 The total takeoff distance for a standard runway is 428.6m (see appendix). Figure 9 The ultra-short takeoff distance is reduced by approximately 33.36%; the takeoff distance for ultra-short takeoff is 131.5m, while the takeoff distance for conventional takeoff is 304.5m, representing a reduction of approximately 56.81% in takeoff distance; the effect is significant.

[0093] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A helicopter overloaded state ultra-short distance nose-down takeoff control strategy and calculation method, characterized in that, The method is as follows: Step 1: Obtain helicopter parameters and calculate power; Step 2: Determine available power With required power Size judgment: If Then proceed to step three; if If the flight mission is cancelled or the takeoff weight is reduced, the flight should return to step one and the required power should be recalculated. ; Step 3: Pre-flight checks of the helicopter; once the checks are passed, the helicopter enters takeoff mode. Step 4: After the helicopter enters takeoff mode, the engine starts running. At this time, keep the brakes on and increase collective pitch until the engine power reaches more than 80% of the maximum available power. Step 5: Close the brakes and begin taxiing. During taxiing, manipulate the control stick to lift the rear landing gear wheels off the ground and touch the front landing gear wheels to the ground. Pitch down and accelerate, maintaining a safe pitch angle and rotor tip clearance. The helicopter control strategy is to use pitch angle limiting in the longitudinal direction, roll angle maintenance in the lateral direction, and yaw angle maintenance in the yaw direction to safely taxi the helicopter to the target takeoff speed. ; Step Six: After reaching the target takeoff speed, increase the collective pitch to climb, using the remaining power to increase the altitude, so that the helicopter can quickly rise until it leaves the ground effect zone. At this point, the short takeoff process is complete.

2. The helicopter overloaded state ultra-short distance nose-down takeoff control strategy and calculation method according to claim 1, characterized in that, The first step is as follows: Obtain the altitude of the helicopter Atmospheric temperature Local air quality density Total takeoff weight of helicopter ; Calculate available power With required power ; Available power The calculation formula is:

3. Among them For engine shaft power, For the efficiency of the transmission system, For installation efficiency (considering intake and exhaust losses). Power loss due to accessories; engine shaft power The corrected power output can be directly obtained from the engine manual by referring to tables based on the current pressure altitude and ambient temperature; transmission system efficiency... The efficiency of power output from the engine, through the transmission system including the main reducer, and finally to drive the rotor, after deducting friction and energy losses, is typically between 0.95 and 0.98; installation efficiency. When the engine is mounted on a helicopter, its intake and exhaust systems, which are not as efficient as those on a test bench due to pressure losses, typically have efficiency values ​​between 0.97 and 0.99; accessory power... The power required to drive the accessories that ensure the normal operation of the helicopter is generally a fixed percentage, approximately 3% to 8% of the shaft power; Power required Through dimensionless power coefficient To calculate:

4. Among them For power coefficient, Local air quality density, The rotor disk area, The rotor angular velocity (rad / s) Where is the rotor radius (m); for a specific helicopter model, the power factor is... The relationship curves between thrust coefficient and advance ratio were obtained through detailed aerodynamic calculations, wind tunnel tests, and flight tests; these curves can be directly consulted to obtain the required power at different weights, altitudes, and speeds; the required power is determined based on the weight, altitude, and target takeoff speed. The minimum power required.

5. The helicopter overloaded state ultra-short distance nose-down takeoff control strategy and calculation method according to claim 1, characterized in that, In step five: The target takeoff speed needs to be calculated separately. With the helicopter engine maintaining maximum power output, the remaining power at different takeoff speeds will be different, resulting in different maximum climb rates that the helicopter can achieve. Total distance required for helicopter takeoff It is divided into two parts, one of which is the helicopter ground taxiing distance. Secondly, the forward flight distance of the helicopter from takeoff to reaching altitude without ground effect. ; 6. The speed-power curve of a helicopter is a saddle-shaped (U-shaped) curve. Therefore, during the acceleration process, there must be a speed point that minimizes the required power, i.e., maximizes the remaining power. If this point is used as the target takeoff speed during the taxiing process, the helicopter can climb at its maximum rate of climb. Relatively short; however, due to the pitch angle limitations during helicopter ground takeoff, there is an upper limit to the maximum ground takeoff acceleration. The higher the target takeoff speed, the greater the acceleration. The longer the length, the better; therefore, the target takeoff speed of a specific helicopter model can be obtained through simulation calculations first. Total distance required for takeoff and landing The relationship curve is used to obtain the optimal target takeoff speed. ; The pitch channel control law is ; in This is a longitudinal periodic pitch control command. The target pitch angle after amplitude limiting. This is the actual pitch angle. For pitch rate, For proportional gain, This is the differential gain; The range is ( , ), It is the pitch angle of a helicopter when the helicopter pitches down so that the lowest position of the rotor tip is within a certain distance from the ground, with both the roll angle and yaw angle being 0. It can be approximately calculated using the longitudinal and vertical distances between the position of the front landing gear tire axle and the position of the foremost rotor tip. It is the pitch angle of a helicopter when it is stationary on the ground; The roll channel control law is ; in This is a lateral periodic pitch control command. Set the target roll angle (always 0). This is the actual pitch angle. For the roll rate, For proportional gain, This is the differential gain; Yaw channel control law is ; in For pedaling commands, The target yaw angle (always 0). This is the actual pitch angle. The yaw rate, For proportional gain, This is the differential gain.

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