Flight control method for tilt-rotor aircraft in tilt transition stage

Abstract

The invention discloses a tilt rotor aircraft flight control method in a tilt transition stage, and the method comprises the steps: determining a reverse tilt state point which is a waypoint of which the to-be-fly distance to the starting point of a multi-rotor mode descent stage is greater than or equal to the shortest design deceleration distance and the height is H; and when the tilt rotor aircraft is located at the reverse tilt state point, controlling the tiltable rotors to tilt reversely according to the tilt angle instruction, and controlling the tilt rotor aircraft to fly forward according to the reverse tilt transition flight speed. In the reverse tilting transition stage, the tilting angle rate is calculated based on the to-be-fly distance, and corresponding flight control strategies are executed for different stages in the reverse tilting transition stage in combination with comparison of the to-be-fly distance and the forward distance threshold value and the tilting angle range, so that accurate control over the position of the aircraft in the reverse tilting transition stage is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aircraft design, in particular to a flight control method of a tilt-rotor aircraft in a tilt transition phase. BACKGROUND

[0002] The tilt-rotor aircraft involves switching of multi-rotor mode, tilt transition mode and fixed-wing mode in the flight process, wherein the flight phase corresponding to the tilt transition mode is the tilt transition phase.

[0003] At present, when the tilt-rotor aircraft is in the reverse tilt transition phase, only the flight attitude and forward flight speed of the aircraft are controlled, and the position of the aircraft is not controlled. The above flight control scheme will cause many uncertainties in the position trajectory of the aircraft in the transition phase, especially in the reverse deceleration transition process. Since the reverse deceleration transition process generally decelerates through pitch angle control or controls airspeed, the control scheme can only slow down and cannot achieve precise position control. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a flight control method of a tilt-rotor aircraft in a tilt transition phase, which calculates the tilt angle rate based on the standby flight distance in the reverse tilt transition phase, and combines the comparison of the standby flight distance and the forward distance threshold and the tilt angle range to execute corresponding flight control strategies in different stages of the reverse tilt transition phase, thereby achieving precise control of the position of the aircraft in the reverse tilt transition phase.

[0005] To achieve the above object, the present application provides the following technical scheme:

[0006] A flight control method of a tilt-rotor aircraft in a tilt transition phase is provided, which includes reverse tilt transition phase flight control, and the reverse tilt transition phase flight control includes:

[0007] determining a reverse tilt state point, the reverse tilt state point being a waypoint with a standby flight distance to the start point of the multi-rotor mode descent phase being greater than or equal to the shortest designed deceleration distance and a height of H;

[0008] When the tilt-rotor aircraft is located at the reverse tilt state point, the tilt-rotor aircraft is controlled to fly forward according to the reverse tilt transition flight speed according to the tilt angle command control of the reverse tilt of the tiltable rotor.

[0009] Compared with the prior art, the present application has the following advantages:

[0010] The application can complete forward flight speed control based on flight speed instruction in forward tilting transition stage and reverse tilting transition stage, simultaneously calculate tilting angle rate based on stand-off distance in reverse tilting transition stage, and dynamically limit the tilting angle, further combine stand-off distance, forward distance threshold comparison, and tilting angle range, and execute corresponding flight control strategy in different stages in reverse tilting transition stage, so as to realize accurate control of the aircraft position, ensure accurate and smooth landing, and save energy consumption of the aircraft. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 A schematic diagram of different flight task stages of the tilt-rotor aircraft;

[0012] Figure 2 A flight schematic diagram of the reverse tilting transition stage of the tilt-rotor aircraft. DETAILED DESCRIPTION

[0013] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0014] Embodiment 1:

[0015] The embodiment provides a flight control method of a tilt-rotor aircraft in a tilting transition stage, wherein, as shown in the figure, the whole flight process of the tilt-rotor aircraft includes: Figure 1

[0016] The multi-rotor mode take-off stage refers to a stage in which the tilt-rotor aircraft takes off in the multi-rotor mode (tilting angle 90°);

[0017] The multi-rotor mode climbing stage refers to a stage in which the tilt-rotor aircraft climbs to a predetermined height in the multi-rotor mode after vertical take-off;

[0018] The forward tilting transition stage (i.e. "forward acceleration transition mode" in the figure) refers to a stage in which the tilt-rotor aircraft tilts forward to switch to the fixed-wing mode after climbing to a predetermined height in the multi-rotor mode; Figure 1

[0019] The fixed-wing mode climbing stage refers to a stage in which the tilt-rotor aircraft climbs to a predetermined height in the fixed-wing mode;

[0020] The fixed-wing mode cruising stage refers to a stage in which the tilt-rotor aircraft cruises in the fixed-wing mode after climbing to a predetermined height.​​

[0021] Fixed-wing mode descent phase (i.e. Figure 1 "fixed-wing mode glide" in the present application) refers to a phase in which the tilt-rotor aircraft descends to a predetermined height in the fixed-wing mode after the level flight phase ends;

[0022] Fixed-wing mode approach phase refers to a phase in which the tilt-rotor aircraft approaches in the fixed-wing mode after the tilt-rotor aircraft descends to a predetermined height in the fixed-wing mode;

[0023] Reverse tilt transition phase (i.e. Figure 1 "reverse deceleration transition" in the present application) refers to a phase in which the tilt-rotor aircraft reverses the tilt to switch to the multi-rotor mode after the approach phase ends;

[0024] Multi-rotor mode descent phase refers to a phase in which the tilt-rotor aircraft descends to a predetermined height at a constant descent rate in the multi-rotor mode;

[0025] Multi-rotor mode landing phase refers to a phase in which the tilt-rotor aircraft gradually decelerates to land according to the ground clearance after the tilt-rotor aircraft descends in the multi-rotor mode, and the descent speed of the tilt-rotor aircraft is less than 0.2 m / s in this phase, and the tilt-rotor aircraft performs ground clearance judgment, ground state switching, automatic stop of the propeller, automatic locking, and the like.

[0026] The tilt transition phase includes the forward tilt transition phase and the reverse tilt transition phase, and the flight control method of the tilt-rotor aircraft in the tilt transition phase includes the following contents:

[0027] (1) Forward tilt transition phase flight control, which includes the following steps:

[0028] S11, obtaining the shortest forward transition path L threshold according to formula (1);

[0029] L threshold = V down × t down (1)

[0030] Wherein, V down , t down are the flight speed corresponding to the lower boundary of the tilt transition corridor and the flight time corresponding to the lower boundary of the tilt transition corridor, respectively; the tilt corridor can be determined in advance by the flight dynamics model of the tilt-rotor aircraft;

[0031] S12, controlling the tilt-rotor aircraft in the forward tilt transition phase to follow the set heading angle and forward tilt transition flight speed V cmdFlight, to perform course lateral control on the lateral channel and forward flight speed control on the longitudinal channel, and during the entire forward tilt transition phase, the flight distance of the tiltrotor aircraft is controlled to be less than or equal to the flight distance threshold. In this embodiment, the value range of the flight distance threshold is 1.5L threshold ~2.0L threshold ; Further, in this embodiment, the forward tilt transition flight speed V cmd Obtained by formula (2):

[0032] V cmd =aβ 3 +bβ 2 +cβ+d (2)

[0033] Wherein, β is the tilt angle of the tilt rotor during forward tilting; a, b, c, and d are the first, second, third, and fourth design coefficients of the forward tilt transition phase, respectively. The four design coefficients can be obtained by fitting a fourth-order polynomial at the discrete points with the optimal power in the tilt transition corridor to reflect the physical meaning of position, velocity, acceleration, and jerk, and the fourth-order polynomial satisfies the following constraints: when β = 90°, 0 < V cmd ≤10m / s, when β=0°, V cmd ≥The cruising speed of a tiltrotor aircraft in fixed-wing mode;

[0034] (2) Flight control during the reverse bank transition phase includes the following steps:

[0035] S21, determining the reverse tilt state point by manual selection or automatic calculation;

[0036] Among them, manually selecting and determining the reverse tilt state point includes:

[0037] Calculate the shortest design deceleration distance dis_hor according to formula (3-1):

[0038] dis_hor=V up ×t up (3-1)

[0039] Among them, V up , t up are the flight speed corresponding to the upper boundary of the tilt transition corridor and the flight time corresponding to the upper boundary of the tilt transition corridor respectively;

[0040] The multirotor mode descent phase starting point (i.e. Figure 2 The distance to be flown (the "multi-rotor modal descent point") is greater than or equal to the shortest designed deceleration distance, and the waypoint with a height of H is determined as the reverse tilt state point. This process can be completed through offline planning and design in advance;

[0041] The to-fly distance refers to the forward distance from the current waypoint of the tilt-rotor aircraft to the start point of the multi-rotor mode descent phase, and the height H is calculated according to formula (3-2):

[0042]

[0043] Wherein, H1 is the height of the start point of the multi-rotor mode descent phase; γ is the descent rate of the tilt-rotor aircraft in the height direction when the tilt-rotor aircraft descends from the current waypoint to the start point of the multi-rotor mode descent phase, and the value range of γ is 0.5-3 m / s; V_cruise is the cruise speed of the tilt-rotor aircraft in the fixed-wing mode cruise; a is the acceleration of the tilt-rotor aircraft in the reverse tilt transition phase;

[0044] The automatic solving and determining of the reverse tilt state point comprises:

[0045] The shortest designed deceleration distance dis_hor is calculated according to formula (3-3):

[0046] dis_hor = V_cruise 2 / 2a (3-3)

[0047] Wherein, V_cruise is the cruise speed of the tilt-rotor aircraft in the fixed-wing mode cruise; a is the acceleration of the tilt-rotor aircraft in the reverse tilt transition phase;

[0048] The waypoint with the to-fly distance greater than or equal to the shortest designed deceleration distance and the height H to the start point of the multi-rotor mode descent phase is determined as the reverse tilt state point;

[0049] Wherein, the definitions of the to-fly distance and the height H are the same as those in the step of "manually selecting and determining the reverse tilt state point", and the calculation method of the height H is the same as formula (3-2);

[0050] S22, when the tilt-rotor aircraft is located at the reverse tilt state point, the tiltable rotor is controlled to reverse tilt according to the tilt angle instruction, and the tilt-rotor aircraft is controlled to fly forward at the reverse tilt transition flight speed V cmd '; the tilt angle instruction comprises a tilt angle and a tilt angle rate;

[0051] Wherein, controlling the tiltable rotor to reverse tilt according to the tilt angle instruction comprises the following steps:

[0052] When the to-fly distance V < the forward distance threshold, a variable proportional feedback control parameter P is determined based on the to-fly distance, and a tilt angle rate during reverse tilt is determined by the variable proportional feedback control parameter P, so that the tiltable rotors of the tilt rotor aircraft are reversed according to the tilt angle rate, and the minimum tilt angle allowed by the current flight speed is less than or equal to the tilt angle, which is less than or equal to the maximum tilt angle allowed by the current flight speed; wherein the forward distance threshold is determined by semi-physical simulation according to the flight time and acceleration of the reverse tilt transition stage, and the value range is 10-100m;

[0053] When the tilt angle is [70°, 90°) and the to-fly distance V ≥ the forward distance threshold, the tilt angle rate is controlled to be 0, and the tilt rotor aircraft is kept forward flight at the current tilt angle;

[0054] When the tilt angle is 90°, if the current flight speed > the speed threshold, the flight speed is reduced until the current flight speed ≤ the speed threshold, and the pitch angle and roll angle are controlled to be within a predetermined range (such as the pitch angle being controlled to be within 2°-12°), and the heading angle is kept unchanged;

[0055] When the tilt angle is 90°, if the current flight speed ≤ the speed threshold, position control is performed on the longitudinal channel by open-loop control, and the current flight speed command is softened to the speed command value output by the position controller, or the variable speed control strategy of the multi-rotor mode is used on the longitudinal channel (such as increasing the speed of the rear rotors and reducing the speed of the front rotors, then the forward flight speed of the aircraft is increased, and vice versa, and vice versa to reduce the forward speed or fly backward, reduce the speed of the rear rotors and increase the speed of the front rotors, then reduce the forward flight speed of the aircraft) to achieve position control; at the same time, the forward flight acceleration command is limited to 0.5m / s 2 ~2.0m / s 2 , and the roll angle and heading angle are controlled to be within a predetermined range to avoid deviation from the course, wherein the heading angle control can be achieved by using rotor differential to control the heading angle on the heading channel;

[0056] The value range of the speed threshold is 2.0m / s-10.0m / s;

[0057] The variable proportional feedback control parameter P is obtained by the following method (4):

[0058]

[0059] Wherein, P max , P min are the first proportional feedback control parameter and the second proportional feedback control parameter, respectively, both of which can be determined by simulation debugging process, and the value range is 1-10, and P max >P min ; V is the to-fly distance, Vmin Vmin is a minimum stand-off distance threshold value, max Vmax is a maximum stand-off distance threshold value, and the minimum stand-off distance threshold value Vmin min , the maximum stand-off distance threshold value Vmax max may be determined through a simulation process, and satisfy Vmin min < Vmax max < dis_hor;

[0060] Further, the tilt angle rate ω during reverse tilt is calculated according to formula (5):

[0061] ω = P * V (5)

[0062] In the embodiment, the minimum tilt angle and the maximum tilt angle allowed by the current flight speed can be determined through the tilt corridor, so that the tilt angle is limited within the tilt corridor range. At the same time, since different flight speeds correspond to different tilt angle upper and lower limits, dynamic amplitude control of the tilt angle can be realized through the tilt corridor.

[0063] Therefore, based on the stand-off distance, the tilt angle command is obtained by using the variable proportional feedback control parameter P feedback control according to the principle of "large distance small gain" and "small distance large gain", that is, as the stand-off distance decreases, the proportional feedback control parameter P (i.e., from the first proportional feedback control parameter P max to the second proportional feedback control parameter P min ) and the tilt angle rate are reduced (for example, when the tilt angle is 70°, the tilt angle rate can be reduced to close to 0), so that when the aircraft maintains the tilt angle and flies forward, a forward pulling force component can be generated to save the energy consumption of the aircraft.

[0064] Further, the reverse tilt transition flight speed V cmd ’ is obtained through formula (6):

[0065] V cmd′ = a'β' + b'β' + c'β + d' (6) 3 2 2

[0066] Wherein, β' is the tilt angle of the tiltable rotor during reverse tilt; a', b', c', and d' are respectively the first design coefficient, the second design coefficient, the third design coefficient, and the fourth design coefficient of the reverse tilt transition stage. The four design coefficients can also be obtained by four-order polynomial fitting through the discrete points with optimal power in the tilt transition corridor.

[0067] ​​​Meanwhile, in order to accelerate the reverse tilt deceleration process, when the tilt wing unmanned aerial vehicle is located at the reverse tilt state point, the pitch angle is increased at a preset pitch angle increasing rate in the longitudinal channel until the pitch angle reaches the preset value, and during the pitch angle increasing process, the roll angle is kept as 0 and the heading angle is unchanged, further, the pitch angle increasing rate is 0.1° / s-1° / s.

[0068] In conclusion, in the present application, when the tilt wing aircraft is in the forward tilt transition stage and the reverse tilt transition stage, the forward flight speed control can be completed based on the flight speed instruction (i.e., the forward tilt transition flight speed V cmd , the reverse tilt transition flight speed V cmd ), especially in the reverse tilt transition stage, the tilt angle rate is calculated based on the standby flight distance, and the tilt angle is dynamically limited, so that the position of the tilt rotor aircraft in the reverse tilt transition stage can be accurately controlled, and further combined with the comparison of the standby flight distance and the forward distance threshold, and the tilt angle range, the corresponding flight control strategy is executed in different stages in the reverse tilt transition stage, the position control effect of the aircraft is strengthened, the accurate and smooth landing of the aircraft is ensured, and the energy consumption of the aircraft is saved.

[0069] It should be noted that in this document, such as the term "include", "contain" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes elements inherent to such process, method, article or equipment. Without more limitations, the element defined by the statement "including a" does not exclude the presence of another identical element in the process, method, article or equipment including the element.

[0070] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, replacements and variations of the embodiments can be made without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A flight control method for a tiltrotor aircraft in a tilt transition phase, characterized in that: Including reverse bank transition phase flight control, and reverse bank transition phase flight control includes: Determine a reverse tilt state point, where the reverse tilt state point is a waypoint at a height H where the distance to be flown from the starting point of the multirotor modal descent phase is greater than or equal to the shortest designed deceleration distance; When the tiltrotor aircraft is located at the reverse tilt state point, the tiltrotor is controlled to tilt reversely according to the tilt angle instruction, and the tiltrotor aircraft is controlled to fly forward according to the reverse tilt transition flight speed.

2. The tiltrotor aircraft flight control method according to claim 1, wherein: The shortest designed deceleration distance dis_hor is calculated according to the following formula: dis_hor=V up ×t up Among them, V up , t up are the flight speed corresponding to the upper boundary of the tilt transition corridor and the flight time corresponding to the upper boundary of the tilt transition corridor respectively; Alternatively, the shortest designed deceleration distance dis_hor may be calculated according to the following formula: dis_hor=V_cruise 2 / 2a Wherein, V_cruise is the cruising speed of the tiltrotor aircraft when cruising in fixed-wing mode; a is the acceleration of the tiltrotor aircraft during the reverse tilt transition phase.

3. The tiltrotor aircraft flight control method according to claim 1, wherein: The height H is calculated according to the following formula: Wherein, H1 is the height of the starting point of the multirotor modal descent phase; γ is the descent rate of the tiltrotor aircraft in the altitude direction when the tiltrotor aircraft descends from the current waypoint to the starting point of the multirotor modal descent phase; V_cruise is the cruising speed of the tiltrotor aircraft when cruising in fixed-wing mode; a is the acceleration of the tiltrotor aircraft during the reverse tilt transition phase.

4. The tiltrotor aircraft flight control method according to claim 1, wherein: Controlling the reverse tilt of the tilt rotor according to the tilt angle command, including: When the distance to be flown V is less than the forward distance threshold, determining a variable proportional feedback control parameter P based on the distance to be flown, and determining a tilt angle rate during reverse tilting using the variable proportional feedback control parameter P, so that the tiltable rotor of the tiltrotor aircraft tilts in the reverse direction according to the tilt angle rate, and such that a minimum tilt angle allowed by the current flight speed is less than or equal to a maximum tilt angle allowed by the current flight speed; The variable proportional feedback control parameter P is obtained as follows: Among them, P max 、P min are the first proportional feedback control parameter and the second proportional feedback control parameter respectively, and P max >P min ; V is the distance to be flown, V min is the minimum distance to be flown threshold, V max is the maximum distance to be flown threshold.

5. The tiltrotor aircraft flight control method according to claim 4, wherein: The tilt angular rate ω during reverse tilting is calculated according to the following formula: ω=P*V.

6. The tiltrotor aircraft flight control method according to claim 1, wherein: The reverse bank transition flight speed V cmd 'Get it through the following formula: V cmd′ =a′β′ 3 +b′b′ 2 +c′β 2 +d′ Wherein, β' is the tilt angle of the tilt rotor during reverse tilting; a', b', c', and d' are the first, second, third, and fourth design coefficients of the reverse tilting transition phase, respectively.

7. The tiltrotor aircraft flight control method according to claim 1, wherein: When the tilt-wing UAV is located at the reverse tilt state point, the pitch angle is increased in the longitudinal channel according to the preset pitch angle increase rate until the pitch angle reaches the preset value.

8. The tiltrotor aircraft flight control method according to claim 1, wherein: Controlling the reverse tilt of the tilt rotor according to the tilt angle command, including: When the tilt angle is [70°, 90°) and the distance to be flown V ≥ the forward distance threshold, the tilt angle rate is controlled to 0, and the tiltrotor aircraft maintains the current tilt angle to fly forward; When the tilt angle = 90°, if the current flight speed is greater than the speed threshold, the flight speed is reduced until the current flight speed is less than or equal to the speed threshold, and the pitch angle and roll angle are controlled within the predetermined range, and the heading angle remains unchanged; When the tilt angle = 90°, if the current flight speed ≤ the speed threshold, position control is performed on the longitudinal channel through open-loop control, and the current flight speed command is softened to the speed command value output by the position controller, or the variable speed control strategy of the multi-rotor mode is adopted on the longitudinal channel to achieve position control.

9. The tiltrotor aircraft flight control method according to claim 1, wherein: The tiltrotor aircraft flight control method further includes forward tilt transition phase flight control, and the forward tilt transition phase flight control includes: The shortest forward transition path L is obtained according to the following formula threshold ; L threshold =V down ×t down Among them, V down , t down are respectively the flight speed corresponding to the lower boundary of the tilt transition corridor and the flight time corresponding to the lower boundary of the tilt transition corridor; the tilt corridor can be predetermined by a flight dynamics model of the tiltrotor aircraft; Control the tiltrotor aircraft in the forward tilt transition phase according to the set heading angle and forward tilt transition flight speed V cmd flight.

10. The tiltrotor aircraft flight control method according to claim 9, wherein: The positive tilt transition flight speed V cmd Obtained through the following formula: V cmd =aβ 3 +bβ 2 +vβ+d Wherein, β is the tilt angle of the tilt rotor during forward tilting; a, b, c, and d are the first, second, third, and fourth design coefficients of the forward tilting transition phase, respectively.

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