Tilting rotorcraft vortex ring boundary protection control method

Abstract

The invention belongs to the field of pneumatic and flight control of tilting rotorcrafts, and relates to a vortex ring boundary protection control method of a tilting rotorcraft. Comprising the steps that firstly, according to the maximum takeoff weight M and the rotor wing radius R of the tilt rotorcraft, the induced speed V1 of rotor wing downwash during hovering of the tilt rotorcraft is determined; 2, according to the induced velocity V1 of rotor wing downwash, the vortex ring boundary of a single rotor wing is determined, and the boundary is a binary quadratic curve composed of a forward flight velocity VX and a vertical velocity Vy; 3, the vortex ring boundary of the whole tilt rotorcraft is determined according to the vortex ring boundary of the single rotor and the flight characteristics of the tilt rotorcraft in the flight process, and the flight characteristics of the tilt rotorcraft in the flight process are that the upper half part of the aircraft entering the binary quadratic curve indicates that the aircraft enters the vortex ring boundary; therefore, whether the airplane enters the upper half part of the binary quadratic curve or not is considered in practice; and 4, reserving a preset safety margin on the basis of the boundary of the vortex ring of the whole tilt rotorcraft, and taking the preset safety margin as an early warning boundary of the vortex ring in the flight process.

Description

Technical Field

[0001] This invention belongs to the field of tiltrotor aerodynamics and flight control, and relates to a method for vortex ring boundary protection control of tiltrotor aircraft. Background Technology

[0002] Tiltrotor aircraft, combining the vertical takeoff and landing capabilities of helicopters with the high-speed cruise characteristics of fixed-wing aircraft, have increasingly broad application prospects in both military and civilian fields. However, like conventional helicopters, tiltrotor aircraft are susceptible to vortex ring conditions during helicopter-style descent. When the aircraft descends vertically or near vertically at high speed, the air beneath the rotor is rapidly "drawn" upwards into the rotor disk area, creating a reverse flow with the original downwash. The interaction of these two airflows forms a ring-shaped vortex beneath the rotor, causing a sharp decrease in rotor lift. When the rotor lift is insufficient to maintain stable gravity, the aircraft will descend rapidly and may even experience a flight accident. Moreover, tiltrotor aircraft have a tandem rotor configuration, making conventional helicopter vortex ring boundary determination methods not entirely applicable. Therefore, determining the vortex ring boundary of tiltrotor aircraft and protecting it through the flight control system is particularly important and urgent. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide a calculation method for the vortex ring boundary during low-speed hovering flight of a tiltrotor aircraft, and to provide a control and protection method to prevent the aircraft from exceeding this boundary, thereby improving flight safety and reducing pilot control load.

[0004] The present invention adopts the following technical solution: In a first aspect, the present invention provides a method for protecting and controlling the vortex ring boundary of a tiltrotor aircraft, the method comprising: Step 1: Based on the tiltrotor's maximum takeoff weight M and rotor radius R, determine the induced velocity V1 of the rotor downwash when the tiltrotor is hovering; Step 2: Based on the induced velocity V1 of the rotor downwash, determine the vortex ring boundary of a single rotor. This boundary is determined by the forward flight velocity V. X A quadratic curve consisting of the vertical velocity Vy and the two variables; Step 3: Determine the vortex ring boundary of the entire tiltrotor based on the vortex ring boundary of a single rotor and the flight characteristics of the tiltrotor during flight. The flight characteristics of the tiltrotor during flight are that the aircraft enters the upper part of the two-dimensional quadratic curve, which means that the aircraft has entered the vortex ring boundary. Therefore, in practice, it is only necessary to consider whether the aircraft enters the upper part of the two-dimensional quadratic curve. Step 4: After leaving a preset safety margin on the boundary of the vortex ring of the entire tiltrotor aircraft, use it as the early warning boundary of the vortex ring during flight.

[0005] Furthermore, the method also includes: Step five: The flight control system monitors the current forward flight speed, descent speed and roll angle rate of the aircraft in real time, and calculates and judges in real time whether the current state breaks through the early warning boundary of the vortex ring.

[0006] Further, the method further comprises: Step six: If the current flight state breaks through the early warning boundary of the vortex ring, an alarm information is sent out through the cockpit display screen of the aircraft, so that the pilot controls the aircraft to change the current state.

[0007] Further, the method further comprises: Step seven: If the flight state of the aircraft approaches the vortex ring boundary of the tilt-rotor aircraft, the vortex ring control law of the aircraft increases the forward flight speed and reduces the vertical speed by outputting additional forward acceleration instruction ACC and upward acceleration instruction HCC, so as to control the aircraft outside the vortex ring boundary.

[0008] Further, the calculation formula of the rotor induced speed V1 in step one is: , wherein g is the acceleration of gravity, M is the flight weight, R is the radius of a single rotor, and p is the air density.

[0009] Further, the calculation formula of the vortex ring boundary of a single rotor in step two is as follows:

[0010] and V x > 0 and V y > (k0+k2)*V1) , wherein k0 is the ratio of the longitudinal coordinate position of the center point of the vortex ring boundary to the rotor induced speed V1, and takes a value of 0.9; k1 is the ratio of the maximum forward flight speed of the vortex ring boundary to the rotor induced speed V1, and takes a value of 0.9; K2=k0-k4, and K4 is the ratio of the minimum descent speed in the vortex ring boundary to the rotor induced speed V1, and takes a value of 0.4.

[0011] Further, the calculation formula of the actual vortex ring boundary of the whole machine in step three is as follows:

[0012] and V x > 0 and V y > k0*V1.

[0013] Further, the calculation method of the vortex ring early warning boundary in step four is as follows: On the basis of the vortex ring boundary of the whole machine in step three, a coefficient k3 is multiplied to obtain the vortex ring early warning boundary of the whole machine, and K3 is not less than 1.2;

[0014] and V x > 0 and Vy >k0*V1.

[0015] Furthermore, the early warning triggering mechanism described in step five is as follows: Real-time acquisition of forward flight speed V X The vertical velocity Vy is the vertical velocity at the aircraft's center of gravity, and the vertical velocity at the rotor is Vy-L*p. When Vy-L*p breaks through the quadratic curve, the forward flight speed V... X When the corresponding warning boundary is reached, a warning alarm is triggered. The pilot recovers from the current state by reducing the aircraft's vertical speed Vy and increasing the aircraft's forward speed, where L is the lateral distance from the rotor hub center to the aircraft's plane of symmetry, and p is the roll rate. The alarm judgment mechanism is as follows:

[0016] And V x >0 and V y >k0*V1.

[0017] Furthermore, the formula for calculating the forward acceleration command ACC mentioned in step seven is as follows: ACC = 4.5 * t, t < 2 ACC=9, t≥2 The physical quantity output by ACC is the angle iN of the nacelle tilting forward, in degrees, and t is the time, in seconds; ACC is the rotor nacelle tilting forward command, which accelerates the aircraft by tilting the rotor nacelle forward. The formula for calculating the upward acceleration command (HCC) is as follows: HCC = 5 * t, t < 1 HCC=5, t≥1 The physical quantity output by HCC is rotor collective pitch Xcol, in degrees, and t is time, in seconds.

[0018] In summary, the beneficial effects of the present invention are as follows: Compared with the prior art, the present invention, employing the above-described technical solution, has the following technical advantages: 1) Based on the flight characteristics of tiltrotor aircraft and from an engineering perspective, this invention clarifies a method for determining the vortex ring boundary applicable to tiltrotor aircraft, and considers the influence of the aircraft's roll motion on the vortex ring boundary.

[0019] 2) The application makes the tilt-rotor aircraft in hover low-speed flight and with a certain descent rate, the flight control system can monitor and determine in real time whether the current flight state enters the vortex ring warning boundary. If the vortex ring warning boundary is entered, the flight control system automatically warns the pilot. If the pilot does not react in time and the aircraft further approaches the dangerous boundary, the flight control system automatically enters the vortex ring escape program, generates forward acceleration command and upward acceleration command, so that the aircraft automatically escapes from the dangerous area, ensuring the safety of the aircraft flight. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Isolated rotor vortex ring boundary schematic diagram; Figure 2 Whole machine vortex ring boundary schematic diagram; Figure 3 Whole machine vortex ring warning boundary schematic diagram; Figure 4 After the flight state enters the vortex ring warning boundary, the warning signal is triggered. If it further approaches the vortex ring boundary, the forced escape control law is triggered; Figure 5 Short nacelle forward tilt forward flight acceleration time domain diagram; Figure 6 Total pitch increase vertical acceleration command time domain diagram; Figure 7 Airplane vertical velocity control protection effect diagram, when the vertical velocity approaches the vortex ring boundary, the forward velocity and the vertical velocity increase rapidly to escape from the dangerous area; Figure 8 Vortex ring boundary calculation and control protection flowchart. DETAILED DESCRIPTION

[0021] The technical solutions of the application will be described in detail below with reference to the accompanying drawings.

[0022] The embodiment of the application provides a vortex ring boundary control protection method for a tilt-rotor aircraft, and the method comprises the following steps: Step 1: According to the maximum take-off weight M of the tilt-rotor aircraft and the rotor radius R, the induced velocity V1 of the rotor downwash flow when the tilt-rotor aircraft hovers is determined.

[0023] Step 2: According to the induced velocity V1 of the rotor downwash flow, the vortex ring boundary of a single rotor is determined, which is a binary quadratic curve composed of forward flight velocity Vx and vertical velocity Vy. X

[0024] Step 3: According to the vortex ring boundary of a single rotor and the flight characteristics during the flight of the tilt-rotor aircraft (the upper half of the binary quadratic curve indicates that the aircraft enters the vortex ring boundary, so in practice, only whether the aircraft enters the upper half of the binary quadratic curve needs to be considered), the vortex ring boundary of the whole aircraft is determined.​

[0025] Step four: Leave a certain safety margin on the basis of the entire tilt-rotor vortex ring boundary as the early warning boundary of the vortex ring during flight.

[0026] Step five: Develop a vortex ring boundary protection early warning program. During the flight of the tilt-rotor aircraft, the roll motion of the aircraft will affect the flight state of the aircraft rotor. Therefore, the flight control system needs to monitor the current forward flight speed, descent speed and roll angle rate of the aircraft in real time, and calculate and judge in real time whether the current state has broken through the early warning boundary of the vortex ring.

[0027] Step six: If the current flight state breaks through the early warning boundary of the vortex ring, the aircraft will issue an alarm message through the display screen in the cockpit of the aircraft, allowing the pilot to control the aircraft to change the current state.

[0028] Step seven: If the flight state of the aircraft further approaches the vortex ring boundary of the aircraft and has reached the vortex ring boundary of the aircraft, the vortex ring control law of the aircraft intervenes, increases the forward flight speed and reduces the vertical speed by outputting additional forward acceleration instructions ACC and upward acceleration instructions HCC, and controls the aircraft outside the vortex ring boundary. At this time, the vortex ring protection control law exits.

[0029] Further, the calculation formula of the rotor induced velocity V1 in step one is as follows:

[0030] In the formula, g is the acceleration of gravity, M is the flight weight, R is the radius of a single rotor, and p is the air density.

[0031] Further, the calculation formula of the vortex ring boundary of a single rotor in step two is as follows: (V x > 0 and V y > (k0+k2)*V1) In the formula, k0 is the ratio of the longitudinal coordinate position of the center point of the vortex ring boundary to the rotor induced velocity V1. Generally, it is 0.9. k1 is the ratio of the maximum forward flight speed of the vortex ring boundary to the rotor induced velocity V1. Generally, it is 0.9.

[0032] K2=k0-k4 K4 is the ratio of the minimum descent speed in the vortex ring boundary to the rotor induced velocity V1. Generally, it is 0.4.

[0033] Further, the calculation formula of the actual vortex ring boundary of the entire machine in step three is as follows: (V x > 0 and V y > k0*V1) The further step in step four describes the method for calculating the vortex ring early warning boundary: Multiply the overall vortex ring boundary obtained in step three by a coefficient of k3 to obtain the overall vortex ring early warning boundary. K3 is not less than 1.2.

[0034] (V) x >0 and V y >k0*V1) The further step five describes the early warning triggering mechanism as follows: Real-time acquisition of forward flight speed V X The vertical velocity Vy is the vertical velocity at the aircraft's center of gravity, and the vertical velocity at the rotor is Vy-L*p. When Vy-L*p breaks through the quadratic curve, the forward flight speed V... X When the corresponding warning boundary is reached, a warning alarm is triggered. The pilot recovers by reducing the aircraft's vertical velocity Vy and increasing its forward speed. Here, L is the lateral distance from the rotor hub center to the aircraft's plane of symmetry, and p is the roll rate. The alarm judgment mechanism is as follows: (V) x >0 and V y >k0*V1) The formula for calculating the forward acceleration command ACC in step seven is as follows: ACC = 4.5*t (t<2) ACC = 9 (t≥2) The physical quantity output by ACC is the angle iN (°) of the nacelle tilting forward, and t is the time (s). ACC is the rotor nacelle tilt command, which accelerates the aircraft by tilting the rotor nacelle forward. The formula for calculating the upward acceleration command HCC in step seven is as follows: HCC = 5*t (t<1) HCC = 5 (t≥1) The physical quantity output by HCC is the rotor collective pitch Xcol (°), where t is time (s). Detailed implementation method Step 1: Taking a flight weight of 6000kg and a rotor radius of 4m as an example, the induced velocity V1 is 16.1m / s; Step 2: The calculation results of the vortex ring boundary of a single rotor based on Formula 2 are as follows: Figure 1 As shown; Step 3: The calculation results of the vortex ring boundary of the whole machine based on Formula 3 are as follows: Figure 2 As shown; Step 4: The calculation results of the vortex ring early warning boundary of the whole machine based on Formula 4 are as follows: Figure 3As shown; Step 5: The vortex ring early warning result is as follows Figure 4 As shown; Step Six: The ACC instruction calculation result based on Formula 6 is as follows Figure 5 As shown; the calculation result of the HCC instruction based on Formula 7 is as follows. Figure 6 As shown, the forced modification of the flight controller produces the following effect: Figure 7 As shown; The entire process is as follows: Figure 8 As shown.

[0035] Compared with the prior art, the present invention, employing the above-described technical solution, has the following technical advantages: 1) Based on the flight characteristics of tiltrotor aircraft and from an engineering perspective, this invention clarifies a method for determining the vortex ring boundary applicable to tiltrotor aircraft, and considers the influence of the aircraft's roll motion on the vortex ring boundary.

[0036] 2) This invention enables the tiltrotor aircraft to monitor and determine in real time whether the current flight state has entered the vortex ring warning boundary during hovering low-speed flight with a certain rate of descent. If the vortex ring warning boundary is reached, the flight control system automatically issues a warning to the pilot. If the pilot's reaction is not timely, causing the aircraft to approach the danger boundary further, the flight control system automatically initiates the vortex ring recovery procedure, issuing forward acceleration and upward acceleration commands to automatically remove the aircraft from the danger zone, ensuring flight safety.

Claims

1. A method for protecting and controlling the vortex ring boundary of a tiltrotor aircraft, characterized in that, The method includes: Step 1: Based on the tiltrotor's maximum takeoff weight M and rotor radius R, determine the induced velocity V1 of the rotor downwash when the tiltrotor is hovering; Step 2: Based on the induced velocity V1 of the rotor downwash, determine the vortex ring boundary of a single rotor. This boundary is determined by the forward flight velocity V. X A quadratic curve consisting of the vertical velocity Vy and the two variables; Step 3: Determine the vortex ring boundary of the entire tiltrotor based on the vortex ring boundary of a single rotor and the flight characteristics of the tiltrotor during flight. The flight characteristics of the tiltrotor during flight are that the aircraft enters the upper part of the two-dimensional quadratic curve, which means that the aircraft has entered the vortex ring boundary. Therefore, in practice, it is only necessary to consider whether the aircraft enters the upper part of the two-dimensional quadratic curve. Step 4: After leaving a preset safety margin on the boundary of the vortex ring of the entire tiltrotor aircraft, use it as the early warning boundary of the vortex ring during flight.

2. The method for protecting and controlling the vortex ring boundary of a tiltrotor aircraft according to claim 1, characterized in that, The method further includes: Step 5: The flight control system monitors the aircraft's current forward speed, descent speed, and roll rate in real time, and calculates and determines whether the current state has exceeded the warning boundary of the vortex ring.

3. The method for protecting and controlling the vortex ring boundary of a tiltrotor aircraft according to claim 2, characterized in that, The method further includes: Step Six: If the current flight status exceeds the warning boundary of the vortex ring, an alarm message will be issued through the aircraft cockpit display screen, instructing the pilot to control the aircraft to recover from the current status.

4. The method for protecting and controlling the vortex ring boundary of a tiltrotor aircraft according to claim 3, characterized in that, The method further includes: Step 7: If the aircraft's flight state approaches the vortex ring boundary of the tiltrotor, the aircraft's vortex ring control law increases the forward speed and decreases the vertical speed by outputting additional forward acceleration command ACC and upward acceleration command HCC, thus controlling the aircraft to stay outside the vortex ring boundary.

5. The method for protecting and controlling the vortex ring boundary of a tiltrotor aircraft according to claim 1, characterized in that, The formula for calculating the rotor induced velocity V1 mentioned in step one is as follows: In the formula, g is the acceleration due to gravity, M is the flight weight, R is the radius of a single rotor, and ρ is the air density.

6. The tiltrotor aircraft vortex ring boundary protection control method according to claim 5, characterized in that, The formula for calculating the vortex ring boundary of a single rotor in step two is as follows: And V x >0 and V y > (k0+k2)*V1) In the formula, k0 is the ratio of the ordinate position of the center point of the vortex ring boundary to the rotor induced velocity V1, which is 0.9; k1 is the ratio of the maximum forward speed of the vortex ring boundary to the rotor induced velocity V1, which is 0.9; K2=k0-k4, K4 is the ratio of the minimum descent speed in the vortex ring boundary to the rotor induced velocity V1, which is 0.

4.

7. The tiltrotor aircraft vortex ring boundary protection control method according to claim 6, characterized in that, The formula for calculating the actual vortex ring boundary of the whole machine described in step three is as follows: And V x >0 and V y >k0*V1.

8. The tiltrotor aircraft vortex ring boundary protection control method according to claim 7, characterized in that, The method for calculating the vortex ring early warning boundary described in step four is as follows: Multiply the overall vortex ring boundary obtained in step three by a coefficient of k3 to obtain the overall vortex ring early warning boundary, where K3 is not less than 1.2; And V x >0 and V y >k0*V1.

9. The tiltrotor aircraft vortex ring boundary protection control method according to claim 8, characterized in that, The early warning triggering mechanism described in step five is as follows: Real-time acquisition of forward flight speed V X The vertical velocity Vy is the vertical velocity at the aircraft's center of gravity, and the vertical velocity at the rotor is Vy-L*p. When Vy-L*p breaks through the quadratic curve, the forward flight speed V... X When the corresponding warning boundary is reached, a warning alarm is triggered. The pilot recovers from the current state by reducing the aircraft's vertical speed Vy and increasing the aircraft's forward speed, where L is the lateral distance from the rotor hub center to the aircraft's plane of symmetry, and p is the roll rate. The alarm judgment mechanism is as follows: And V x >0 and V y >k0*V1.

10. A method for protecting and controlling the vortex ring boundary of a tiltrotor aircraft according to claim 9, characterized in that, The formula for calculating the forward acceleration command ACC mentioned in step seven is as follows: ACC = 4.5 * t, t < 2 ACC=9, t≥2 The physical quantity output by ACC is the angle iN of the nacelle tilting forward, in degrees, and t is the time, in seconds; ACC is the rotor nacelle tilting forward command, which accelerates the aircraft by tilting the rotor nacelle forward. The formula for calculating the upward acceleration command (HCC) is as follows: HCC = 5 * t, t < 1 HCC=5, t≥1 The physical quantity output by HCC is rotor collective pitch Xcol, in degrees, and t is time, in seconds.

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