A method for designing a helicopter rotor speed correction control law

Abstract

The present application belongs to the technical field of helicopter overall design, and particularly relates to a kind of helicopter rotor speed correction control law design method. Including: S1, obtain static pressure and external atmospheric temperature, calculate relative atmospheric density;Based on atmospheric density and true airspeed, calculate the corrected rotor speed Ω1;S2, based on the speed adjustment amplitude under the hovering state, the rotor speed is corrected, and the unrestricted correction speed Ω2 is obtained;S3, according to the adjustment range of rotor speed, the correction speed Ω3 considering boundary limit is calculated;S4, according to the rotor speed variation rate limit, the rotor target speed Ω of current time step is calculated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of helicopter overall design, and particularly relates to a helicopter rotor speed correction control law design method. BACKGROUND

[0002] For a conventional configuration of a helicopter, the rotor is the main source of lift, and the rotor speed is an important parameter in the design of the helicopter. Generally, the rotor speed of the helicopter is fixed, but in the process of flight of the helicopter, the atmospheric environment and the flight state are constantly changing. If the rotor speed can be adjusted within a certain range according to the atmospheric environment and the flight state, the rotor capacity and environmental adaptability of the helicopter can be effectively improved. When flying at high altitudes, the rotor speed can be appropriately increased to avoid the decrease of lift and improve the helicopter capacity. When flying at low altitudes, the rotor speed can be appropriately reduced to effectively reduce the noise. At the same time, when flying at a high speed, the rotor speed can also be reduced to effectively avoid the bow shock of the forward blade. SUMMARY

[0003] The application aims to design a helicopter rotor speed correction control law design method, which adjusts the rotor speed of the helicopter within a certain range based on atmospheric density compensation and flight state correction, so as to compensate for the lift of the rotor at high altitudes, reduce the noise at low altitudes, and improve the flight capacity of the helicopter.

[0004] To achieve the above-mentioned purpose, the application adopts the following technical solutions.

[0005] A helicopter rotor speed correction control law design method, the method comprising:

[0006] S1, obtaining the static pressure and the external atmospheric temperature, calculating the relative atmospheric density, and calculating the corrected rotor speed Ω1 based on the atmospheric density and the true airspeed;

[0007] S2, correcting the rotor speed based on the speed adjustment range in the hovering state to obtain the unrestricted corrected speed Ω2;

[0008] S3, calculating the boundary-limited corrected speed Ω3 according to the adjustment range of the rotor speed;

[0009] S4, calculating the rotor target speed Ω of the current time step according to the rotor speed change rate limit.

[0010] Further,

[0011] S1, obtaining the static pressure and the external atmospheric temperature, calculating the relative atmospheric density, and calculating the corrected rotor speed Ω1 based on the atmospheric density and the true airspeed;

[0012] C ρ = 288.15 / (273.15 + T) x (P / 1013.25)

[0013] wherein C ρ denotes the relative atmospheric density, T denotes the measured outside atmospheric temperature in °C, and P denotes the measured static pressure in hPa.

[0014] Further,

[0015] S1, the method for calculating the corrected rotor speed Ω1 is specifically:

[0016] The corrected rotor speed Ω1 is:

[0017] wherein Ω0 denotes the reference rotor speed, Ω V min denotes the corrected speed under low speed conditions, Ω V max denotes the corrected speed under high speed conditions, C V denotes the true airspeed conversion factor.

[0018] Further,

[0019] The true airspeed conversion factor C V has a value of:

[0020] C V = 0 (V < V min )

[0021] C V = (V-V min ) / (V max -V min ) (V min ≤ V ≤ V max )

[0022] C V = 1 (V > V max )

[0023] wherein V denotes the true airspeed, V min denotes the minimum critical speed for speed correction, and V max denotes the maximum critical speed for speed correction.

[0024] Further,

[0025] In S2, the method for calculating the unrestricted corrected speed Ω2 is specifically:

[0026] Ω2 = Ω1 + ΔΩ hover × (1-C V )

[0027] wherein ΔΩ hover denotes the rotor speed adjustment amplitude under hovering state.

[0028] Further,

[0029] The modified rotating speed Ω3 considering the boundary limit in S3 is specifically:

[0030] Ω3=MIN(MAX(Ω2,Ω min ),Ω max ]

[0031] Wherein, MIN(a,b) represents the smaller value between a and b, MAX(a,b) represents the larger value between a and b, Ω min represents the lower limit of rotating speed in the adjustable range, Ω max represents the upper limit of rotating speed in the adjustable range.

[0032] Further,

[0033] In S4, the target rotating speed Ω of the current time step is calculated as:

[0034] Ω=MIN(Ω3,Ω t-1 +k×Δt)(Ω>Ω t-1 )

[0035] Ω=MAX(Ω3,Ω t-1 -k×Δt)(Ω<Ω t-1 )

[0036] Wherein, Ω t-1 represents the target rotating speed of the previous time step, k represents the rotating speed change rate of the rotor, and Δt represents the time step length.

[0037] Further,

[0038] After S4, the method further comprises:

[0039] S5, only when the difference between the target rotating speed Ω of the rotor and the rotating speed of the previous time step is greater than a preset threshold, a rotating speed change instruction is sent, and the target rotating speed Ω of the rotor is reached at a non-exceeding limit speed;

[0040] If the difference between the target rotating speed Ω of the rotor and the rotating speed of the previous time step is less than the preset threshold, the target rotating speed Ω of the rotor adopts the rotating speed of the previous time step.

[0041] A helicopter rotor rotating speed correction control law designed by the application can adjust the rotor rotating speed in a variable range by using atmospheric density compensation and true airspeed correction, and can avoid small amplitude oscillation of the rotor rotating speed. The rotating speed correction control law in the application can effectively compensate the lift loss of the rotor under the condition of low atmospheric density at high altitude, reduce the rotor noise under the premise of ensuring the rotor capability at low altitude, delay the generation of blade tip shock at high speed forward flight, and effectively improve the rotor capability and environmental adaptability of the helicopter. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 A flowchart of a design method of a helicopter rotor speed correction control law provided by an embodiment of the application is shown. DETAILED DESCRIPTION

[0043] The technical solutions of the application will be described in detail below with reference to the accompanying drawings.

[0044] The rotor speed correction control law in the application considers atmospheric density compensation and true airspeed correction, and ensures that the target speed is between the upper and lower speed limits. In order to avoid endless small oscillations around a stable value, a speed change command is sent only when the difference between the target speed and the speed at the previous time step is not less than a certain threshold, and an attempt is made to reach the target speed at a suitable rate. If the difference between the target speed and the speed at the previous time step is less than the threshold, the speed is locked.

[0045] When calculating the target speed, the relative atmospheric density is first calculated using the measured static pressure and external atmospheric temperature, and the rotor speed is compensated based on the relative atmospheric density and the true airspeed to obtain the rotor speed Ω1 corrected based on atmospheric density and true airspeed, as shown in the following formula:

[0046]

[0047] C ρ = 288.15 / (273.15 + T) x (P / 1013.25)

[0048] C V = 0 (V < V min )

[0049] C V = (V - V min ) / (V max - V min ) (V min ≤ V ≤ V max )

[0050] C V = 1 (V > V max )

[0051] Where Ω0 represents the reference rotor speed, Ω V min represents the corrected speed under low-speed conditions, Ω V max represents the corrected speed under high-speed conditions, C V represents the true airspeed conversion factor, C ρ represents the relative atmospheric density, T represents the measured external atmospheric temperature (unit: °C), P represents the measured static pressure (unit: hPa), V represents the true airspeed, V minVmin represents the minimum critical speed of the speed correction max Vmax represents the maximum critical speed of the speed correction. When the vacuum speed is less than the minimum critical speed of the speed correction, the vacuum speed conversion factor is set to 0; when the vacuum speed is greater than the maximum critical speed of the speed correction, the vacuum speed conversion factor is set to 1; when the vacuum speed is between the maximum and minimum critical speeds of the speed correction, the vacuum speed conversion factor is linearly interpolated.

[0052] Then, the rotor speed is further corrected based on the speed adjustment amplitude in the hovering state to obtain an unrestricted corrected speed Ω2, as shown in the following formula:

[0053] Ω2 = Ω1 + ΔΩ hover × (1 - C V )

[0054] Wherein, ΔΩ hover represents the speed adjustment amplitude in the hovering state.

[0055] Since the rotor speed has a certain adjustment range, the corrected speed needs to be limited to ensure that the corrected rotor speed is within the speed limit. If the corrected rotor speed exceeds the adjustable range, the boundary value close to the corrected speed is taken as the corrected speed Ω3 considering the boundary limit, as shown in the following formula:

[0056] Ω3 = MIN [MAX (Ω2, Ω min ), Ω max ]

[0057] Wherein, MIN (a, b) represents the smaller value of a and b, MAX (a, b) represents the larger value of a and b, Ω min represents the lower limit of the speed in the adjustable range, and Ω max represents the upper limit of the speed in the adjustable range.

[0058] Finally, the speed change rate limit needs to be considered. If the difference between the corrected speed considering the boundary limit and the speed at the previous time step is too large, the target speed Ω at the current time step needs to be limited to ensure that the rotor speed change rate will not be out of limit, as shown in the following formula:

[0059] Ω = MIN (Ω3, Ω t-1 + k × Δt) (Ω > Ω t-1 )

[0060] Ω = MAX (Ω3, Ω t-1 - k × Δt) (Ω < Ω t-1 )

[0061] Wherein, Ω t-1 represents the target speed at the previous time step, k represents the rotor speed change rate, and Δt represents the time step length.

[0062] The target rotating speed calculation logic based on atmospheric density compensation and vacuum speed correction is seen in the attached drawings.

[0063] The technical scheme (1) of the present application corrects the rotating speed of the helicopter rotor by using atmospheric density and vacuum speed, compensates the lift of the rotor at high altitude, reduces the noise at low altitude, and improves the flight capability of the helicopter; (2) fully considers the low-speed state characteristics of the helicopter, and further corrects the rotating speed of the rotor corrected based on atmospheric density and vacuum speed by using the rotating speed adjustment range in the hovering state; (3) uses threshold setting to avoid endless small oscillation of the rotating speed around a stable value, and uses the rotating speed change rate as the target rotating speed limit to avoid too fast change of the rotating speed.

[0064] The rotating speed correction control law designed by the present application can adjust the rotating speed of the rotor in a variable range by using atmospheric density compensation and vacuum speed correction, and can avoid small amplitude oscillation of the rotating speed. The rotating speed correction control law in the present application can effectively compensate the lift loss of the rotor under the condition of low atmospheric density at high altitude, reduce the rotor noise under the premise of ensuring the rotor capability at low altitude, delay the generation of the blade tip shock at high speed forward flight, and effectively improve the rotor capability and environmental adaptability of the helicopter.

Claims

1. A method of designing a control law for modifying the speed of a helicopter rotor, characterized in that, The method comprises: S1, obtaining static pressure and external atmospheric temperature, calculating relative atmospheric density, and calculating corrected rotor speed Ω1 based on atmospheric density and vacuum speed; S1, obtaining static pressure and external atmospheric temperature, calculating relative atmospheric density, and calculating corrected rotor speed Ω1 based on atmospheric density and vacuum speed; C ρ = 288.15 / (273.15 + T) x (P / 1013.25) where C ρ represents the relative atmospheric density, T represents the measured external atmospheric temperature, in °C, and P represents the measured static pressure, in hPa; S1, calculating the method of the corrected rotor speed Ω1 is specifically: Modified rotor speed Ω1: wherein Ω0represents a reference rotor speed, Ω Vmin represents a correction rotor speed under low speed conditions, Ω Vmax represents a correction rotor speed under high speed conditions, C V represents a true airspeed conversion factor; Vacuum velocity conversion factor C V has a value of: C V = 0 (V < V min ) C V = (V-V min ) / (V max -V min )(V min ≤V≤V max ) C V = 1 (V > V max ) where V represents the vacuum velocity, V min represents the minimum critical velocity of the speed correction, V max represents the maximum critical velocity of the speed correction; S2, correcting the rotor speed based on the speed adjustment range in the hovering state to obtain an unrestricted corrected speed Ω2; in S2, calculating the unrestricted corrected speed Ω2 is specifically: Ω2 = Ω1 + ΔΩ hover x (1 - C V ) wherein ΔΩ hover represents the amplitude of the rotational speed adjustment in the hovering state; S3, calculating a boundary-limited corrected speed Ω3 according to the adjustment range of the rotor speed; S3, calculating a boundary-limited corrected speed Ω3 according to the adjustment range of the rotor speed; Ω3 = MIN[MAX(Ω2, Ω min ), Ω max ] where MIN(a,b) denotes the smaller of a and b, and MAX(a,b) denotes the larger of a and b, Ω min denotes the lower limit of the rotational speed within the adjustable range, Ω max denotes the upper limit of the rotational speed within the adjustable range; S4, calculating the rotor target speed Ω of the current time step according to the rotor speed change rate limit; in S4, calculating the rotor target speed Ω of the current time step is specifically: Ω = MIN(Ω3, Ω t-1 + k x Δt)(Ω > Ω t-1 ) Ω = MAX(Ω3, Ω t-1 -k x Δt) (Ω < Ω t-1 ) where Ω t-1 denotes the target rotational speed of the previous time step, k denotes the rotor speed change rate, and Δt denotes the time step length.

2. The method of claim 1, wherein After S4, the method further comprises: S5, only when the difference between the rotor target speed Ω and the speed of the previous time step is greater than a preset threshold, a speed change instruction is sent, and the rotor target speed Ω is reached at a speed that does not exceed the limit; If the difference between the rotor target speed Ω and the speed of the previous time step is less than the preset threshold, the rotor target speed Ω adopts the speed of the previous time step.

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