A new method for evaluating the aerodynamic and static load of a rod in the hovering state of a rotor with a new blade tip

Abstract

The present application belongs to the technical field of helicopter aerodynamic design, and relates to a new type of blade tip rotor suspension state pull rod aerodynamic static load evaluation method. The present application determines rotor tension T, rotor rotation angular velocity and rotor radius; calculates rotor tension coefficient CT; calculates rotor blade average lift coefficient according to rotor tension coefficient CT; determines profile airfoil pitching moment coefficient according to average lift coefficient; calculates aerodynamic hinge moment airfoil contribution item; calculates aerodynamic hinge moment lift bias contribution item; calculates blade static aerodynamic hinge moment; and preferably calculates variable-pitch pull rod load. The calculation method of the present application is used to evaluate the aerodynamic static load of the new type of blade tip rotor pull rod in the suspension state. Compared with the wind tunnel test results and the calculation results based on the high-precision CFD method, the degree of agreement is better, indicating that the method proposed by the present application can effectively calculate the aerodynamic item in the pull rod static load.

Description

Technical Field

[0001] This invention belongs to the field of helicopter aerodynamic design technology and relates to a novel method for evaluating the aerodynamic static load of the rotor tip lever in hovering state. Background Technology

[0002] The rotor pitch control link is a rod that connects the rotor blade pitch control arm and the swashplate rotating ring. Its function is to enable the rotor blades to respond to changes in the swashplate position under collective / cyclic pitch control. The pitch control link is generally a straight rod with radial bearings at both ends. The bending moment at both ends of the pitch control link is zero, and the pitch control link can only withstand tension or compression.

[0003] The surge in stick load is one of the main factors limiting the increase of helicopter forward speed. Increased flight speed leads to a sharp increase in stick load, making pitch maneuvers difficult or impossible, and preventing the engine from continuously delivering power to the rotor. Structurally, it also limits the expansion of the flight envelope; the effects of large-scale alternating loads can cause fatigue failure of the control system. Pitch-dependent stick loads include contributions from dampers, ball bearings, inertial forces, and aerodynamic forces, with aerodynamic forces accounting for 80% and being the primary influencing factor. Therefore, accurate calculation of the aerodynamic loads on the stick is of great engineering significance.

[0004] For rotor aerodynamic layout design, especially for rotors with novel blade tip shapes, the tie rod load is a crucial constraint. If the tie rod static load is too large, the aerodynamic shape of the blades needs to be redesigned. During the iteration process of blade aerodynamic schemes, especially in the early "mass calculation" stage, it is necessary to quickly and accurately obtain the blade aerodynamic hinge torque to calculate the tie rod load. Therefore, this invention proposes an engineering method for evaluating the aerodynamic static load of the tie rod of a novel blade tip rotor in hovering mode. Summary of the Invention

[0005] The purpose of this invention is to establish an engineering algorithm that takes the overall parameters, aerodynamic parameters, and flight state parameters of the rotor as inputs, and takes into account the influence of the blade aerodynamic shape, so as to quickly and relatively accurately give the aerodynamic static load of the rotor tie rod load, providing reference and support for the optimized design of rotor aerodynamic layout.

[0006] The technical solution of this invention: A novel aerodynamic static load evaluation method for a rotor tip hovering state lever, comprising the following steps:

[0007] (1) Determine the overall parameters and flight status of the rotor, and specify the rotor thrust T, rotor rotational angular velocity Ω, and rotor radius R;

[0008] (2) Calculate the rotor thrust coefficient CT;

[0009] (3) Calculate the average lift coefficient C of the rotor blades based on the rotor thrust coefficient CT.l The subscript 'l' represents lift.

[0010] (4) According to the average lift coefficient C l Determine the pitching moment coefficient C of the airfoil profile. m The subscript m represents the pitching moment;

[0011] (5) Calculate the airfoil contribution term Mb of aerodynamic hinge moment. foil The subscript "foil" indicates an airfoil shape.

[0012] (6) Calculate the contribution of pneumatic hinge torque lift offset. M b i The subscript i represents lift.

[0013] (7) Calculate the static aerodynamic hinge torque Mb of the blade;

[0014] (8) Calculate the load on the variable pitch tie rod.

[0015] The rotor thrust T is determined by the takeoff weight in flight, and its value is equal to the weight of the helicopter.

[0016] The rotor rotational angular velocity Ω is given by the overall rotor parameters;

[0017] The rotor radius R is given by the overall rotor parameters;

[0018] The rotor thrust coefficient CT: according to the formula Solve for ρ, where ρ is the air density;

[0019] The average lift coefficient C of the rotor blades l According to the formula Solve for σ, where σ is the rotor real number;

[0020] The pitching moment coefficient C of the airfoil profile m According to the C of the airfoil l ~C m Obtained by table lookup;

[0021] The aerodynamic hinge moment airfoil contribution term Mb foil According to the formula The solution is performed, where r is the blade profile position and c is the profile chord length;

[0022] The pneumatic hinge torque lift bias contribution term Mb l According to the formula Solve for x, where x is the distance from the point on the 1 / 4 chord of the profile to the variable pitch axis (negative for sweepback);

[0023] The static aerodynamic hinge torque Mb of the blade is calculated using the formula Mb = Mb foil +Mbl Solve the problem;

[0024] The load Fb of the variable pitch tie rod: according to the formula The solution is performed, where L is the distance from the blade pitch axis to the pitch control rod. Fb is positive when the rod is under tension and negative when it is under compression.

[0025] The technical effects of this invention are as follows: The calculation method of this invention is used to evaluate the aerodynamic and static loads of a rotor linkage in its hovering state. This rotor blade has a forward sweep of 10° from 0.8R and a backward sweep of 20° from 0.9R, exhibiting a forward-sweeping and backward-sweeping tip shape different from conventional rectangular blades. Here, R is the rotor radius. The calculation results of this invention show good agreement with wind tunnel test results and calculation results based on high-precision CFD methods, indicating that the method proposed in this invention can effectively calculate the aerodynamic terms in the static loads of the novel rotor linkage. Attached image description:

[0026] Figure 1 This is a flowchart of the tie rod load calculation proposed in this invention;

[0027] Figure 2 A schematic diagram of the shape of the new type of tip rotor blade;

[0028] Figure 3 This is a comparison chart of the calculation results, experimental results, and high-precision calculation results of this invention. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings:

[0030] like Figure 1-3 As shown, a novel aerodynamic static load assessment method for a rotor tip hovering state includes the following steps:

[0031] (1) Determine the overall parameters and flight status of the rotor, and specify the rotor thrust T, rotor rotational angular velocity Ω, and rotor radius R; rotor thrust T: determined by the takeoff weight in flight status, its value is equal to the gravity of the helicopter; the rotor rotational angular velocity Ω: given by the overall rotor parameters; the rotor radius R: given by the overall rotor parameters;

[0032] (2) Calculate the rotor thrust coefficient CT; the rotor thrust coefficient CT is solved according to the formula CT=T / (0.5ρ(ΩR)^2), where ρ is the air density;

[0033] (3) Calculate the average lift coefficient C of the rotor blades based on the rotor thrust coefficient CT. l The subscript l represents lift; the average lift coefficient C of the rotor blades l According to the formula Solve for σ, where σ is the rotor real number;

[0034] (4) According to the average lift coefficient C of the blade l Determine the pitching moment coefficient C of the airfoil profile. m The subscript m represents the pitching moment, and the pitching moment coefficient C of the airfoil profile. m According to the C of the airfoil l ~C m Obtained by table lookup;

[0035] (5) Calculate the airfoil contribution term Mb of aerodynamic hinge moment. foil The subscript "foil" indicates the airfoil shape; the airfoil contribution term Mb of the aerodynamic hinge moment is... foil According to the formula The solution is performed, where r is the blade profile position and c is the profile chord length;

[0036] (6) Calculate the contribution term Mb of the aerodynamic hinge torque lift offset. i Subscript l represents lift; the pneumatic hinge torque lift offset contribution term Mb l According to the formula Solve for x, where x is the distance from the point on the 1 / 4 chord of the profile to the variable pitch axis (negative for sweepback);

[0037] (7) Calculate the static aerodynamic hinge torque Mb of the blade; the static aerodynamic hinge torque Mb of the blade: according to the formula Mb=Mb foil +Mb l Solve the problem;

[0038] (8) Calculate the load on the variable pitch tie rod: The load Fb on the variable pitch tie rod is calculated according to the formula. The solution is performed, where L is the distance from the blade pitch axis to the pitch control rod. Fb is positive when the rod is under tension and negative when it is under compression.

[0039] Figure 3 This is a comparison chart of the calculation results, experimental results, and high-precision calculation results of this invention. Figure 3 It can be seen that the calculation results of this invention are in good agreement with the wind tunnel test results and the calculation results based on the high-precision CFD method, indicating that the method proposed in this invention can effectively calculate the aerodynamic terms in the static load of the novel rotor tip rod.

Claims

1. A novel method for evaluating the aerodynamic static load of a rotor tip in hovering state, comprising the following steps: S1: Determine the overall parameters and flight status of the rotor, and specify the rotor thrust T and rotor rotational angular velocity. Rotor radius R; S2: Calculate the rotor thrust coefficient CT; CT is based on the formula... To solve, where air density; S3: Calculate the average lift coefficient of the rotor blades based on the rotor thrust coefficient CT. Subscript For lift; It is based on the formula To solve, where For rotor realism; S4: According to the average lift coefficient Determine the pitching moment coefficient of the airfoil profile. Subscript For pitching moment; S5: Calculate the airfoil contribution of aerodynamic hinge moment. Subscript It is an airfoil; It is based on the formula The solution is performed, where r is the blade profile position and c is the profile chord length; S6: Calculate the contribution of pneumatic hinge torque lift offset. Standard For lift; It is based on the formula Solve for x, where x is the distance from the point on the 1 / 4 chord line of the section to the variable pitch axis, and sweepback is negative; S7: Calculate the static aerodynamic hinge torque of the blades. ; According to the formula The solution is obtained; S8: Calculate the load on the variable pitch tie rod.

2. The novel aerodynamic static load evaluation method for the lever in the hovering state of a rotor tip as described in claim 1, characterized in that, The rotor thrust T is determined by the takeoff weight in flight, and its value is equal to the weight of the helicopter.

3. The novel aerodynamic static load evaluation method for the lever in the hovering state of a rotor tip as described in claim 1, characterized in that, The pitching moment coefficient of the airfoil profile According to the airfoil Obtained by looking up the table.

4. The novel aerodynamic static load evaluation method for the hovering state of a rotor tip as described in claim 1, characterized in that, The load of the variable pitch tie rod ,in It is the distance from the blade pitch axis to the pitch control rod, when the rod is under tension. When positive, it becomes negative when under pressure.

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