A method for designing a split hub of a tilting propeller

Abstract

The present application relates to the field of helicopter component strength design, and particularly relates to a kind of upper and lower split type tiltable hub strength design method.The method comprises: according to the structure and load of upper and lower split type tiltable hub, carry out force transmission route analysis, and determine dangerous position;According to the load and dangerous position of upper and lower split type tiltable hub, determine the characteristic load set of all dangerous positions;According to the structure of upper and lower split type tiltable hub, using finite element simulation or engineering method, determine the lift direction load / bending moment distribution relationship on upper and lower hub and its connecting structure;Step four: according to the structure and variable pitch and variable speed control process of upper and lower split type tiltable hub, determine the load action range of variable pitch rocker structure;According to the results of step one to step four, carry out finite element simulation of upper and lower split type tiltable hub structure, and carry out stress calculation.

Description

Technical Field

[0001] This invention relates to the field of strength design for helicopter components, and in particular to a strength design method for a split-type tiltable rotor hub. Background Technology

[0002] With the rapid development of the new energy industry and continuous breakthroughs in battery and motor technologies, electric vertical takeoff and landing (VTOL) aircraft are gradually acquiring both military and civilian applications and possessing broad market prospects. The electric tiltrotor aircraft is a new type of electric vertical takeoff and landing aircraft that, while achieving vertical takeoff and landing, can also increase flight speed, exhibiting high economic efficiency and technological innovation.

[0003] like Figure 1 As shown, the split-type tilting rotor hub is an important component of electrically driven tiltrotor aircraft, and a crucial structure for achieving variable collective pitch and variable speed control. Compared to traditional flexible spherical rotor hubs and rigidly connected rotor hubs used in helicopters, the split-type tilting rotor hub does not contain splines, conical rings, or other structures, and exhibits completely different characteristics in terms of torsional moment transmission, hub center moment transmission, and lift direction load / moment transmission. Summary of the Invention

[0004] The purpose of this invention is to provide a strength design method for a split-type tilting propeller hub, including force transmission path analysis, selection of critical locations, selection of characteristic loads, load distribution in the lift direction, determination of the control range, stress calculation, static strength analysis, and fatigue strength analysis. First, based on the structure and loads of the split-type tilting propeller hub, a force transmission path analysis is conducted to determine critical locations and corresponding characteristic loads. Details such as load distribution are refined, and stress calculations are performed. Based on the stress calculation results, static strength analysis and fatigue strength analysis are completed, thus finalizing the strength design.

[0005] Technical solution:

[0006] A method for designing the strength of a split-type tiltable propeller hub is provided, including:

[0007] Step 1: Based on the split-type tiltable propeller hub structure and load, conduct force transmission path analysis and identify critical areas;

[0008] Step 2: Based on the load of the split tiltable propeller hub and the critical parts, determine the set of characteristic loads for all critical parts;

[0009] Step 3: Based on the upper and lower split tiltable propeller hub structure, use finite element simulation or engineering methods to determine the load / bending moment distribution relationship in the lift direction on the upper and lower propeller hubs and their connecting structures;

[0010] Step 4: Determine the load range of the variable pitch rocker arm structure based on the upper and lower split tiltable propeller hub structure and the variable collective pitch and variable speed control process.

[0011] Step 5: Based on the results of Steps 1 to 4, conduct finite element simulation of the split-type tiltable propeller hub structure and perform stress calculation.

[0012] Furthermore, the method also includes:

[0013] Step Six: Based on the results of Step Two and Step Five, conduct static strength analysis and fatigue strength analysis of the split tiltable propeller hub structure to complete the strength design.

[0014] Furthermore, the hazardous areas include static strength hazardous areas and fatigue hazardous areas. Based on the upper and lower split tilting hub structure and loads, a force transmission path analysis is conducted to determine the hazardous areas, including:

[0015] Based on the analysis of the force transmission path, it can be determined that the load and bending moment transmitted by the upper and lower rotor hubs to the rotor blades, and the control load transmitted by the pitch control arm and control structure all exhibit characteristics that change with time, which are fatigue loads. Therefore, it is determined that the upper and lower rotor hubs, pitch control arm, control structure and related connecting structures are all parts of static strength and fatigue risk.

[0016] Furthermore, based on the loads of the split-type tilting propeller hub and the critical locations, the characteristic load set of all critical locations is determined, including:

[0017] Based on the loads and critical locations of the split tiltable propeller hubs, the characteristic loads of the upper and lower propeller hubs are determined to include blade centrifugal force, blade shear force, and bending moment; the characteristic loads of the pitch control arm and control structure are taken as control loads; and the loads related to the connected structure are taken as characteristic loads of the connecting structure.

[0018] Furthermore, based on the split-type tilting rotor hub structure, finite element simulation or engineering methods are used to determine the load / bending moment distribution relationship in the lift direction on the upper and lower rotor hubs and their connecting structures, including:

[0019] Apply bolt preload according to the design value and fix the upper and lower propeller hubs together with bolts;

[0020] Based on the actual contact and connection methods, the upper and lower rotor hubs, connecting bolts, and lift direction bearings are combined and modeled for force transmission analysis. During modeling, the model structure is simplified without affecting the structural stiffness. The simplified model is analyzed to obtain the load / bending moment distribution relationship in the direction of rotor lift, i.e., the distribution ratio of lift between the upper and lower rotor hubs.

[0021] Furthermore, the load range of the root variable pitch rocker arm structure is 5–15 mm.

[0022] Furthermore, based on the results of steps one through four, finite element simulation of the split-type tilting hub structure is conducted, and stress calculations are performed, including:

[0023] Identify all characteristic loads, their locations and modes of action, for each component of the split tiltable propeller hub; determine the constraint locations and modes of action; perform detailed modeling and stress analysis of each component as a separate body; apply loads with corresponding proportions to the upper and lower propeller hubs when loads / bending moments are applied in the lift direction; select the two ends and the middle point of the load range within the variable pitch rocker arm structure for loading, and analyze the stress at different load locations of the variable pitch rocker arm structure; complete the stress calculation.

[0024] Beneficial effects:

[0025] This invention effectively solves the key aspects of the strength design process for split-type tiltable propeller hub structures. By using force transmission analysis methods such as combined modeling, it quantitatively analyzes the characteristic load values ​​of each component of the split-type propeller hub structure. Through precise simulation of each component's separate body, it determines the stress at critical locations for static strength and fatigue strength. This solves the problems of force transmission and load decomposition in split-type tiltable propeller hub structures, improves the accuracy of stress analysis, and meets the needs of engineering design. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a split-type tiltable propeller hub structure.

[0027] Figure 2 This is a schematic diagram of the variable pitch rocker arm's movement range within the control structure.

[0028] Figure 3 This is a schematic diagram showing the loading position of the variable-pitch rocker arm within the motion range of the control structure.

[0029] 1-Upper propeller hub, 2-Lower propeller hub, 3-Variable pitch rocker arm, 4-Upper and lower propeller hub connecting bolts, 5-Control mechanism. Detailed Implementation

[0030] This invention provides a strength design method for a split-type tiltable propeller hub, comprising:

[0031] Step 1: Based on the split-type tiltable propeller hub structure and load, conduct force transmission path analysis and identify dangerous components / locations, including static strength dangerous locations and fatigue dangerous locations;

[0032] Step 2: Based on the load of the split tiltable propeller hub and the critical parts, determine the characteristic loads of the critical parts, which generally include load extremes, static loads, and dynamic loads.

[0033] Step 3: Based on the upper and lower split tiltable propeller hub structure, use finite element simulation or engineering methods to determine the load / bending moment distribution relationship in the lift direction on the upper and lower propeller hubs and their connecting structures;

[0034] Step 4: Determine the load range of the variable pitch rocker arm structure based on the upper and lower split tiltable propeller hub structure and the variable collective pitch and variable speed control process.

[0035] Step 5: Based on the results of Steps 1 to 4, conduct finite element simulation of the split-type tiltable propeller hub structure and perform stress calculations; for bolts, lugs, etc., engineering methods can be used for stress calculation as appropriate.

[0036] Step Six: Based on the results of Step Two and Step Five, conduct static strength analysis and fatigue strength analysis of the split tiltable propeller hub structure to complete the strength design.

[0037] The following section uses the strength design of a certain type of aircraft with a split, tiltable propeller hub as an example, and further describes the invention in detail with reference to the accompanying drawings:

[0038] Step 1: The split-type tilting rotor hub structure of a certain type of aircraft consists of an upper rotor hub 1, a lower rotor hub 2, a pitch control arm 3, a control structure 5, and related connecting structures 4, etc. The upper and lower rotor hubs do not contain splines, conical rings, or similar structures. Figure 1 As shown. The lower rotor hub is fixed to the motor with bolts; the centrifugal force of the blades is transmitted to the upper and lower rotor hubs through bearings, where they are balanced; the blade torque is transmitted to the control mechanism through the blade root and pitch control arm, where it is balanced with the control load; the blade shear force and bending moment are transmitted to the rotor hub through the blade root bearing, forming the main shaft bending moment, shear force, and rotor hub torque. According to the force transmission path analysis, the upper and lower rotor hubs transmit the load and bending moment of the blades, while the pitch control arm and control mechanism transmit the control load. Except for the centrifugal force, all of the above loads exhibit time-varying characteristics and are typical fatigue loads. Therefore, the upper and lower rotor hubs, pitch control arm, control mechanism, and related connecting structures are all components / parts that are at risk of static strength and fatigue.

[0039] Step 2: Based on the loads and critical locations of the split tiltable propeller hubs, the characteristic loads of the upper and lower propeller hubs include blade centrifugal force, blade shear force, and bending moment; the characteristic loads of the variable pitch rocker arm and control structure are control loads; the characteristic loads of the connecting structure are related to the connected structure.

[0040] Step 3: The upper and lower propeller shells are fixed together with bolts, and the bolt preload is applied according to the design value. Based on the actual contact and connection methods, a combined modeling and force transmission analysis is performed on the upper and lower propeller shells, connecting bolts, and lift direction bearings. During modeling, the connecting bolts and the upper and lower propeller shells can be in bonded or frictional contact; frictional contact is used between the upper and lower propeller shells; bearings and other components can be appropriately simplified without affecting structural stiffness, and coupling constraints are used between the simplified bearings and the upper and lower propeller shells. Based on the analysis results, the lift direction load / bending moment transmitted by the upper and lower propeller shells is extracted separately. According to the analysis results, the upper propeller shell transmits 45% of the lift direction load / bending moment, and the lower propeller shell transmits 55% of the lift direction load / bending moment. Step 4: Motion simulation is performed based on the upper and lower split tilting hub structure and the variable collective pitch and variable speed control process. The motion range of the variable pitch rocker arm in the control structure is obtained as 5–15 mm, and the contact position at the boundary of the motion range is as follows: Figure 2 As shown;

[0041] Step 5: Based on Steps 1 and 2, determine all characteristic loads of each component, their application locations and methods, determine the constraint locations and methods, and perform detailed modeling and stress analysis of the separated components; based on Step 3, when applying loads / bending moments in the lift direction, apply corresponding proportional loads to the upper and lower rotor hubs respectively, such as... Figure 2 As shown; according to step four, loads are applied at both ends and the middle of the load range within the variable pitch rocker arm structure's load range, as follows: Figure 3 As shown at points A, B, and M, analyze the stress at different load positions of the variable pitch rocker arm structure; complete the stress calculation under different combinations of characteristics.

[0042] Step Six: Based on the results of Steps Two and Five, conduct static strength analysis and fatigue strength analysis on the split-type tilting rotor hub structure. The static strength analysis should meet the following requirements:

[0043]

[0044] Where, σ limit It is the structural constraint stress, K safe It is the safety factor; K link It is the joint coefficient of each connection part, σ 02 σb is the yield strength of the material, and σb is the ultimate tensile strength of the material.

[0045] During fatigue strength analysis, the static stress σ of different critical components / parts in state i is obtained. si and dynamic stress σ di The equivalent dynamic stress is calculated as follows:

[0046] σ eqi =σ di / (1-(σ si / σ 02) 2 )

[0047] Where, σ 02 It is the yield strength of the material.

[0048] Based on the material safety SN curve and load spectrum, fatigue damage in each state can be obtained:

[0049] lgN i =a0-b0×lg(σ) eqi -σ ∞ (3)

[0050]

[0051] Where a0 and b0 are material parameters, σ ∞ It is the material's safe fatigue limit when the number of cycles is infinite, n i N is the frequency of the i-th state per hour. i It is the equivalent dynamic stress σ eqi Number of destructions under the action, D i It represents the damage in the i-th state.

[0052] Based on Miner's linear cumulative damage theory, the safe fatigue life of each critical component / part is obtained:

[0053]

[0054] Where m is the load level in the load spectrum, and L is the safe fatigue life.

[0055] Furthermore, in step one, the upper and lower split tiltable propeller hub structure can generally be made of aluminum alloy, structural steel, and titanium alloy, etc.

[0056] Furthermore, in step three, when establishing the contact relationship between various parts, the friction coefficient is determined based on the material of the contact parts and the fit relationship, and can generally be taken as a coefficient between 0.02 and 0.2.

[0057] Furthermore, in step six, low-cycle fatigue damage can be further considered based on the structure and load spectrum.

[0058] Furthermore, in step six, K safe A value of 1.5 is generally acceptable for K. link A value of 1.15 is generally acceptable.

Claims

1. A strength design method for a split-type tiltable propeller hub, characterized in that, include: Step 1: Based on the split-type tiltable propeller hub structure and load, conduct force transmission path analysis and identify critical areas; Step 2: Based on the load of the split tiltable propeller hub and the critical parts, determine the set of characteristic loads for all critical parts; Step 3: Based on the upper and lower split tiltable propeller hub structure, use finite element simulation or engineering methods to determine the load / bending moment distribution relationship in the lift direction on the upper and lower propeller hubs and their connecting structures; Step 4: Determine the load range of the variable pitch rocker arm structure based on the upper and lower split tiltable propeller hub structure and the variable collective pitch and variable speed control process. Step 5: Based on the results of Steps 1 to 4, conduct finite element simulation of the split-type tiltable propeller hub structure and perform stress calculation; Step Six: Based on the results of Step Two and Step Five, conduct static strength analysis and fatigue strength analysis of the upper and lower split tiltable propeller hub structure, and complete the strength design; The hazardous areas include static strength hazardous areas and fatigue hazardous areas. Based on the upper and lower split tilting rotor hub structure and loads, a force transmission path analysis is conducted to determine the hazardous areas, including: Based on the analysis of the force transmission path, it can be determined that the load and bending moment transmitted by the upper and lower rotor hubs to the rotor blades, and the control load transmitted by the pitch rocker arm and control structure all exhibit characteristics that change with time, which are fatigue loads. Therefore, it is determined that the upper and lower rotor hubs, pitch rocker arm, control structure and related connecting structures are all static strength and fatigue risk areas. Based on the loads of the split-type tilting propeller hub and the critical locations, determine the characteristic load set for all critical locations, including: Based on the load and critical parts of the split tiltable propeller hub, the characteristic loads of the upper and lower propeller hubs are determined to include blade centrifugal force, blade shear force and bending moment. The characteristic loads of the variable pitch rocker arm and the control structure are used as control loads. The loads associated with the connected structure are identified as characteristic loads of the connected structure.

2. The method according to claim 1, characterized in that, Based on the split-type tilting rotor hub structure, using finite element simulation or engineering methods, determine the load / bending moment distribution relationship in the lift direction on the upper and lower rotor hubs and their connecting structures, including: Apply bolt preload according to the design value and fix the upper and lower propeller hubs together with bolts; Based on the actual contact and connection methods, the upper and lower rotor hubs, connecting bolts, and lift direction bearings are combined and modeled for force transmission analysis. During modeling, the model structure is simplified without affecting the structural stiffness. The simplified model is analyzed to obtain the load / bending moment distribution relationship in the direction of rotor lift, i.e., the distribution ratio of lift between the upper and lower rotor hubs.

3. The method according to claim 2, characterized in that, The load range of the root variable pitch rocker arm structure is 5-15mm.

4. The method according to claim 3, characterized in that, Based on the results of steps one through four, finite element simulation of the split-type tilting hub structure is conducted, and stress calculations are performed, including: Determine all characteristic loads, their locations and modes of action, and constrain the components of the split tiltable propeller hub. Perform detailed modeling and stress analysis of each component as a separate body. When a load / bending moment is applied in the lift direction, a load of the corresponding proportion is applied to the upper and lower rotor hubs respectively; Loading was performed at both ends and the middle point of the load range of the variable pitch rocker arm structure, and the stress at different load positions of the variable pitch rocker arm structure was analyzed. Complete the stress calculation.

5. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the method described in any one of claims 1-4.

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