Method for determining weight fraction change of hypersonic flight vehicle in climbing stage

Abstract

The invention belongs to the technical field of aircraft climbing stage weight fraction change determination, and particularly relates to a hypersonic aircraft climbing stage weight fraction change determination method, which comprises the steps of 1, acquiring the height hn and the speed Vn of an aircraft at a tn moment; step 2, acquiring the height hn + 1 and the speed Vn + 1 of the aircraft at the tn + 1 moment; step 3, calculating the change dV of the speed of the aircraft in the [tn, tn + 1] time period, the ratio of the height to the speed change and the ratio of the speed change to the speed; step 4, acquiring the average thrust and the average resistance of the aircraft in the [tn, tn + 1] time period; step 5, calculating the weight fraction change of the aircraft in the [tn, tn + 1] time period, g is gravitational acceleration; isp is the specific impulse of the engine.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of determining weight fraction change of a hypersonic aircraft in a climb phase, and particularly relates to a method for determining weight fraction change of a hypersonic aircraft in a climb phase. BACKGROUND

[0002] Hypersonic aircrafts have great application potential in space exploration and civil high-speed transportation due to their high-speed flight capability. For example, in the field of space exploration, it helps to reduce the cost of transportation between earth and space, and expand the boundary of human exploration of the universe.

[0003] The climb phase in the flight process of a hypersonic aircraft is a crucial link. Accurate grasp of the weight fraction change of the aircraft in the climb phase plays a key role in optimizing aircraft design, ensuring flight safety and improving flight efficiency. However, current calculation of the weight fraction of a hypersonic aircraft in the climb phase faces many severe challenges.

[0004] Currently, the calculation method of aircraft weight is mostly based on theory and empirical formula under low-speed flight conditions, which has significant limitations when applied to hypersonic aircrafts.

[0005] The hypersonic flight environment is extremely complex and fundamentally different from low-speed flight. In the hypersonic state, the physical properties of air change significantly, and factors such as viscosity and compressibility have a huge impact on the aerodynamic force of the aircraft. For example, in hypersonic flight, the frictional resistance caused by air viscosity increases sharply, and due to the change in boundary layer characteristics, the existing commonly used frictional resistance calculation model is no longer applicable. At the same time, the compressibility of air makes the generation and propagation of shock waves an important factor affecting the aerodynamic force of the aircraft, and the calculation of shock wave resistance involves complex shock wave dynamics theory, which is difficult for current methods to accurately consider. The performance of the engine of a hypersonic aircraft is also restricted by various factors. Small changes in factors such as air intake, flight speed, and altitude will have a significant impact on the thrust of the engine. For example, at different flight altitudes and speeds, the air intake efficiency of the engine will change, causing the combustion process to be unstable, and thus affecting the thrust output. In addition, hypersonic flight is accompanied by extreme conditions such as high temperature and high pressure, which not only affect the structural weight of the aircraft, such as causing thermal expansion and mechanical property degradation of structural materials, but also change the physical and chemical properties of fuel, affecting the fuel consumption rate, which further increases the complexity of calculating the weight fraction change of a hypersonic aircraft in a climb phase.

[0006] The change of the weight fraction of the hypersonic vehicle in the climbing stage is calculated by using the current theoretical and empirical formula under the low-speed flight condition, and it is difficult to comprehensively and accurately consider the complex factors of the hypersonic flight environment. They are either too simplified model, ignoring the influence of some key factors, such as shock wave resistance, the influence of high temperature on the performance of materials, or the calculation model used is no longer applicable under the hypersonic condition, resulting in a large deviation between the calculation results and the actual situation.

[0007] At present, the insufficient calculation accuracy of the change of the weight fraction of the hypersonic vehicle in the climbing stage has brought a series of serious problems to the design and flight of the hypersonic vehicle. If the change of the weight fraction is not accurately calculated in the design stage of the vehicle, the structure design may be unreasonable, so that the strength and stiffness of the vehicle cannot meet the actual flight requirements, thereby affecting the flight safety. In terms of flight mission planning, inaccurate calculation of the change of the weight fraction will lead to incorrect estimation of fuel reserves, affecting the range and task execution ability of the vehicle, and even may cause the task to fail. Therefore, designing a method capable of adapting to the hypersonic flight environment and accurately calculating the change of the weight fraction of the vehicle in the climbing stage has become an important problem to be solved in the field of aerospace. In view of this, the present application is proposed. SUMMARY

[0008] The purpose of the present application is to provide a method for determining the change of the weight fraction of a hypersonic vehicle in the climbing stage, to overcome the problems of insufficient accuracy and inability to comprehensively consider complex factors in the current calculation method in the field of hypersonic speed, and to accurately calculate the change of the weight fraction of the hypersonic vehicle in the climbing stage, to provide key data support for the design, performance evaluation, flight control and mission planning of the vehicle, and to promote the technical development of the hypersonic vehicle.

[0009] The technical solution of the present application is:

[0010] A method for determining the change of the weight fraction of a hypersonic vehicle in the climbing stage, comprising:

[0011] Step one, obtaining the height h n and speed V n of the vehicle at time t n ;

[0012] Step two, obtaining the height h n+1 and speed V n+1 of the vehicle at time t n+1 ;

[0013] Step three, calculating the change dV of the speed of the vehicle in the time period [t n , t n+1 ], the ratio of the change of the height to the speed , and the ratio of the change of the speed to the speed

[0014] Step four, obtaining the average thrust of the aircraft in the time period [t n ,t n+1 ] average drag

[0015] Step five, calculating the weight fraction change of the aircraft in the time period [t n ,t n+1 ]

[0016]

[0017] wherein,

[0018] g is the acceleration of gravity;

[0019] Isp is the specific impulse of the engine.

[0020] According to at least one embodiment of the present application, in the above-mentioned method for determining the weight fraction change of a hypersonic aircraft in a climbing phase, in step three, the change dV of the speed of the aircraft in the time period [t n ,t n+1 ] is calculated, and the ratio of the change in height to the change in speed the ratio of the change in speed to the speed Specifically,

[0021] dV = V n+1 -V n ;

[0022]

[0023]

[0024] According to at least one embodiment of the present application, in the above-mentioned method for determining the weight fraction change of a hypersonic aircraft in a climbing phase, in step four, the average thrust of the aircraft in the time period [t n ,t n+1 ] is obtained Specifically,

[0025] wherein, T n is the thrust of the aircraft at time t n , and T n+1 is the thrust of the aircraft at time t n+1 .

[0026] According to at least one embodiment of the present application, in the above-mentioned method for determining the weight fraction change of a hypersonic aircraft in a climbing phase, in step four, the average thrust of the aircraft in the time period [t n ,t n+1average resistance in the time period Specifically,

[0027] D(t) is the resistance of the aircraft at time t n D(t) is the resistance of the aircraft at time t n D(t) is the resistance of the aircraft at time t n+1 D(t) is the resistance of the aircraft at time t n+1 D(t) is the resistance of the aircraft at time t

[0028] According to at least one embodiment of the present application, in the above-mentioned hypersonic aircraft climb phase weight fraction change determination method, in step five, the gravitational acceleration g is 9.81 m / s^2. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a schematic diagram of the force on the aircraft in the climb phase provided by the embodiments of the present application;

[0030] Figure 2 is a schematic diagram of the hypersonic aircraft climb phase weight fraction change determination method provided by the embodiments of the present application.

[0031] In order to better illustrate the embodiments, some contents of the drawings may be omitted, enlarged or reduced, and are only used for exemplary description, and cannot be understood as a limitation on the present application. DETAILED DESCRIPTION

[0032] In order to make the technical solutions of the present application and its advantages clearer, the technical solutions of the present application will be further clearly and completely described below in conjunction with the drawings. It should be understood that the specific embodiments described herein are only part of the embodiments of the present application, and are only used to explain the present application, but not to limit the present application. It should be noted that, in order to facilitate description, only parts related to the present application are shown in the drawings, and other related parts can be referred to the usual design.

[0033] In addition, unless otherwise defined, the technical terms or scientific terms used in the description of the present application should be the usual meaning understood by the general technical personnel in the field to which the present application belongs. In the description of the present application, "including" indicates that the concept appearing before the word covers the concepts listed after the word and its equivalents, and does not exclude other related concepts.

[0034] For the calculation of the weight fraction change of the hypersonic aircraft in the climb phase, two important assumptions can be made.

[0035] Firstly, the earth can be assumed to be a plane. In the local flight range of the hypersonic aircraft in the climb phase, the influence of the flight trajectory relative to the curvature of the earth is small, and the earth can be regarded as a plane to simplify the calculation model, which can effectively reflect the main motion characteristics of the aircraft in this phase and provide a reasonable basis for subsequent calculation.

[0036] Secondly, it is assumed that the thrust is aligned with the velocity vector. In the ideal climb process of hypersonic vehicles, in order to achieve efficient acceleration and height increase, the thrust is usually applied along the direction of the speed, which is consistent with the basic mechanics of the hypersonic vehicle climbing stage, and helps to simplify the analysis and calculation process of forces.

[0037] The schematic diagram of forces acting on the aircraft climbing stage is shown in Figure 1 According to Newton's second law, along the speed direction in the climbing stage of hypersonic vehicles, the force balance equation can be established, that is, the basic dynamics equation of the climbing stage of hypersonic vehicles:

[0038]

[0039] T is the thrust, which is the power source for the forward and climbing of the aircraft, generated by the engine. The size of the thrust is affected by many factors, including the type of engine, working state, flight speed, height, and air intake condition, etc. Different types of engines, such as ramjet, scramjet, etc., have different thrust characteristics in hypersonic flight.

[0040] D is the drag, which is complex in hypersonic flight, mainly including frictional drag, pressure difference drag and shock wave drag, etc. Frictional drag is caused by the friction between air and the surface of the aircraft, and factors such as the roughness of the aircraft surface and the boundary layer state will affect it. The pressure difference drag is closely related to the shape design of the aircraft, and reasonable shape design can reduce the pressure difference drag. Shock wave drag is a unique form of drag in hypersonic flight, when the speed of the aircraft exceeds the speed of sound, shock waves will be generated, and the formation and propagation of shock waves will consume energy, thus generating shock wave drag.

[0041] W is the weight of the aircraft, which will change with the consumption of fuel, the use of airborne equipment and the possible jettisoning during flight.

[0042] γ is the flight path angle, reflecting the angle between the flight direction of the aircraft and the horizontal plane, which will change with the adjustment of the flight attitude during the climbing process of the aircraft.

[0043] m is the mass of the aircraft.

[0044] dV / dt represents the derivative of velocity with respect to time, that is, acceleration, which reflects the speed change of the aircraft during the climbing stage.

[0045] According to the principle of flight kinematics, the following relationship exists:

[0046] Vsinγ=dh / dt…………(2)

[0047] The relationship between the flight path angle γ and the rate of change of the height dh / dt and the velocity V of the aircraft is characterized.

[0048] Substituting equation (2) into equation (1), we obtain:

[0049]

[0050] In hypersonic flight, the height and velocity of the aircraft change rapidly and are related to each other. Through this relationship, the motion state of the aircraft in space can be more comprehensively and accurately described, which can provide an important basis for further analyzing the balance of forces.

[0051] In order to facilitate subsequent calculation and analysis, equation (3) is transformed by multiplying both sides by g / W. Since m = W / g, m*(g / W) = 1, the equation becomes:

[0052] (T-D)*(g / W)-(g / V)*(dh / dt)=dV / dt…………(4)

[0053] Further rearrangement moves the terms containing (g / V)*(dh / dt) and dV / dt to one side of the equation, resulting in:

[0054] (T-D)*(g / W)=(g / V)*(dh / dt)+dV / dt…………(5)

[0055] Again, transform (T-D)*(g / W) to T(1-D / T)*(g / W), then the equation becomes:

[0056] T(1-D / T)*(g / W)*dt=(g / V)*(dh)+dV…………(6)

[0057] During hypersonic flight, the value of D / T changes dynamically with the change of flight state. This transformation can more clearly reveal the influence of the mutual relationship between thrust, drag and other related factors on the motion of the aircraft.

[0058] Thrust T and the rate of change of weight And specific impulse Isp has the following relationship:

[0059]

[0060] Specific impulse Isp is an important indicator of engine performance, reflecting the impulse generated by the engine when consuming a unit mass of propellant. Different types of engines have different specific impulse values. Substituting equation (7) into equation (6) can establish a close relationship between thrust and the change in the weight of the aircraft, which is crucial for accurately calculating the change in the weight fraction of the aircraft.

[0061]

[0062] The formula (8) can be modified as follows:

[0063]

[0064] Since dh=(dh / dV)*dV, the formula (9) can be further modified as:

[0065]

[0066] The formula (10) comprehensively considers the thrust, resistance, speed, height, specific impulse and other key factors, and can accurately calculate the weight fraction change of the aircraft during the climbing process based on the formula.

[0067] In the actual calculation process, the flight trajectory of the aircraft can be divided into multiple small time periods. In each time period, it is assumed that the changes of various parameters are continuous and approximately linear. By measuring or estimating the parameters in each time period and substituting them into the formula (10), the weight fraction change of the aircraft during the entire climbing stage can be gradually obtained. For example, in a certain time period [t n ,t n+1 ], the initial speed V n , the final speed V n+1 , the height change Δh, the average thrust , the average resistance , and the engine specific impulse Isp of the aircraft are known. The weight fraction change dw / w in this time period can be calculated using the formula (10), and then the weight fraction change in the entire climbing stage can be accumulated through iterative calculation.

[0068] The formula (10) can be modified as:

[0069]

[0070] Further, we have:

[0071]

[0072] ΔR=0.5*(V n+1 +V n )(t n+1 -t n )…………(13)

[0073] For the cruising stage, we have:

[0074]

[0075] ΔR=VΔt…………(15)

[0076] Before the hypersonic vehicle flies, the initial parameters of the vehicle can be obtained, including initial weight W0, initial speed V0, initial height h0, initial thrust T0 of the engine, specific impulse Isp, and initial drag D0 estimated according to the vehicle shape and flight conditions. These parameters can be obtained through the design documents of the vehicle, the previous test data, and the preparation work before flight. During the climbing process of the hypersonic vehicle, high-precision sensors can be used to monitor the changes of parameters such as thrust T, drag D, speed V, and height h in real time. For example, the thrust T is measured in real time by the thrust sensor installed on the engine, the drag D is calculated by measuring the pressure distribution on the surface of the vehicle using aerodynamic sensors, and the speed V and height h are accurately measured by laser speed meters and radar altimeters respectively. The sensors transmit the collected data to the onboard computer in real time.

[0077] On this basis, the real-time data collected can be substituted into the formula for calculation. In the calculation process, the method of numerical integration is used to solve . The flight process is divided into multiple small time periods, and in each time period, it is approximately considered that the changes of various parameters are linear. For example, in a time period [t n ,t n+1 ], the speed changes from V n to V n+1 , the height changes from h n to h n+1 , the thrust changes from T n to T n+1 , and the drag changes from D n to D n+1 . According to these changes, the weight fraction change in this time period is calculated. Then through iterative calculation, the weight fraction change of the vehicle in the entire climbing stage is gradually obtained.

[0078] Based on the above, the present application provides a method for determining the weight fraction change of a hypersonic vehicle in the climbing stage, as shown in Figure 2 .

[0079] Step one, obtain the height h n and speed V n of the vehicle at time t n .

[0080] Step two, obtain the height h n+1 and speed V n+1 of the vehicle at time t n+1 .

[0081] Step three, calculate the weight fraction change of the vehicle in the time period [t n ,t n+1The change in velocity dV over the time period, the ratio of the change in height to the change in velocity The ratio of the change in velocity to the velocity

[0082] dV = V n+1 -V n .

[0083]

[0084]

[0085] Step four, obtain the average thrust of the aircraft over the time period [t n , t n+1 ] Average drag

[0086] Where T n is the thrust of the aircraft at time t n , and T n+1 is the thrust of the aircraft at time t n+1 .

[0087] Where D n is the drag of the aircraft at time t n , and D n+1 is the drag of the aircraft at time t n+1 .

[0088] Step five, calculate the change in the weight fraction of the aircraft over the time period [t n , t n+1 ]

[0089]

[0090] Where,

[0091] g is the acceleration due to gravity, which is typically taken to be 9.81 m / s^2;

[0092] Isp is the specific impulse of the engine.

[0093] In one specific example, a hypersonic aircraft, over a flight phase, has an initial velocity V n = 1000 m / s, a final velocity V n+1 = 1200, a height that varies from h n = 20000 m to h n+1 = 25000 m, an average thrust an average drag Engine specific impulse Isp = 300 s, gravitational acceleration g = 9.81 m / s2, the method for determining the weight fraction change of the hypersonic vehicle in the climbing phase disclosed in the above embodiment is implemented as follows:

[0094] Calculate dh / dV, since the parameter change is approximately linear in this time period, dh / dV = (h n+1 -h n ) / (V n+1 -V n ) = (25000-20000) / (1200-1000) = 25 m / (m / s).

[0095] According to dw / w = -(dV+g(dh / dV)*(dV / V)) / (Isp*g(1-D / T), calculate the weight fraction change:

[0096] dw / w = -((1200-1000)+(9.81)((25000-20000) / (1200-1000))*((1200-1000) / 1000)) / (300*9.81(1-10000 / 50000) = -0.02.

[0097] The calculated weight fraction change is -0.02, which means that the weight fraction of the vehicle decreases by 2% in this flight phase. By calculating multiple such time periods for the entire climbing phase of the vehicle and iteratively accumulating, the weight fraction change in the entire climbing phase can be obtained.

[0098] The calculated weight fraction change results are applied to the design, performance evaluation, flight control and mission planning of the aircraft. In the design stage of the aircraft, the structural design, fuel system design, etc. of the aircraft can be optimized according to the calculation results, and the overall performance of the aircraft is improved. For example, by analyzing the weight fraction change in different flight stages, the structural strength requirement of the aircraft at the key position is determined, the lighter and higher strength material is used, the structural weight is reduced, and the safety is ensured. In the fuel system design, the fuel consumption is predicted according to the weight fraction change, the fuel tank layout and fuel delivery system are optimized, and the fuel utilization efficiency is improved. In the flight control process, the pilot can adjust the flight parameters according to the real-time weight fraction change to ensure the stable flight of the aircraft. When the weight fraction change shows that the fuel consumption is too fast, it may mean that the flight resistance abnormally increases, and the pilot can adjust the flight attitude according to the calculation results to reduce the resistance and ensure the smooth and safe flight. In the mission planning, the fuel consumption and flight route are reasonably arranged according to the weight fraction change, and the success rate and efficiency of the task execution are improved. For example, in the execution of long-range reconnaissance task, the fuel consumption of each flight stage is accurately planned according to the calculated weight fraction change, the optimal flight route is selected, and the aircraft has enough fuel to return to the base after completing the reconnaissance task. At the same time, the range and endurance time of the aircraft can be predicted according to the weight fraction change, which provides more accurate basis for mission planning, makes the mission planning more scientific and reasonable, and improves the comprehensive combat and application ability of the aircraft.

[0099] The weight fraction change determination method for the climbing stage of the hypersonic aircraft disclosed in the above embodiment fully considers the interaction between various complex factors in hypersonic flight during calculation, compared with the current calculation method, can more accurately calculate the weight fraction change of the hypersonic aircraft in the climbing stage, effectively improves the calculation precision, and provides more reliable data support for the design and performance evaluation of the hypersonic aircraft.

[0100] Based on the weight fraction change determination method for the climbing stage of the hypersonic aircraft disclosed in the above embodiment, the accurate weight fraction calculation result can provide a key basis for the flight control and mission planning of the aircraft. The pilot can adjust the flight parameters such as thrust and flight attitude more accurately according to the real-time weight fraction change, and realize more efficient flight control. In the mission planning, by accurately estimating the weight change in the climbing stage, the fuel consumption, flight task radius and suitable flight route can be reasonably arranged, and the success rate and efficiency of the flight task are improved. For example, in the execution of the hypersonic reconnaissance task, the fuel can be more reasonably planned, so that the aircraft can safely return to the base after completing the reconnaissance task, and the task execution ability is effectively improved.

[0101] The method for determining the weight fraction change in the climbing phase of the hypersonic vehicle disclosed in the above embodiments is not only suitable for the hypersonic research vehicle, but also can be widely applied to other types of hypersonic vehicles, such as space-air vehicles. Meanwhile, the method can provide a reference for weight calculation in different flight phases, has strong universality and expansibility, can provide a high-precision calculation method for vehicle design, performance evaluation and flight control in the entire field of aviation and spaceflight, has important popularization value, and provides strong support for the research and development of the hypersonic vehicle.

[0102] So far, the technical solution of the application has been described in combination with the preferred embodiments shown in the drawings, and those skilled in the art should understand that the protection scope of the application is obviously not limited to these specific embodiments, and those skilled in the art can make equivalent changes or replacements to the related technical features without departing from the principles of the application, and the technical solutions after the changes or replacements will fall within the protection scope of the application.

Claims

1. A method for determining weight fraction change during a hypersonic vehicle's climb phase, characterized in that: include: Step 1: Get the aircraft at t n The height at the moment h n , speed V n ; Step 2: Get the aircraft at t n+1 The height at the moment h n+1 , speed V n+1 : Step 3: Calculate the aircraft's n ,t n+1 ]The change in speed dV during the time period, the ratio of the change in altitude to the change in speed Ratio of speed change to speed Step 4: Get the aircraft in [t n ,t n+1 ] Average thrust during the time period Average resistance Step 5: Calculate the aircraft's n ,t n+1 ] Weight fraction change during the time period in, g is the acceleration due to gravity; Isp is the engine specific impulse.

2. The method for determining weight fraction change during a hypersonic vehicle climb phase according to claim 1, wherein: In step 3, calculate the aircraft's n ,t n+1 ]The change in speed dV during the time period, the ratio of the change in altitude to the change in speed Ratio of speed change to speed Specifically: dV=V n+1 -V n ; 3. The method for determining weight fraction change during a hypersonic vehicle climb phase according to claim 2, wherein: In step 4, obtain the aircraft in [t n ,t n+1 ] Average thrust during the time period Specifically: Among them, T n For the aircraft at t n The thrust of the moment, T n+1 For the aircraft at t n+1 The thrust of the moment.

4. The method for determining weight fraction change during a hypersonic vehicle climb phase according to claim 3, wherein: In step 4, obtain the aircraft in [t n ,t n+1 Average resistance during the time period Specifically: Among them, D n For the aircraft at t n The resistance of the moment, D n+1 For the aircraft at t n+1 The resistance of the moment.

5. The method for determining weight fraction change during a hypersonic vehicle climb phase according to claim 4, wherein: In step 5, the acceleration due to gravity g is taken as 9.81m / s^2.

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