Курчаткина Г.П., Стручкова С.Б. Обучение чтению литературы на англ.языке по спец. САУ для студентов старших курсов (2014) (1257062), страница 4
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Find the following word combinations in the text and give their Russianequivalents:missile flight control system; overall homing loop; a simplified block diagram; theterminal phase of flight; the missile and target motion relative to inertial space; theangle between an inertial reference and the missile-to-target line-of-sight (LOS)vector; in the parlance of feedback control; the overall stability and performanceof the control system; the dynamics of each element in the loop; in concert with theother elements; feedback control loop within the overall homing loop; a deflectionangle; to turn the autopilot command into the physical motion of the controleffector.Task 3.
Read text A using a dictionary and translate it. Choose, underline andwrite out words and word combinations which are essential for your speciality.Remember them.Text A. Missile Flight Control SystemsThe missile flight control system is one element of the overall homing loop.Figure 10 is a simplified block diagram of the missile homing loop configured forthe terminal phase of flight when the missile is approaching intercept with thetarget. The missile and target motion relative to inertial space can be combinedmathematically to obtain the relative motion between the missile and the target.The terminal sensor measures the angle between an inertial reference and themissile-to-target line-of-sight (LOS) vector, which is called the LOS angle. Thestate estimator uses LOS angle measurements to estimate LOS angle rate andperhaps other quantities such as target acceleration.
The state estimates feed aguidance law that develops the flight control commands required to intercept thetarget. The flight control system forces the missile to track the guidancecommands, resulting in the achieved missile motion. The achieved missile motionalters the relative geometry, which then is sensed and used to determine the next23set of flight control commands, and so on. This loop continues to operate until themissile intercepts the target.In the parlance of feedback control, the homing loop is a feedback controlsystem that regulates the LOS angle rate to zero.
As such, the overall stability andperformance of this control system are determined by the dynamics of eachelement in the loop. Consequently, the flight control system cannot be designed ina vacuum. Instead, it must be designed in concert with the other elements to meetoverall homing-loop performance requirements in the presence of targetmaneuvers and other disturbances in the system, e.g., terminal sensor noise (notshown in Fig.10), which can negatively impact missile performance.Figure 10. A missile homing loop.Figure 11 shows the basic elements of the flight control system, which itselfis another feedback control loop within the overall homing loop depicted in Fig.10.An inertial measurement unit (IMU) measures the missile translational accelerationand angular velocity.
The outputs of the IMU are combined with the guidancecommands in the autopilot to compute the commanded control input, such as adesired tail-surface deflection or thrust-vector angle. The actuator turns theautopilot command into the physical motion of the control effector, which in turninfluences the airframe dynamics to track the guidance command.(2066)24Figure 11.
The basic elements of the flight control system shown in the grey box.Task 4. Match a verb in A with words in B. Make up sentences with the resultingword combinations using the information learnt from the text.ABto estimatethe airframe dynamicsto influenceoverall homing-loop performance requirementsto forceLOS angle rateto meetthe missile to track steering commandsto impactthe targetto interceptmissile performanceTask 5. Give definitions to:homing loop; LOS angle.Task 6.
Answer the questions.1. What is considered to be one element of the overall homing loop?2. What can the missile and target motion relative to inertial space be combinedmathematically for?3. What does the terminal sensor measure?4. What does a guidance law do?5. Are the overall stability and performance of the control system determined bythe dynamics of each element in the loop?6.
Does terminal sensor noise positively impact missile performance?7. Which elements of the flight control system are shown in Figure 11?8. Are the outputs of the Inertial Measurement Unit combined with the guidancecommands in an actuator ?9. What is an actuator used for?10. What do the airframe dynamics respond to?11.What is the basic objective of the flight control system?Task 7.
Speak about the missile flight control system as an element of the overallhoming loop using Figures 10 and 11.Task 8. Skim text B and speak about its main points.25Task 9. Work in groups of five, A, B, C, D and E. Study text B to know its contentin detail and make brief notes on the main points in each of the texts. Get ready toexchange the information with others in your group.Student A Read text 1Student B Read text 2Student C Read text 3Student D Read text 4Student E Read text 5Text B.
Flight Control System Elements1 Guidanсe InputsThe inputs to the flight control system are outputs from the guidance lawthat need to be followed to ultimately effect a target intercept. The specific formof the flight control system inputs (acceleration commands, attitude commands,etc.) depends on the specific application. In general, the flight control system mustbe designed based on the expected characteristics of the commands, which aredetermined by the other elements of the homing loop and overall systemrequirements.
Characteristics of concern can be static, dynamic, or both.(461)2 Airframe DynamicsThe dynamics of the airframe are governed by fundamental equations ofmotion, with their specific characteristics determined by the missile aerodynamicresponse, propulsion, and mass properties.Consider the diagram in Fig.12, which shows the missile flying in spaceconstrained to the vertical plane. In the pitch plane, the missile dynamics andkinematics can be described by four variables. Az is the component of thetranslational acceleration normal to the missile longitudinal axis. The angle ofattack (AOA), α, is a measure of how the missile is oriented relative to the airflowand is the angle between the missile velocity vector and the missile centerline.
Theflight-path angle γ is a measure of the direction of travel relative to inertial space,i.e. the angle between the missile velocity vector and an inertial reference. Thepitch angle Ө defines the missile orientation relative to inertial space and is the26angle between the inertial reference and the missile longitudinal axis.Figure 12. The missile dynamics and kinematics described by four variablesAcceleration in the direction normal to the missile Az derives from two sources.The non-zero AOA generates aerodynamic lift. Normal acceleration also can bedeveloped by a control input δ such as tail-fin deflection or thrust-deflection angle.In general, the missile acceleration also has a component along the centerline dueto thrust and drag.
For the simple model being developed here, we assume that thisacceleration is negligible.(1274)3 ActuatorThe missile actuator converts the desired control command developed bythe autopilot into physical motion, such as rotation of a tail fin, that will effect thedesired missile motion. Actuators for endoatmospheric missiles typically need tobe high-bandwidth devices (significantly higher than the desired bandwidth of theflight control loop itself) that can overcome significant loads.
Most actuators areelectromechanical, with hydraulic actuators being an option in certain applications.(420)4 Inertial Measurement UnitThe IMU measures the missile dynamics for feedback to the autopilot. Inmost flight control applications, the IMU is composed of accelerometers and27gyroscopes to measure three components of the missile translational accelerationand three components of missile angular velocity.Like the actuator, the IMU needs to be a high-bandwidth device relative to thedesired bandwidth of the flight control loop. In some applications, other quantitiesneed to be measured, such as the pitch angle for an attitude control system. In thiscase, other sensors can be used (e.g.
an inertially stabilized platform), or IMUoutputs can feed strapdown navigation equations that are implemented in a digitalcomputer to determine the missile attitude, which then is sent to the autopilot as afeedback measurement.The flight control system must be designed such that the missile dynamicsdo not exceed the dynamic range of the IMU. If the IMU saturates, the missile willlose its inertial reference, and the flight control feedback is corrupted. The formermay be crucial, depending on the specific missile application and the phase offlight.
The latter may be more problematic if the dynamic range is exceeded for toolong, particularly if the missile is statically unstable.(1061)5 AutopilotThe autopilot is a set of equations that takes as inputs the guidancecommands and the feedback measurements from the IMU and computes thecontrol command as the output.
As mentioned previously , the autopilot must bedesigned so that the control command does not cause oversaturation of the actuatoror the IMU. Because the autopilot usually is a set of differential equations,computingits output involves integrating signals with respect to time. Mostmodern autopilots are implemented in discrete time on digital computers, althoughanalog autopilots are still used.(482)Task 10. Describe the missile dynamics and kinematics by means of four variablesin Fig.
12.Task 11. Make up a plan of the text in the form of questions. Discuss the questionswith others in your group.28Task 12. a) Read the text again and ask additional questions embracing itscontents. b) Combine your answers into a short summary of the text.Task 13. Skim text C and say what it deals with.Task 14. Read the text using a dictionary to know its content in detail andcomplete the tasks that follow.Text C. Types of Flight Control SystemsThe specific type of flight control system depends on several factors,including the overall system mission and requirements, packaging constraints, andcost . In many applications, the type of flight control system changes with differentphases of flight.Acceleration Control SystemOne type of flight control system common in many endoatmosphericapplications is designed to track commanded acceleration perpendicular to themissile longitudinal axis.
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