Attitude Guidance and Control for a Spinning, Asymmetrical Vehicle

Creagh, Michael (2010). Attitude Guidance and Control for a Spinning, Asymmetrical Vehicle PhD Thesis, School of Mechanical and Mining Engineering, The University of Queensland.

       
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Author Creagh, Michael
Thesis Title Attitude Guidance and Control for a Spinning, Asymmetrical Vehicle
School, Centre or Institute School of Mechanical and Mining Engineering
Institution The University of Queensland
Publication date 2010-08
Thesis type PhD Thesis
Supervisor Prof. David Mee
Prof. Michael Smart
Total pages 200
Total colour pages 27
Total black and white pages 173
Subjects 09 Engineering
Abstract/Summary Some hypersonic vehicles, such as those used in the HyShot supersonic combustion experiments conducted over the past decade, leave and re-enter the atmosphere while spinning. There is interest in whether it is possible to control the trajectory of such supersonic and hypersonic asymmetric spinning vehicles using control surfaces. The main aim of research presented in this thesis is to investigate whether it is possible to develop a guidance and control scheme for a spinning, aerodynamically asymmetrical vehicle. The HyShot Stability Demonstrator (HSD) was chosen to be the basis for modelling and simulation of such a scheme. The HSD is a 4.24 kg supersonic vehicle that uses four aerodynamic control surfaces arranged in a square configuration for manoeuvring. It was designed to represent the dynamics of a typical HyShot mission that has two scramjet engines arranged back-to-back on the fore body. The HSD is unique in that it has equal moments of inertia in pitch and yaw, which results in rotational dynamic equations that are equivalent to most missiles. However, the aerodynamic coefficients are not the same in pitch and yaw and this results in a unique control problem. Due to the combined asymmetry and aerodynamic control properties of the HSD, there are currently no existing guidance / control schemes in the open literature. The HSD is intended for future launch on a 5-inch Zuni sounding rocket. As a result, an important consideration for the guidance and control systems being developed is that they could be implemented in real-time in a flight computer. Attitude manoeuvres of an aerodynamically asymmetrical spinning vehicle are complicated primarily by the fact that the dynamics cannot be linearised in a mathematically well-posed fashion. The non-linear roll angle transformation results in plant dynamics that are insufficient for a linear attitude controller. One solution to the problem of asymmetrical spinning vehicle attitude control is presented in this thesis. A non-linear guidance law acts as an outer loop to issue commands to an autopilot system. The Angular Velocity Guidance law accepts sensor inputs and desired attitude information and calculates pitch and yaw-rate commands for autopilot input, based on error in attitude and additional compensation terms derived from Euler’s rotational equations. Aerodynamic properties of the HSD are calculated based on 2D shock-expansion theory with computational fluid dynamics corrections. The aerodynamic model is limited to Mach numbers above 1.8. The HSD has static stability derivatives Cm-alpha and Cn-beta of -2.37 and 5.37 at Mach 3.5 flow conditions. This results in different aerodynamic natural frequencies in each plane of the HSD. The non-linear and perturbation equations of motion are derived and discussed for two dynamic reference frames. The dynamics derived for the non-rotating body frame and the rotating body frame differ greatly and it is shown that for the HSD, the rotating body frame must be used to retain information in each plane of the HSD. Two body rate autopilot schemes were investigated for the attitude manoeuvres. The first scheme utilises two self-adaptive single-input, single-output (SISO) proportional plus integral controllers, derived using the pole placement technique. These controllers neglect cross-coupling due to spin-rate and are appropriate for use in the flight experiment as they are easily gain-scheduled for a range of Mach numbers and unknown spin-rate. The second scheme investigated is a multi-input, multi-output H-infinity controller that is shown to outperform the SISO controllers as long as the vehicle has a known, constant spin-rate. This controller was discounted for use in a flight experiment as it is more computationally intensive, is not easily tuned for spin-rate and has an H-infinity norm greater than 1 (hence does not meet the robustness criteria). A six degree-of-freedom numerical simulation was programmed in Computer Aided Design of Aerospace Concepts as a means of proving the guidance and control system. The simulation can be split into various modules such as kinematics, inertial navigation system, actuators, etc. The input/output characteristics of each module are discussed. It was found that due to the high aerodynamic natural frequencies of the small HSD payload, a simulation step time of 0.5 ms with the use of a predictor-corrector method of state-variable integration is necessary for a solution independent of integration time step. The simulations show that with the Angular Velocity Guidance developed in this thesis, the HSD would be capable of performing attitude manoeuvres at spin-rates of up to 3.5 Hz. The magnitude of manoeuvre possible is dependent on spin-rate. A 1 degree attitude change is possible in 0.7 s at a 3.5 Hz spin-rate, whereas at a spin-rate of 2.0 Hz the attitude change may be greater than 4.2 degrees in 0.5s. The device limitations that prevent manoeuvres at higher spin-rates for the HSD are the autopilot and actuator bandwidths and the inertial measurement unit. An overview of the hardware associated with a proposed future flight experiment is provided. Information on actuators, sensors, airframe and flight computer hardware and software allows future work to be carried out on the project.
Keyword Guidance
control
flight mechanics
spinning
missile
autopilot
attitude
angular velocity
Additional Notes Colour page numbers: 34, 41, 42, 53, 69, 70, 74-76, 86-90, 112, 113, 118, 119, 121, 163, 164, 166, 168, 171-174.

 
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Created: Mon, 22 Nov 2010, 17:40:29 EST by Mr Michael Creagh on behalf of Library - Information Access Service