On Stability and Control of Hypersonic Vehicles

This report has been produced in order to address aerodynamic characteristics and stability and control issues relating to hypersonic vehicles that are deemed to be significantly different from those of the conventional (subsonic or supersonic) air vehicles. In particular we have addressed issues that are relevant to stability and control of hypersonic vehicles. This report should add to the existing knowledge of missile guidance and control engineers and make, other researchers and engineers involved in hypersonic experimentation, aware that these vehicles may not be dynamically stable and require active control augmentation in order to achieve and maintain desirable flight characteristics. RELEASE LIMITATION Approved for public release Published by Weapons Systems Division DSTO Defence Science and Technology Organisation PO Box 1500 Edinburgh South Australia 5111 Australia Telephone: (08) 8259 5555 Fax: (08) 8259 6567 © Commonwealth of Australia 2009 AR-014-663 November 2009 APPROVED FOR PUBLIC RELEASE On Stability and Control of Hypersonic Vehicles Executive Summary Hypersonic flight presents major challenges to airframe and control system designers. High velocity can cause a hypersonic vehicle to be highly sensitive to changes in flight conditions that can result in instability or weakly damped transient oscillations of the airframe. The design problem is further compounded by the fact that hypersonic aerodynamic parameters, as predicted from ground tests or theoretical computational methods, do not reflect the actual flight parameters; there are significant uncertainties in the parameter values required for airframe and control system design. Conventional techniques do not always lead to a design that is stable and at the same time robust to parameter uncertainties. From the reported work in hypersonic vehicle stability and control, we are able to highlight aerodynamic characteristics that may have a strong bearing on our approach to the analysis, synthesis and performance evaluation of hypersonic weapons systems. The key findings and recommendations are as follows:  Active control will be required to maintain stability in case of changes to the CG position and maintain adequate damping during flight.  Uncertainties in aerodynamic parameters require a control system design based on robust techniques. Adaptive control techniques may be required to maintain desirable vehicle flight performance.  At hypersonic speeds the drag and lift forces become non-linear functions of the angle of attack. Compared to subsonic and supersonic speeds, the maximum value of the lift/drag ratio for hypersonic vehicles is significantly lower.  Heating has a negative affect on vehicle structural integrity and, depending on the airframe, may cause structural vibration which needs to be catered for by an appropriate control system design.