Air-Breathing Hypersonic Cruise: Prospects for Mach 4–7 Waverider Aircraft

There is currently a renewal of world-wide interest in hypersonic flight. Vehicle concepts being considered range from cruise missiles to SSTO and TSTO vehicles. The new characteristics of these vehicles are that they will be powered by air-breathing engines and have long residence times in the air-breathing corridor. In the Mach 4–7 regime, waverider aircraft are being considered as candidates for both long-range and short-range cruise missions, as hypersonic missiles, and as high-L/D highly maneuverable vehicles. This paper will discuss the potential for near-term and far-term application of air-breathing engines to the above-mentioned waverider vehicle concepts and missions. In particular, the cruise mission is discussed in detail and attempts are made to compare and contrast it with the accelerator mission. Past criticisms levied against waveriders alleging low volumetric efficiency, lack of engine/airframe integration studies, poor off-design performance, poor take-off and landing capability, have been shown by ongoing research to be unfounded. A discussion is presented of some of the technical challenges and ongoing research aimed at realizing such vehicles: from turboramjet and scramjet technology development, propulsion-airframe integration effects on vehicle performance, aeroservothermoelastic systems analysis, hypersonic stability and control with aeroservothermoelastic and propulsion effects, etc. A unique and very strong aspect of hypersonic vehicle design is the integration and interaction of the propulsion system, aerodynamics, aerodynamic heating, stability and control, and materials and structures. This first-order multidisciplinary situation demands the ability to integrate highly coupled and interacting elements in a fundamental and optimal fashion to achieve the desired performance. Some crucial technology needs are found in propulsion-airframe integration and its role in configuration definition, hypersonic boundary-layer transition and its impact on vehicle gross-weight and mission success, scramjet combustor mixing length and its impact on engine weight and, CFD (turbulence modeling, transition modeling, etc) as a principal tool for the design of hypersonic vehicles. Key technology implications in thermal management, structures, materials, and flight control systems will also be briefly discussed. It is concluded that most of the technology requirements in the Mach 4–7 regime are relatively conventional, making cited applications near-term, yet offering very significant advancements in aircraft technology.