Design studies for a Mach 8 dual mode ramjet flight test vehicle

Abstract

With view to potential future space launchers or other hypersonic vehicles the demonstration of high speed airbreathing propulsion, and especially of the dual mode ramjet combining subsonic and supersonic combustion, is still of great interest. After the national hypersonic research and technology programs in Germany and France (German Hypersonic Technology Program and French Research and Technology Program for Advanced Hypersonic Propulsion - PREPHA (1), the mastery of high-speed airbreathing propulsion technologies is not sufficient to allow the development of an operational vehicle. Therefore, ONERA and DLR decided to join in a common research program that investigates an airbreathing propulsion system operating from Mach 4 to Mach 8. The general goal of this project, named JAPHAR (Joint Airbreathing Propulsion for Hypersonic Application Research), is to demonstrate the feasibility of the dual mode ramjet and to develop a methodology for on-ground and in-flight performance demonstration. Concurrently with engine studies, the project includes conceptional design studies to define an experimental vehicle for dual mode ramjet testing between Mach 4 and Mach 8 and to find a methodology to evaluate its in-flight performances. Furthermore, this vehicle is the leading configuration for the different component studies within the project and it is used for the global synthesis of the obtained results. In order to be able to obtain results at different Mach numbers between Mach 4 and 8, even if the scramjet thrust should be lower than expected, the vehicle is boosted up to Ma*=8 and then performs a few combustion periods on a decelerating trajectory. In order to be representative for a full scale scramjet operation, the engine height was chosen equal to 100mm. This results in a global vehicle length of 11.5m and a weight of about 2 tons. The vehicle is not reusable. During the first design cycle ONERA provided a first definition of the vehicle engine and the associated propulsion dataset. Using this engine ONERA studied a preliminary definition of a vehicle based on the wing-body concept (Fig. 1). Based on the given propulsion geometry DLR additionally defined a waverider configuration (Fig. 2). Using the experiences of former waverider studies (2), (3) which showed that waveriders are excellent designs for TSTO missions the aim is to reduce the required thrust for a horizontal flight at M*=8. In order to choose the best solution for the project continuation both configurations were compared in detail. Trajectories were defined to compare the global performances. The goal was to obtain significant acceleration to demonstrate the dual mode ramjet thrust and the positive vehicle propulsion balance. The comparison of both vehicles included aerodynamic performances, weight estimations, vehicle global and structural design and trim calculations along the considered trajectories. Based on Navier-Stokes calculations special attention was paid to the flowfield at the entrance of the air intake. The proposed paper will present the details of this comparison.