Supersonic combustion data obtained at the low static temperatures appropriate for an efficient scramjet engine are reviewed. Attention is directed at the methods by which the fuel was ignited and combustion maintained. The cited supersonic combustion experiments are grouped under the six headings: chemical intiators; non-uniform flows; turbulent flameholding; combustion induced compression; partial subsonic combustion and plasma sources. The paper is drawn from the NATO RTO AVT WG10 report on technologies for propelled hypersonic flight which aims to summarise the state of the art, identifying the key issues still hindering scramjet development.

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NOMENCLATURE aspeed of sound (ms -1 ) C p specific heat of cool air at constant pressure, 1004 J.kg -1 .K -1 f source function (m) F Whitham's function (m ½ ) g local gravity (ms -2) ) h geopotential altitude (m) H potential function, (J.kg -1 ) k function of M, Equation (22) L reference length (m) M free stream Mach number P pressure (Pa) p Riemann invarient (ms -1 ) q radial function, Equation (32) (m -½ ) r radius (m) R gas constant of air, (287 J.kg -1 .K -1 ) R b radius of body (m) S entropy (J.kg -1 .K -1 ) t time, or running variable, (s or m) T temperature (K) u xcomponent of velocity (ms -1 ) u perturbation of u (ms -1 ) v ycomponent of velocity (ms -1 ) V total velocity (ms -1 ) ABSTRACTCurrent sonic boom theory is based on linear midfield solutions coupled with acoustic propagation models. Approximate corrections are made within the theory to account for non-linearities, in particular for the coalescence of compression waves and the formation of weak shocks. A very large adjustment is made to account for the increasing acoustic impedance that the waves encounter as they propagate from the low density air at cruise altitude to the high density air at sea level. Typically this correction reduces the calculated over pressure levels by a factor of three. Here the method of characteristics (MOC) is used to prove that the density gradient within a hydrostatic atmosphere has no direct effect on the propagation or intensity of the wave. However gravity and ambient temperature both affect the wave propagation and the combined pressure level attenuation is not dissimilar to that previously attributed to acoustic impedance. Although the flawed acoustic theory has given reasonable predictions of measured sonic booms, the omission of gravity from the equation of motion and the inclusion of a false impedance modification, makes the model unreliable for prediction of future designs, particularly those focused on boom minimisation. As an aid to quiet supersonic aircraft design, Whitham's theory is extended to include gravity and ambient temperature variation and shown to be in good agreement with a MOC solution for the real atmosphere.propagation. It is this supposed non linear effect that results in delayed development of the N wave and increases the possibility of achieving an overpressure below that calculated by Jones. Once an N wave has formed the George-Seebass-Jones' minimisation theory reduces to that of Jones, and hence the extension of the theory that underpinned the boom minimisation work in the US High Speed Research programme (9) , and the DARPA/NASA Shaped Sonic Boom Demonstrator (SSBD) (10) is removed. This is not to say that N waves are inevitable, on the contrary, even a cursory exploration of the problem using the MOC reveals the possibility of: signatures with character; and bow shock overpressures much less than predicted by Jones. At this stage it is necessary to mention that this is not the first application of MOC to the sonic boom problem. Ferri and colleagues (11) at New York University wrote ...

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The effect of plasma generator propulsive efficiency on aircraft fuel requirement is calculated by analysis of a turbojet engine cycle in which the plasma generator electrical power is extracted from the turbine. Using this, it is shown that a previous experimental result appears to indicate substantial and efficient drag reduction with corona from the nose of a low drag body. Electroaerodynamics is revisited, past work is reviewed and a new analytical model for electron distribution near a shock wave in weakly ionised gas is formulated based on plasma sheath theory.

This paper describes heat transfer measurements on the external surface of a Natural Laminar Flow (NLF) nacelle. The measurement technique employed temperature sensitive liquid crystals and platinum resistance thermometers (PRTs) to measure the surface temperature over an electrically heated pad. This gave an immediate visual indication of the transition location. The heat transfer distribution along the length of the pad has been determined and is compared with a simple theoretical model. Results are presented for the cruise condition of Mach 0.56 at an altitude of 6400m.

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