This paper presents a comparison of turbulent skin-friction coefficients measured by floating element balances in zero pressure gradient conditions for a wide range of Mach numbers and Reynolds numbers. From these comparisons it is clear that although a large number of measurements have been made it is impossible to use these measurements to find the skin-friction coefficient for a given Mach number and Reynolds number to an accuracy of better than ±2 to 3%. This estimate of accuracy applies only to the range of Mach numbers and Reynolds within which there are a reasonable number of measurements to compare. Outside this range, say for Reynolds numbers based on momentum thickness greater than 40,000 and Mach numbers greater than 2 the uncertainty is greater.

'Life extension’ is the theme of this paper. However, unless there is a clear understanding of what ‘life’ means it is not readily obvious as to the appropriate means to adopt for its ‘extension'. This paper will explore some of the background to the meaning of life and the means being adopted to extend it for fixed wing civil transport aircraft. The focus will be on the safety of airframe structures from a regulatory viewpoint.

A comparative review is made of the evolution, on both sides of the Atlantic, of civil aviation requirements for the fatigue, failsafe and damage tolerance design of structures. Definitions of life are discussed in the context of recent developments of ageing aircraft structural programmes. These definitions are accompanied by an extensive reference list.

Example results are presented from a recent research study which compares the performance of a number of fracture mechanics analysis methods with conventional fatigue endurance approaches to the prediction of lives. The work was carried in a way directly representative of the current aircraft design environment. It was undertaken by three separate aircraft manufacturers and applied to a range of aircraft structural features that were not necessarily originally designed to damage tolerant principles.

Some aspects of propulsion integration issues for ramjet powered missiles are outlined in this paper. The benefits of ramjet propulsion in the Mach 2-4 range over other types of airbreathing propulsion and rocket propulsion are well known. Compared with solid rocket motors, ramjet engines offer a much higher specific impulse and the capability of thrust management, enabling longer stand-off ranges and more flexible operation.

An overview of the ramjet engine cycle is given, highlighting engine/intake matching issues. This is followed by a performance comparison between a generic ramjet and a solid rocket powered missile (the air-to-air configuration is examined by way of example in this paper). As well as overall performance, intake integration and missile steering issues are considered.

A description of a wind tunnel test model, intake design and tunnel testing is given. The effects of design Mach number and side-wall removal have been investigated for twin ventral rectangular intake configurations. These tests were aimed at optimising performance at different flight conditions and improving tolerance to yawed flight. The impact of the alternative intake designs on missile performance is discussed.

This paper describes and compares various analyses leading to the development of approximate models for the linear stability modes of the non-rigid airship. The progress of the analyses was variously dependent on assumptions made from the detailed scrutiny of linear numerical models for three airships. For each airship studied, the linear models were obtained from non-linear simulation models by linearising about a number of chosen trim speeds representative of a typical speed envelope. The decoupled linear models comprised the longitudinal and lateral-directional state equations of the neutrally buoyant airship, for speeds from the hover to 30m/sec. Since the fidelity of the earliest airship models was not known, the principal purpose of this paper is to re-visit the original analysis using a later airship model of known excellent fidelity.

The longitudinal modes of the airship comprise the surge mode, the heave-pitch subsidence mode and the oscillatory pitch-incidence mode. The lateral-directional modes of the airship comprise the sideslip subsidence mode, the yaw subsidence mode and the oscillatory roll pendulum mode. Approximate models for these modes are derived and expressed in terms of concise aerodynamic stability derivatives. The mode characteristics are discussed, and the approximate models are compared with the actual airship modes over the typical airspeed envelope.

Direct Numerical Simulation (DNS) results are presented for high speed nonreacting mixing layer in a confined test section. The hyper-velocity mixing layer experiment of Erdos et al with H2/N2 stream is simulated by discretizing two dimensional Navier Stokes equation using a higher order (fourth order spatial and second order temporal) compact numerical algorithm. A favourable comparison of the computation with experimentally measured wall static pressure forms the basis of further analysis. Instantaneous flow picture and the mean profiles of various flow variables were examined to determine the development and general characteristics of the confined mixing layer. It has been found that the growth of the mixing layer is towards the high speed side of the layer. Various turbulence quantities were derived from the stored time series data of the DNS calculation and the results were compared with the experimental results of supersonic free shear layer as no experimental results of turbulence statistics are available for the confined hypervelocity mixing layer. The increasing Reynolds stress data with the flow direction indicate that the turbulence is sustained by transferring the energy from the mean flow to the fluctuating field as the shear layer develops. Although the Reynolds stress is negligible in the most portion of the wall boundary layers, effect of counter gradient effect is observed in the far downstream location of the lower wall boundary layer. The general conclusion that for the supersonic mixing layer, various turbulence quantities like Reynolds stress, turbulence intensities (both streamwise and transverse) decrease with the increase in the convective Mach number is also confirmed by our results.