The economic losses occasioned by forest fires in Canada are serious. Although the forest lands are largely under the jurisdiction of the provincial governments the forest resources are of national interest. For this reason the federal government, through the Department of Forestry, carries out a national programme of forestry research. The research in forest fire control encompasses the use of aircraft. This paper reviews the early developments in the use of aeroplanes in Canadian forestry operations. The more recent developments of direct fire suppression techniques, such as water dropping, are discussed in detail.

Static probes, although widely used in supersonic tunnels and in flight, have not formed the basis for many reports on their design and behaviour at high Mach number.

It is known, however, that the flow over the nose of the probe causes pressure variations such that it is some distance along the probe before the static pressure is equal to free stream static pressure. The NPL, in a series of tests at M = 1.6 showed that the pressure measured at a point situated less than 10 calibres (probe diameters) downstream of the beginning of the parallel portion of the probe was dependent on the shape of the nose.

An attempt is made in this note to extend Glauert(1948) analysis to predict the increase in induced drag and decrease in lift due to a split in an aerofoil of finite span placed in a free stream. The values of induced drag obtained from this analysis is compared with Munk and Cario's (1917) experimental values and Prandtl and Betz's (1927) theoretical values. A modified analysis for low gap/length ratio, which takes into account the lift retained at the tip, gives better agreement with Munk's experimental values for gap/length ratio (Ω) less than 0·012. The effect of slot diminishes as the aspect ratio is increased.

In the light of what was now known, the only change that might have been made in the programme would have been the elimination of the animal flight; actually, systems for manned flight were ready to “go” at that time. The lecturer considered that the ballistic part of the programme would still have been needed to get the people ready for this sort of thing as well as for checking the systems control and for developing the recovery technique. The sea landing approach was chosen because it was a simpler system to develop within the brief time schedule available and would provide the lowest impact loads on the pilot and spacecraft alike.

Since I have not been concerned with matters thermo-dynamic for some years, I have hesitated to enter the lists on the recent discussions on “The Speed of Sound and Mach Number Effects,” but I cannot let the comments of Mr. Naylor (Journal, January 1964, p. 63) and the reply by Messrs. Bragg and Smith stand without further comment.

I am in agreement with Mr. Naylor in the specific circumstances with which he deals, but I believe his concentration upon the polytropic efficiency obscures the more fundamental approach.

Morgan has described a spatial instability in the flow through screens or grids of small open-area ratio. Head and Rechenberg and others have observed large span-wise variations in the thickness and shear stress of nominally two-dimensional boundary layers on flat plates and aerofoils in wind tunnels. It now appears that these spanwise variations are caused by the instability of flow through the screens. The jets of air issuing from the pores of the screen attempt to entrain more air by the usual mixing processes, but can only entrain it from each other, so that groups of jets coalesce in rather random (steady) patterns determined by small irregularities in the weave. The resulting variations in axial velocity are virtually eliminated by the wind tunnel contraction, but variations in flow direction are not so greatly reduced: a theoretical analysis shows that the observed variations of boundary-layer thickness, which often reach ± 10 per cent of the mean, can be produced by directional variations in the working section of the order of ± 1/20 deg, with a spanwise wavelength of the same order as the boundary-layer thickness.

Water tunnel flow visualisation experiments on a slender delta wing have revealed some new phenomena connected with vortex breakdown. Vortex breakdown hysteresis has been found, there being two steady flow states at some incidences, one with breakdown on the wing and one without. The formation of vortex breakdown has been studied and found to be a non-axisymmetric instability. It is suggested that pressure gradient plays a more general part in the phenomenon than has been thought hitherto.

In air-tunnel studies it is often necessary to measure the absolute magnitudes of pressure and velocity or to conduct tests at a given Reynolds number. For this purpose it is important to determine precisely the density of the air in the tunnel as a function of temperature, humidity, and barometric pressure. Because of the laborious evaluation involved, the influence of the latter two quantities is usually neglected, despite the fact that it is of the same order of magnitude as the influence of temperature. In the following a nomogram is developed which permits determination of the air-density without time-consuming calculation. The effect of density changes upon pressure and velocity measurements is illustrated by a factor C for the instrument most commonly employed in air-tunnel studies: a Pitot tube as the sensing element and a differential manometer as the recording device. An analogous factor could be derived for other measuring techniques.

In the past, attempts have been made to evaluate injectors for rocket engine combustion chambers by the use of water analogy rigs and model combustion systems that simulated the injection and combustion phase change occurring in the actual engine. To confirm that conditions in the engine were being correctly simulated, a technique was evolved for determining the mixture ratio distribution achieved by the combustion system of a Spectre variable thrust rocket engine. Gas samples extracted from the rocket-efflux were analysed, and the technique has been applied to evaluate the Spectre's standard central mushroom type injector and also a multi-head injector.

Tests have been conducted over a thrust range of 2000 lb to 8000 lb and at oxidant/fuel ratios from 7·5 to 13·0.

In parallel with this external sampling, a probe has been designed and developed for extracting gas samples from selected points across a diameter of the combustion chamber itself. This probe has been successfully operated for several minutes under combustion conditions of 500 p.s.i.a. and 2600°K, without sustaining any damage.

Analysis of the oxidant/fuel ratio pattern within the combustion chamber and in the efflux, at comparable operating conditions, indicates that little change in distribution occurs between these two points of the system. Also, the distribution found with the standard injector was that for which the combustion system was designed. It is demonstrated that loss of performance depends on the degree of non-uniformity of mixing. A 5 per cent loss in performance at full thrust and optimum mixture ratio occurs with the standard injector.

The Vast amount of knowledge on the operation of long-haul jet aircraft will inevitably pass on to the short-haul jet; but it is felt that, in the take-off régime, further study must be done. A short-haul jet will probably average 8 to 12 take-offs a day—considerably more than a long-haul jet— and many of these take-offs will involve relatively minor airfields with short runways. In addition, on a world-wide basis, there is an increasing awareness of obstacles under the flight path. Roberts of North Central Airlines and Cooke of United Airlines have emphasised this aspect from the operator's point of view. As an example, calculation of a single point involving an obstacle limited take-off weight would take a pilot at least an hour. For efficient short-haul operation, this wastage of time is prohibitive.

Bragg, in ref. 1, gives a theoretical treatment for the variation of the discharge coefficient in compressible flow of any shaped nozzle with applied pressure ratio given one set of values. This shows that the discharge coefficient of any nozzle with a value less than unity at a pressure ratio approaching unity, rises continuously as the pressure ratio increases and reaches the maximum at a pressure ratio of infinity (zero back pressure). This is based on the assumption that the flow conditions at the Vena contracta are uniform and at unity Mach number once the applied pressure ratio is equal to/ or above the critical (sonic) value.

It is now generally recognised that liquid hydrogen offers a considerable increase in vehicle performance over the more conventional fuels, despite its relatively low density.

A design study on an upper stage, which uses a liquid hydrogen/ liquid oxygen chemical propulsion system, revealed a number of problem areas which extend beyond the current levels of experience and knowledge in rocket technology existing in the U.K. This study was made on the third stage of a communication satellite launching vehicle, and a number of the problems high-lighted during the course of the investigation, covering both the propulsion system and the structure, are described and discussed in terms of their importance and their effects on the launcher system. Solutions are suggested where possible—although, lacking practical confirmation, these must be tentative in the circumstances.

While no fundamental difficulties are anticipated in the development of a rocket engine using hydrogen, it is essential to accumulate some background of data and experience to ensure that early policy and designs are sound; the importance of beginning practical work as soon as possible is emphasised.

This subject is one that seems to have received more consideration in agricultural, legal and insurance circles in the U.S.A., Australia and New Zealand than in England which is, perhaps, understandable in view of the differences in terrain, crops and aircraft operating facilities between the various countries.

There are a number of American legal reports touching upon crop spraying liability and several Australian and New Zealand cases, but few English cases. Certainly there have been a number of claims in this country for damage to persons and property arising from crop spraying operations, but it is seldom that these claims proceed to trial and perhaps the reasons for this will become apparent as the various aspects of liability are considered.

It is of interest to investigate the design of a damped vibration absorber as a problem in feedback control. The method can then be compared with the vector solution presented in reference 2.

The auxiliary system M2, K2, c is regarded as a feedback element modifying the response of the main system. The method leads to the use of approximations to construct the response curve and for optimising the design of the damper.

A recent paper on the potential incompressible flow through two-dimensional contracting ducts raises some interesting points that are relevant to the hodograph technique for solving this problem.

In this paper, Lau obtains a contraction shape by placing a source in a uniform flow that is contained in a doubly infinite strip. The resulting flow pattern is sketched in Fig. 1. The flow is from a region of unit velocity to one of velocity R, where R is the contraction ratio. A streamline, intermediate in position between ψ = 0 and ψ=1.0, is adopted as the contraction profile.

Bending analysis of rectangular orthotropic plates due to lateral loads has been considered by many writers. A small initial curvature has no effect on the bending of a plate due to the action of a lateral load, and the final deflection curve may be obtained by superposing the ordinates due to the initial curvature on the deflections calculated as for a straight plate, but when the plate is subjected to compressive forces acting in the plane of the plate, the initial curvature influences considerably the deflections produced by these forces. The analogy between bending of orthotropic plates with small initial curvature and the plate vibration is established here by expressing the ratio of the initial deflection to the additional deflection in terms of the frequencies of free vibration.

The need for simultaneous use of more than one type of camera to record Schlieren images of aerodynamic phenomena has led a recent investigator to employ a system in which an additional image was reflected from the Schlieren stop when it intercepted a deflected beam. This note describes an alternative arrangement capable of producing at least four images, although in its present form it is only designed to produce three.