The 969th Lecture to be given before the Society and the 22nd Main Lecture to be held at a Branch Centre, “ Free Flight Techniques for High Speed Aerodynamic Research ” by J. A. Hamilton, M.B.E., B.Sc, A.M.I.Mech.E., A.F.R.Ae.S., and P. A. Hufton, M.Sc, was given under the auspices of the Boscombe Down Branch on 1st December 1955. Air Commodore R. A. Ramsay Rae, O.B.E., President of the Branch welcomed the guests and said how delighted he was to see the President of the Society, Mr. N. E. Rowe and members of the Council and Main Society at the Aeroplane and Armament Experimental Establishment.

At approximately 14.00 hours on an overcast December day in 1954, persons in the vicinity of Idlewild Airport, New York, were startled by a violent explosion followed by the signs of an intense fire. Investigation revealed that an incoming European aircraft, a DC-6B, had crashed into the pier supporting the approach lights to Runway 4, had been demolished by the impact and had carried 26 persons to their deaths in the icy waters of Jamaica Bay. An inquiry into the accident was made by the Civil Aeronautics Board and their findings published. The probable cause of the accident was determined as an erratic approach which resulted in a descent too low to avoid striking the pier, but a significant rider was added to the effect that a contributing factor was pilot fatigue due to the particular and difficult circumstances of the flight.

Some purely aerodynamical phenomena, which might profitably be investigated by means of electrical analogue computors, are described. No attempt has been made to furnish a complete catalogue of problems but rather to present current issues, the solution of which would aid the development of practical aerodynamics.

Consideration has only been given to those questions which can be solved more suitably by an analogue computor rather than by a digital machine, although the feasibility of partially solving certain of them by the use of an analogue computor, and completing the work with a digital machine, is mentioned.

In scope, the survey includes two and three dimensional aerofoils as well as interference and a number of special problems.

The relative merits of the various forms of analogue computors are not extensively discussed.

The problems associated with the fatigue life of aeroplane structures have been so thoroughly discussed by experts of international repute that it is with some trepidation that the present speaker ventures into this difficult and controversial field. However, the need for more experimental fatigue data on actual structural components (as distinct from idealised test specimens) is undeniable; further, it is hoped that the present paper may stimulate discussion. Opinions expressed in this paper are the author's personal views, and do not necessarily reflect the policy of the Ministry of Supply.

A comprehensive bibliography on this subject has been given recently by Lundberg in the 18th Wright Brothers’ Lecture.

It is shown that the flow in a region of recirculation may be divided into a core, in which the vorticity may be constant, and a boundary layer surrounding the core. An approximate solution is given for the flow inside a circular cylinder with partly fixed and partly moving walls.

Flow patterns which include regions of recirculation occur frequently, for example, behind bluff bodies, in sharp bends, and in sudden expansions in ducts. Little is known about this type of flow, which will be referred to, for brevity, as ‘cavity’ flow. It used to be thought that the velocities in the ‘ cavity ’ were small compared with the stream velocity, but it is now known that the maximum velocity in the cavity may be about 30 per cent. of the stream velocity. This implies that the motion within the cavity cannot be neglected.

Recent interest has been shown in stability problems in which the parameters in the relevant characteristic equations are not constant. For instance, the coefficients in the characteristic equation for the stability of flutter of an aeroplane's wings are functions of the speed of the aircraft. When the aircraft is accelerating or decelerating it is therefore necessary to consider whether the resulting variation of the coefficients is sufficiently rapid to invalidate a calculation of stability which is based on the assumption that the coefficients are constant. Similar stability problems arise in connection with guided missiles.

In a recent article Lundberg has made reference to use of the “ Hydraulic Analogy ” for quantitative investigation of gas dynamics phenomena. This is quite feasible provided that the basic analogy and its limitations are properly understood. In fact, considerable progress has already been made and it has been proved possible to utilise the analogy for both supersonic and transonic research.

A study of the mathematical analogy indicates that the strongest physical analogy between a two-dimensional (inviscid) gas flow and a three-dimensional (viscous) water flow exists for the transonic case when the water depth is approximately one quarter inch and the model is towed. Only thin profiles with small incidence can be sensibly investigated. Under such conditions the analogous water flow may be considered as a distorted dissimilar model of a corresponding prototype gas flow.

In the November 1955 issue of the Journal there is a Note, “ A New Method for the Numerical Evaluation of Determinants.” I would point out that this method is not new, but is given in “ The Theory of Determinants, Matrices and Invariants” by Turnbull (published by Blackie) at page 340, paragraph 7, under the heading “ Dodgson's Method of evaluating a determinant by condensation.”

March 18th is the 50th anniversary of a free flight of some 40 ft. made at Montesson, near Paris, by Traian Vuia credited by L'Aérophile (September 1906) with being “ the first person in France to have really attempted, with a machine able to carry a man, the direct take-off of an aeroplane having a wheeled undercarriage.”

Vuia, a Rumanian, submitted a paper to the Academy of Sciences in February 1903 which included a description of what he called an “ aeroplane-automobile ” which was a light weight monoplane with wheels and an engine driving a single tractor propeller; it was to be controlled by a rudder and by altering the incidence of the wing.