Before 1960 we should be in a position to inaugurate services of large size 40/45 seater Helicopters probably cruising at a minimum of 150 m p h These could be used to cope with passenger traffic to and from city centres and coastal airstrips

Hitherto during the first 30 years of our Civil Aviation we have been compelled to concentrate air traffic into one Airport for London First Croydon and then Heath Row were selected The coming of the Helicopter is going to provide a unique opportunity for dispersing air traffic away from busy cities to coastal airstrips It is suggested that the most careful study be given to this novel plan for dispersal as against the dangers of continued concentration The traffic for instance, attracted by British Overseas Airways Corporation through tourism as well as by their excellent Service, through the first two months of cut rate traffic (May and June, 1952) rose 37 per cent above the comparable period of 1950 It might have been even higher had not the oil strike m U S A restricted allotment of fuel

The paper attempts to underline the difficulties of determining, from the various recorded opinions, papers and performances, the possible usefulness of the helicopter and of its future It seeks to point out some of the technical and economic difficulties which must be surmounted before it can be considered a commercial project It suggests a different concentration of effort on present and future development work and finally concludes that not enough is yet known of the capabilities, operational or commercial, for any definite assessment of its transport use to be safely made

This talk should perhaps begin with a brief reference to the initial development and research made by the Company into the helicopter as a crop spraying machine Many will remember the early experiments made by Dr W E RIPPER, using one of the original Sikorsky R4 helicopters These trials were made at Henley and Cambridge m the early part of 1945 The results were sufficiently encouraging to consider helicopter possibilities in this industry However, the flying limitations of the R4 helicopter did not allow a full investigation into operational and economical findings

Some measurements of the noise of a pulse jet working in the open have been made Octave analyses show that the bulk of the noise energy is contained in the fundamental, the source approximating to the classical simple acoustic source This results in a relation for the mean noise level in decibels,

where ρo is the ambient air density, c the velocity of sound and V that of the jet of exit area S and pulsation frequency f, r being the distance from the source (The units are c g sfor which ρoc = 42) This gives a good approximation to the mean noise level, in practice the level decreasing as the angle from the jet stream is increased, and the character of the noise also becoming rather less unpleasant to the ear Although noise due to the intake of air past the valves, and the valves themselves, is undoubtedly present, it has not been considered separately, since there is no indication suggesting that it is appreciable in comparison with that of the pulsating exhaust Its existence, however, should not be overlooked

Since the generator of the acoustic energy can be likened to a simple source, the “efficiency” of the process is high, about 1% compared with a simple jet where a quadrupole field is more appropriate For a thrust of about 18 lbs, measurements indicate acoustic energy of the order of 400 watts

A second flatter and lower peak is also present in the spectra, being attributed to aerodynamic noise of the jet Although swamped by the other noise, its level is higher than that of a steady “cold” jet producing the same thrust by 25 or 30 db

Since the pulsating flow is an essential characteristic of this form of prime mover, the problem of noise reduction at source is severe A certain amount of cancellation by the mutual interference of two units might be achieved if it is possible for two units to run in close proximity to each other at a definite frequency

Casualty Evacuation Flight was formed in May, 1950, at Royal Air Force Station, Changi, and was disbanded on the 31st January, 1953, and its aircraft and personnel were absorbed into No 194 Squadron, on formation, at R N A S, Sembawary

The helicopters, Westland Dragonfly II (S 51 with fabric blades) were assembled and test-flown at Seletar in April, 1950 When the unit based at Changi trials were carried out to deduce the aircrafts performance using as many combinations of individual pilot and aircraft as possible at various times throughout the day to obtain varying humidity and temperature variations and their effects on performance