I must depart at once from my script to thank Wing Commander BRIE for his kind introduction, and add that with such a formidable array before me my immediate reaction is to take refuge in a corner and re-write much of my little paper packing it with graphs, square roots and at least a mention of omega However, time does not permit this

As you know, this is a short paper outlining some experiences that have come my way while testing helicopters I hope I have been able to strike the right note, and that in my avoidance of “digging up” technical data and figures, the general facts are not too woolly

Increased helicopter operational requirements and the consequent advances in operating techniques are producing problems which need early recognition It is true that an increased requirement usually means an improvement in performance, but invariably each advance in performance introduces new handling problems In this short paper I will discuss two such handling problems as they effect the present military use of helicopters

Already the extension of pure helicopter flight for world-wide operation in any reasonable weathers and up to higher ceilings has provided new handling problems which we encounter regularly in our present work These I will discuss under the general headings of high altitude and instrument flight I am considering the problem of high altitude handling as a manufacturers problem, and instrument flight as a users problem

I wish to signify my appreciation of the honour of being asked to address the Members of The Helicopter Association of Great Britain and their guests I would also like to thank the Chairman for his introduction, and to pay tribute to the notable work being done by the first two speakers Both are test pilots of exceptional skill and experience, and congratulations are due to them on the papers they have delivered this evening My paper deals with the development flying on a new British type of helicopter from a civil operator's point of view and, quite frankly, I find it a most difficult task, not because the subject matter is difficult, but because to date we have only flown 120 hours on this new type in 15 months The slow rate of progress was due mainly to the many teething troubles associated with prototype aircraft

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

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