It is my very great honour to be asked as an operator to cover the Bell 212s part in the story of IFR operation of medium helicopters.

None of us should forget that two great British companies have for years been blazing a trail in the IFR operation of two helicopters, the S-61 and the Wessex 60, and I can only assume that it was because Irish Helicopters was, I understand, the first operator to put the CAA approved Bell 212/IFR into operation that the privilege of giving this talk has come my way, and I speak humbly and mindful of the invaluable efforts of others before us.

In the modified free-streamline theory for the separated flow past bluff bodies due to Roshko, the velocity on the separated free streamlines is expressed as

Uv=kU0,

where U0 is the velocity of the undisturbed stream and k is a constant. If it is assumed that the pressure on the base of the body is uniform and equal to the pressure on the free streamline, then application of Bernoulli's equation leads to;

k =(1-Cpb)½,… (1)

where Cpb is the base pressure coefficient.

The plane free jet is a difficult flow in which to make accurate measurements because of the high intensity of the turbulence. Nevertheless, a reasonable agreement might be expected between comparable measurements of a quantity such as growth rate.

As can be seen in Table I, however, a variation of 10% exists in measurements made by various experimenters in fully-developed jets (x/b>100). If the results are grouped according to the value of (x/c)max,where c is the width of the wall in the x = 0 plane (see Fig. 1), a consistent variation can be seen, with the rate of growth for x/c<1, being 10% higher than for x/c>l.

Before starting this discussion I must apologise to the many people here who have considerably more experience of civil instrument flying in helicopters than I. However, the major part of this talk is merely a history of the certification of the Bölkow BO. 105 for instrument flying. We all realise that flying under IFR is not the all weather flying quoted in the title of today's symposium however for the light helicopter it is a very significant step forward. My personal experience of this programme is very limited, and indeed the Civil Aviation Authority knows more of both the design philosophy behind the IF installation and the actual tests conducted than I. I intend to give a short historical description of the problems encountered and envisaged in getting the certification, followed by the equipment required in the aircraft and the use that an operator could make of a machine of this size when IF equipped.

The aim of this presentation is to provide a survey of civilian VTOL activities in the United States. However, because of space limitations, attention can be focused on only a few topics. Nevertheless, it is believed that a representative picture of technical and organisational activities, current and future trends, and problems is presented.

The unique capability of vertical-lift systems (permitting take-offs and landings from restricted areas) generates a special market for these aircraft, because the needs of carrying both people and goods cannot be fulfilled equally well by other modes of transport. In this respect, the helicopter, which at present is the only operational VTOL concept, has demonstrated that a demand for its services, especially in such fields as offshore oil rig support, business flying, crane operations, etc, generates its own momentum of spontaneous growth, which should become quite visible from this presentation.

This investigation originated when some difficulties were experienced in establishing good flow conditions in a circular pipe to study the effects of longitudinal cooling on slanted hot-wires.

In the past many investigators have presented results on turbulent flow through pipes and it is now generally assumed that this flow field is known in sufficient detail. For example, Schlichting has given a through description of the mean velocity distribution for turbulent flow through pipes based on the experimental results of Nikuradse. On the other hand Townsend describes the structure of the flow based on the results of Laufer. Although the investigation of Nikuradse and Laufer are classical works there appears to be some uncertainty in whether or not their turbulent flows down pipes were really fully developed.

As described in Mr. Austin's paper “The Concept of the WG-13”, the Lynx stems from a series of project studies for a small tactical twin-engined helicopter, begun as long ago as 1963.

In 1967, an agreement was reached between the French and British Governments to produce, jointly, three helicopter types as a package for service with the Armed Forces of both nations. The package consisted of the Puma (SA.330-14000 lb auw) the Gazelle (SA.341-3500 lb auw) and the Lynx (WG-13 basic aircraft-8000 lb auw).

It is well established that the change of entropy across a normal shock is of third order when expressed in terms of the static pressure rise. The purpose of this note is to draw attention to weaknesses in one method of establishing this result, and to put forward an alternative analysis.

This paper deals with the conception of the initial programme, the management and development of this programme up to its present philosophy and how this programme is now being managed to meet the future of the Lynx in relation to the current development knowledge. Some aspects of the development manufacture are also covered.

Any duplication from the preceding papers given by Messrs. Austin and Rogers is considered to be given as reiteration of points necessary for completeness of this paper in its own right.