In designing rotor blades their strength on the ground, their torsional stiffness, their aerodynamic shape and smoothness, etc, have all to be considered, but the primary purpose of rotor blades is to sustain helicopters in controlled flight in the air, and one of the most difficult problems arising is that of assessing the bending stresses to which rotor blades are then subjected The present treatment is, therefore, largely concerned with the estimation of the bending stresses to which rotor blades are subject in flight

The loads tending to bend blades are first taken as being identical with those to which an idealised inflexible blade is subjected These loads are analysed along and perpendicular to the blade length, and equations for the bending equilibrium of flexible blades in the lift and drag planes are developed Difficulties associated with the solution of these equations are overcome by the construction of special solutions, called “Type Solutions,” which satisfy these equations and the end support conditions of the blade These type solutions give a physical picture of the problem and help in the calculation of blade stresses

The differences between the loads on an idealised inflexible blade and flexible blades are discussed In the lift plane it is demonstrated that they are, in general, small, but the possibility of dynamic amplification of higher harmonics in the loading system is brought out, and it is suggested that there may be a need for further work on this aspect of the problem, particularly for high speed helicopters

When first I heard that I was to be asked to give this Paper to the Association, one of those present asked me what I knew about Rotor Stations I had to admit that it was very little Some of the remarks I shall make in the paper will seem so obvious as to appear platitudes Others, particularly those relating to the dimensions of the landing area, are offered in the absence of a significant amount of directly applicable data and may be treated as one individual’s guess In these circumstances, the discussion which follows should be of even greater importance relative to the Paper than is normally the case in our meetings

A Rotor Station can be viewed from a number of standpoints Those of the public user, the town planning authority and the civil-engineer-architect will be dealt with by other speakers I propose to look at it from the standpoint of the scheduled operator

The previous speaker has briefly stated the requirements which for satisfactory operation of a helicopter service should govern the siting of a Rotor Station they may be summarised as—commercially “a central location in the town, with convenient access by road and rail”, and—operationally “relative freedom from local ‘smog’ and from high obstructions”

It is probable that the travelling public also would describe their chief requirement as “a central location and convenient road and rail access”, but when the question of siting is viewed disinterestedly—as it must be by the town planning authority—when account is taken of the probable effect that the Rotor Station, its use and its situation, may have upon the public in general, and on the owners and occupiers of adjacent property in particular—a rather different set of criteria must be considered

Previous papers have dealt with the operational and planning criteria for Rotor Stations The architectural and engineering aspects will derive directly from the site selected in accordance with these requirements Such sites can be classified into the categories of ground level, roof-top, bridge platform and flexible pontoon sites These will be examined in detail, together with some estimates of the clear spans and floor areas of the buildings required to serve the stations

Ground level sites have much to commend them from the engineering point of view For relatively low rates of operation, the landing area may be turf, provided that the subgrade is well drained For aircraft movements of the order of 10 to 15 per hour, however, a paved surface will be required The buildings necessary will comprise the terminal building and control tower, fuel store, and open air parking facilities for aircraft passengers’ and staff cars, and in some cases hangars and workshops From the layout aspect, it would be desirable to keep all buildings to one side of the landing area, though the car parking area need not be so located

In presenting this paper an attempt has been made to outline some of the additional problems which are connected with the design and construction of rotor blades driven by jets at the tips

The complications which arise when ram or pulse jets are fitted are not discussed in detail as it is considered that these problems are also included among those which occur when pressure jets are used as the means of propulsion

This short paper will therefore be confined to a discussion on the engineering of rotor blades driven by pressure jets at the tips

May I congratulate Mr WHITBY on his excellent and lucid paper It has filled me with interest and admiration Interest, because the subject is one in which for some time past I have tried, by preaching and propaganda, to interest others Admiration, because, judging by my own reaction, he seems likely to succeed where I have failed

From this well deserved tribute to the lecturer I do not wish it to be inferred that I agree with all he has said on the subject

He has stated at the outset that the “public user” and other aspects are left by him to be dealt with by other speakers—in the case of the “public user” this is my unfortunate self But he nevertheless goes on, in the latter part of his paper under the heading of “Traffic requirements for booking and handling passengers,” to state what the passenger or public user must do to satisfy the operator

This short talk describes the manufacture of the metal rotor blades now going into quantity production for the S 51 and S 55 Helicopters at the Westland Aircraft Works These blades are a Sikorsky development so that there are many details both of design and construction which I am not at liberty to discuss On the other hand I hope to give a general indication of the way in which they are made, and of the scale of facilities which are available They are the first all metal helicopter main rotor blades to go into quantity production outside the United States

The backbone of the blade is an extruded light alloy spar which begins life as a billet in the extrusion presses at Messrs Birmetals Since the blades of the S 55 Helicopter use the same type of extrusion as the smaller S 51 blades, in future all extrusions will be delivered to us in the longer length and will be cut down for the manufacture of S 51 spars Each extrusion contains two shear webs inside the main contour and these run the entire length of the spars

In some ways I am an intruder into this discussion on the Design and Construction of Rotor Blades, because my paper deals with what happens to rotors long after they have been designed and constructed, when, that is to say, they are passing through the hands of the test pilot, the operating pilot and the maintenance engineer I shall try to confine myself to those parts of the rotor’s career which have repercussions on design and construction

Tuning, whether of an engine or a musical instrument, consists of adjusting all the variables available in a systematic manner calculated to make the device as a whole work in the best way possible If the device is a piano, this may mean doing what the piano tuner does on his three-monthly visit, but it may perhaps involve a bit of what happened when the earlier types of piano were developed into what J S BACH called his “well-tempered clavier”

Our Company has been making wooden helicopter blades of different types since 1937 I want to tell you something of their materials and manufacture and would welcome questions in the course of my talk

Fig 1 shows a cross-section of the big Cierva blade as used on the W 11 This is monocoque construction Notice the centre of gravity of the blade and the incidence of the tip superimposed on that at its widest section

The main spar is built up at one-inch thick blocks of compressed wood laminated of 1/32 inch Canadian birch veneers bonded with resin film and pressed to about 2,000 lbs per square inch at 300°F The density is about 1 2

As a matter of interest, by laminated wood we mean that the grain in all the laminations runs parallel, whereas in plywood the grain of adjoining laminations is at right angles