The 987th Lecture to be given before the Society was the 24th Main Lecture to be given at a Branch of the Society and was also the First Chadwick Memorial Lecture. The Lecture, inaugurated by and held under the auspices of the Manchester Branch was given by Mr. H. Rogerson, M.B.E., A.M.I.Mech.E., F.R.Ae.S., before a large and distinguished audience on the 21st March 1956, at the College of Technology, Manchester.

The main purpose of this paper is to outline the position which the propeller holds in current aircraft propulsion, its construction, operation and its future. The paper has been arranged in four parts, as follows:–

1. 1. Present and future types of aircraft foreseen with propellers.

2. 2. Engines for turbo-prop power units.

3. 3. The Propeller.

4. 4. The Future.

In the present military field propellers are used for the following types of aircraft:—Heavy transport and Army reconnaissance, for example the Beverley and Pioneer, Submarine reconnaissance, Naval Strike Fighters and R.A.F. Trainers as exemplified by the Gannet, Wyvern and Provost.

Existing methods of estimating the blade loadings on a helicopter rotor in forward flight have suffered from the necessity of using false simplifying assumptions in order to make possible an analytical approach. The following list gives the most usual of these assumptions:

1. (i) Blades have no twist or taper, or are twisted and tapered in a particular way.

2. (ii) The coning angle is small enough to neglect the resulting changes in velocities, angles, and so on.

3. (iii) The disc is horizontal.

4. (iv) The components of velocity parallel to the blade length may be neglected, and forces are calculated for and act with reference to the velocities normal to the blade length.

5. (v) There is no variation in downwash over the disc, or the variation is capable of simple expression.

6. (vi) The blades extend from hub, and tip losses are neglected.

7. (vii) The blades have pure flapping hinges and the analogy between flapping and feathering enables loadings calculated for flapping blades to be referred to a “hingeless” rotor system.

The “ China-Film ” technique was developed by Murphy and Phinney from the “ China Clay” technique for indicating transition originated by Richards and Burstall. It consists in applying a suspension of china clay in a volatile liquid to a surface subsequently subjected to air flow. Not only is transition indicated, but when all the liquid has evaporated, the china clay remains deposited on the surface in patterns which may be interpreted to yield information on the direction of air flow near the surface and the incidence of shocks thereon.

Experiments were carried out, at supersonic and subsonic air speeds, to determine the process by which the patterns form and to establish the aerodynamic meaning of the “ flow lines ” of the pattern. The influence of the viscosity of the carrier liquid was also studied. Indications of flow direction were found to be unreliable near a trailing edge, on a vertical surface at low speeds and in regions where the surface shear stress is only of the same order of magnitude as the product of pressure gradient and film thickness.

A procedure was discussed in Ref. 1 for dealing with structural discontinuities by making the strain energy of the structure a minimum, subject to the conditions that the members to be cut out are entirely free from load, and the proof was based on the well-known method of Lagrangian Multipliers. Here is another proof.

This note describes an investigation of experimental and theoretical data on the lift increment due to the deflection of full and part span controls. For full span controls, existing Data Sheets in the Royal Aeronautical Society Aerodynamics series are found to be inadequate for some of the plan forms currently in use, but the investigation shows that with one additional set of curves the sheets may be applied to almost any plan form. For part span conversion factors, a revision also is proposed.

In view of the strong claims for offset flapping and drag hinges made by Mr. Payne in his Technical Note (September 1955) I would like to make the following comments.

Many of his conclusions depend on the assertion that there is a steady inertia force on the rotor hub when the rotor tilts. This force is simply the reaction on the hub due to the sideways thrust component and should not be included with the external forces on the helicopter.

As one being intimately concerned with the development of the jet-propelled helicopter for the past thirteen years, I would like to comment on some of the statements in the Technical Note by P. R. Payne, published in the May 1955 Journal, which I feel are misleading and indeed wrong.