This paper is concerned with a suggested technique whereby light alloys, already possessing high mechanical properties due to heat-treatment, may have these properties further enhanced by the judicious use of cold-work. It is proposed that in the search for methods of reducing the weight of important aircraft components, the question of mechanical properties in general, and ductility in particular, should be reconsidered from an unorthodox angle.

This paper presents the results of co-ordinated research by The Pratt and Whitney Aircraft Co. (engines), the Chance Vought Corp. (airplanes), and the U.A.T. Research Division, all subsidiaries of the United Aircraft and Transport Corp. These studies were directed toward improving the performance of airplanes through reducing the drag of radial air-cooled powerplant installations as nearly as possible to the minimum necessary for adequate cooling.

As pointed out in previous work, in the method of collocation the functions used usually need not be orthogonal or integrable in closed form. Therefore function of different types may be mixed together in representing unknown quantities. Such function may be aptly called hybrid functions. Also, it has been found that usually it is better to represent unknown quantities by similarly looking functions instead of by a series involving higher harmonics. The idea is that by using similar looking functions it is possible to avoid poor regions for collocation, such as near nodal points, and so on, and closer fit in certain regions is assured. Thus if one knows approximately what the function sought looks like, one should try to find a set of function all of which resemble this desired shape, instead of taking an arbitrary set of harmonics when using the method of collocation. Simple examples below illustrate this approach and indicate the good results that can be expected in general.

Airscrew development has proceeded along four main lines :–

1. (1) Aerodynamic design.

2. (2) Materials.

3. (3) Adaptation to engine and aircraft.

4. (4) Fans for cooling and ventilating purposes.

Section (4) I have omitted. It may form the subject of a paper elsewhere. Section (1) I have barely outlined. It is of great interest, but I have concentrated on Sections (2) and (3) as being of immediate practical concern.

In the present paper it is demonstrated that variations in the Reynolds number as due to altitude are unimportant, provided that NR at sea level is in the region of 107.

That under these conditions the law of velocity in relation to altitude, is implicitly contained in the expression W= K L ρV 2 x area, in which ρ and V only are variables; i.e., the velocity of flight must vary in the inverse ratio of .

That the velocity limit due to the elasticity of air is lower at high altitude, for the velocity of sound is lower, the optimum flight velocity is higher. The facts concerning this are set forth.

A new graphical method of predicting aeroplane performance has been evolved by utilising the unique properties of Eiffel's logarithmic propeller chart. Its substitution for rigorous numerical methods results in the saving of labour without sacrifice of accuracy. Particularly convenient when constant speed propellers are involved, this method yields performance characteristics for altitudes below, as well as above, the critical ones for supercharged engines.

Although coupling of the word “ rigorous ” with any method of aeroplane performance prediction may be somewhat of a misnomer, the title of this paper is intended to identify a method which falls short of complete rigour only to the extent dictated by acceptance of the following simplifying assumptions :—

1. (1) That the propeller thrust acts along the direction of the flight path, and

2. (2) That lift is equal to weight in steady rectilinear flight.

The amount of labour involved in predicting the performance of a modern aeroplane with even this degree of rigour is so great that methods which incorporate additional simplifying assumptions have come into common use—despite their sacrifice of accuracy to convenience—and the more laborious methods are now rarely employed except in studies of very painstaking character. The desirability of minimising the drudgery of rigorous prediction has long impressed the writer and it is the purpose of this paper to describe a graphical method of attaining that objective.

The principal departure which characterises the new method is the adaptation of Eiffel's logarithmic propeller chart to the construction of available power curves. The use of “ indicated airspeed ” (σ1/2V) and the analogous quantity “ indicated power ” (σ1/2 h.p.) as co-ordinates causes a single curve to represent the power requirements for level flight at all altitudes. Other simplifications arising from the recognition of certain engine characteristics, utilisation of the unique properties of the Eiffel chart and development of a convenient method for evaluating the excess available power (from logarithmic curves) make it possible to eliminate a large portion of the labour previously required for rigorous performance prediction. The method is not only applicable to, but especially convenient in, the case of the constant speed propeller; moreover, it yields complete level flight and climb characteristics for altitudes below, as well as above, the critical altitudes of supercharged engines.