The theory of thin aerofoils at small incidence and flap deflection is very well established. For certain purposes it is desirable to know how an aerofoil will behave in potential flow when the flap is deflected through large angles.

To this end, an attempt has been made to develop a theory of thin aerofoils in which the flap deflection angle may be large.

The results obtained are compared with those derived by an alternative method of direct conformal transformation by F. Keune.

In the November 1955 issue of the Journal there is a Note, “ A New Method for the Numerical Evaluation of Determinants.” I would point out that this method is not new, but is given in “ The Theory of Determinants, Matrices and Invariants” by Turnbull (published by Blackie) at page 340, paragraph 7, under the heading “ Dodgson's Method of evaluating a determinant by condensation.”

In a recent note Professor Duncan gives a method for finding the reciprocal of a matrix which is triply partitioned both horizontally and vertically. In spite of the apparent complication of the formulae, such a procedure may shorten the calculations in the case when the submatrices involved are especially simple (e.g. null or diagonal), or when their arrangement exhibits some symmetry. In Ref. 1, the submatrices a to j of the desired reciprocal are obtained by a series of operations summarised in equations (3) to (19); these operations consist altogether of 5 inversions of submatrices, 29 matrix multiplications of various orders and 15 matrix additions.

This note shows how a pure resistance analogue can be used to find the lift on low aspect ratio wings travelling, with small incidence, at speeds close to the sonic velocity.

The method is applicable to flat, twisted or cambered wings and is simple in operation; the results obtained being in close agreement with those obtained by calculations based on the same theory.

The solutions given in this note are essentially those corresponding to the Jones theory, which is applicable to low aspect ratio wings at small incidence, travelling with velocity close to the sonic value. Under these conditions it has been shown that the three-dimensional problem reduces to a series of two-dimensional problems in planes perpendicular to the direction of motion. Thus the wing can be considered as a series of spanwise sections, the solution for each section, in terms of the velocity potential, being considered in turn.

A presentation of the solution of linear equations with complex coefficients is given, in which current checks can be introduced to obviate inaccuracies and thus engender confidence in use. The method is based on the elementary concept of elimination of each unknown in turn, and details only of its application are given since the theory demands lengthy exposition. Evaluation of determinants is also illustrated.

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.

March 18th is the 50th anniversary of a free flight of some 40 ft. made at Montesson, near Paris, by Traian Vuia credited by L'Aérophile (September 1906) with being “ the first person in France to have really attempted, with a machine able to carry a man, the direct take-off of an aeroplane having a wheeled undercarriage.”

Vuia, a Rumanian, submitted a paper to the Academy of Sciences in February 1903 which included a description of what he called an “ aeroplane-automobile ” which was a light weight monoplane with wheels and an engine driving a single tractor propeller; it was to be controlled by a rudder and by altering the incidence of the wing.