A linearised two-dimensional incompressible potential flow theory for two-element aerofoil sections is developed. It is capable of predicting the effects of angle of attack, flap deflection, camber, thickness, stagger and overlap of aerofoil elements on the forces. These effects are summarised in integrals which are analogous to the one-element thin aerofoil theory Munk integrals. Analytical expressions for the forces on tandem NACA 23012 aerofoils have been derived and results are presented. Comparisons are also made with a realistic slotted flap configuration with overlap for which experimental data is available. The linearised theory is seen to correlate with these real flow results as well as and better than it does in the one-element regime.

Following Part 1, experimental data is given for the boundary-layer flow past single roughness trips of spherical shape. Correlations are given for the start and end of transition, for the recovery position and for the effective origin of the turbulent layer. There is evidence of a spanwise array of vortices which are found to influence both the downstream turbulent layer and the wedge growth of turbulence.

Seven composite laminates, three carbon, one Kevlar and three hybrid as supplied by an aircraft manufacturer were assessed for damage tolerance. Rectangular coupons were subjected to low velocity impact in the range 0-4 Joules by a swinging pendulum. The coupons were ultrasonically C-scanned to measure delamination area and visually inspected for damage. Residual strength tests in tension, compression, flexure and shear were then carried out on the damaged coupons. Visual damage, delamination damage and strength reduction thresholds were determined from the data and compared. Of the three thresholds, delamination damage and strength reduction tended to coincide. For the various lay-ups these were in the range of 1·5 to 2·0 J for the longer (tensile) specimens or in the case of the smaller (shear) specimens between 0·2-0·3 J. In all cases onset of visible damage occurred at slightly higher values of impact energy. The significance of specimen stiffness was noted.

The object of this paper is to uncover the nature of the destabilising coupling that is the major cause of body-freedom flutter and to see whether a simple cure for the flutter can be found. To do this frequency-coalesence theory is applied to a simple aircraft. It is shown that the aircraft is liable to flutter if it has a sweptforward wing and a positive ‘tail-off’ cg margin or a sweptback wing and a negative cg margin but a simple cure for the flutter does not appear to exist.