A theoretical prediction scheme has been developed for the tone noise generated by a counter-rotation propeller. We start by deriving formulae for the harmonic components of the far acoustic field generated by the thickness and steady loading noise sources. Excellent agreement is shown between theory and measurements. Asymptotic approximation techniques are described which enable us to simplify considerably the complex radiation formulae, whilst retaining all of their important characteristics, and thus save, typically, 95% of computer processing time. Next we derive formulae for the radiated sound field generated by aerodynamic interactions between the blade rows. Here, however, the inputs to the formulae include a knowledge of the fluctuating blade pressure fields which cannot generally be assumed given and must therefore be calculated within the prediction scheme. In the case of viscous wake interactions we consider various models for the wake profile which is written as a series of harmonic gusts. The fluctuating pressure distribution on the downstream blades can then be calculated in the high frequency limit. Comparisons are made between measurements and predictions for a counter-rotation propeller and for rotor/stator interaction on a model fan rig. For potential field interactions we describe the flow fields due to blade circulation and blade thickness in terms of harmonic gusts with the flow assumed incompressible. The blade response is calculated for both finite and semi-infinite airfoils. Some important differences between these two cases are noted in both high and low frequency limits. Predicted noise levels are much improved over those obtained using only the viscous wake model. The inclusion of compressibility, in both flow field and airfoil response calculations, provides a further improvement in the predicted noise levels. The discrepancy between measurements and predictions at this stage is, typically, 2 or 3 dB.

A thorough evaluation of the airworthiness of a manned aircraft is vitally important, regardless of the size or function of the aircraft. However, the methods used in light and particularly microlight aircraft certification were largely based upon rules of thumb or methods better suited to larger, higher energy, aircraft programmes. A programme of research has been carried out to develop means by which microlight aircraft certification could be carried out appropriately to this class of aircraft. The stall and immediately post-stall behaviour of an aircraft are shown to be a function of the deceleration rate prior to the stall; therefore it is necessary to use a representative deceleration rate when determining the acceptability of stall and post-stall handling qualities. This research has found means by which the range of deceleration rates likely to be seen in a particular type can be estimated, so that flight test programmes can ensure these rates are included, and thus aircraft are confirmed to have acceptable stalling characteristics. Weightshift controlled microlight aeroplanes, using a Rogallo type wing, rarely show a conventional (square law) relationship between stalling speed and loading; the reason being identified as aeroelastic deformation of the wing with loading. A means by which stalling speed may be estimated for such aircraft at a variety of loadings has been developed. This will allow designers the maximum flexibility in determining operating limits and shows how the stall speed at various flight conditions may be predicted in aircraft operating documentation. The spin is a serious and potentially fatal mode of flight; a spinning evaluation, even for non-aerobatic aeroplanes, is therefore essential. A best practice has been developed and tested for the spin-resistance or spinning evaluation of microlight aeroplanes, including equipment, aircraft and crew preparation, and reporting. The developed methodology is shown to be successful, using the results of certification flight test programmes, and the in-service safety record of aircraft which had been evaluated using these methods. The tumble mode is a little known mode of departure from controlled flight experienced by weightshift controlled microlight aeroplanes. It has been a very significant factor in fatal accident records, being non-recoverable without the use of external safety devices. The mode consists of a nose-down autorotation at a rate of up to 400°/s. The tumble entry mechanism is explained, and advice to operators developed which should prevent tumble entry. Evidence is shown of the nature of the developed tumble – both modelled and through wind tunnel results, which explain how the autorotation occurs. It is also shown how this theory may be applied during testing of an aircraft to develop a tumble resistant aircraft.