Two major technologies in aeronautics promise substantial improvements in the fields of economy and ecology. One is laminar flow technology and the other arises from new developments related to aircraft turbofan engines. The trend in turbofan engine development is towards engines possessing higher bypass ratios. This, however, entails larger engine dimensions, leading not only to an increase in the skin friction drag but also to negative engine-airframe interactions. As a consequence, the need for laminar flow nacelles becomes all the more important as part of the general process of engine-air-frame integration optimisation for advanced transport aircraft.

This paper deals with some results obtained from flight tests with a laminar flow nacelle demonstrator and specifically addresses the topic of aerodynamics of intakes and nozzles. The results described relate to a European collaborative programme in which a natural laminar flow (NLF) nacelle was flight tested. Results of the effect of the angle of yaw on the static pressure distribution on the fan cowl including the intake of an NLF nacelle are presented for the maximum cruise flight condition. At zero yaw, a comparison of Euler calculations with flight test data is made. Measured flow variables of the fan nozzle flow directly downstream of the fan nozzle exit, exemplified by the Mach number and the flow density distributions, are also presented for the condition of maximum cruise.