This paper describes a study to characterise the impact threat to aircraft from runway debris. This work investigated the likelihood of an event exceeding a critical impact energy; it did not address the probability of an event occurring. Runway debris was collected from six airfields and parameters such as size fraction, mass, density, bluntness and material type were characterised. The distribution of the stone mass against frequency was accurately modelled and based on this, an expression was developed for the probability of an impact exceeding a critical level during a single take-off or landing. By considering the probability of a 50J impact from runway debris as a once in a lifetime event, the implication is that the actual threat is significantly more than the currently perceived threat. This study provides the foundations for more comprehensive studies and will give the designers improved understanding of the threat to aircraft from runway debris.

The flow in many wind tunnel experiments is affected by the presence of test section walls. The resulting interference can be minimised by correcting the measured model pressures, or by influencing the model flow directly with the use of ventilated or adaptive test section walls. The objective behind the latter technique is to guide the flow in the test section to achieve low interference (i.e. free flow) condition at the model. The most successful technique of flexible, adaptive walls is still restricted to small research wind tunnels due to its mechanical complexity. However, a very promising alternative is the use of adaptive slots in the test section walls. This concept combines the method of passive slotted walls, as they are already implemented in many large wind tunnels, and flexible walls. Additionally, this technique presents the opportunity of full 3D adaptations because the slots can be situated in all four test section walls.

This paper presents preliminary experimental results and the latest numerical calculations on the effectiveness of adaptive slots. The experiments were conducted under high subsonic flow conditions in the new slotted test section of the transonic wind tunnel at TU Berlin’s Aeronautical Institute (ILR).

The numerical results presented are focussed on the 2D slot adaptation of a 2D-model (CAST7 aerofoil) and the 3D slot adaptation of a body of revolution (3D-ETB). In addition, basic studies were made of the flows associated with a single slot on one wall and a bump on the other.

The numerical and the first experimental investigations have shown the potential of adaptive slots to reduce wall interferences effectively. The adaptation accuracy of the investigated slot configurations deviated not more than 3% from the reference case (2D-wall adaptation).

Hybrid laminar flow control (HLFC) is an active drag reduction technique that permits extended laminar flow on an aircraft surface and thus offers the potential for significant fuel savings. This is at the expense of an increase in system weight and specific fuel consumption. An overview of HLFC system failure types and consequences is presented as an introduction to this study, which investigated the impact of a potential loss of laminar flow due to flight in cirrus clouds. At typical cruising altitudes, the ice crystals are of a sufficient size and may result in sufficient particle flux to cause a temporary transition of the boundary layer. A computer performance model of a twin engine aircraft in the class of the Boeing 757 has been used to study the impact of alternative fuel planning scenarios on the fuel consumed by a HLFC aircraft, taking into account a model of probable cloud encounter. Based on the models, the study showed that if the fuel planning assumed 25% time-in-cloud (TIC) during the cruise, then in the extreme case of 55% TIC during the cruise, the contingency fuel (taken as 3% of the trip fuel), would be sufficient for the aircraft to complete the mission (including the alternate leg and hold).

Surface pressure measurements on the CAST-10-2/DOA 2 aerofoil, conducted in the IAR l.5m wind tunnel and supported by CFD simulations, are used to validate some new theoretical analyses of transonic wall interference. Based on the transonic freeze principle, it is shown that the stream Mach number correction is indeterminate near Mach one.

Coatings of chiral-nematic liquid crystals are known to change colour under different levels of surface shear stress. In this study, the liquid crystal coating was used to provide information about flow separation and reattachment on a backward facing step and a delta wing respectively. The tests were carried out at a free-stream velocity of 25ms-1. The Reynolds number based on the step height of the backward facing step is 16,000 and based on the chord length of the delta wing is 270,000. The study revealed that the locations of boundary-layer separation and reattachment can be identified from spatial variations in the surface colour. Agreement was obtained between the results acquired from liquid crystal and surface oil flow technique. The variation in hue was used to improve the determination on the location of flow characteristics. This study showed that the liquid crystal coating is an effective method for the qualitative study of separated flow characteristics.