Observations of Wake Vortex Instability Flowfields and Aircraft Response to Encounters

Abstract

* from 0.5 to 3. The second phase, studied wakes from 5 to approximately 30 nm in length, or t * from 1 to 6. Sampling was conducted at 32 Hz. More recently, the NRC CT- 133 aeroplane, with 600Hz sampling air and inertial data systems, has conducted an additional data gathering flight against enroute jet transports. Through the course of all flights, a variety of condensation wake conditions prevailed, with condensation intensity and longevity varying between the upper engine exhaust jet wake and the lower trailing pair vortex wake domains. The sampling aeroplane conducted helical flightpaths around, rather than through, the condensation flow regimes. However, following the onset of significant multi-wavelength long- period instability (at enroute speeds, generally beyond 6 nm wake lengths), a number of entrainments of the Falcon 20 into wake vortex cores occurred. The effects of wake vortex core entrainments upon aerodynamic loading, flightpath stability and systems operation have been of particular interest. In loading, such entrainments were multi-axis, with severe (defined as >0.3g deviation) aZ and a Y and severe (defined as >90°s -2 for roll and >30°s -2 for yaw) roll/yaw angular accelerations. The angular acceleration loadings resulted in gross flightpath deviations and upsets. Such encounters with a B747-400 wake are studied in detail, in terms of their flowfield characteristics and the effects upon the Falcon. Cross-plane re-construction is used, in order to correlate structural characteristics and the changes in structure, with increasing wake age. In the case of the B747-400 entrainments, one occurred at the point of vortex linking, and one occurred with the wake vortex in a probable ring state. Although the loading was multi-axis in the former case, in the latter case the loading affected aZ only. The aircraft loading and flightpath upsets of an NRC CT-133 survey of an A310 wake vortex, which included deliberate vortex core traverses, are also discussed. Initial comparisons between the Falcon and CT-133 core penetrations suggest that the parameters of be/rC and bf/be might be significant factors for the magnitudes of loading and flightpath upset experienced during core passage.