Interactional Aerodynamics—A New Challenge to Helicopter Technology

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Abstract
Interactional Aerodynamics (I/A) is the study of the flow anomalies and the associated forces that result from combining the passive and active components to form the helicopter configuration. I/A also covers anomalies that occur when operating the helicopter near the ground or proximate to obstacles or other aircraft. Modern helicopters will show a greater susceptibility to I/A‐related problems because of design trends to higher disk loading, compactness, and the need to operate in the Nap‐Of‐the‐Earth (NOE). I/A phenomena are extremely complex, and existing theories are inadequate for analysis and prediction. Before mathematical models can be rationally constructed, the physical processes at work must be observed and measured, and the significant cause and effect relationships defined. Some of this required understanding has been gleaned from recent studies of I/A phenomena encountered during the Boeing Vertol UTTAS development program. Technical data was obtained from the results of powered wind tunnel model testing. These studies were supported initially by the Applied Technology Laboratory, U.S. Army Research and Development Laboratories (AVRADCOM), under Contract DAAJ02‐77‐C‐0020 and subsequently by the U.S. Army Research Office under contract DAAG29‐78‐C‐0021. This paper describes the broad field of interactional aerodynamic phenomena, classifies the problems into logical categories, and establishes a matrix of interactions and problems. A structured basis is thereby provided for systematic problem identification and interaction analysis according to needs and priorities. Specific interactions are analyzed where sufficient data is available. These include the rotor/hub/fuselage/empennage, rotor/fuselage, main‐rotor/fin/tail‐rotor, rotor/ground, rotor/fuselage/ground, and tail rotor/main rotor/ground interactions. The evident trends are discussed and conclusions drawn regarding significant physical mechanisms. Finally further research is recommended to expand the data base, to foster theory development, and to develop meaningful design guidelines. The meager state of the art in this field of demonstrated major problems presents a new challenge to helicopter aerodynamic technology, which until now has emphasized the isolated rotor in research and development.

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