Parametric Transonic Evaluation of Type a VSTOL Nacelle Drag.

A parametric evaluation of the zero lift drag characteristics attributable to the large nacelles found on some Type A VSTOL candidate aircraft was conducted in the 7- by 10-foot transonic wind tunnel of the David W. Taylor Naval Ship Research and Development Center. Mounting the nacelles in proximity to the wings and fuselage yields levels of interference drag three to four times the isolated drag which results in the nacelle interference drag producing approximately 50 percent of the total aircraft drag. Movement of the nacelles away from the wings either longitudinally or vertically tends to reduce drag. Except for the nacelles mounted forward of the wing, the nacelles have an adverse effect on lift. The particular wide nose body used proved to be highly unstable longitudinally although adding nacelles above or behind the wings tended to reduce this instability. Five pairs of axisymmetric nacelles, four pairs of pylons, three longitudinal and two vertical positions were investigated on a 10-percent scale, low (supercritical) wing model. (Author)