EFFECTS OF BALLISTIC DAMAGE ON THE AERODYNAMICS OF HELICOPTER ROTOR AIRFOILS

Experiments were conducted to estimate the effects of ballistic damage on the aerodynamics of helicopter rotor airfoil sections. The lift, p itching moment, and drag were measured on nominally two-dimensional bl ade specimens with representative prescribed and actual ballistic dama ge. The measurements were made at chord Reynolds numbers between 1 x 1 0(6) and 3 x 10(6) and Mach numbers up to 0.28. Force balance measurem ents were complemented by chordwise and spanwise pressure measurements to assess the three-dimensional nature of damage on the aerodynamics. The quantitative data were supplemented by surface oil-now visualizat ion, Generally, it was found that ballistic damage degraded the aerody namic performance of the blade specimens, with a reduction in lift acc ompanied by significant increase in drag and change in the center of p ressure. However, in some cases significant damage produced surprising ly mild effects. The results are useful in helping to model and assess the overall vulnerability of helicopters to ballistic damage.