A Tunnel Spanning Airfoil Testing Technique

A series of helicopter airfoil blade sections have been tested in the Naval Ship Research and Development Center (NSRDC) 7 x 10-Foot Transonic Wind tunnel to acquire transonic two-dimensional airfoil data. The models were full tunnel spanning airfoils with a span of 10 feet and a chord of 16 inches. Angles of attack from 0 to 16 degrees were measured for Mach numbers of 0.30 to 1.075. The airfoil models were designed to mount around a main spar that spanned the wind tunnel test section and mounted to supports contained in the tunnel walls that extended into the tunnel plenum chamber. Two six-component Task balances were mounted parallel to the airfoil span in the spar, making the center 8 inch airfoil section metric. The metric airfoil section was mounted to the outer shell of the forward balance by pins and clamps. The rear balance forces were transferred from the airfoil to the rear balance through bearing blocks. A gap of . 03 inches was left on each side of the metric section and was sealed by wrapping the model at the metric brakes with 0.005 inch thick dental dam rubber tape. Center span and 16 inches on either side of center were instrumented with a series of pressure orifices. The Center span pressures were integrated to calculate lift, pitching-moment and drag. The outer pressures were used to check the consistency of flow over the airfoil.