Observations and Analyses of Natural Laminar Flow over a Nonlifting Airframe Surface

In the last decade, significant aerodynamic and manufacturing progress has been made in the area of achieving natural laminar flow over practical swept and unswept lifting surfaces. Further significant reduction in total aircraft drag is predicted by achieving significant amounts of additional natural laminar flow also over fuselages and other nonlifting airframe components. To date, only limited experimental results are available that examine the applicability of laminar flow over nonaxisymmetric fuselage shapes. The paper presents details of a cooperative NASA/Cessna flight experiment using a light twin-engine propeller-driven aircraft, to investigate transition location and transition mode over the nonaxisymmetric fuselage forebody. A discussion is given of the transition-instrumentation layout and the planned flight-test matrix. Some transition location observations obtained thus far in this ongoing test program are compared with boundary-layer stability calculations for the fuselage forebody. Measurement of transition location and the extent of the transition process in varying freestream and propeller conditions in this test program will provide information on transition mechanisms and the significance of crossflow instability on transition over a practical nonaxisymmetric aircraft fuselage forebody at angles of attack and sideslip.