Velocity Profile Measurements Under the Ramp of a Lockheed Martin C-130 Aicraft 2004-01-3099

Predicting the aerodynamic forces in the wake of an object can be difficult using theoretical and computational methods. This is particularly true for airframes that have multiple engines and whose flight envelope involves the use of large control surfaces. One such aircraft is the C-130 which adds the further complication of a rear cargo door and ramp. Modeling the wake near the rear of this aircraft can be difficult and inaccurate unless validated against actual flight data. For this study a simple test apparatus, developed by the authors, was used to measure the velocity profile in the wake area of the rear cargo door of such an aircraft.

The test apparatus contained 32 pressure ports, one of these ports was assigned to a static pressure probe. All pressures were referenced to an additional static pressure measured at the edge of the cargo ramp. The remaining, 31 pressure probes were distributed regularly between three vertical rake assemblies. The area sampled by the probes was 60 inches wide by 24 inches tall. Temperature and absolute pressure were recorded to correct the pressure port measurements of the electronic scanning pressure transducer (ESP) to standard temperature and pressure. Two 3-axis accelerometers were also mounted on the test apparatus to record the mechanical vibrations present during flight allowing for future quantification of the vibration forces experienced by equipment located in the wake area.

Proper operation of the measurement apparatus was verified prior to flight, through tests on a moving automobile. Actual data was obtained while flying on an H-2 variant C-130 aircraft from the 130^th Airlift Wing out of Charleston, West Virginia. Upon analysis, the measurements from the flight exhibited the expected trends. These included the differences from left to right in the velocity profile due to the interaction of the prop-wash onto the aircraft fuselage. This difference resulted from the propellers, which all spin in the same direction, causing an upward wash on left rake and the downward wash on the right rake. The velocity profile of the right and the center rake illustrated the existence of a flow separation region under the cargo ramp. This was not observed for the left rake and is likely a result of the asymmetry caused by the propellers’ rotation.