Reduction of Aft Fuselage Drag on the C-130 Using Microvanes

‡The aft fuselage of the C-130 is upswept to accommodate the aft cargo ramp. The upswept aft fuselage accounts for as much as 11% of the total vehicle drag at cruise. While concepts to reduce this contribution to the C-130 drag were developed in the past, they interfered with air drop operations and were never integrated into the fleet. Using flow control technology, a relatively simple, structurally benign, microvane concept with minimal air drop impact has been developed. In a collaborative Lockheed Martin, Air Force Research Laboratory program, the microvane concept was matured. Using CFD, the microvane configuration was optimized. Integration and air drop constraints were evaluated and an air drop compliant, retrofittable microvane configuration was identified. Flight testing verified the accuracy of the CFD based drag reduction predictions and confirmed the viability of the design. The flight test configuration saves between 14 and 30 gallons of fuel per hour, resulting in a potential fleet wide savings to the USAF of 2.4 million gallons of fuel per year. With no impact on operational capability and a proven flight test technology readiness level (TRL), this low-risk solution offers benefits of low-cost and rapid deployment to the fleet. The Lockheed Martin (LM) C-130 Hercules tactical military transport incorporates a dual use aft cargo ramp which acts as both a loading ramp and a fairing which closes out the aft fuselage shape. This integrated cargo ramp design is responsible for as much as 11% of the total aircraft drag due to the resulting large aft fuselage upsweep angle. Numerous studies have been performed over the last 40 years to reduce this large drag contribution through the incorporation of relatively large aft fuselage mounted strakes. These strake concepts were developed in the 1970’s – 1980’s through wind tunnel and extensive flight testing. While strakes are effective at reducing aircraft drag, they create integration problems. Results from USAF operational test and evaluations of C-130 aft fuselage strakes in 1981 indicated that “C-130 airdrop capabilities are severely limited with the strakes installed” and that “large container-like loads may require strake removal prior to on or off loading.” 1 They were not incorporated primarily for these reasons. However, current research has indicated that microvanes, devices approximately 10 inches long and 0.5 to 1.2 inches tall arrayed along the breakline of the aft fuselage as shown in Figure 1, can significantly reduce the aft fuselage drag penalty while maintaining compatibility with air drop and loading operations. These devices have been developed using advanced computational fluid dynamics (CFD) methods and their drag reduction performance has been successfully verified with recent flight testing. These tests verified a