Nonlinear Effects of Inlet/Strake Length and Vertical Tail Geometry on the Longitudinal Stability of a 5th-Generation Aerial Target Configuration

摘要

The Fifth-Generation Target Study (5GTS) was a conceptual design task for a large target drone aircraft capable of representing key 5th-generation fighter signature and performance attributes. The target drone's intended uses are to test air-to-air and surface-to-air missiles, and to ensure that modern tracking systems are capable of identifying and targeting Sth generation fighters. A delta-winged 5GTS design exhibited a non-linear pitching moment curve when tested with long inlet/strake structures sticking out ahead of the wings. Tests in the United States Air Force Academy's (USAFA) subsonic wind tunnel revealed that this undesirable behavior disappeared when vertical tails were relocated or canted inward and also when inlet length was reduced. Flow visualization in the USAFA water tunnel showed that leading edge vortices shed from the nose chines, inlet lips, and wing leading edges remained separate from each other and interacted negatively with the vertical tail when the inlet/strakes were relatively large. However, when inlet/strake length was reduced to a critical value, the three separate vortices interacted positively by merging into a single vortex centered well away from the vertical tails.