Study in Drag Reduction of Close Formation Flight Accounting for Flight Control Trim Positions and Dissimilar Formations

摘要

This thesis further defines the position of greatest fuel savings benefit for the trail aircraft flying in a two-ship formation. The HASC95 vortex lattice code was used for the examination. Investigations of a similar formation of F-16 aircraft and a dissimilar formation of a lead KC-135 aircraft and a trail F-16 aircraft were conducted. The analyses determined the effects of varying airspeed on the optimal position. In addition, flight control surface deflections were taken into account during the analyses. Both investigations trimmed the aircraft in the yaw and roll axes to determine the optimal savings. The similar analysis was conducted at an altitude of 20,000 feet and three airspeeds: cruise speed of 300 knots, maximum range airspeed of 271 knots, and maximum endurance airspeed of 211 knots. The savings for the trail aircraft were determined to be 16%, 21%, and 34%, respectively, at a constant wing tip overlap of 13.5% of the wingspan. The dissimilar formation was completed at an altitude of 20,000 feet and 300 knots airspeed. This resulted in a 26% savings for the trail aircraft with a wing tip overlap of 16.7% of its wingspan. A flight test was flown for the similar formation profile of F-16s. The flight test investigated the change in vertical positioning and lateral spacing from the first analysis and captured data at 300 knots. The results of the flight test were inconclusive. However, the determined area of apparent savings was bounded by 7.9% to 19.9% wing tip overlap and -3.2% to -7.3% vertical separation. At the bounds, fuel savings of 12% and 13% +/-7% were observed. The drag savings profile had the capability to increase the range of existing airframes, providing the benefit at no cost. The analytical study was conducted at the Air Force Institute of Technology, Wright- Patterson AFB. The flight test was conducted at the U.S. Air Force Test Pilot School, Edwards AFB, California.