Flight Test Results of Close Formation Flight for Fuel Savings

This paper explores the benefits of flying in a tight formation, mimicking the natural behavior of migratory birds such as geese. Based on computational work, some reduction in drag for the wingman is predicted based on the amount of wingtip overlap with the leader. The flight test looked specifically at four different lateral positions with varying degrees of wingtip overlap, all flown at 300 KIAS and 10,000 feet pressure altitude. The flight test had two primary objectives: 1.) The first objective was to evaluate the fuel savings in four different formation positions, and determine which was optimal. 2.) The second objective was to determine if the savings would increase further for trailing positions in a larger formation. The aircraft were manually flown, and positioning in the formation was achieved using visual clues. The results of the two-ship flight tests showed with 80% confidence that the wingman saved fuel in the predicted optimal position, 86% wingspan lateral spacing. This position yielded fuel savings of 8.8% ± 5.0%. The other lateral positions did not show a statistically significant fuel savings. The results were inconclusive as to the best position for the wingman to fly since none of them are statistically distinct. The three-ship formation results did not yield the expected results. Not only was there no significant difference between the two wingmen, but neither wingman showed any statistically significant fuel savings. The authors feel that the three-ship formation data is inconclusive due to the difficulty of trying to fly a stable position as the third aircraft in a formation, without precise relative location information and station-keeping ability.