Aircraft Drag Reduction Through Extended Formation Flight
Aircraft Drag Reduction Through Extended Formation Flight

Author: Simeon Andrew Ning

Publisher: Stanford University

Published: 2011

Total Pages: 146

ISBN-13:

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Formation flight has the potential to significantly reduce the fuel consumption of long range flights, even with existing aircraft. This research explores a safer approach to formation flying of transport aircraft, which we term extended formation flight. Extended formations take advantage of the persistence of cruise wakes and extend the streamwise separation between the aircraft by at least five wingspans. Classical aerodynamic theory suggests that the total induced drag of the formation should not change as the streamwise separation is increased, but the large separation distances of extended formation flight violate the simple assumptions of these theorems. At large distances, considerations such as wake rollup, atmospheric effects on circulation decay, and vortex motion become important to consider. We first examine the wake rollup process in the context of extended formations and develop an appropriate physics-based model. Using this model, this dissertation addresses three aspects of formation flight: longitudinally extended formations, compressibility effects, and formations of heterogeneous aircraft. Uncertainty analysis is used to investigate the induced drag savings of extended formations in the presence of variation in atmospheric properties, limitations of positioning accuracy, and uncertainty in model parameters. Next, the methodology is integrated with an Euler solver to assess the impact of compressibility while flying in formation. Finally, we examine the important considerations for optimally arranging formations of non-identical aircraft.

Aircraft Drag Reduction Through Extended Formation Flight
Aircraft Drag Reduction Through Extended Formation Flight

Author: Simeon Andrew Ning

Publisher:

Published: 2011

Total Pages:

ISBN-13:

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Formation flight has the potential to significantly reduce the fuel consumption of long range flights, even with existing aircraft. This research explores a safer approach to formation flying of transport aircraft, which we term extended formation flight. Extended formations take advantage of the persistence of cruise wakes and extend the streamwise separation between the aircraft by at least five wingspans. Classical aerodynamic theory suggests that the total induced drag of the formation should not change as the streamwise separation is increased, but the large separation distances of extended formation flight violate the simple assumptions of these theorems. At large distances, considerations such as wake rollup, atmospheric effects on circulation decay, and vortex motion become important to consider. We first examine the wake rollup process in the context of extended formations and develop an appropriate physics-based model. Using this model, this dissertation addresses three aspects of formation flight: longitudinally extended formations, compressibility effects, and formations of heterogeneous aircraft. Uncertainty analysis is used to investigate the induced drag savings of extended formations in the presence of variation in atmospheric properties, limitations of positioning accuracy, and uncertainty in model parameters. Next, the methodology is integrated with an Euler solver to assess the impact of compressibility while flying in formation. Finally, we examine the important considerations for optimally arranging formations of non-identical aircraft.

An Analytical Study of T-38 Drag Reduction in Tight Formation Flight
An Analytical Study of T-38 Drag Reduction in Tight Formation Flight

Author:

Publisher:

Published: 2002

Total Pages: 122

ISBN-13:

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This thesis explores the benefits of flying in a tight formation, mimicking the natural behavior of migratory birds such as geese. The first phase of the research was to determine an optimal position for the wingman of a tight formation flight of T-38 Talon aircraft using the HASC95 vortex lattice code. A second wingman was then added to determine the benefit derived by increasing formation size. The second wingman was predicted to derive an even greater induced drag benefit than the first wingman for T-38s operating at Mach 0.54 at a 10,000-foot altitude. The predicted values were 17.5% savings for the second wingman versus 15% for the first wingman. The flight test phase flew two and three-ship formations to validate the computational work. 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 actual fuel savings of 8.8% 5.0% versus the predicted 15%. The other lateral positions did not show a statistically significant fuel savings. The flight test team felt that the three-ship formation data was inconclusive due to the difficulty of trying to fly a stable position as the third aircraft in the formation without station-keeping ability.

An Analytical Study of T-38 Drag Reduction in Tight Formation Flight
An Analytical Study of T-38 Drag Reduction in Tight Formation Flight

Author: Eugene H. Wagner

Publisher:

Published: 2002-03-01

Total Pages: 122

ISBN-13: 9781423512134

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This thesis explores the benefits of flying in a tight formation, mimicking the natural behavior of migratory birds such as geese. The first phase of the research was to determine an optimal position for the wingman of a tight formation flight of T-38 Talon aircraft using the HASC95 vortex lattice code. A second wingman was then added to determine the benefit derived by increasing formation size. The second wingman was predicted to derive an even greater induced drag benefit than the first wingman for T-38s operating at Mach 0.54 at a 10,000-foot altitude. The predicted values were 17.5% savings for the second wingman versus 15% for the first wingman. The flight test phase flew two and three-ship formations to validate the computational work. 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 actual fuel savings of 8.8% 5.0% versus the predicted 15%. The other lateral positions did not show a statistically significant fuel savings. The flight test team felt that the three-ship formation data was inconclusive due to the difficulty of trying to fly a stable position as the third aircraft in the formation without station-keeping ability.

Sustainable Development, International Aviation, and Treaty Implementation
Sustainable Development, International Aviation, and Treaty Implementation

Author: Armand L.C. de Mestral

Publisher: Cambridge University Press

Published: 2018-09-06

Total Pages: 381

ISBN-13: 1107153115

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The international community has succeeded in developing rules to limit greenhouse gas emissions in the atmosphere from international civil aviation. This book examines the development of international law and policy in an area that has remained largely outside the general framework of international environmental law.

Evaluating and Augmenting Fuel-saving Benefits Obtained in Aircraft Formation Flight
Evaluating and Augmenting Fuel-saving Benefits Obtained in Aircraft Formation Flight

Author: Wendy Awele Okolo

Publisher:

Published: 2015

Total Pages: 235

ISBN-13:

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When an aircraft flies, it generates wake vortices, which induce a non-uniform wind distribution in its wake. A trail aircraft, placed in the wake of a lead's aircraft vortices experiences this non-uniform wind distribution with varying directions and magnitudes, depending on the location within the wake. It has been demonstrated that there is a "sweet spot" within the wake of a leader in which a trail can experience upwash which leads to reduced drag. Through this mechanism, aircraft can save significant amounts of fuel by flying at the sweet spot of the lead aircraft's wake. This dissertation provides two metrics of obtaining the sweet spot and evaluating the benefits to the trail aircraft at the sweet spot: a static and a dynamic study. The static study, similar to wind tunnel tests in which aircraft are statically placed in formation without trimming, investigates the induced aerodynamic forces and moments on the trail aircraft as it varies its position within the wake of the lead aircraft, and assigns the relative location of maximum lift-to-drag ratio as the static sweet spot. The dynamic study, similar to flight tests which account for trim, analyzes the control surface deflection and thrusts for the trail aircraft as it varies its position within the lead's wake and assigns the location of minimum thrust as the dynamic sweet spot. The static and dynamic analyses are applied to aircraft formations with different relative sizes and varying configurations of trail aircraft such as a flying-wing and a conventional aircraft. Results indicate that sweet spot locations and associated bene ts are dependent on the weight of the leader and the relative sizes of the aircraft pair in the formation. This dissertation then augments the fuel-savings by investigating alternate lateral trimming methods to reduce the need for drag-inducing control effector deflections required at the static sweet spot. Internal fuel transfer and differential thrusting are employed to increase the thrust saved at the static sweet spot, making it comparable to the dynamic sweet spot. Formation simulations of extended durations are also studied to understand the impact of significant weight variations in the leader on the formation benefits. In longduration flights, the lead and trail aircraft weights decrease due to fuel burn. Since the upwash generated by the leader decreases with lift and weight as fuel is burned, the magnitudes of the non-uniform wind induced and thus bene ts for the trail decrease. This decrease is investigated for a 6.5-hour formation simulation. Although there is a reduction in the benefits with time, the overall benefits of flying in formation is significant enough to motivate formations of such long durations. Finally, the feasibility of formation flying is also considered from a perspective of comfort levels for passengers or aircrew in the trail aircraft. Using international standards for likely reactions of a person subjected to discomforts characterized by vibrations, it is shown that there is no additional detrimental degradation of comfort levels for a person onboard a trail aircraft in formation as compared to a solo flight.

Decadal Survey of Civil Aeronautics
Decadal Survey of Civil Aeronautics

Author: National Research Council

Publisher: National Academies Press

Published: 2006-10-27

Total Pages: 212

ISBN-13: 0309101581

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The U.S. air transportation system is very important for our economic well-being and national security. The nation is also the global leader in civil and military aeronautics, a position that needs to be maintained to help assure a strong future for the domestic and international air transportation system. Strong action is needed, however, to ensure that leadership role continues. To that end, the Congress and NASA requested the NRC to undertake a decadal survey of civil aeronautics research and technology (R&T) priorities that would help NASA fulfill its responsibility to preserve U.S. leadership in aeronautics technology. This report presents a set of strategic objectives for the next decade of R&T. It provides a set of high-priority R&T challengesâ€"-characterized by five common themesâ€"-for both NASA and non-NASA researchers, and an analysis of key barriers that must be overcome to reach the strategic objectives. The report also notes the importance of synergies between civil aeronautics R&T objectives and those of national security.