Formation flying
[1] Birds have been known to receive performance benefits from formation flight for over a century, through aerodynamic theory of Wieselsberger in 1914.
[3] By World War II, pilots had discovered other strategic advantages to formation flight such as enhanced stability and optimal visibility.
The drag reduction occurred in the drafting is due to a reduction in flow speed in the wake of a leading vehicle, reducing the amount the flow needs to accelerate to move around the body, reducing pressure in front of the trailing vehicle.
This leads to a lesser pressure differential between the frontal and rear projected surfaces of the body, and hence, less drag.
The flow becomes separated from the airfoil and rotates about a low pressure wake that forms the core of the vortex.
This vortex acts to change the direction of the flow for trailing aircraft, increasing the lift over a segment of the wing and allowing for a reduction in induced drag by lowering its angle of attack.
Haffner (1977) experimented with birds flying in wind tunnels and calculated a range extension of a more conservative value of 22%.
Willis et al (2007) found that optimal phasing of flaps accounts for 20% of power saving, suggesting that positioning is more important than perfectly caching the oncoming vortex.
[8][1] Studies of birds have shown that the V formation can greatly enhance the overall aerodynamic efficiency by reducing the drag and thereby increasing the flight range.
[9] Insect swarms are a collective animal behavior that is an area of active research for the application of drones.
[10] The smallest unit of a formation is called a section or element, consisting of two aircraft; these pilots are a leader and wingman.
[11]: 8 A nonstandard formation results when the flight leader has requested, and air traffic control has approved dimensions that do not conform with the stated boundaries; when operating within an authorized altitude reservation or under the provisions of a Letter of Agreement; or when flight operations are being conducted in a specially-designated airspace.
[12]: Art 17.01 The challenge of achieving safe formation flight by unmanned aerial vehicles has been extensively investigated in the 21st century with aircraft and spacecraft systems.
For aerial vehicles the advantages of performing formation flight include fuel saving,[13] improved efficiency in air traffic control and cooperative task allocation.
In 2013, the Air Force Research Laboratory's Surfing Aircraft Vortices for Energy project showed 10–15% in fuel savings, installed on two Boeing C-17 Globemaster IIIs.
In 2017, NASA measured 8–10% lower fuel flow with two Gulfstream III aircraft on wake surfing test flights.
In 2018, the ecoDemonstrator, a Boeing 777F freighter from FedEx Express, had its fuel consumption reduced by 5–10% with the autopilot maintaining the 4,000 ft (1.2 km) separation based on ADS-B and TCAS information.
[16] By taking advantage of wake updraft like migrating birds (biomimicry), Airbus believes an aircraft can save 5–10% of fuel by flying 1.5–2 nmi (2.8–3.7 km) behind the preceding one.
Certification for shorter separation is enabled by ADS-B in oceanic airspace, and the only modification required would be flight control systems software.
Comfort would not be affected and trials are limited to two aircraft to reduce complexity but the concept could be expanded to include more.
Commercial operations could begin in 2025 with airline schedule adjustments, and other manufacturers' aircraft could be included.
