Aerodynamic Performance of Extended Formation Flight

Ning, Andrew; Flanzer, Tristan C.; Kroo, Ilan

doi:10.2514/6.2010-1240

Cited by 14 publications

(3 citation statements)

References 30 publications

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“…15 Ning examined "Extended" formation flight (aircraft separated longitudinally by more than 10 spans), and showed an induced drag reduction of 38-45% for several different three-ship formation geometries including uncertainties in relative position within the formation. 16 In addition to theoretical results, several flight research programs in the last two decades have validated the predicted drag reduction and fuel savings benefit from formation flight. In 1995, Hummel documented a 15% power reduction for the trail aircraft of two Dornier (Dornier Technologie GmbH Co. & KG, Uhldingen-Mühlhofen, Germany) Do-28 aircraft.…”

mentioning

confidence: 95%

An Initial Flight Investigation of Formation Flight for Drag Reduction on the C-17 Aircraft

Pahle

Berger

Venti³

et al. 2012

AIAA Atmospheric Flight Mechanics Conference

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Many theoretical and experimental studies have shown that aircraft flying in formation could experience significant reductions in fuel use compared to solo flight. To date, formation flight for aerodynamic benefit has not been thoroughly explored in flight for large transport-class vehicles. This paper summarizes flight data gathered during several two-ship, C-17 formation flights at a single flight condition of 275 knots, at 25,000 ft MSL. Stabilized test points were flown with the trail aircraft at 1,000 and 3,000 ft aft of the lead aircraft at selected cross track and vertical offset locations within the estimated area of influence of the vortex generated by the lead aircraft. Flight data recorded at test points within the vortex from the lead aircraft are compared to data recorded at tare flight-test points outside of the influence of the vortex. Since drag was not measured directly, reductions in fuel flow and thrust for level flight are used as a proxy for drag reduction. Estimated thrust and measured fuel flow reductions were documented at several trail test point locations within the area of influence of the lead's vortex. The maximum average fuel flow reduction was approximately 7-8%, compared to the tare points flown before and after the test points. Although incomplete, the data suggests that regions with fuel flow and thrust reduction greater than 10% compared to the tare test points exist within the vortex area of influence. Nomenclature AFF = autonomous formation flight AWODS = advanced wireless open data system F = engine thrust, lbf FFS = formation flight system HUD = heads up display KCAS = knots calibrated airspeed NASA = National Aeronautics and Space Administration N2 = engine core rotor speed, percent RPM SKE = station keeping equipment USAF = United States Air Force V= velocity w f = fuel flow, pounds per hour Y offset = cross-track distance between vehicle fuselage centerlines, ft Z offset = vertical distance between vehicle fuselage waterlines, ft δ a = aileron deflection, deg δ s = spoiler deflection, deg ____________________________

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mentioning

confidence: 95%

An Initial Flight Investigation of Formation Flight for Drag Reduction on the C-17 Aircraft

Pahle

Berger

Venti³

et al. 2012

AIAA Atmospheric Flight Mechanics Conference

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“…interaction of two large transport aircraft in formation flight. Earlier studies include Bangash et al (2006) and Ning, Flanzer, and Kroo (2011). The UCT study was based on physical and aerodynamic parameters of a Boeing 747 aircraft extracted from an paper by Heffley and Jewell (1972) and the wing model was simplified to remove dihedral and sweep.…”

Section: Modellingmentioning

confidence: 99%

Large transport aircraft: Solving control challenges of the future

Jones

2014

Annual Reviews in Control

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“…The result is a forward-tilted lift vector that provides increased lift and a reduction in induced drag and can lead to significant energy savings. 13 Recently, Ning et al 14 performed an investigation of several factors affecting the benefits and feasibility of ex-tended formation flight for three aircraft in canonical echelon and V-type arrangements. These factors included wake roll-up, vortex core size, vortex decay and gust effects.…”

Section: Introductionmentioning

confidence: 99%

Transient Encounters of a NACA0012 Wing with a Streamwise-Oriented Vortex

Garmann

Visbal

2015

45th AIAA Fluid Dynamics Conference

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A high-fidelity numerical study has been conducted to examine the unsteady interactions resulting from a finite wing maneuvering into a streamwise-oriented vortex as a representative problem of wake encounters. A NACA0012 wing at an angle of α = 4 • and operating at a Reynolds number of Re = 2.0 × 10 5 is dynamically maneuvered into the path of a stationary vortex, and the transient encounter is analyzed for three side-slip velocities corresponding to 10%, 20%, and 40% of the free stream. The wing is shown to traverse a range of flow regimes, including instances of vortex pairing of the tip and incident vortices that lead to mutual induction and attenuation of the pair, tip vortex suppression as the impingement passes inboard of the wingtip, and induced separation that precipitates an abrupt transition at the leading edge. The overall flow structure is mostly consistent among the wing speeds examined, indicating an almost quasi-stationary response with relative vortex position. However, a notable lag is observed in the development of a spiraling instability in the incident vortex just upstream of the wing. With slower encounter speeds, the vortex core exhibits a pronounced spiraling undulation that persists farther upstream earlier in the motion. The advanced development is attributed to prolonged exposure to the adverse pressure gradient from stagnation on the underside of the wing that decelerates the core axial flow below known stability bounds of the vortex. Additionally, a dynamic loading effect is identified prior to the vortex crossing inboard of the wingtip, whereby the incident structure's relative position at peak loading shifts outboard with increased wing speed. The peak magnitudes of lift, pitching moment, and rolling moment coefficients are also shown to scale proportionally with the wing's side-slip speed as they are predicated upon an enhanced tip vortex development. In all cases as the wing approaches the vortex, an upstream progression of separation, transition, and reattachment over the leading edge leads, which forward tilts the force vector and reduces the drag. Once the vortex is brought inboard, however, the drag saturates, and the other quantities exhibit a nearly quasi-stationary response with vortex position as the wingtip unloads.

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Aerodynamic Performance of Extended Formation Flight

Cited by 14 publications

References 30 publications

An Initial Flight Investigation of Formation Flight for Drag Reduction on the C-17 Aircraft

An Initial Flight Investigation of Formation Flight for Drag Reduction on the C-17 Aircraft

Large transport aircraft: Solving control challenges of the future

Transient Encounters of a NACA0012 Wing with a Streamwise-Oriented Vortex

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