Experimental Determination of Lift and Lift Distributions for Wings In Formation Flight

Abstract

Experimental methods for the investigation of trailing vortex strengths, total lift, and lift distributions for three-dimensional wings in close proximity flight were developed. With these experiments we model compound aircraft flight either docked tip-to-tip, or flying in formation. There is a distinct lack of experimental formation flight data using three-dimensional wing models for tests. The absence of fixed walls on either end of the wing permits the development of the asymmetric shedding of vortices, and the determination of the asymmetric circulation distribution induced by the proximity of the leading wing. The pair consisted of a swept NACA-0012 non-cambered wing simulating one half of a leading aircraft and a rectangular cambered NACA 63-420 wing simulating the trailing aircraft. Important aspects of the work included theoretical development, experimental setup, data acquisition and processing, and results validation.Experimentally determining the lift for formation flight, in addition to the local flow behavior for a pair of wings, can provide valuable insight for the proposition of flying actual aircraft in formation to increase mission efficiency. To eliminate the need for bulky mounting stings and direct load measurement devices that can potentially interfere with the local flowfield, a minimally invasive velocity probe method is developed. A series of experiments were performed to assist with the development of the method. Velocity and vorticity distributions obtained along a near-field plane were processed to calculate wingtip vortex strengths. Additionally, vortex position instabilities and the shedding of vorticity inboard of the wingtips were observed. To determine the circulation distributions for the trailing wing, the initial method is modified. By processing velocity information acquired in a near-field plane, both the lift and induced drag were calculated for the trailing airfoil. Comparisons are made to directly measured loads and to results reported earlier. Directly measured lift and drag coefficients were found to agree with existing literature.iii DedicationCreation seems to come from imperfection. Creation of a significant entity when beginning with something imperfect is the ability to achieve. To every person who cannot, will not, and then does not give up nor give in when trying to accomplish what seems to be the impossible. You will prevail.iv Acknowledgements I would like to thank my primary advisor, Dr. Demetri Telionis, first and foremost for providing me with guidance as needed throughout the duration of my studies. He has always been available whenever I was in need of assistance. I would also like to extend appreciation to Dr. Pavlos Vlachos, and Dr. Saad Ragab for serving on my graduate advisory committee. Although I didn't often seek out their expertise, of which they both have much in their respective fields, I have no doubt that they would have welcomed my inquiries without hesitation.In addition to my technical advisors, I would like to express gratitude towards my pa...

Meta Aircraft Flight Dynamics

“…Their analysis showed a direct decrease in weight due to lower bending moment of the connected wing as well as an L∕D increase of 8-10% from the single-vehicle configuration [7]. Formation flight has also been investigated due to a potential increase in L∕D [8]. Magill et al considered two compound aircraft transport configurations where wing tips are docked permanently and another where the aircraft fly in close formation [9].…”

Velocity data-based determination of airfoil characteristics with circulation and fluid momentum change methods, including a control surface size independence test

“…(3)) can be used, taking advantage of the velocity circulation around the profile. In Gibbs et al (2005), the velocity circulation was measured to illustrate a span-wise distribution of the lift force for a wing in formation flight. The method was used by Dobrev and Massouh (2011) to determine sectional loads of the rotating wind turbine blade.…”

“…In Dobrev and Massouh (2011), where the circulation method was applied, the authors do not examine the size of the contour and no verification of the obtained lift results was proposed neither. In Gibbs et al (2005), an attempt to expand the velocity circulation measurement procedure was proposed by using partial contours apart from the full ones. Large discrepancies in magnitudes of circulation were observed, however.…”

Experimental Control of Two Connected Fixed Wing Aircraft

“…The concept of flying in the trailing vortex has been a source of research for quite sometime [2] with problems such as time-delay effects [3] or self spacing issues [4]. Although numerous work has been done on formation flight with benefits categorized, it is a potentially dangerous maneuver and quite costly in terms of control to ensure station keeping in such a turbulent flow regime [5][6][7].…”