Abstract—This research paper investigates the aerodynamics of a twin-wing aircraft whilst taking-off and determines the influences of down wash from various angles of attacks with a positive stagger. The results identify that having different angles of attack allows more lift to be generated by the lower wing and maximizes the lift from the upper wing. Recommendations are made as to how twin-wings can be designed when low take-off speeds are needed, either by short runways, or heavy payloads. Index Terms—Aerodynamics, twin-wing, take-off speeds. I. INTRODUCTION In this research paper, the basis of a twin-wing is researched and investigated. Its aim is to determine the possibility of use with Unmanned Aerial Systems, UAV. This line of research follows as a side topic of twin-wing designs to achieve high altitude at low speed. It also included the Angle of Attach, AoA, for certain phases of flight. Before that is possible, they need to be effective at take-off with either short runways or high payloads. Previous research by the authors have investigated the possibility of the height and AoA of the wing and stagger [1]. Take-off introduces more aerodynamic influences than any other stage of flight, for example the influence of the ground affecting and directing flow underneath the lower wing in this case. Twin-wing design, commonly called Biplanes, used the extra wing to generate more lift with aircraft that had low power output and were initially designed without a full understanding of aerodynamics. These designs had lower stall speeds and high maneuverability than monoplanes, and characteristically other possibilities for current applications of UAVs. Their principal weakness was the struts used to make the system rigid by securing the upper and lower wing together and the upper wing to the fuselage. These struts were needed, and created additional drag, limiting its maximum speed. Various streamlining designs were used for the struts; however, the form drag was considerable and increased quadratically as speeds increases. Modern Manuscript received November 19, 2017; revised January 19, 2018. Ian R. McAndrew FRAeS is with Embry Riddle Aeronautical University-Worldwide, College of Aeronautical Science, Earnley, UK (e- mail: McAnd4f1@erau.edu). Elena Visnehvskaya is with Embry Riddle Aeronautical University- Worldwide, College of Arts and Sciences, Bitburg, Germany (e-mail: Navarroj1@erau.edu). Kenneth L. Witcher, Embry Riddle Aeronautical University-Worldwide, College of Aeronautical Science, Daytona Beach, Florida (e-mail: Witchea8@erau.edu). materials can now be used that eliminate the need for struts and produce a clean flow shape. Composites are rigid and it is possible to have twin-wings, which are independent. An additional feature, stagger, is the offset of the upper wing to the lower. Negative stagger has been typical to allow the pilot to enter the cockpit. There are four other demands, shown in Fig. 1. 1) Taxing and landing. 2) Vertically above to see other aircraft when increasing altitude. 3) Behind and 4) Below when descending. Negative stagger is not the effective position aerodynamically and the pilots, which needs outweigh all other. With a UAV, this stagger can be modified to suit aerodynamic needs and not the pilot means that requirement is removed. Fig. 1. Biplane with struts and negative stagger. Struts can be clearly seen in this Figure above and overall the drag is much higher than ideal configerations. The lower wing is attached directly to the fuselage, as conventional commerical aircraft. The upper wing is held in place with these strtuts to the cockpit opening and also the lower wing too. Stagger (offset) may have the three classic configurations, and are shown in Fig. 2. Their interactions have been researched and suggested alternatives made [2]. Positive stagger is better for higher lift, zero stagger offers little more than negative. AoA at each configuration will influence both with advantages and disadvantges the effectiveness, and this research is comparing the relationship at take-off. Fig. 2. Biplane with struts and negative stagger. Establishing Angle of Attach for NACA 6412 Twin-Wing on Take-off Downwash Influences on Lift and Drag Ian R. McAndrew, Elena Visnehvskaya, and Kenneth L. Witcher 255 International Journal of Materials, Mechanics and Manufacturing, Vol. 6, No. 4, August 2018 doi: 10.18178/ijmmm.2018.6.4.386