Analysis of the flight characteristics of a highly swept cranked flying wing by means of an experimental test

Abstract

The Flying V is a concept proposed and patented by Benad and Airbus Operations GmbH, which is a flying wing aircraft in the shape of the letter V. Multiple researches already showed promising results, with a 25% increased lift over drag ratio compared to conventional aircraft like the Airbus A350-900. Before research of sub-scale flight testing can be conducted, research into the flight characteristics is necessary. Based on the identification of the problems, the research question for the thesis research is defined as: "What are the flight characteristics of the Flying V sub-scale model at approach speed and high angles of attack?" In total, three different wind tunnel campaigns were conducted at the Open Jet Facility of the Delft University of Technology. During the wind tunnel campaigns, experiments were conducted to acquire data through balance measurements and flow visualisation techniques by means of oil, tufts ans smoke. The untrimmed maximum lift coefficient was estimated to be 1.09 at 41 degrees angle of attack and positive stability was found up to 20 degrees angle of attack. Flow visualisation results showed that large leading edge vortices acted on the surface of the wing, originating from the root towards the crank of the wing. A leading edge separated vortex spread over the wingtip, which originated at the kink of the leading edge. Investigations into the trimmed flight of the aircraft concluded that due to trim limitations the centre of gravity is bound between 1.345 and 1.425 meter behind the nose. The centre of gravity has an optimal location at 1.365 meter behind the nose, providing a static margin of about 9%. With the trimmed lift curve and the optimal centre of gravity location, the flight speed of 35 meter per second can be flown at 3.6 degrees angle of attack. Due to limitation in maximum deflection of the control surfaces, the maximum lift coefficient is estimated at 0.95, at 28.5 degrees angle of attack at a stall speed of 14.8 meter per second. At 20 degrees angle of attack, where the static stability switches from positive to negative, the lift coefficient is estimated at 0.73 at 17.2 meter per second and is defined as the 'safe' stall speed. Taking the FAA and ICAO regulations into account, the approach speed is estimated at 19.2 meter per second, at an angle of attack of 15.9 degrees at a lift coefficient of 0.58.