Lift-induced drag

About: Lift-induced drag is a research topic. Over the lifetime, 2861 publications have been published within this topic receiving 41094 citations.

The effects of wing twist in slow-speed flapping flight of birds: Trading brute force against efficiency

Abstract: In aircraft propellers that are used to propel aircraft forward at some speed, propeller blade twist is important to make the individual propeller 'wings' operate at a relatively constant effective angle of attack over the full span Wing twist is sometimes also assumed to be essential in flapping flight, especially in bird flight For small insects, it has however been shown that wing twist has little effect on the forces generated by a flapping wing The unimportance of twist was attributed to the prominent role of unsteady aerodynamic mechanisms These were recently also shown to be important in bird flight It has therefore become necessary to verify the role of wing twist in the flapping flight of birds The aim of the study is to compare the efficiency and the aerodynamic forces of twisted and non-twisted wings that mimic the slow-speed flapping flight of birds The analyses were performed by using physical models with different amounts of spanwise twist (0°, 10°, 40°) The flow was mapped in three-dimensions using digital particle image velocimetry The spanwise circulation, the induced drag, the lift-to-drag ratio and the span efficiency were determined Twist and Strouhal number (St) both determine the local effective angles of attack of the flapping wing Wings with low average effective angles of attack (resulting from high twist and/or low St) are more efficient, but generate significantly lower aerodynamic forces High average effective angles of attack result in lower efficiency and high aerodynamic forces Efficiency and the magnitude of aerodynamic forces are competing parameters Wing twist is beneficial only in the cases where efficiency is most important-eg in cruising flight Take-off, landing and maneuvering, however, require large and robust aerodynamic forces to be generated The additional force comes at the cost of efficiency, but it enables birds to perform extreme manoeuvres, increasing their overall fitness

Scale Effect on Clark Y Airfoil Characteristics From NACA Full-Scale Wind-Tunnel Tests

Abstract: This report presents the results of wind tunnel tests conducted to determine the aerodynamic characteristics of the Clark Y airfoil over a large range of Reynolds numbers. Three airfoils of aspect ratio 6 and with 4, 6, and 8 foot chords were tested at velocities between 25 and 118 miles per hour, and the characteristics were obtained for Reynolds numbers (based on the airfoil chord) in the range between 1,000,000 and 9,000,000 at the low angles of attack, and between 1,000,000 and 6,000,000 at maximum lift. With increasing Reynolds number the airfoil characteristics are affected in the following manner: the drag at zero lift decreases, the maximum lift increases, the slope of the lift curve increases, the angle of zero lift occurs at smaller negative angles, and the pitching moment at zero lift does not change appreciably.

Vertical take-off and landing aircraft

Abstract: The present invention discloses an aircraft capable of vertical take-off and landing. The aircraft comprises a single constant speed variable pitch propeller (3), a fuselage (2), an empennage (21, 22) and main wings (6) fixed to the fuselage (2); arranged similar to a conventional aircraft, but sized and positioned for vertical flight. A stator is positioned a minimal distance behind the propeller so as to compensate the torque caused by the propeller. The aircraft comprises high lift and high drag devices such as flaps (19) and a leading edge slat (7) on the main wings (6), and a fuselage spoiler (18). The positioning of the center of gravity (23) allows for a stable nose-up take-off and landing, NUTOL, position. The propeller generated airflow (PGA) over the main wings (6) and high lift and drag devices (7, 18, 19) creates lift and drag forces. Due to the NUTOL position, the sum of the propeller thrust, the lift forces and the drag forces on the aircraft results in a vertical force and no forward (horizontal) force, thus enabling vertical flight. Roll, pitch and yaw control is achieved by aerodynamic surfaces positioned inside and outside of the PGA.