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.

Cylindrical wing tip with helical slot

Abstract: The invention concerns a device having the shape of a spiral and/or helical slot cylindrical cavity (15) for reducing induced drag, tip vortex and to increase lift-drag ratio. The device securely fixed to the wing tip (10) or securely articulated to said wing tip, can be adapted to all profiles, in particular to aeroplane wings, to gliders, to helicopter blades and to driving, pusher or propelled airscrew tips such as wind turbine blades or for craft such as boats or submarines using lift or steering in their three-axis movement, vertical, horizontal and yawing. For existing rates of efficiency, the invention enables the use of low traction systems, longer and faster trips while consuming less energy or while producing more as with wind turbines for example, the use of greater loads, the increase and approach of aerodrome or airport transit/landing/take-off traffic more safely. When used in reverse (active surface/passive surface) on high-speed land vehicles or racing cars, said device fixed to each wing tip, produces a result inversely proportional to its speed. The faster the vehicle runs the less drag it produces and the more it adheres to the ground.

Drag of Spheroid-Cone Shaped Airship

Abstract: Drag coefficients of streamlined bodies and complete airships are compared to confirm some general trends. Data obtained from flight testing an electrically powered, helium-filled, dirigible balloon with a spheroid-cone hull form are analyzed. Wind-tunnel tests indicate that placing a cone behind a sphere reduces its drag coefficient by about 50%, but flight-test data suggest the drag coefficient of the spheroid-cone airship is relatively high. The influence of atmospheric turbulence and nonsteady flow effects are discussed.

Effects of Auxiliary Lift and Propulsion on Helicopter Vibration Reduction and Trim

Abstract: This paper examines the vibration reductions caused by the introduction of auxiliary lift and propulsion, individually, as well as in combination, on a light [5800-lb (2640 kg)] helicopter with a four-bladed hingeless rotor, at flight speeds close to the maximum cruise velocity of the baseline helicopter. The changes in trim (vehicle orientations and control settings) because of auxiliary lift and propulsion are also examined in detail, and the fundamental mechanisms that produce the changes in trim and associated vibration reductions are identified. Based on results using a comprehensive aeroelastic analysis, it was concluded that auxiliary lift, alone, produces relatively small reductions in vibration. On the other hand, significant vibration reductions were obtained through auxiliary propulsion alone. A combination of lift and propulsion was most effective and reduced the vibration index by over 90%. It was also observed that auxiliary lift significantly reduces the main rotor thrust but increases the nose-down pitch attitude and tip-path-plane forward tilt to provide the required propulsive force. This increases the downwash through the rotor disk and requires a larger rotor longitudinal cyclic pitch input. In contrast, auxiliary propulsion that minimizes vibration produces little reduction in main rotor thrust, but results in a slightly nose-up pitch attitude (the auxiliary propulsion exceeds vehicle drag) along with a backward tilt of the tip-path plane. This decreases the downwash through the rotor disk and requires a smaller rotor longitudinal cyclic pitch input. A combination of auxiliary lift and propulsion minimizes vibration results in an even larger backward tilt of the tip-path plane and a net upwash through the rotor disk. The rotor collective pitch undergoes little change as a result of auxiliary lift, even though the main rotor thrust is decreased. In contrast, for auxiliary propulsion it decreases significantly even though the rotor thrust undergoes only small reductions. This counterintuitive observation is explained. The reduced downwash with auxiliary propulsion, or upwash with combined lift and propulsion, puts the rotor in a partial autorotation state, drastically reducing the induced drag, main rotor torque, and power. Auxiliary lift produces modest reductions in main rotor power, primarily because of a reduced profile drag associated with lower rotor loading. Because the rotor loading is lower with auxiliary lift than with auxiliary propulsion, but larger vibration reductions are produced with the latter, it can be deduced that vibration reductions are less a result of “unloading” of the rotor per se and more because of overall changes in trim, especially the reduction in longitudinal cyclic pitch (seen with auxiliary propulsion).