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.

A new Approach to Aerodynamic Performance of Aircraft under Turbulent Atmospheric Conditions

Abstract: In the present study the influence of atmospheric turbulence on aircraft performance has been investigated and a relation between flight physics and meteorology has been established. Special attention was paid on aircraft with natural laminar flow airfoils because they exhibit an additional possibility of performance loss due to increased drag caused by a premature laminar-turbulent transition. A theoretical analysis was performed and the aerodynamic problem was extracted from the performance problem. A new wing glove for the G109b measurement aircraft as well as measurement equipment capable of detecting unsteady aerodynamic effects were developed. In-flight measurements for the validation of performance loss theories were carried out resulting in a new approach to aircraft performance under turbulent atmospheric conditions. Generally, a loss of flight performance can be the result of decreased lift, increased drag or a combination of both. The aerodynamic state and therefore the possible influencing mechanisms of atmospheric turbulence vary with the flight condition. Based on aircraft performance considerations, three principal flight conditions were determined for an in-depth study of the aerodynamic state related to these flight conditions. The flight conditions are slow flight, best glide and cruise flight. A new wing glove with favorable characteristics for aerodynamic in-flight experiments, retaining the flying qualities of the aircraft besides the asymmetric configuration, has been designed. A survey of the base flow on the glove in non-turbulent conditions by means of flight tests, wind tunnel tests and numerical simulations was conducted prior to the investigations under turbulent conditions. The results were essential as baseline data and showed that the numerous design requirements for the new wing glove were fulfilled. The flight test results show that the assumption of steady inflow conditions is incorrect for flight in atmospheric turbulence. An elevated level of micro-scale turbulence in the atmosphere is related to increased angle of attack variations. Therefore, unsteady changes in the airfoil pressure distribution are prevalent when an elevated turbulence level is encountered. Turbulence levels of 0.5% and more, which lead to different transition scenarios according to the results from flat plate experiments in transition research, do not occur in only light atmospheric turbulence, which is in turn the prerequisite for almost steady pressure distributions. The unsteady lift variations related to the angle of attack variations due to gusts are well predicted by unsteady thin-airfoil theory. A quasi-stationary approach does not cover the entire unsteady lift effects but in the case of laminar airfoils it predicts when the laminar drag bucket is left and airfoil drag increases. Especially in slow flight very close to the upper limit of the laminar drag bucket, angle of attack variations lead to increased airfoil drag. Flying at a lower angle of attack simply solves this problem. Only a slight increase in velocity is required to lower that angle of attack sufficiently.

System for controlling flight direction

Abstract: An aircraft that is enabled to turn in a desired direction, and a method for controlling the flight direction of an aircraft, by employing differential drag on the respective wings. A control means that receives a control signal indicating a left turn increases the incidence angle on the left wing and reduces it on the right wing. For a right turn the opposite action is performed. The aircraft comprises airfoils that have increased drag as the incidence angle increases but have a generally constant lift.

Separation control on high Reynolds number multi-element airfoils

Abstract: Small surface-mounted vortex generators were investigated as means for the control of a boundary-layer separation on a 2D single-flap three-element high-lift system at near-flight Reynolds numbers and in landing configurations. Wind-tunnel results obtained for small vane-type vortex generators mounted on a multielement airfoil showed that vortex generators as small as 0.18 percent of total chord can effectively reduce or eliminate boundary-layer separation on the flap at approach conditions. It was found that both the outerrotating and the corotating streamwise vortices were effective in reducing flow separation.

Aerodynamic Analysis of Aircraft Wing

Abstract: Aerodynamic problems in general are often difficult to solve by analytics analysis. Experimental or numerical simulation can be used to analyze these computational models. However, due to the large expenses required in the experimental method, the numerical method is more preferred. This paper presents the modeling and simulating processes of computational fluid dynamic (CFD) problem on a aircraft wing model, using typical section as NACA 2412 airfoil. This wing model might be chosen in the future experimental design. ANSYS Fluent is used to analyze the pressure and velocity distribution on the surface of wing. The lift and drag forces are also determined by ANSYS Structural. Additionally, the coefficients of lift and drag forces can be calculated through the data obtained when the relative velocity inlet between the airflow and airfoil changes from 0 to 50 m/s. The numerical results shown are compatible with those of the theory, thus suggesting a reliable alternative to predict the aerodynamic characteristics of the tested wing model in fabricating the Unmanned Aircraft Vehicles (UAVs).