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UAS Airframe Design
Published in R. Kurt Barnhart, Douglas M. Marshall, Eric J. Shappee, Introduction to Unmanned Aircraft Systems, 2021
Michael T. Most, Michael Stroup
Drag is the sum of all forces opposing movement of an aircraft through the viscous medium of the atmosphere. Total aircraft drag develops from multiple sources. As stated, creating lift produces induced drag, the result of tip vortices. High-pressure air spills from under lower wing surface, curling around the wingtips into the low-pressure area above to create a swirl of air, or vortex, trailing off the tip and behind and below the aircraft. The dissipation of energy in these vortices is the source of drag attributable to a wing generating lift. The horizontal tail can also contribute induced drag. The remainder of total drag is referred to as parasite drag. Components of parasite drag include skin friction, form drag, base drag, interference drag, cooling drag, leakage drag, and the strong influence of compressibility effects, sometimes referred to as compressibility drag or wave drag. Because airflows may pass through the speed of sound (Mach) as it accelerates over the cambered surfaces of airfoils and other curved surfaces of the airframe (e.g., the canopy) when the airspeed of the aircraft is around 75% of Mach (or, 0.75M), compressibility drag is a factor in the design of a very few UA (e.g., the Lockheed Martin QF-16, the 3+ Mach D-21 developed at Lockheed’s Skunk Works® and Boeing’s scramjet-powered, hypersonic X-51 Waverider) (Figures 10.1 and 10.2).
Elementary Aerodynamics
Published in Rama B. Bhat, Principles of Aeroelasticity, 2018
There are four types of drag: skin friction drag, form drag, induced drag, and wave drag. They can also be categorized in two ways: parasitic and induced. The sum of all the components of drag makes up the total drag force. Induced drag or drag due to lift is a small amount of excess (lift) force generated in the opposite direction of the motion. Wave drag generally only occurs when an airplane is flying near the speed of sound (transonic) or faster (supersonic). The form drag, also called pressure drag, is affected by the shape of the body. A smooth, streamlined shape generates less form drag than a blunt body. Automobiles are streamlined to increase gas mileage. Another type of drag, called interference drag, is a component of parasitic drag, which is caused by vortices. Whenever two surfaces meet at a sharp angle, the airflow has a tendency to form a vortex that contributes to drag.
Canard Airplanes and Biplanes
Published in James DeLaurier, Aircraft Design Concepts, 2022
This study, as well as others, showed that the wing's lift is diminished by the downwash from the canard. The top figure shows the wing-alone lift distribution. The middle figure shows the wing's lift decrement caused by the canard; and in the bottom figure, the decrement is added to the wing-alone lift to give the modified span-wise lift distribution. This significantly reduces the wing's efficiency because the span-wise loading is far from the elliptical shape that gives the minimum induced drag for a given total lift. Observe in the middle figure how the decrement approximately follows the span of the canard. This observation will prove useful for an approximate analysis described further on.
Experimental study of a winglet added small wind turbine with a flanged diffuser for domestic applications
Published in International Journal of Ambient Energy, 2022
M. Udhayakumar, P. Saravanan, K.M. Parammasivam
It's a small attachment that has the same cross section of the blade at the tip of the blade. The objective of mounting the winglet to the blades of wind turbine is to reduce the total blade drag and increase the turbine's aerodynamic efficiency. If the additional drag of the winglet is less than the reduction of the induced drag on the remaining blade length, the total drag is obtained. The design of winglet optimises drag reduction, maximises power generation and minimises thrust increase (Johansen and Sorensen 2006). The pressure difference in the operating wind turbine blade is the inward span wise flow on the suction side and the outward span wise flow on the pressure side near the tip. There is a vorticity at the trailing edge, which is the origin of the induced drag. A winglet is a device that reduces the span wise flow, diffuses and moves the tip vortex away from the rotor plane reducing the induced drag on the blade (Dreese 2000). A range of parameters are involved in the winglet design, such as winglet height, angle of sweep, angle of tip, radius of curvature, angle of toe and twist angle as shown in Figure 1. In the aerodynamics perspective, it is proposed to study the effect of winglet on this small wind turbine rotor efficiency. Teak wood blade model was fabricated with a scale of 1:120 and used as a standard for GFRP (Glass Fiber Reinforced Polymer) blades (Figures 2 and 3) (Martin and Hansen 2008).
Vorticity Confinement Applied to Accurate Prediction of Convection of Wing Tip Vortices and Induced Drag
Published in International Journal of Computational Fluid Dynamics, 2021
Alex Povitsky, Kristopher C. Pierson
Induced drag becomes the major component of drag for aircraft in subsonic flight with shorter aspect ratio wings, higher angle of attack, and higher Mach numbers. Utilisation of computational fluid dynamics (CFD) for the design of wing planforms for the purpose of induced drag reduction requires multi-variant design optimisation using moderately sized numerical discretisation grids that allow for only a few grid points per tip vortex diameter. This causes significant numerical dissipation of modelled tip vortices that was overcome in the current study by combined use of VC and TVD.