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GT AE 1350 - AE 1350 Lecture Notes

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AE 1350 Lecture Notes #8We have looked at..Airfoil Drag Polar Cd vs. ClForm DragSupersonic wave DragShock wavesHow can shock waves be minimized?Slide 8In your design...Effect of Thickness and Sweep on Wave DragSupercritical AirfoilsConventional vs. Supercritical AirfoilsWing DragTIP VORTICESEffect of Tip VorticesInduced DragVariation of Drag with SpeedAt High Values of a Wings StallAchieving High LiftSlide 20Slide 21Slide 22Slide 23Leading Edge Slats Help avoid stall near the leading edgeHigh Lift also Causes High DragAE 1350 Lecture Notes #8We have looked at..•Airfoil Nomenclature•Lift and Drag forces•Lift, Drag and Pressure Coefficients•The Three Sources of Drag:–skin friction drag in laminar and turbulent flow–form drag–wave dragAirfoil Drag Polar Cd vs. ClRough airfoilshave turbulent flowover them, high drag.Smooth airfoils havelaminar flow overat least a portionof the surface.Low Drag.Form DragSource: http://www.allstar.fiu.edu/aerojava/flight46.htmForm drag may be reducedby proper design, andstreamlining the shape.Supersonic wave DragFor a given airfoil or wing or aircraft, as the Mach numberis increased, the drag begins to increase above afreestream Mach number of 0.8 or so due to shock waves thatform around the configuration.Shock wavesHow can shock waves be minimized?•Use wing sweep.•Use supercritical airfoils, which keep the flow velocity over the airfoil and the local Mach number from exceeding Mach 1.1 or so.•Use area rule- the practice of making the aircraft cross section area (from nose to tail, including the wing) vary as smoothly as possible.How can shock waves be minimized?Use sweep.M= 0.80.8cos3030  sweepIn your design...•The Maximum Mach number is 0.85•Wings for supersonic fighters are designed to reduce wave drag up to 80% of the Maximum speed. •In our case, 80% of 0.85 is 0.68.•If we use a wing leading edge sweep angle of 30 degrees or so, the Mach number normal to the leading edge is 0.68 cos 30° ~ 0.6Effect of Thickness and Sweep on Wave DragSource: http://www.hq.nasa.gov/office/pao/History/SP-468/ch10-4.htmSupercritical AirfoilsTheir shape is modified to keep the Mach number on the airfoilsfrom exceeding 1.1 or so, under cruise conditions.Conventional vs. Supercritical AirfoilsWing Drag•Since a wing is made up of airfoils, it has–skin friction drag–profile drag–wave drag at high speeds, and–Induced drag due to tip vorticesTIP VORTICESEffect of Tip VorticesDownwashInduced DragInduced drag is caused by the downward rotation of the freestream velocity, which causes a clockwise rotation of the liftforce.From AE 2020 theory, e 2,ARCCLiDe= Oswald efficiency factorVariation of Drag with SpeedInduced drag decreases as Vincreases, because we need lessvalues of CL at high speeds.Other drag forces (form, skin friction , interference) increase.Result: Drag first drops, then rises.At High Values of  Wings StallWe need high CL to take-off and land at low speeds.http://www.zenithair.com/stolch801/design/design.htmlAchieving High LiftOne form of flaps, called Fowler flaps increase the chord length asthe flap is deployed.High energy air from the bottom side of the airfoilflows through the gap to the upper side, energizes slow speedmolecules, and keeps the flow from stalling.How do slats and flaps help?1. They increase the camber as and when needed- duringtake-off and landing.Leading Edge SlatsHelp avoid stall near the leading edgeHigh Lift also Causes High


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