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AE 2350 Lecture Notes #8

AE 2350 Lecture Notes #8. April 30, 1999. We 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 drag Read Chapter 8 of text.

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AE 2350 Lecture Notes #8

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  1. AE 2350 Lecture Notes #8 April 30, 1999

  2. We 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 drag • Read Chapter 8 of text.

  3. Airfoil Drag Polar Cd vs. Cl Rough airfoils have turbulent flow over them, high drag. Smooth airfoils have laminar flow over at least a portion of the surface. Low Drag.

  4. Form Drag Form drag may be reduced by proper design, and streamlining the shape. Source: http://www.allstar.fiu.edu/aerojava/flight46.htm

  5. Supersonic wave Drag For a given airfoil or wing or aircraft, as the Mach number is increased, the drag begins to increase above a freestream Mach number of 0.8 or so due to shock waves that form around the configuration.

  6. Shock waves

  7. How 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.

  8. How can shock waves be minimized? Use sweep. 0.8cos30 30  sweep M= 0.8

  9. In your design... • The Maximum Mach number is 2.0 • Wings for supersonic fighters are designed to reduce wave drag up to 80% of the Maximum speed. • In our case, 80% of 2 is 1.6. • If we use a wing leading edge sweep angle of 60 degrees or so, the Mach number normal to the leading edge is 1.6 cos 60°=0.8

  10. Effect of Thickness and Sweep on Wave Drag Source: http://www.hq.nasa.gov/office/pao/History/SP-468/ch10-4.htm

  11. Supercritical Airfoils Their shape is modified to keep the Mach number on the airfoils from exceeding 1.1 or so, under cruise conditions.

  12. Conventional vs. Supercritical Airfoils

  13. Wing Drag • Since a wing is made up of airfoils, it has • skin friction drag • form drag • wave drag at high speeds, and • Induced drag due to tip vortices

  14. TIP VORTICES

  15. Effect of Tip Vortices Downwash

  16. Downwash changes lift direction Lift Direction without downwash New Lift Direction including downwash Wind direction without downwash a V Downwash New wind direction including downwash

  17. Induced Drag Induced drag is caused by the downward rotation of the freestream velocity, which causes a clockwise rotation of the lift force. From AE 2020 theory, e= Oswald efficiency factor

  18. Parasite Drag and Interference Drag Parasite Drag is simply Skin Friction Drag+ Form Drag + Interference Drag + Wave Drag

  19. Variation of Drag with Speed Induced drag decreases as V increases, because we need less values of CL at high speeds. Other drag forces (form, skin friction , interference) increase. Result: Drag first drops, then rises.

  20. At High Values of a Wings Stall We need high CL to take-off and land at low speeds. http://www.zenithair.com/stolch801/design/design.html

  21. Achieving High Lift

  22. One form of flaps, called Fowler flaps increase the chord length as the flap is deployed.

  23. How do slats and flaps help? 1. They increase the camber as and when needed- during take-off and landing. High energy air from the bottom side of the airfoil flows through the gap to the upper side, energizes slow speed molecules, and keeps the flow from stalling.

  24. Leading Edge SlatsHelp avoid stall near the leading edge

  25. High Lift also Causes High Drag

  26. MIG-29 Length: 14.87mWingspan: 11.36mHeight: 4.73mWeight Empty: 10 900kg Max T/O: 18 500kgMax Speed: Mach 2.3Range: 2100kmCeiling: 17 000mPowerplant: Two Klimov/Sarkisov RD-33 turbofansThrust: 98.8kN

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