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High Speed Flight

High Speed Flight. Chapter 7. Pressure Change. Pressure change affect the density of air pressure in its vicinity At low speeds (100-200mph) the density change is slight

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High Speed Flight

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  1. High Speed Flight Chapter 7

  2. Pressure Change • Pressure change affect the density of air pressure in its vicinity • At low speeds (100-200mph) the density change is slight • In low speed flight, the air is incompressible meaning that the density of the air flowing over the aircraft does not change from the surrounding ambient air

  3. Supersonic Flight • The Bell X-1 was the first taken to supersonic flight by Chuck Yeager Oct. 14, 1947. • The significance of the speed of sound is that sound is due to pressure disturbances in the air. • We hear sounds because of pressure disturbances being transmitted to our ears in wave like fashion through the air.

  4. Mach Number • M= true airspeed/speed of sound • M < 1 = subsonic • M > 1 = supersonic • M= 1= sonic • M < 0.8 = subsonic • M= 0.8 to 1.2= transonic • M= 1.2 to 5.0= supersonic • M> 5.0= hypersonic

  5. Shock Waves • Figure 7-2 A B C • Mach Wave • Shock Wave • Oblique Shock Wave

  6. Critical Mach Number • Critical mach number is the value of the free stream that causes the flow to reach mach 1 somewhere on the airfoil. • Figure 7-4A B • Bow wave

  7. Wave Drag • Wave Drag is the combined effect of energy loss across and the wake formed behind the shock wave. • At speeds slightly above critical mach number is due mostly to the energy dissipation. • Figure 7-5, 7-6, 7-7

  8. Swept Wings • Swept wings allowed for high critical Mach numbers. • Swept wing pros • Swept wing cons

  9. High Speed Airfoils • The ideal supersonic airfoil is one with a sharp leading edge. • Very poor low speed characteristics • Used for military fighters & missiles • Another desirable trait is to have the point of maximum thickness far back on the airfoil.

  10. Control Problems • Shock wave can cause separation to occur on the airfoil surfaces and form small wakes behind. • Vortex Generators • Supersonic flight at the junction of stabilizer and elevator can form a shock wave that prevents any influence of the elevator on the stabilizer. • All moveable surfaces

  11. Area Rule • Richard Whitcomb experimented with many wing-body shapes in a high speed wind tunnel. • Whitcomb found that for a low aspect ratio the drag rise in the transonic region. • Figure 7-16 • Sears-Haack/Coke bottle

  12. Hypersonic Flight • Traveling at above or below Mach not as good. Why? • Aerodynamic effects • Aircraft Concepts • Propulsion Systems

  13. Quiz on Chapter 7 Please take out a sheet of paper Include today’s date and your name

  14. Quiz on Chapter 7 • What is a critical Mach number? • List and explain one advantage and one disadvantage to the swept wing. • Explain the purpose of a vortex generator.

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