High%20Speed%20Flight

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 lt 1 subsonic
• M gt 1 supersonic
• M 1 sonic
• M lt 0.8 subsonic
• M 0.8 to 1.2 transonic
• M 1.2 to 5.0 supersonic
• Mgt 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 todays 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.