Module 4 | Calculation of Lift and Drag of a Supersonic Wing

Flight in Supersonic Speed

• Air conditions for flight vary at different speeds
• supersonic airfoils must be designed:
  • Enough Lift is Generated
  • Efficient manner without compromising the performance of other aircraft components

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Shockwaves

• it is a result of a fluid being unable to react due to sudden disturbances caused by an object - the aircraft.

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@ Subsonic Speed and Mach One

• Wave Fronts react first before the aircraft

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@ Supersonic Speed

• Aircraft comes first before wave fronts react
• Thus, production of “Shock Cone”

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*As air flows going through the Shockwave…

• differences in density, temperature, and pressure
• perceived as an Explosion on the ground called “Sonic Boom”

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Supersonic Airfoil Design

• Different types of Drag in Supersonic Airfoil

  • Skin Friction Drag
  • Wave Drag
  • Drag resulting to the lift

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• How do we counter drag-inducing effects?

  • airfoil cross-section is generally made to be thin
  • Sharp leading edge
  • Sharp Trailing edge

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Characteristics of a Supersonic Airfoil Section

• Thinness
• Sharp Leading Edge
• Maximum Thickness at Half Chord
• Symmetry

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Characteristics of a Supersonic Airfoil Sections

• Infinitely thin, flat plate (best wing section in theory)
  • Not used due to structural integrity

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Double Wedge Airfoil Section

• Produce same amount of lift as flat plate
• more wave drag produced compared to flat plate due to cross sectional area

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Biconvex Airfoil Section

• Consists of two symmetrical circular arc
• Produces the same amount of lift as flat plate
• Produces the most amount of Wave Drag due to its cross sectional area
  • still used due to structural integrity and needs more cross sectional area

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Lift Generation

• All the Same

Drag Generation

• Biconvex (Highest)
• Double Wedge
• Flat Plate (Lowest)

Structural Integrity

• Biconvex (Highest)
• Double Wedge
• Flat Plate (Lowest)

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Ackeret Theory

• It is a linearized, first order theory based on sweeping assumptions which nevertheless give quite good results provided that the Mach number is not too low (Can be applied to supersonic) and the airfoil section is not too thick (relevant to thinness characteristics)
• Most basic theory (direct substitution)
• Wave drag is only considered
• Wave drag comprises of roughly 20% of the Total Drag

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