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Supersonic Aerodynamics Key Points

Prepare for your supersonic aerodynamics tests with these key points:

Aerodynamic Center

  • Point about which pitching moment remains constant. 0.25 MAC

Center of Pressure

  • Point where lift acts.

Critical Mach

  • Supersonic flow first appears.

Supercritical Airfoil

  • Delays shock formation. 0.6 t/c

Aileron Buzz

  • A very rapid oscillation of an aileron, at certain critical airspeeds on some aircraft, which does not usually reach large magnitudes nor become dangerous. It is often caused by shock-induced separation of the boundary layer.

Aileron Snatch

  • A violent back and forth movement of the aileron control as airflow changes over the surface.

Drag Divergence

  • A phenomenon that occurs when an airfoil’s drag increases sharply and requires substantial increases in power (thrust) to produce further increases in speed.

Mach Buffet

  • The airflow separation behind a shock wave pressure barrier caused by airflow over flight surfaces exceeding the speed of sound.
  • Buffet free = No shock stall

Mach Tuck

  • The result of an aft shift in the center of pressure causing a nose-down pitching movement.

Shock Stall

  • Flow separation at the smallest angle of attack.

Maximum Operating Limit Speed (Mmo) in Mach

  • An airplane’s maximum certificated Mach number. Any excursion past Mmo, whether intentional or accidental, may cause induced flow separation of the boundary layer air over the ailerons and elevators of an airplane and result in a loss of control surface authority and/or control surface buzz or snatch.

Accelerated Stall

  • A jet aeroplane cruises buffet free at high constant altitude in significant turbulence. Which type of stall can occur if this aeroplane decelerates?
  • Not Shock stall, buffet free.
  • Not Deep Stall, Swept wing (tendency to pitch-up approaching CL max or T-tail due to blanketing).
  • Significant Turbulence = causes large changes in angle of attack. Cruising velocity = at angle of attack below CL max.
  • Deceleration in significant turbulence will cause the angle of attack to change to CL max Angle of attack; causing it to stall at a speed above the Stalling speed.

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