Sweepback

[Ref. Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 5-18, 5-19]

Source: FAA-H-8083-25B Page 5-48

Sweepback

Function of Sweepback design?

  1.  (Main function) to delay the onset of compressibility during high-speed flight
  2. provide (relatively stronger) Positive Lateral Stability  – roll back and restore to its original flight attitude
  3. provide Positive Directional Stability

 

HOW Sweepback helps in delaying the onset of compressibility?

  • The concept is that only the component of the airflow perpendicular to the leading edge of the wing that affects pressure distribution and formation of shock waves – A wing with sweepback is struck by the same airflow at an angle smaller than 90°.

HOW Sweepback helps in lateral Stability?

  • the lower wing presents its leading edge at an angle that is more perpendicular to the RAF (relative airflow), as a result, the lower wing acquires more lift, rises, and the aircraft is restored to its original flight attitude.

HOW Sweepback helps in Directional Stability?

  • When aircraft yaw to one side, the airspeed of the forward wing increases and it acquires more drag than the back wing. The additional drag on the forward wing pulls the wing back and so the nose of the aircraft turning back to its original path.

 

Disadvantage of using swept wings?

stall at the wingtips first (rather than at the wing roots) – wingtip stall causes the CL (CP) to move forward on the wing, forcing the nose to rise further.

Notes: The tendency for tip stall is greatest when wing sweep and taper are combined.

 

Read More –

# Sweepback and Taper wing – Stalling at the wing tip first

# Dutch roll (Free Directional Oscillations) – Lateral stability > Directional stability

#swept #back

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