Longitudinal Stability (Pitching)

[Ref. Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 5-15]

Longitudinal Stability (Pitching)


Static longitudinal stability is dependent upon 3 factors:

1. Location of the wing with respect to the CG
2. Location of the horizontal tail surfaces with respect to the CG
3. Area or size of the tail surfaces



increase of power may tend to make the nose rise – this can be offset by “high thrust line” – line of thrust passes above the CG;

In contrast, “low thrust line” would tend to add the nose-up effect.

Design for positive longitudinal stability  – “Negative AOA on horizontal stabilizer” , “CG-CL-T”

  • wing’s CL is to the rear of the CG  – i.e CG-CL (Nose Heavy)
  • By setting the horizontal stabilizer at a slight negative AOA – in order to let the downwash to balance the aircraft (conterbalancing the “heavy” nose) and prevent the nose continually pitching downward – i.e CG-CL-T
    (Indeed, the downwash is air from the wings – This downwash strikes the top of the stabilizer and produces a downward pressure on tail)

Notes: Here, CL is also known as the center of pressure (CP)

HOW “Negative AOA on horizontal stabilizer”  helps the aircraft back to its longitudinal stability?

Airspeed ∝ Downwash ⇒ Nose and Attitude Changed ⇒ Airspeed Changed ⇒ Downward force on the tail Changed

Airspeed ↑ ⇒ Downwash ↑ ⇒ Nose up, climbing attitude ⇒ Airspeed ↓ ⇒ Downward force on the tail ↓

Airspeed ↓ ⇒ Downwash ↓ ⇒ Nose down, pitch down attitude ⇒ Airspeed ↑ ⇒ Downward force on the tail ↑


Read More –

# How CG and CP position affect nose pitching tendency?

CP, AOA , AC, CG – WHAT is…. and HOW is the relationship between

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