AA.I.D.K1FAA-S-ACS-11A · Nov 2023Knowledge
Aerodynamics of large transport category airplanes, including flight characteristics of...
Aerodynamics of large transport category airplanes, including flight characteristics of swept wing airplanes (e.g., Mach buffet).
Bottom line
Mach buffet arises when airflow separates on the upper surface of a wing behind a shock wave. Mach buffet is a function of the speed of the airflow over the wing, not necessarily the forward speed of the airplane. Swept wings delay shock wave formation and raise critical Mach number, but tend to stall at the wingtips rather than the roots.
Key numbers
| Number | What it means |
|---|---|
| Exceeds critical Mach by 5 to 10 percent for most airfoils | Force divergence |
| Activates five to seven percent above stall speed | Stick shaker |
| Approximately 1 to 2 in. in height | Vortex generators |
FAA references
- AFH ch. 16 (p. 16-6) — FAA-H-8083-3C
- PHAK ch. 5 (pp. 5-48–5-49) — FAA-H-8083-25C (2023)
- AC 61-107, para. 3-2, 3-3 — AC No: 61-107B
Build understanding you can use
Unlock the full lesson and continue studying this element.
- Full teaching sections: What it is; Key points; Rules and numbers; How it is done
- Check your understanding with answers you can reveal
- Common mistakes paired with the FAA facts that correct them