buffet boundary

buffet boundary

buffet boundaryclick for a larger image
A typical nil turbulent buffet speed boundary graph for an airliner.
The speed boundaries within which airflow separates from the wing and the buffet is experienced. The low-speed buffet is caused by flow separation as the aircraft approaches the stalling angle of attack. At higher Mach numbers, the high-speed buffet is caused by flow separation from the wings as occurs behind the shock wave. Normally, high-speed aircraft flight manuals have at least three graphs called initial buffet boundary charts. One is for level flight and nil turbulence, the second is for 40° bank angle/moderate turbulence, and the last one is for 50° bank angle/high turbulence. These correspond to load factor values of 1, 1.3, and 1.6, respectively. These graphs are used in selecting a suitable flight level, given the atmospheric conditions forecast or actually experienced. The turbulence penetration speeds are also displayed, along with maximum normal operation speeds, as indicated air speed (VMO) up to a specified flight level and as a Mach number (MMO) thereafter. The illustration here is for the first case and does not show penetration speed and VMO.
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This wing ensures a large flight envelope with a wide buffet boundary, enhancing safety and stability while permitting exceptional short field and hot and high altitude performance.
Significant accomplishments in the test program during the first year of MD-90 flight include more than 200 successful autolandings, the clearing of the flight envelope to design speeds, successful completion of stall testing, assessment and demonstration of buffet boundary and successful autopilot testing and high altitude testing.