Symmetrical

Flap-up case

Gust criteria are based uppon the fact that turbulent conditions of varying intensity occur in the air through which the aircraft flies. As with maneuver requirments, all critical combinations of altitude, weight and c.g. position must be investigated for all critical points around the periphery of the gust V-n diagram.

Special considerations apply when acceleration caused by gusts are computed for flexible swept wing configuration.

Flap-down case

The requirements call for positive and negative 25 fps (feet per second) gusts for speeds up to \(V_F\) (flap speed).

Unsymmetrical

Rolling case

The condition of unsymmetrical gusts must be considered by modifying the symmetrical gusts at 'B' or 'C' on the gust V-n diagram. 100% loads are applied to one side and 80% on the other.

Yawing case

The aircraft is assumed to encounter lateral gusts while in unaccelerated flight. The derived gusts at the related aircraft speed of \(V_B\) (design speed for maximum gust intensity), and \(V_D\) (design dive speed) must be investigasted for flap-up and flap-down conditions.

Dynamic loads

In actual circumstances aircraft structures will deform and vibrate ander certain rates of loading. It must be shown by analysis that the aircraft can meet the symmetrical and unsymmetrical gust load conditions in flight when various rates of gust load application are considered. These dynamic flight loads must then be considered in ultimate design loads.