<P> Flaps are mounted on the trailing edge on the inboard section of each wing (near the wing roots). They are deflected down to increase the effective curvature of the wing . Flaps raise the maximum lift coefficient of the aircraft and therefore reduce its stalling speed . They are used during low speed, high angle of attack flight including take - off and descent for landing . Some aircraft are equipped with "flaperons", which are more commonly called "inboard ailerons". These devices function primarily as ailerons, but on some aircraft, will "droop" when the flaps are deployed, thus acting as both a flap and a roll - control inboard aileron . </P> <P> Slats, also known as leading edge devices, are extensions to the front of a wing for lift augmentation, and are intended to reduce the stalling speed by altering the airflow over the wing . Slats may be fixed or retractable - fixed slats (e.g. as on the Fieseler Fi 156 Storch) give excellent slow speed and STOL capabilities, but compromise higher speed performance . Retractable slats, as seen on most airliners, provide reduced stalling speed for take - off and landing, but are retracted for cruising . </P> <P> Air brakes are used to increase drag . Spoilers might act as air brakes, but are not pure air brakes as they also function as lift - dumpers or in some cases as roll control surfaces . Air brakes are usually surfaces that deflect outwards from the fuselage (in most cases symmetrically on opposing sides) into the airstream in order to increase form - drag . As they are in most cases located elsewhere on the aircraft, they do not directly affect the lift generated by the wing . Their purpose is to slow down the aircraft . They are particularly useful when a high rate of descent is required . They are common on high performance military aircraft as well as civilian aircraft, especially those lacking reverse thrust capability . </P> <P> Trimming controls allow a pilot to balance the lift and drag being produced by the wings and control surfaces over a wide range of load and airspeed . This reduces the effort required to adjust or maintain a desired flight attitude . </P>

The effect of gravity on an aircraft is called