An investigation at low speeds over a still and a moving ground plane was made to determine the effects of ground proximity on the longitudinal aerodynamic characteristics of a model of a transport airplane. The four-engine model was equipped for blowing over the flaps for boundary-layer control. Compressed air was used to furnish flap blowing as well as to furnish the thrust for the two inboard engines. in and out of ground effect through an angle-of-attack range, a flap blowing momentum range, and a thrust range.

Results show that flap blowing substantially increases (100 percent ata= 0°) the lift coefficient through the angle-of-attack range in or out of ground effect. The presence of the ground reduces the lift and drag coefficients and reduces the down load on the tail; thereby, more negative tail incidence is required for trim. The lift reduction increases with increase in flap blowing and height reduction to a maximum of about 20 percent of the out-of-ground-effect lift. The still and the moving ground planes show negligible difference in effect on model forces and moments except for the model very close to the ground and with a large amount of blowing momentum where the more realistic moving ground plane shows small increments of increased lift, decreased drag, and positive pitch when compared with the still ground plane.