During its near-ground hovering phase a Short Take-Off and Vertical Landing (STOVL) aircraft creates a complex three-dimensional flow field between jet streams, the airframe surface and the ground. A proper understanding and numerical prediction of this flow is important in the design of such aircraft. In this paper an experimental facility, used to gather validation data suitable for testing Computational Fluid Dynamics (CFD) model predictions of multi-jet ground impingement flows, is described. Water is used as the working medium and Laser Doppler Anemometry (LDA) measurements of three-poster impinging jet flow fields are reported. Emphasis is placed on the presentation of the mean and rms velocity contours in the fountain formation region between the jets. The effect of jet imbalance and splay-angle were studied. An overview were provided to guide users through the data and highlight several important flow features which have already emerged from the data and which are considered of importance to CFD model validation.