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This paper reports studies of jet-induced upwash fountains for twin-nozzle, short take-off and vertical landing (STOVL) aircraft. Experimental and 3-D computational fluid dynamics studies were carried out using twin circular jets at nozzle pressure ratios (NPR) between 1.05 and 3, impingement heights between 2.5 and 8.5 nozzle diameters and a nozzle separation of 7 diameters. This paper describes an extension to our previous work on jet-induced fountain unsteadiness, with the development of pressure-instrumented ground and suck-down plates and a vertically-moving ground landing simulator. The aims of the studies were to model and measure the average pressure and time-varying fluctuations present around the upwash fountain and to correlate this information with flow visualisation data and hence to understand better the flow mechanisms involved in upwash fountain flapping, with application to modern STOVL aircraft.