A process for testing a full-sized aircraft or full-sized gas turbine engine in a wind tunnel and includes the steps of securing a full-sized aircraft or engine in a wind tunnel for testing; filling an underground storage reservoir with compressed air; passing pre-treated compressed air from the underground storage reservoir through the wind tunnel for testing of the full-sized aircraft or engine; connecting an outlet of the wind tunnel to an ejector; and, passing compressed air from the underground storage reservoir through the ejector to decrease the exit pressure at the wind tunnel during testing of the full-sized aircraft or engine. The step of pre-treating compressed air from the underground storage reservoir includes preheating the compressed air; and, passing the higher temperature compressed air into the wind tunnel.