sentences:  Although Theodorsen leaned strongly toward basic theoretical analysis, he usually accompanied his work with experimental verification.He was highly innovative in engineering and experimental activities, where he always sought a theoretical framework or was guided by physical intuition.He was responsible for proposing a wind tunnel for flutter work that employed a mixture of air and freon with variable pressure to greatly increase the scope of research with aeroelastic models throughout the Mach range and with lower horsepower requirements.