Abstract : A study is being made of the effect on aerodynamic drag of boundary layer irradiation by radioactive sources. A blow-down wind tunnel and a skin friction drag balance have been designed and constructed. The balance is of the null-position type, and is operated using an automatic control system to maintain the null position of the drag plate. High accuracy and stability are observed at flow velocities up to 200 m/s and resolutions of up to 0.1% of changes in drag have been achieved. In separate experiments, a study of the effect of radioactive emission on gas viscosity is being made with a specially designed torsion disc viscometer. Measurements to date have been at atmospheric pressure with both pieces of apparatus. No significant changes in drag have been found except at low flow speeds. However, future work will be extended to lower pressures where there are reports of a decrease in viscosity with radiation. An objective of new research will be to find the optimum conditions for any drag reduction.