申論題

六、 An airship is lo operate at 20 m/s in air at standard conditions (the pressure is 101 kpa). A model is constructed lo 1/20 scalc and tested in a wind tunnel at Ihc same air Icmpcralurc lo determine the drag. What criterion should be considered lo obtain dynamically similarity ? If the model is tested at 75 m/s, what pressure should be used in the wind tunnel ? If the model drag forcc is 250 N, what will be the drag of the prototype ? (25%)