The length of a proposed submarine is 100 m and the planned speed is 20 km/hr. In order to estimate the power requirements for the propulsion system, the vehicle resistance must be evaluated. It was proposed to build a wind tunnel model of the submarine and test it in air. If using the similitude assumption (e.g., keeping Re the same), what is the required length of the wind tunnel model if test speed is 80 m/sec? Is this a good idea?