In order to undertake predictions of the lift and drag force on a scale model of an aircraft during a section of its operational envelope involving sea level flight at 100 m s−1, where the speed of...

In order to undertake predictions of the lift and drag force on a scale model of an aircraft during a section of its operational envelope involving sea level flight at 100 m s−1, where the speed of sound may be taken as 340 m s−1 , it is proposed to utilize a cryogenic wind tunnel with nitrogen at 5 atmospheres of pressure and a temperature of −90°C, conditions at which the nitrogen density and viscosity may be taken as 7.7 kg m−3 and 1.2 × 10−5 N s, respectively. The speed of sound in nitrogen at this temperature is 295 m s−1. Determine the wind tunnel flow velocity, the scale of the model to ensure full dynamic similarity and the ratio of forces acting on the model and the prototype.