Create the dimensionless relationship and design of modern combat aircraft

Working as an aircraft engineer in the Ministry of Defense, you have been requested to design a modern combat aircraft with your project team member. This modern combat aircraft is designed to be able to fly in the air and travel underwater. Your team has designed a scale model of the modern combat aircraft and carried out an experiment with it in both wind tunnel and water tunnel (Figure 1). The wind tunnel was employed at a temperature of 20°C and atmosphere pressure, while fresh water at the same temperature was utilized to operate the water tunnel. Three model sizes were tested, and the drag force on each model was measured at different velocities. The collected data is presented in Table 1.

• It is known that the drag force, 𝐹𝐹𝐷𝐷 is a function of the density, ρ, viscosity, 𝜇𝜇, velocity, V, and aircraft model length, L. Create the dimensionless relation for this problem and plot the data above In this dimensionless manner. Discuss on the dimensionless relation created, and comment on the possible uncertainty of the experimental results.
• Next, your team is using this combat aircraft model geometry to build a large-scale combat aircraft. If you desire the maximum drag force should not be exceeded 0.15 N, what would be the proper length of the modern combat aircraft travel with an average velocity of 55 km/h underwater? Do you think the calculated combat aircraft length is feasible and suitable to be used to travel underwater? Identify the possible limitations of aircraft design.