At low-speeds (Mach number < .3 or so) the Reynolds number dominates the equations that govern the forces on an aerodyanic body. [Anderson, 35-50] The basic formulation of the Reynolds number is

Rho_inf * V_inf * l / Mu_inf [citation-needed]

The tricky part in there is the factor of 'l'. For a model that is, say 1:20 the value of 'l' would (for the real craft) be 20 times larger. Consequently, to reproduce the same Reynolds Number, Rho_inf * V_inf / Mu_inf must be 20 times larger. Even still, the compressability effects will start coming into play when your mach number exceeds 0.3. Consequently, the highest speed at which your wind tunnel can operate is ~230 mi/hr. Given that the speed must be 20 times higher, to compensate for the size of the 1:20 model, the maximum speed that can be simulated on that model in a low-speed subsonic wind tunnel is 11.5 mi/hr.

Not very flattering.

Alternatives to increasing the velocity, are to increase the densty, or decrease (Rho_inf), or decrease the viscosity (Mu_inf). Freon-12 was used by NASA et al. until the EPA banned its use. Other gasses are available with the appropriate properties, but their use would be prohibitively expensive for this project. [citation-needed]

Loss coefficients can be presented in two manners: in reference only to the local section and in reference to the test-section. The former and latter differ only by a factor of the ratio of the dynamic pressures between the local section and the test-section.

The pressure-drop across the test-section is dependent upon the area and the length thereof; though, it is independent upon the shape. The aerodynamic and construction requirements of the test-section dominate the selection process for its shape. Relatively uniform flow characteristics would be nice to have, making corner-fillets a possibility, though, at this time, will not be included. Because of the thickening boundary layer (leading to nozzling effects on the flow) the walls of the test-section will be angled out by ~1/2 degree each (rule-of-thumb). The design may be refined later. [citation-needed]