The design effort produced a number of wooden models. A 24-inch long model, made of balsa wood, demonstrated placement of internal structure and access doors. An "Air & Space" article noted "The model shop found it nearly impossible to make all the flat surfaces come to a single point in one corner. Engineers later encountered the same difficulty fabricating the prototype on the factory floor." For early tests of the design, two ⅓-scale wooden mock-ups were constructed. One model, coated in metal foil, was used to verify ECHO 1's RCS calculations, while the other was earmarked for wind tunnel tests. Afterwards, a model was moved to the Grey Butte Range radar-testing facility in the Mojave Desert near Palmdale, which allowed more accurate tests of the aircraft's RCS. In the event, the aircraft's RCS level confirmed ECHO 1's predictions. This meant Ben Rich won a quarter from Johnson, who previously insisted that the D-21 had less RCS than "Have Blue".