Test of 4" x 20" Clark-Y airfoil model in Full-Scale Tunnel (FST). On June 26, 1929, Elton W. Miller wrote to George W. Lewis proposing the construction of a model of the full-scale tunnel. "The excellent energy ratio obtained in the new wind tunnel of the California Institute of Technology suggests that before proceeding with our full scale tunnel design, we ought to investigate the effect on energy ratio of such factors as: 1. small included angle for the exit cone; 2. carefully designed return passages of circular section as far as possible, without sudden changes in cross sections; 3. tightness of walls. It is believed that much useful information can be obtained by building a model of about 1/16 scale, that is, having a closed throat of 2 ft. by 4 ft. The outside dimensions would be about 12 ft. by 25 ft. in plan and the height 4 ft. Two propellers will be required about 28 in. in diameter, each to be driven by direct current motor at a maximum speed of 4500 R.P.M. Provision can be made for altering the length of certain portions, particularly the exit cone, and possibly for the application of boundary layer control in order to effect satisfactory air flow. This model can be constructed in a comparatively short time, using 2 by 4 framing with matched sheathing inside, and where circular sections are desired they can be obtained by nailing sheet metal to wooden ribs, which can be cut on the band saw. It is estimated that three months will be required for the construction and testing of such a model and that the cost will be approximately three thousand dollars, one thousand dollars of which will be for the motors. No suitable location appears to exist in any of our present buildings, and it may be necessary to build it outside and cover it with a roof." George Lewis responded immediately (June 27) granting the authority to proceed. He urged Langley to expedite construction and to employ extra carpenters if necessary. Funds for the model came from the FST project. In a 1979 presentation made by Abe Silverstein, Donald Baals noted that credit for the design of the model was given to Clinton H. Dearborn.