Schematic diagram of (VDT) - open throat design

Schematic diagram of Variable-Density Tunnel (VDT) - open throat design. Eastman Jacobs and Ira Abbott note in NACA TR 416 (p. 305) that a serious fire destroyed the tunnel (not the steel shell) in August 1927. The original design had a closed-throat test section five feet in diameter. After the fire it was decided to convert to an open throat design as depicted here. Jacobs and Abbott reported that this design was not satisfactory. "The difficulties, which included excessive vibration, unsteady velocity at the test section, a rather large pressure gradient along the axis of the test section, and excessive effects of extraneous air currents on the balance, were overcome by rebuilding parts of the tunnel." L2742.03: After a fire in August 1927 destroyed the VDT (not the steel shell), engineers decided to replace the original closed throat design with an open throat test section. This was wholly unsatisfactory and was immediately replaced with a new closed-throat design. Eastman Jacobs and Ira Abbott wrote: "The whole interior structure was changed to the closed-throat type. A new exit cone having a smaller divergence angle and a new entrance cone having a better form were built. The synchronous-drive motor was replaced by a direct-current motor. These changes were completed in December, 1930." (NACA TR No. 416, p. 305)

NASA Identifier: L2742