Fire in Variable Density Wind Tunnel

Fire gutted interior of Variable-Density Tunnel (VDT). On August 1, 1927 a major fire broke out inside the VDT. Clean-up, repair, redesign and reinstallation of equipment took about 8 months. From the Variable Density Tunnel Log Book: "Aug. 1. Computation of the previous tests were in progress in the office and the tank had been pumped up to 20 atmospheres and run to equalize the temperatures about 11:25 a.m. The 20 atmosphere run on the M-6 polished air foil was started and two readings had been taken when sparks were seen to pass in the return passage. Mr. Turner yelled "Fire!" and shut off the drive motor and opened the blow off valve. Through the peep holes it could be seen that the fire had a good start. It soon fogged up inside so that it could no longer be seen. We then waited for the pressure to go down. However, due to the burning inside, the pressure probably continued to rise. We noticed that the blow off pipe was becoming very hot and that smoke was coming out around the propeller shaft. Suddenly (sic) there was a loud bursting noise and every one left the building. This was probably the blowing of the gasket around the blow off valve. Later the top peep hole blew out and the blow off pipe blew out from the valve. The pressure then began to go down and we returned. The building was full of smoke. When the pressure had gone down the blow off was closed. The tank was very hot and the roof of the building somewhat scorched. The office was then partially cleaned up but it was decided to leave the tunnel closed until the next day." "Aug. 2. The tunnel door was opened in the morning and the compressor run to expel the gasses. About noon it was possible to swing back the honeycomb. It was apparent that the damage was very wide spread. All of the woodwork seemed to be charred and the upper part of the balance ring and the propeller tips and glass windows near the test section were melted. The remainder of the day was spent ventilating the tunnel and taking photographs both inside and outside of the tunnel." The 1927 fire was not the first in the VDT as this September 15, 1924 entry from the "Variable Density Tunnel Log Book" indicates: "The final runs on Airfoil 97 at twenty atmospheres was completed past the burble point. Fire broke out before the last point was obtained. The tunnel was running at 315#/*" at the time. Flames were visible from the drag peep hole, in the window straight ahead filling up the entire window. Switches were immediately pulled and blow off valve opened. Turner did these. Fire dept. was called. When pressure reached 50#/*" obs lower drag peep hole was broken in and fire hose nozzle directed inside. In the meantime the large door was forced open and entrance beyond the large honeycomb was affected. Fire was now practically out. Turner smashed in window in outer cone and finished the flame with our own small hose. Upon examination, probable cause of the fire was: - Tubular light bulb crushed, terminal wires welded to reflector, heated and burned the insulation outside of the socket and set fire to surrounding wood. The auxiliary shelf used by Prof. Hempke (about 12 in x 18 in.) was burned badly. Total damage to tunnel consisted in one broken window, one peep hole glass, and a small charred section. Repairs were well underway by evening." Note the abbreviations used in the entry above mean: "315 pounds per square inch" and "50 pounds per square inch". This is how they were written down in the log book. Finally, another fire caused by faulty wire insulation broke out on February 9, 1925 but repairs were swiftly made and the tunnel was back in operation five days later.

NASA Identifier: L1993