HIGH FLYING

Evening Post, Volume CXXVII, Issue 111, 13 May 1939, Page 28

HIGH FLYING

STRATOSPHERE PLANES

AMERICA EXPERIMENTING

(From "The Post's" Representative.)

VANCOUVER, March 29

The first of three stratosphere planes approaching completion at the Boeing works at Seattle was put through tests that demonstrate its ability to fly "above the weather" without the slightest discomfort to passengers. Unfortunately, it has since been wrecked, "but the others will undergo tests shortly. The craft are designed to operate at 20,000 .feet and each will carry 33 passengers. "Sub-stratosphere flights" were made without the plane leaving the hangar. This was done.simply by introducing compressed air into the sealed cabin, to test its ability to withstand difference in pressure between the air inside and outside, as would be required, to give passengers the benefit of normal atmosphere at high levels. The situation would be reversed in actual flight, as then the pressure on the outside atmosphere would decrease, while the pressure on the air inside would remain substantially constant, whereas, in tests, the air pressure was increased inside, while it remained constant outside. The' cabin was tested for pressures far exceeding any that would be encountered in actual service. The performance of the plane under different flying strains was likewise tested in the "rehearsal," 28 tons of lead being used for this purpose. Ingots weighing one hundredweight were placed inside, in place of passengers, crew, and cargo, and heavy weights were placed in the tail section to simulate and exceed the flight loads of the most severe air conditions or unusual manoeuvres. "It was interesting to note," said the Assistant General Manager, "that the cabin supercharging actually added to the strength of the body, by virtue of the internal air pressure." The shell of the plane was coated with a film of soap during the pressure tests, so that bubbles would appear wherever there was the slightest leak. The leaks were filled at once with a sealing compound by workmen inside the cabin. Some leakage of the cabin during flight was not objectionable, the expert added, because as much air must be discharged as entered the cabin through the supercharger blowers and ventilation ducts. But, for efficient air distribution for ventilation purposes, it was desirable to reduce leakage to a minimum. He explained that the plane was equipped with two superchargers, either of which could keep the air pressure at the desired level by itself. The superchargers accelerated the incoming fresh air in the vanes of a rapidly-rotating wheel, and the air was then slowed down to build up the pressure. In the laboratory, the apparatus was tested under refrigeration at temperatures far lower than would be encountered.