National Geographic : 1925 Jan
THE NATIONAL GEOGRAPHIC MAGAZINE Official Photograph, U. S. Navy SAN DIEGO RESIDENTS GETTING THEIR FIRST VIEW OF A RIGID AIRSHIP Before beginning the fabrication of the Shenandoah's frame, it was necessary to produce a new metallic substance, duralumin, an alloy of aluminum and copper, with the strength of steel and the lightness of aluminum. If the tips of a girder of duralumin 16 feet long and so light that it could be balanced upon one's little finger, are placed on blocks, it will bear the load of eight men sitting upon it. mast which he has just left and which the ship's tail seems to be clearing by inches. "Stand by to cut out fuel tanks," Lans downe orders, and Bauch scampers up the ladder, pulling the cutting pliers from his pocket. Even fuel must go if necessary. The speeding motors can increase the ship's lift 10 per cent, but that means tipping her nose upward by means of the ele vators. After an angle of 13 degrees is reached, the maximum lift is obtained and the only relief is to drop ballast. CASTING OFF TAKES 16 MINUTES The casting off, including the inter ruptions from clouds and delayed fuel, had taken only 16 minutes. The waiting until the sun generated sufficient heat was of several hours. "Climb as fast as you can," Lansdowne orders. "She's climbing, sir," responds Allenly at the wheel. Patches of mist lie over the bay. The city seems too near for comfort. Auto mobiles and persons around the mast are becoming specks. "She's 500 feet above the mast, sir," says Hancock, as we circle upward. "Keep her climbing," Lansdowne re peats. "How high, sir ?" Houghton asks. "As high as she'll go, Regg," the skip per replies, as the tension relaxes. "Take her to pressure height." Pressure height usually is 4,500 feet that is, if the ship starts with her bags 85 per cent full of helium. As she ascends into more rarefied atmosphere the gas ex pands, keel officers and riggers pulling and straightening the bags, until at 4,500 feet they are full. Through the keel, in the apex of the triangular tunnel, runs a big rubber pipe, connected with each of the 20 bags. When the twine which closes their mouths is unwrapped, the gas circulates from one to another until the pressure in each is equal.