MODERN MIRACLE

Auckland Star, Volume LXIX, Issue 139, 15 June 1938, Page 13

MODERN MIRACLE

BIG 'PLANE TESTED. CARRIED OUT IN HANGAR. triumph of mathematics. SANTA MONICA (Calif.), May 20. Aviation is credited with another modern miracle! Out in Santa Monica, California, Dou-las engineers have just finished the job of tlying and landing tinnation's largest and finest commercial transport plane without taking it out ot the hangar. It was a task in which mathematics and a million pounds of lead bars were Handled in e(]ual proportions, with slide rules and elbow grease doing their share "i ,e " tl,e las t test was finished and the final figures cheeked and re-checked the big DC-4, designed and built bv Douglas to the order of the five major airlines, was pronounced readv and fit for its acceptance flights. Every critical condition of taxiing, flying and landing was reproduced 111 these experiments. Reduced to mileage the "indoor flights" of the DC-4, as tliev were recorded in load applications and vibration tests, were sufficient in force and duration to have taken the big plane nearly three times around the world. To accomplish these things without taking the 'plane outside its construction hangar required 100.000 hours of shop and engineering labour, 175.000 pounds of structural steel and scores of toas of equipment, including hydraulic jacks, blocks and tackles, chains and special riggings. Ordinarily first models of 'planes are tested by piling loads 011 wings and body after the ship is turned upside down. The DC-4, a 42-passenger, fourmotored, low-wing monoplane, is I:s9ft from tip to tip and 24ft high—a metal leviathan entirely too large to be handled so unceremoniously. Consequently, special methods and" structures had to be designed to test this 'plane under scientific conditions. Rehearsals Were Held. Complete co-ordination was important. Several rehearsals were held to make certain each man knew his routine. There were 201 separate points on the aeroplane at which deflection readings were taken from sensitive instruments as each successive load was applied. Some tests were made to load factors Jof three.and one-third times the gross j weight of the ship.

Fully loaded with a crew of five, "} tons of mail, baggage and express, and fueled for transcontinental flight, the DC-4 will weigh 65.000 pounds. Most complicated and spectacular were the tests of deflection in outerwing panels of the big 'plane during flight. To reproduce tlias condition Douglas engineers erected huge steel structures, not unlike small skyscrapers, from which pulleys and cablcs hooked on to the leading edge and upper skin of the wing tugged upward to simulate uploads or "suction" lift during flight. Twelve men at the end of blocks and tackles gradually increased this load at given signals, while under the innerwing sections of the 'plane hydraulic jacks, operated from a central" control board, pushed up with tremendous force. The steel structures supporting the outer-wing riggings were each 40ft long and 30ft high. A total of 180,000 pounds of uploads was applied to the wings during some of the tests. In the down-load conditions a combination of dead-weight of pig lead and hydraulic jacks pulling against engine nacelles exerted another 180,000 pounds. Of this tremendous sum, fuselage ballast represented 80,000 pounds, outer nacelles 24,000 pounds, inner nacelles 26,000 pounds, and down-load on horizontal tail surfaces 12.000 pounds. The maximum load imposed on the main landing wheels was 170.000 jKiunds. The engineers applied sideloads of 35.000 pounds to each wheel and a maximum up-load of 42,000 pounds, and a side-load of 10,000 pounds on the "nose" wheel. This wheel is retractable in flight and is one of the outstanding features of the DC-4. It provides the big 'plane with a "tricycle" landing gear, for safer and shorter landings and better take-offs. One of the interesting tests was the application to the aeroplane of loads encountered in the "high angle of attack" position. This reproduced in the hangar all of the forces exerted in "zooming" the big 'plane upward while travelling in the air at 240 miles per hour and climbing at" the rate of 2000 feet per minute. Lead bare carried in and out of the 'plane for the various tests weighed 1,000.0001b. . More than 50 "landings" were made in a special test laboratory by dropping the main wheels and the "nose" wheel with terrific force and speed. Some of the interesting statistics of these "indoor flights" follow: — Wind tunnel tests of DC-4 model. 866 runs, averaging 25 minutes each, or a total of 63.875 miles "flown." Actual impact loads registered in landing gear drop test, up to 120.0001b each; "nose" wheel, 25 tests with impact load of 54.0001b. Vibration tests for gasoline tanks and other units, 250 hours.