OPERATION GUILLOTINE

[Music] this is the 707 boeing's prototype jet airliner capable of speeds and altitudes which will revolutionize commercial air travel the production airliners will fly at high speeds and high altitudes for economical operation the high altitudes require more fuselage pressure than present airplanes to maintain the passenger comfort level it is known that certain combinations of pressure stress level and detailed design could produce a catastrophic explosion of the fuselage a catastrophic explosion such as this one during tests in a program directed toward eliminating such a possibility and toward producing a tear resistant fuselage structure for the 707 the boeing structure staff has conducted a series of tests on various fuselage construction configurations for these tests a full-scale 707 fuselage panel 100 inches long was installed on a steel jig to form a pressure chamber pressure for the test was supplied from a 100 psi plant air source making possible cycling during tests between 1.5 and 9 psi with pressure released from the chamber through this dump valve located on the floor of the jig strain gauges were installed and sealed to measure indicated stress in skin and frames during tests and deflection dial indicators were installed for the first tests of each configuration with up to nine psi pressure applied to test the extent to which the structure will deflect when brought up to pressure these tests were conducted to measure stress level in the skin data necessary in designing a fail-safe panel the results of these static tests were recorded on a photographical siligraph as were the crack propagation tests which followed the first panel tested was of a basic frame stiffener construction the initial test was a crack propagation test with pressure cycled up to 8.6 psig and an initial saw cut of six inches sawed in the skin with additional cuts made periodically to accelerate crack propagation resulting in a catastrophic failure occurring during the 194th cycle at a critical crack length of 18 inches prior to failure the four circumferential frames failed in tension and the crack propagated longitudinally along the entire length of the panel this graph shows the relationship between total cracked length and number of pressure cycles the test program was accelerated by lengthening the crack with saw cuts indicated by the vertical steps on the curve at the left an experimental fail-safe design constructed with reinforced frames and sheer tie angles connecting frames to the skin was also subjected to crack propagation tests for the test pressure was cycled between 1.5 psig and 8.9 psig while saw cuts of various lengths were made with cuts eventually reaching an overall length of 40 inches resulting in local failure only some of the saw cuts such as one along a riveted splice were sawed in short lengths so that the material left between the cuts would fail dynamically at greater than 8 psi pressure no crack propagation along the splice resulted following each propagation test a patching procedure was completed in which an aluminum sheet was riveted over the crack to seal it before the next test could be conducted a series of three tests using 15 inch wide heavy steel guillotine blades dropped through the pressurized section to simulate in-flight damage was then made the first two tests were made by dropping the blade in the center of the panel resulting in local failure only the third blade was dropped diagonally through the stiffener hat section completely shearing the stiffener a fourth test on this configuration employed two 15-inch wide blades dropped simultaneously straddling a frame which had been considerably weakened by sawing off a portion of reinforcement catastrophic failure occurred it should be noted that the blades were nearly through the skin before rapid failure began indicating that a less weakened frame probably would have withstood the damage without catastrophic failure another experimental fail-safe design was tested which consisted of the basic construction with the addition of circumferential straps attached to the skin at 20-inch spacing numerous crack propagation and fail-safe tests were conducted resulting in local failures only these pictures show one of the double blade guillotine tests test which resulted in local failure only assisting in demonstrating the effectiveness of the tear resistant design additional tests were conducted on a fourth panel with design improvements based on what had been learned in the previous tests three fuselage section designs were used on this panel the strap design shear tie with reinforced frames and basic design with thick skin for this panel spot welding was substituted for rivets in parts of the configuration simulating production aircraft methods in constructing the panel the basic stiffener frame panel with thick skin in a spot welded design was installed on top of the jig the sheer tie configuration with revised reinforcements similar to that proposed for the production 707 airplane and the spot welded circumferential strap design were installed at the sides of the jig in the circumferential strap design cracks were propagated from saw cuts reaching a maximum length of 40 inches but did not propagate through the straps or the contiguous skin similar tests were made in the other parts of the panel which represented the sheer tie with reinforced frames design and the basic design with thick skin in this combined configuration a series of seven blade drops was made with the panel pressurized to eight point nine psig and pierced by one or two three-quarter inch thick steel blades of these drops three were in the basic design with thick skin two in the sheer tie and two in the strap area the skin was patched after each test the results of each of these tests were uniformly satisfactory resulting in local failure only this scene in high speed photography of a double blade test and the thick skin design area demonstrates the effectiveness of the panel despite the numerous cuts and drops made on this panel complete structural integrity was maintained to further prove the design safety and freedom from fatigue of the design the cuts were patched and sealed and 25 000 air pressure cycles were applied with the section filled with styrofoam blocks two cycles of pressure per minute were possible without fatigue failure these tests have proven three different designs which can withstand substantial damage with safety based on structural and manufacturing considerations the strap design is used generally in the upper portion of the 707 fuselage the basic design with thick skin is used in a local area over the wing while sheer ties and reinforced frames are used in the lower portion of the fuselage the many cuts and drops conducted on the final test panel followed by 25 000 pressure cycles demonstrate that boeing structural engineers have devised a design which is failed safe with no danger due to a crack developing in the pressurized airplane skin guaranteeing that the 707 jet straddle liner will be safe in flight you