The de Havilland Comet was the first commercial jet airliner. It had four turbojet engines and...

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The de Havilland Comet was the first commercial jet airliner. It had four turbojet engines and a pressurized cabin. It began commercial service in 1952. About two years after entering service, two airliners experienced a catastrophic break-up within about two weeks of each other during ascent to cruising altitude. Both accidents happened over the Mediterranean Sea. Most of the wreckage of the first airliner was recovered but not the second airliner. Subsequent analysis of the wreckage of the first airliner determined that the cause of the break-up was fatigue failure of the airframe. It was determined that a crack had formed at a rivet hole near the automatic direction finder (ADF) antenna cutout, which was square in shape. This crack propagated throughout the upper part of the canopy and resulted in the break-up of the airliner. The two primary causes of the fatigue were determined to be that the rivet holes during manufacturing were punched, instead of drilled, and that the stresses at the ADF cutout were much larger than had been estimated. a) Explain why the shape of the ADF cutout caused a large stress increase and describe a possible redesign of the cutout to reduce the stress. As a rough estimate of a pressurized airliner airframe, assume a cylindrical tube of aluminum 20 feet in diameter. b) How thick would the wall of the cylindrical tube need to be to accommodate an internal pressure of 10 psi relative to the outside pressure? Assume that the yield stress of the Al alloy is 50,000 psi. The de Havilland Comet was the first commercial jet airliner. It had four turbojet engines and a pressurized cabin. It began commercial service in 1952. About two years after entering service, two airliners experienced a catastrophic break-up within about two weeks of each other during ascent to cruising altitude. Both accidents happened over the Mediterranean Sea. Most of the wreckage of the first airliner was recovered but not the second airliner. Subsequent analysis of the wreckage of the first airliner determined that the cause of the break-up was fatigue failure of the airframe. It was determined that a crack had formed at a rivet hole near the automatic direction finder (ADF) antenna cutout, which was square in shape. This crack propagated throughout the upper part of the canopy and resulted in the break-up of the airliner. The two primary causes of the fatigue were determined to be that the rivet holes during manufacturing were punched, instead of drilled, and that the stresses at the ADF cutout were much larger than had been estimated. a) Explain why the shape of the ADF cutout caused a large stress increase and describe a possible redesign of the cutout to reduce the stress. As a rough estimate of a pressurized airliner airframe, assume a cylindrical tube of aluminum 20 feet in diameter. b) How thick would the wall of the cylindrical tube need to be to accommodate an internal pressure of 10 psi relative to the outside pressure? Assume that the yield stress of the Al alloy is 50,000 psi.