I enjoy your aircraft articles. I've always been doubtful of aircraft structural integrity. My structural experience is in heavy steel and concrete, so I always got a little queasy when looking out the window of a corporate King Air and seeing the fine cracks radiating from wing rivets. The cracking was stopped by tiny holes drilled at the end of the cracks. I understand how stress relief works but my guiding principals were that there is no excuse for tension failures and when in doubt make it stout. If I designed an airplane, it would require Saturn rockets to get off the ground.
I once had a structural engineering Ph.D. assigned to my group who was laid off at Lockheed when most of their government contracts ended. He told me that the safety factor in aircraft structures were sometimes barely 1 instead of the higher numbers I was used to. He knew I hated flying, but I don't believe he was kidding.
There are a lot of trade offs in aircraft design. The higher thrust-to-weight of newer engines has made things a lot easier, but there is still a lot stress involved. You probably know better about that than I do. Airliners especially do a lot of takeoff and landing/pressurization cycles. I know that inspections play a huge role, but stress and metal fatigue have played a role in quite a few accidents.
I will say that the F-1 engines in the first stage of the Saturn V is stunning in how much thrust they generated to develop the necessarily escape velocity to get that massive rocket into space and eventually beyond earth orbit. NASA's SLS is about 365 ft tall, but unlike the Saturn V, utilizes solid fuel boosters to obtain part of its thrust. It'll be interesting to compare the specs between these giant rockets. The SLS I think uses essentially the same boosters that the Space Shuttle used, except it is taller with an additional segment. From what I read, these boosters won't have the parachute to land in the ocean for reuse. I'm wondering if NASA is now considering the boosters to be expendable, as opposed to being reusable.
I can't speak for small aircraft like a King Air. But one thing I can say for sure is that the strongest part of a commercial jet, is the wing box. That is the area where the wings join the fuselage. And the safety factor in the structural integrity of the wings in Boeing and Airbus commercial jets is at least 150%. And we are talking about 150% of the stresses the aircraft would ever potentially experience during flight. Most of the turbulence that we experience at times during flight doesn't come close to the 100% level. Boeing actually achieved a FoS of 154 % in the 777 widebody jet during the design/build phase in the early 1990s, and attached cables to deflect the wings until they broke.
That's beyond anything I ever studied. I'm more into concrete gravity dams and sixteen feet deep (would be deeper if railroad bridges had more clearance) boiler suspension girders with a safety factor of at least 3 instead of 1.5. Needless to say, I'm very conservative.
And what you studied is something I don't much about, and I'd probably learn a lot from you there. And your conservatism is a good thing! Especially when it comes to dams. I would agree with you in getting a really high FoS.
As for FoS in aircraft structural integrity, the 100% level represents are turbulence of the exceedingly rare extreme. And aircraft would probably have to take some evasive, non routine in-flight maneuvers to approach such a level. So in reality, 1.5 may not seem like a lot, but given what flights experience routinely, it makes for commercial aircraft wings from Airbus and Boeing to be exceptionally strong.
I always love hearing your insights and expertise when it comes to aviation, given your experiences as a pilot. Pilots are some of the most rational and level headed people I've know, and that I can see that in your thoughtful and insightful political punditry as well.
When you mentioned in-flight structural failure, the first things that come to mind are Japan Air Lines 123, and China Airlines 611. Both were 747-200s, and both jets had tail strike incidents 7 and 22 years before their accidents, respectively. The Japan Airlines flight had damaged the rear pressure bulkhead, which Boeing technicians installation of a splice place didn't comply with Boeing's repair procedures. And in China Airlines, they had a tail strike in 1980 when landing, which damaged the skin. Their tech ops didn't cut out the damaged skin and just threw on a doubler patch that didn't even cover all the damaged areas, which would later spread into cracks. In Japan Airlines 7 years later, structural failure of the rear pressure bulkhead resulted in a explosive decompression, and blew off most of the tail fin. But what made the airplane uncontrollable, was that all of its hydraulic lines were cut with subsequent total hydraulic failure. These pilots spent the next 30 minutes desperately trying to control the jet through the thrust levers. Eventually, they crashed into a mountain near Fuji, and 520 souls were killed. In China Airlines, the cracks developed and spread over time from repeated pressurization/depressurization, and eventually broke apart at cruising altitude. In both cases, improper repair and maintenance cost a total of 745 lives.
I think when it comes to commercial aviation, safety of course is paramount. But what is unavoidable, is that the design of the aircraft also has to consider economics of operation in mind as well. So there will inevitably be tradeoffs in performance, economics, and safety during the design phase, which has to be mitigated in careful compromises among the demands required by each of these criterion and others. The challenge for any commercial aircraft manufacturer is to find the sweet spot that doesn't unduly compromise the safety and airworthiness of the aircraft, yet delivers sufficient levels of performance and economics to where it is commercially viable. The 737 NG has proven to be a very safe and reliable model, and I think they will get to the bottom of it sooner or later. It's great that they already found the FDR, and will eventually find the CVR. I think we'll sooner or later find out the cause of this China Eastern accident. So much easier than when an aircraft crashes into the ocean, and trying to find the black boxes and other crucial debris on the ocean floor. I still hope someday, they can eventually crack the mystery of Malaysia Airlines 370.
That truck the guy was driving looks like an early 2000s Chevy Silverado. I remember back in those days the "Like A Rock" TV commercials bragging how rugged their trucks are. What better way to show that your product is tough as a rock then when it gets tossed about by a tornado, and still drives away from it this intact? GM ought to give this guy a free replacement pickup, and brag about how a twister can't even stop one of their trucks in an upcoming ad.
I enjoy your aircraft articles. I've always been doubtful of aircraft structural integrity. My structural experience is in heavy steel and concrete, so I always got a little queasy when looking out the window of a corporate King Air and seeing the fine cracks radiating from wing rivets. The cracking was stopped by tiny holes drilled at the end of the cracks. I understand how stress relief works but my guiding principals were that there is no excuse for tension failures and when in doubt make it stout. If I designed an airplane, it would require Saturn rockets to get off the ground.
I once had a structural engineering Ph.D. assigned to my group who was laid off at Lockheed when most of their government contracts ended. He told me that the safety factor in aircraft structures were sometimes barely 1 instead of the higher numbers I was used to. He knew I hated flying, but I don't believe he was kidding.
There are a lot of trade offs in aircraft design. The higher thrust-to-weight of newer engines has made things a lot easier, but there is still a lot stress involved. You probably know better about that than I do. Airliners especially do a lot of takeoff and landing/pressurization cycles. I know that inspections play a huge role, but stress and metal fatigue have played a role in quite a few accidents.
I will say that the F-1 engines in the first stage of the Saturn V is stunning in how much thrust they generated to develop the necessarily escape velocity to get that massive rocket into space and eventually beyond earth orbit. NASA's SLS is about 365 ft tall, but unlike the Saturn V, utilizes solid fuel boosters to obtain part of its thrust. It'll be interesting to compare the specs between these giant rockets. The SLS I think uses essentially the same boosters that the Space Shuttle used, except it is taller with an additional segment. From what I read, these boosters won't have the parachute to land in the ocean for reuse. I'm wondering if NASA is now considering the boosters to be expendable, as opposed to being reusable.
I can't speak for small aircraft like a King Air. But one thing I can say for sure is that the strongest part of a commercial jet, is the wing box. That is the area where the wings join the fuselage. And the safety factor in the structural integrity of the wings in Boeing and Airbus commercial jets is at least 150%. And we are talking about 150% of the stresses the aircraft would ever potentially experience during flight. Most of the turbulence that we experience at times during flight doesn't come close to the 100% level. Boeing actually achieved a FoS of 154 % in the 777 widebody jet during the design/build phase in the early 1990s, and attached cables to deflect the wings until they broke.
That's beyond anything I ever studied. I'm more into concrete gravity dams and sixteen feet deep (would be deeper if railroad bridges had more clearance) boiler suspension girders with a safety factor of at least 3 instead of 1.5. Needless to say, I'm very conservative.
And what you studied is something I don't much about, and I'd probably learn a lot from you there. And your conservatism is a good thing! Especially when it comes to dams. I would agree with you in getting a really high FoS.
As for FoS in aircraft structural integrity, the 100% level represents are turbulence of the exceedingly rare extreme. And aircraft would probably have to take some evasive, non routine in-flight maneuvers to approach such a level. So in reality, 1.5 may not seem like a lot, but given what flights experience routinely, it makes for commercial aircraft wings from Airbus and Boeing to be exceptionally strong.
I always love hearing your insights and expertise when it comes to aviation, given your experiences as a pilot. Pilots are some of the most rational and level headed people I've know, and that I can see that in your thoughtful and insightful political punditry as well.
When you mentioned in-flight structural failure, the first things that come to mind are Japan Air Lines 123, and China Airlines 611. Both were 747-200s, and both jets had tail strike incidents 7 and 22 years before their accidents, respectively. The Japan Airlines flight had damaged the rear pressure bulkhead, which Boeing technicians installation of a splice place didn't comply with Boeing's repair procedures. And in China Airlines, they had a tail strike in 1980 when landing, which damaged the skin. Their tech ops didn't cut out the damaged skin and just threw on a doubler patch that didn't even cover all the damaged areas, which would later spread into cracks. In Japan Airlines 7 years later, structural failure of the rear pressure bulkhead resulted in a explosive decompression, and blew off most of the tail fin. But what made the airplane uncontrollable, was that all of its hydraulic lines were cut with subsequent total hydraulic failure. These pilots spent the next 30 minutes desperately trying to control the jet through the thrust levers. Eventually, they crashed into a mountain near Fuji, and 520 souls were killed. In China Airlines, the cracks developed and spread over time from repeated pressurization/depressurization, and eventually broke apart at cruising altitude. In both cases, improper repair and maintenance cost a total of 745 lives.
I think when it comes to commercial aviation, safety of course is paramount. But what is unavoidable, is that the design of the aircraft also has to consider economics of operation in mind as well. So there will inevitably be tradeoffs in performance, economics, and safety during the design phase, which has to be mitigated in careful compromises among the demands required by each of these criterion and others. The challenge for any commercial aircraft manufacturer is to find the sweet spot that doesn't unduly compromise the safety and airworthiness of the aircraft, yet delivers sufficient levels of performance and economics to where it is commercially viable. The 737 NG has proven to be a very safe and reliable model, and I think they will get to the bottom of it sooner or later. It's great that they already found the FDR, and will eventually find the CVR. I think we'll sooner or later find out the cause of this China Eastern accident. So much easier than when an aircraft crashes into the ocean, and trying to find the black boxes and other crucial debris on the ocean floor. I still hope someday, they can eventually crack the mystery of Malaysia Airlines 370.
That truck the guy was driving looks like an early 2000s Chevy Silverado. I remember back in those days the "Like A Rock" TV commercials bragging how rugged their trucks are. What better way to show that your product is tough as a rock then when it gets tossed about by a tornado, and still drives away from it this intact? GM ought to give this guy a free replacement pickup, and brag about how a twister can't even stop one of their trucks in an upcoming ad.