gcb5196 wrote:trpmb6 wrote:My goodness. This thread makes me want to quit engaging the airliners community. It's almost as bad as the non-av threads.
Where to begin. I have been involved in many tests like this one. This is hardly newsworthy. If only you had seen the things I've seen.
What do you expect us engineers to do? We design aircraft to meet a specific set of regulations and we push the design as far as possible to be the most efficient aircraft. You guys want cheaper tickets, more range using less fuel. Only way to do that is take the weight out. This is what you get. Mind you no aircraft in service would ever see this flight condition.
Boeing likely tested the frame to this condition to A) see what she could handle and B) help with production MRB, fleet repairs etc. We often will overload structure in a test for a couple reasons.. helps us justify repairs and defects etc. We actually will introduce failures into the structure to see what residual strength remains.
One thing folks also don't understand is we sometimes discover that to get a certain load level in one part of the fuselage you have to overload another area because of how our test cradles are set up. When in real life everything is a nice distributed load, the only way to test it without exorbitant costs is using cradles and wiffletrees that introduce point loads into the frame. This can lead to failures.
Fact is, this is a great test result. Sure they missed it by 1% but yall are extremely naive if you think that is catastrophic. Considering all the factors involved. Consider just some of the simplest points, someone developed the loads. Some margin of error there. Tolerance build up in the manufacturing process. Could be everything came in on the thin side. Maybe the stiffnesses in their FEMs was slightly off. The way the load is introduced to the test, as mentioned earlier, overloads local areas. We overload to account for thermal and environmental conditions. Remember CFRP wing with aluminum fuselage. Need to overload that to account for thermal mismatch.
That is why we test.
As for transparency, when I originally read the release about the failure it was clear to me they were discussing the cargo door surround structure. That's exactly what the pictures show. Don't blame Boeing, blame the folks who either misunderstood or simply don't know how this works.
Kudos to the Boeing engineers working this, they executed an excellent test. Hats off to you.
To the rest of you armchair engineers, I won't criticize you for how you do your job, don't criticize us until you go and get the degree and do the job we do. We keep you safe, a little respect would be nice.
Parting gift: almost certain the FAA would have had representatives present for the test. So any talk of a coverup is simply fearmongering/conspiracy peddling nonesense.
Well said and thank you. Okay, from the FARs, "Strength requirements are specified in terms of limit loads (the maximum loads to be expected in service) and ultimate loads (limit loads multiplied by prescribed factors of safety)." FAR 25.301. What is the factor of safety? "Unless otherwise specified, a factor of safety of 1.5 must be applied to the prescribed limit load which are considered external loads on the structure." FAR 25.303. So, the limit load is the maximum load to be expected in service and the safety factor is 1.5 times that. This and many other tests are designed to see that safety factor. The idea that this failure at 149% means that during turbulence the plane is somehow unsafe is absurd. Read the FARs. Maximum loads expected in service is 100%, that's turbulence, higher than normal g's, a higher gust of wind, a hard landing, bird crap on the window, maybe the sun hitting the fuselage at a weird angle. I don't know what the maximum expected loads are, but someone does and they have worked so far. The extra 50% is on top of all that, in addition to, 1.5 times. 1 is normal up to and including the O.S! moments, the .5 is so they can all live to tell about it. All transport category aircraft are certified at that. If you aren't comfortable with that then I don't suggest flying on any aircraft.
Also, to further my point, this is one test frame that this is performed on. There are variations in manufacturing and materials. This one frame stands in for and behalf of every plane that comes after it. The 1.5 safety factor covers most of those variations including fatigue. One plane may be stronger and one inherently weaker. Every plane that takes to the sky is not tested to ultimate failure because of that safety factor. It is factored in all the planes from every transport category aircraft manufacturer. If you are uneasy about flying on a Boeing 777X because it passed it's limit load test exceptionally well but barely failed the ultimate load test I wouldn't recommend flying on any other aircraft. If it had failed at 99% I would be concerned, the fact that it failed so close to the 1.5 safety margin means it's safe, just not certifiably safe, yet. And in praise to the engineers, it was almost perfect. Same kudos to engineers at all manufacturers who get it almost there, don't want to be seen as a fanboy. By the way if given the opportunity to fly on an A380 I would, wing spar cracks and all.
The point is just, that the frame did not reach the 150%. All your rant does not change that.
If this was the last test in the row of tests, than yes, testing will cease and the engineers will have to decide, what strengthening will have to be done, to bring this frame to above the 150% or 1.5 safety factor.
Yes test flights can begin, you do not need the frame to have finished the static testing before that, but changes will have to be done to production frames and at least one production frame with the changes will have to do test flights.
Anyway, not every frame is tested to destruction in the static tests. Boeing did not do it with the 787, testing was ceased when the frame had passed the mark.