Boeing 7*7: the saga continues…

[Kartoffelkuchen]

4 hours ago, PakledHostage said:

In this case, the problem is happening on a type that's still in flight testing and that hasn't yet entered service. That's when you're supposed to find problems. They found the problem, they're going to fix it.

Generally agree. However, finding a critical issue like this with the engine pylon on their whole test fleet, after the aircrafts only flew a very limited number of cycles (think of all the grounding that's happened in between tests) does not speak well for their engineering department.

[mikegarrison]

8 hours ago, PakledHostage said:

In this case, the problem is happening on a type that's still in flight testing and that hasn't yet entered service. That's when you're supposed to find problems. They found the problem, they're going to fix it.

Exactly. That's why you do flight testing.

[PakledHostage]

8 hours ago, Kartoffelkuchen said:

does not speak well for their engineering department.

It is odd, but there could be other explanations that don't require a mistake by their engineering department. It could be something like a maintenance procedure that loaded the links in a bad way while installing the engine or inspecting something else, as was the case in the Amarican Airlines Flight 191 crash. In that case, American Airlines mechanics used a non-approved procedure to lower the pylon for an inspection and caused a crack in the pylon's aft bulkhead in the process. The crack went unnoticed and the aircraft was sent back out flying with disastrous results. Douglas and the DC10 took a decades long publicity hit from that accident, but as usual, there was more to the story than what reached the 6 o'clock news. 

[mikegarrison]

4 hours ago, PakledHostage said:

It is odd, but there could be other explanations that don't require a mistake by their engineering department.

You're talking about an interface between two different systems, the plane and the engine. Made by two different companies. Interfaces are always tricky.

I never worked engine/airplane interfaces except one time. I was a Noise guy before I was an Emissions guy (and I was a Combustor guy before that). In that one case, we had an "Engine Vibration Related Noise" problem in the cabin. No matter how much we balanced the engines before installing them, we still had these harmonic tones that were loud in the cabin. It turned out that the problem was that the impedance of the test stand was different than the impedance of the airplane, and that affected the harmonics of the engine balance. So balancing on the test stand was useless. Instead, we had to balance the engine when it was installed on-wing. That solved the problem.

I'm retired, and have no experience working thrust links anyway, but while it *may* have been some kind of engineering mishap, it may also have been something unpredictable. The engine has been reworked now a LOT, which is the main reason why the plane is so late.

As I said, that's why they do testing. Just like when SpaceX crashes rocket after rocket because they are testing, until they figure out the issues.

[PakledHostage]

13 minutes ago, mikegarrison said:

You're talking about an interface between two different systems, the plane and the engine. Made by two different companies. Interfaces are always tricky.

I assumed (incorrectly) in my earlier comments that these were thrust links in the pylon, which are part of the linkage system that connects the pylon to the wing, but they're not. They are the ones between the engine and pylon. Mea culpa.