Boeing again 47

[Alistair_Heaton]

They have just put out that if the leap 1B engines have a bird strike. There is a small chance that smoke makes it through the bleed system into the cabin.

Apparently the were above certification size of birds that caused it in real life..

A horrible stink in the cabin on the turboprops was normal. Haven't had one on the jet yet . I was a mass murderer of birds on the turboprops.

 

[1503-44]

Did they get a good look at you?


--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Alistair_Heaton]

made me laugh...

 

[JohnRBaker]

Speaking of Boeing, it appears that the two NASA astronauts may be stuck on the International Space Station as their Boeing Starliner is leaking helium which is used in the thruster controls. At the moment, they're trying to trouble shoot the problems from the ground. It would be ironic is Space X is called on to mount a 'rescue mission' to return the NASA crew to Earth using one of their Dragon capsules.

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[3DDave]

The explanation that makes most sense was a claim that the problems are all in the service module that is jettisoned prior to re-entry so that any chance of investigation goes away at that point. The reports are they have leak rates in the range that they will become inoperative in a year or more, so that isn't the limitation.

Reference picture:

https://ichef.bbci.co.uk/news/640/cpsprodpb/29cc/live/778a4a00-0950-11ef-bee9-6125e244a4cd.png.webp

on

https://www.bbc.com/news/articles/cpeg21x7n7qo

BBC: Starliner: Nasa to fly new craft to space station

 

[Alistair_Heaton]

https://spacenews.com/fifth-helium-leak-detected-on-starliner/

Why is helium the gas of choice for this application?

When ever it's been involved in anything I have looked at it's an absolute pig to stop it leaking.

The old MRI medical imagers had loads of it... Or NMR's as they were called when I was a kid.

 

[zeusfaber]

Don't use the "N" word!

 

[FacEngrPE]

Good question - the common use of Helium I encounter is leak testing
Fundamentals of helium leak testing ASM Link

https://youtu.be/h3XHdeGo4r8

 

[Heaviside1925]

Helium is used because its boiling point is lower than hydrogen. Since hydrogen has a high propensity of leaking as well, using helium to purge the lines is preferred since any other gas might freeze in the line and you'd much rather your flight crew sounding like micky mouse, than them being crispy critters due to an H2 leak. It also gives the flight crew in situ leak checks of all the lines, so helium is also "the canary in the coal mine" in this sense.

 

[Alistair_Heaton]

Thanks for answering why it's used. Makes sense.

And Zeus for making me laugh. My dad was an academic in bio medical physics in Aberdeen, Nottingham got the Nobel prize for NMR. My dad was on the ionising and none radiation side of things.

An add on to 787 fasteners issue.

Apparently the problem is a procedure issue.

The fasteners were ment to be torqued up driving the nut. In practice on the production line the nut was held and the head was driven.

They are running data for the way it was physically done in practice. Once that's done it can become a compliant practice.

Any ideas what might be the result between the difference between head holding or nut holding methods? Presume there were washers both sides.

 

[Heaviside1925]

Torque apparent vs torque applied. A washer is only a means to distribute force statically, dynamically there are frictional surfaces, either on the nut or screw head side that are likely nonlinear based on run-in speed. This may be significant or may not, hopefully their testing won't reveal any major discrepancies.

PS, I am new here and I'm not trying to hijack the posts, it's just the last two posts fell right in my wheelhouse. Great discussions btw.....almost took a job with Boeing in a past lifetime, lol.

 

[Alistair_Heaton]

Mate great replies, I am an ex mechanical who had a career change from FEA in his early 30's to become a commercial airline pilot, now early 50's.

I was watching the forum and joined when I felt I could add something useful when the MAX kicked off.

 

[1503-44]

Some of those later strikes might have been kamikazis.
I've seen them behave that way with my cat.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[3DDave]

The main, and slight difference, is that if the contacting surface of the structure is not perfectly perpendicular to the restraining feature for the bolt, the bolt head will have, at the last stages of tightening, an oscillatory bending load of however many turns it takes from developing an initial load of consequence to the final load. If this happens to the nut side, the contact point for that bending on the fastener thread remains at a constant angular position and no oscillation takes place in the fastener body. So, this is to avoid the almost imperceptible introduction of fatigue cycles.

They should not be using torque as the defining feature and instead be using torque + turn, which eliminates 95% of friction related variability.

---

Hydrogen can produce hydrogen embrittlement and no one wants that. It's also oxygen safe, so can be used to pressurize oxidizer tanks.

 

[Alistair_Heaton]

And do they specify a method normally for line maintenance? As well?

Haven't seen anyone use power tools at work on the line but I presume the c check do.

Must admit when on the spanners with none aviation stuff at home I find it easier to have a ring spanner on the nut and use an impact driver on the head.

 

[Heaviside1925]

Ex mechanical.... No such thing! Once a mechanical always a mechanical! I will give you "former mechanical".

This is anecdotal and I hope things have changed for the better at Boeing. Time frame, mid 90's. I was getting out of the military with aviation experience as well as a degree in aeronautics. The two largest corporate recruiters who were allowed first crack at us were Boeing and Sun Microsystems. Boeing = aviation, makes sense, no idea why Sun Microsystems. Having had gone clubbing the night/morning before my LSAT, my first and last career option became Boeing. I am a little fuzzy on the exact details, but I talked to some Boeing managers who made some very hefty offers but before I could matriculate into Boring(edit: Freudian slip I think) Boeing culture and sign a contract, there was a mandatory, prospective Boeing employee orientation I had to attend. In this orientation, it was impressed on us, that we were only going to be a cog in a much larger system. The part of the orientation that was most determinative in my decision not to join Boeing was the presenter saying, " You will be issued a Boeing Employee Identification Number, You will remember this number, It will become your identity and you will be known by it throughout your entire career at Boeing" and I thought "Yeah, this isn't for me". Take from this what you want but this is how my opinion is colored whenever I read about issues with Boeing.

 

[Heaviside1925]

3DDave
They should not be using torque as the defining feature and instead be using torque + turn, which eliminates 95% of friction related variability. So I still get 5% for friction!

Thank you for a more detailed explanation. My background was coming from contact mechanics where we looked at this type of interface. So back to the initial question, it's only to avoid the fatigue cycles depending on if the torque + turn is applied to the nut or bolt?

 

[waross]

If the bolt is an interference fit and is meant to be pulled in by the nut, then turning the bolt may cause complications due to friction, galling and heat.
But this is speculation on top of speculation, for discussion only.
I hope we hear the results of the investigation.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Alistair_Heaton]

Tis true engineering does alter your thoughts processes for life.

Let's you build mancaves and the like. (Details in hobby forum)

 

[SWComposites]

it really and highly depends on the type of fastener.
many aerospace fasteners for composites structures do not have a head that can be torqued (hi-loks, lockbolts, etc).
in any case, fastener clamp-up is critical to joint fatigue performance. torqueing a fastener from the head side can produce a different level of clamp up for a given torque than applying the torque to the nut/collar side.
and in many installations, washers are not used under the head, only under the nut/collar.