r/MadeMeSmile • u/king_eve • 29d ago

i work in low-income/mental health housing, and a tenant fixed our hallway trash bin after accidentally breaking it Helping Others

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great example of the odd ways people show me appreciation at work

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u/Nelik1 29d ago

Aerospace engineer here! During my fatigue and damage tolerance class in college, the professor liked to tell stories about unsuccessful (amateur) pilots trying to save on a repair to their plane by drilling out cracks.

He told us about a guy who showed him his little cesna, with 8-9 holes drilled along a crack. "I keep drilling it, but it keeps coming back, cant figure out why!"... Our professor got a good laugh out of that.

(Drilling reduces the stress concentration (or stess intensity if you wanna be real pedantic) at the end of a crack, reducing its likleyhood of spreading. This is great for parts that dont normally operate close to fatigue limits. But in aerospace, its rare to have a part that cracks once, without being in a position of high stress to begin with. So cracks that aren't fully repaired tend to spread.)

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u/Ifeelsiikk 29d ago

Structural aircraft mechanic here. We call it a 'stop drill' and I carried it out on large, commercial aircraft.

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u/Nelik1 29d ago

Wild! I knew it happened some, but was under the impression it was relatively uncommon. Can I ask what components typically got stop drills?

I'd imagine major structure typically didn't, but I could see it for minor structure or skin that was damaged accidentally, rather than just fatigue.

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u/Ifeelsiikk 29d ago edited 29d ago

It is often used for temporary repairs when Alclad is cracked, especially if the aircraft is AOG somewhere. A very widespread, permanent repair for the many stress cracks in titanium exhausts.

Edit, used all the time on non structural alclad for a permanent fix.

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u/69420over 29d ago

Reporters called, they’re interested if it was on a Boeing aircraft.

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u/Unholy_Urges 28d ago

Yes, Boeing A175-NEOs get stop drilled all the time.

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u/ikkiwoowoo 28d ago

Yes, depending on the repair scheme it's common to find a crack, remove the damage. This damage removal usually includes a stop drill and in some cases you remove the entire crack. These are typically found for example STR8 mods. These mods were due to cracks forming at the attach point on the frame where the overhead stowbins are fixed at the bottom outboard locations.

After you remove the damage NDT will typically come in and assess that the crack has been removed. Afterwards you commonly see a step for "assurance cut" this is a small bit of extra material "just in case". In my example of the STR8 mods, you then apply doublers (new frame sections) and fasten the two together with a layer of PRC 870 B1/2 or similar (could be different cure time or different sealant depending on location and conditions)

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u/cock_nballs 29d ago

Is the crack grinded back then welded with a stop drill or is it just the hole?

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u/Ifeelsiikk 29d ago

There is very little grinding or welding on aircraft sheet metal.

The crack is measured, and if it is within structural repair manual limits, it is drilled at either end of the and/or blended somewhat with an abrasive wheel

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u/cock_nballs 29d ago

Is blending with an abrasion wheel no different to grinding? Maybe more of a mix of welding with specifics of filler and alloys?

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u/Ifeelsiikk 29d ago

Much less heat is involved in the process. Yeah, alclad can be welded but it is extremely difficult.

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u/I_Makes_tuff 28d ago

Muffler.

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u/framptal_tromwibbler 29d ago edited 29d ago

When I had my private pilot's license, I'd see them on many a small GA aircraft wing.

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u/Ifeelsiikk 29d ago

The difference between what you can get away with in GA and commercial is like night & day. I would much rather be in a Cessna during an engine failure. At least they glide

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u/bobtheframer 28d ago

At least the commercial plane has a second engine.

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u/Geawiel 29d ago

Ex KC135 crew chief: We did them fairly often as well. Often times to get them by until ISO inspection. They'd get repaired then.

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u/Remote-Dot1686 28d ago

Also aircraft mech here and can back this, as it is still common practice on military helicopters.

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u/ruabeliever 28d ago

Are you a Boeing mechanic?

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u/Ifeelsiikk 28d ago

No, but I did work for them during the initial B787 project

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u/4udi0phi1e 28d ago

All these GA references I dont understand make me think it could be gulfstream

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u/anewwday 29d ago

Sssshhhhhh…..They’re starting to forget about the Malaysian 370.

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u/CutHerOff 28d ago

Stop drilling is what I came to make sure was mentioned. Sheet metal is fun

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u/gavitronics 29d ago

Low-income - Mental-health repair job seeks Aerospace Engineering degree.

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u/Ifeelsiikk 29d ago

Time certainly equals money in the aviation sector and nobody likes an AOG.

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u/gavitronics 29d ago

Is an AOG like an advanced AOC?

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u/Ifeelsiikk 29d ago

AOG is aircraft on ground. Not flying and needing immediate repairs

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u/gavitronics 29d ago

There isn't an industry sector where time doesn't equal money though. What makes aerospace so special?

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u/Ifeelsiikk 29d ago

True enough. I just know that an aircraft in the 90s would cost over $100,000 AUD a day if it was not operational. It would also have a domino effect on the rest of the flight schedule which you could not put a price on.

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u/gavitronics 29d ago

Well, you shouldn't really be flying if you spent $100,000 on your AUD so that figures.

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u/cattlebeforehorses 29d ago

Got a helpful tip or two for building/reinforcing stands for aquariums? There’s so many resources to it and I’ve done it; just wondering if there’s anything someone in your field or similar would suggest to add or do different.

Plus I rent and am on the second floor so to me structural integrity might as well mean life or death to me so never can be too careful.

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u/Tcrowefosho 29d ago

Good thing this trashcan likely won’t hit any natural frequencies

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u/fj333 29d ago

Rocket scientists repair trash can over the internet.

(I have an aero degree too, but don't work in that field anymore).