That, combined with the lack of a fatigue limit for aluminum. Unlike some other materials (like steel), no matter how small the stresses are on an aluminum part, it will eventually fail. Smaller stresses give longer lifetimes, but it’s always a finite. Steel, in contrast, does have a fatigue limit–meaning that if you keep stresses under a certain level, the part will last forever (ignoring other factors like corrosion).
I’ve said it so many times - I learn all sorts of things here on the SDMB that I never even knew I didn’t know about (“unknown unknowns”, I guess).
Thanks for this info. Interesting.
Glad to be of service. Obviously, the situation is more complicated than I described in a short summary, but at a high level, it’s a significant difference between steel and aluminum. You can see the effect in this graph:
Below a certain stress level, the cycle life for steel shoots off to infinity. But for aluminum, you have to keep lowering the stress if you want to increase the cycle life.
Metal scrap.
Sure, not as much money as selling them as replacement parts, but hey, the metal is free to the guy stealing it, right? So even scrap money is money ahead for him.
There have been a few instance of radiation sources winding up in scrap yards due to that sort of thing, along with a few scrappers suffering serious injury or death from such activities. I expect aircraft parts are no more immune to this sort of thing than any other thing made of metal.
It seems like the Vietnam POW thing to me - I could never understand why people thought Vietnam was keeping POWs after they said they were all back and/or dead. If (ala various Stallone and Norris movies) some were found and repatriated, the blow back would be way larger than any potential benefit. If Vietnam found that some rogue colonel/general still had an active camp, the best real-politik solution is to kill the general, the guards and the POWs.
The same would be true of repatriating Ukrainian citizens. At some point, any remaining involuntarily would be too much of an embarrassment.
I veteran explained his view to me, “They are mean as hell.”
Breaks my heart to see the F-15 being called a really, really old plane. I’ll admit in my heart I still think of the F-4 as a current fighter. A really really old jet fighter is something like a Sabre.
Designed in 1969, first flight 1972, first entered operational service in 1976. Fair to say it is a half-century old in basic design 
.
Jesus Christ that’s me: conceived in 69, first steps in '72, started school in 76.
(I’m playing fast and loose with those numbers by a few months on each, but close enough.)
That plane is old as shit because so am I.
But my inner knowledge of what jets are being flown is based on my days of building models back in the eighties.
Yup. But it was the late 60s to mid 70s for me.
We be ancient. Just like those jets.
Constant updates, still in production; I should be so well taken care of! It’s gone from being an air superiority fighter to a bomb and missile truck. (Still no slouch as a fighter, the missiles are doing most of the work). This aircraft isn’t George Washington’s axe.
I would have thought it best to aim for goal 3. When that is achieved, it would be time to contemplate goal 4. Going 4 right now seems to me like getting ahead of oneself, but maybe the leaders have something up their sleeve I can’t know about yet, that made it seem a good idea.