{"id":20888,"date":"2023-01-24T00:01:01","date_gmt":"2023-01-24T08:01:01","guid":{"rendered":"https:\/\/exhaustnotes.us\/blog\/?p=20888"},"modified":"2026-04-10T06:15:05","modified_gmt":"2026-04-10T13:15:05","slug":"the-wayback-machine-later-gator","status":"publish","type":"post","link":"https:\/\/exhaustnotes.us\/blog\/index.php\/2023\/01\/24\/the-wayback-machine-later-gator\/","title":{"rendered":"The Wayback Machine: Later, Gator…"},"content":{"rendered":"
By Joe Berk<\/h6>\n

I had a tough time choosing a title for this blog.\u00a0 I went with what you see above because it reminds me of one of my favorite Dad jokes…you know, the one about how you tell the difference between a crocodile and an alligator.\u00a0 If you don’t see it for a while, it’s a crocodile.\u00a0 If you see it later, well, then it’s a gator.\u00a0 The other choice might have been the old United Negro College Fund pitch:\u00a0 A Mine is a Terrible Thing to Waste.\u00a0 But if I went with that one I might be called a racist, which seems to be the default response these days anytime anyone disagrees with anyone else about anything.<\/p>\n

Gresh likes hearing my war stories.\u00a0 Not combat stories, but stories about the defense industry.\u00a0 I never thought they were all that interesting, but Gresh is easily entertained and he’s a good traveling buddy, so I indulge him on occasion.\u00a0 Real war stories…you know how you can tell them from fairy tales?\u00a0 A fairy tale starts out with “once upon a time.”\u00a0 A war story starts out with “this is no shit, you guys…”<\/p>\n

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Don’t forget to click on the popup ads…it’s how we get paid and how we keep the blog alive.<\/span><\/h3>\n
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So, this is a “no shit” story.\u00a0 It sounds incredible, but it’s all true.\u00a0 I was an engineer at Aerojet Ordnance, and I made my bones analyzing cluster bomb failures.\u00a0 They tell me I’m pretty good at it (I wrote a book about failure analysis, I still teach industry and gubmint guys how to analyze complex systems failures, and I sometimes work as an expert witness in this area).\u00a0 It pays the rent and then some.<\/p>\n

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So this deal was on the Gator mine system, which was a real camel (you know, a horse designed by a committee).\u00a0 The Gator mine system was a Tri-Service program (three services…the Army, the Navy, and the Air Force).\u00a0 It was officially known as the CBU-89\/B cluster munition (CBU stands for Cluster Bomb Unit).\u00a0 The way it worked is instead of having to go out and place the mines manually, an airplane could fly in and drop a couple of these things, the bombs would open on the way down and dispense their mines (each cluster bomb contained 94 mines), the mines would arm, and voila<\/em>, you had a minefield.\u00a0 Just like that.<\/p>\n

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It sounds cool, but the Gator was a 20-year-old turkey that couldn’t pass the first article test (you had to build two complete systems and the Air Force would drop them…if the mines worked at a satisfactory level, you could start production).\u00a0 The UNCF slogan notwithstanding, the folks who had tried to take this Tri-Service camel and build it to the government’s design wasted a lot of mines.\u00a0 In 20 years, several defense contractors had taken Gator production contracts, and every one of them failed the first article flight test.\u00a0 When my boss’s boss decided we would bid it at Aerojet, I knew two things:\u00a0 We, too, would fail the first article flight test, and it would end up in my lap.\u00a0 I was right on both counts.\u00a0 We built the flight test units per the government design and just like every one else, we failed with a disappointing 50% mine function rate.\u00a0 And I got the call to investigate why.<\/p>\n

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So, let’s back up a couple of centuries.\u00a0 You know, we in the US get a lot of credit for pioneering mass production.\u00a0 \u00a0Rightly so, I think, but most folks are ignorant about what made it possible.\u00a0 Nope, it wasn’t Henry Ford and his Model T assembly line.\u00a0 \u00a0It was something far more subtle, and that’s the concept of parts interchangeability.\u00a0 Until parts interchangeability came along (which happened about a hundred years before old Henry did his thing), you couldn’t mass produce anything.\u00a0 And to make parts interchangeable, you had to have two numbers for every part dimension:\u00a0 The nominal dimension, and a tolerance around that dimension.\u00a0 When we say we have a 19-inch wheel, for example, that’s the nominal dimension.\u00a0 There’s also a \u00b1 tolerance (that’s read plus or minus) associated with that 19-inch dimension.\u00a0 If the wheel diameter tolerance was \u00b10.005 inches, the wheel might be anywhere from 18.995 to 19.005 inches.\u00a0 Some tolerances are a simple \u00b1 number, others are a + something and a – something if the tolerance band is not uniform (like you see in the drawing below).\u00a0 But everything has a tolerance because you can’t always make parts exactly to the nominal dimension.<\/p>\n

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Where companies get sloppy is they do a lousy job assigning tolerances to nominal dimensions, and they do an even worse job analyzing the effects of the tolerances when parts are built at the tolerance extremes.\u00a0 Analyzing these effects is called tolerance analysis.\u00a0 Surprisingly, most engineering schools don’t teach it, and perhaps not so surprisingly, most companies don’t do it.\u00a0 All this has been a very good thing for me, because I get to make a lot of money analyzing the failures this kind of engineering negligence causes.\u00a0 In fact, the cover photo on my failure analysis book is an x-ray of an aircraft emergency egress system that failed because of negligent tolerancing (which killed two Navy pilots when their aircraft caught fire).<\/p>\n

I don\u2019t think people consciously think about this and decide they don\u2019t need to do tolerance analysis.\u00a0 I think they don\u2019t do it because it is expensive and in many cases their engineers do not have the necessary skills.\u00a0 At least, they don\u2019t do it initially.\u00a0 In production, when they have failures some companies are smart enough to return to the tolerancing issue.\u00a0 That’s when they do the tolerance analysis they should have done during the design phase, and they find they have tolerance accumulations that can cause a problem.<\/p>\n

Anyway, back to the Gator mine system.\u00a0 The Gator system had a dispenser (a canister) designed by the Air Force, the mines were designed by the Army, and the system had an interface kit designed by the Navy.\u00a0 Why they did it this way, I have no idea. It was about as dumb an approach for a development program as I have ever seen.\u00a0 Your tax dollars at work, I guess.<\/p>\n

The Navy’s Gator interface kit positioned the mines within the dispenser and sent an electronic pulse from the dispenser to the mines when it was time to start the mine arming sequence.\u00a0 This signal went from coils in the interface kit to matching coils in each mine (there was no direct connection; the electric pulse passed from the interface kit coils to the mine coils).\u00a0 You can see these coils in the photo below (they are the copper things).<\/p>\n

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In our first article flight test at Eglin Air Force Base, only about 50% of the mines worked.\u00a0 That was weird, because when we tested the mines one at a time, they always worked.\u00a0 I had a pretty good feeling that the mines weren’t getting the arming signal.\u00a0 \u00a0The Army liked that concept a lot (they had design responsibility for the mines), but the Air Force and the Navy were eyeing me the way a chicken might view Colonel Sanders.<\/p>\n

I started asking questions about the tolerancing in the Navy’s part of the design, because I thought if the coils were not centered directly adjacent to the matching coils in each mine, the arming signal wouldn’t make it to the mine.\u00a0 The Navy, you see, had the responsibility for the stuffing that held the mines in place and for the coils that brought the arming signal to the mines.<\/p>\n