I was told that most aircraft had depleted uranium on board as counterweights. I have not seen one myself. Do all current modern aircraft have depleted uranium on board?
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12$\begingroup$ Related: What is the reasoning behind using depleted uranium as counterweights in the 747?, most of the counterweights were replaced with tungsten, so no, most aircraft don't use DU weights. $\endgroup$– Ron BeyerFeb 4, 2019 at 14:53
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1$\begingroup$ You don’t need anything that exotic; Steel or tungsten will work just fine for that role $\endgroup$– Romeo_4808NFeb 4, 2019 at 18:35
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2$\begingroup$ Counterweight to what? I've never noticed any in my 1973 Cessna single engine 4 seater. $\endgroup$– CrossRoadsFeb 4, 2019 at 18:55
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2$\begingroup$ @CrossRoads - Why are “counterweights” used in aircraft production? $\endgroup$– user14897Feb 4, 2019 at 19:23
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$\begingroup$ I suspect small aircraft just use a big chunk of shaped lead, and not depleted uranium. That would be a nightmare for A/Ps out in the field if any trimming was needed for example. My parts manual does not appear to say what the parts are made out of. $\endgroup$– CrossRoadsFeb 4, 2019 at 19:45
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3 Answers
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From my research, it looks like about 0.1% of all aircraft carry depleted uranium counterweights.
The Systematic Radiological Assessment of Exemptions for Source and Byproduct Materials (NUREG-1717), on page 3–260, gives a table showing that 430 domestic United States aircraft were delivered with depleted uranium counterweights, and says that "A reasonable estimate is that 50% of these aircraft still contain DU counterweights." So there are about 200 aircraft in the United States which contain depleted uranium counterweights.
Meanwhile, the FAA's "Air Traffic by the Numbers" publication says that there are over 200,000 aircraft in the United States currently.
So no, very few aircraft use depleted uranium counterweights.
answered Feb 4, 2019 at 16:37
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6$\begingroup$ … but those with DU are the very heavy and big beasts, so per mass the fraction is quite a bit higher. Still, it's insignificant. $\endgroup$ Feb 4, 2019 at 22:40
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2$\begingroup$ Is this "all aircraft" in the US, or the world? $\endgroup$– isanaeFeb 4, 2019 at 23:58
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2$\begingroup$ @isanae Well, the 0.1% figure is for aircraft in the US, and it seems reasonable to guess that the number is similar for the rest of the world. In particular, the number is certainly not 100%. $\endgroup$ Feb 5, 2019 at 4:39
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That material is dangerous and expensive. It is used only in special situations where the design requirements are stringent and heavily constrained.
For example, the C-5A cargo plane used depleted uranium (DU) to counterweight its main control surfaces.
answered Feb 4, 2019 at 19:29
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11$\begingroup$ It's not really expensive, at least at acquisition time. "Tungsten markets for \$25 to \$45 per pound depending on the form of the metal" "Depleted uranium costs \$5 per pound from old stockpiles" and lead is \$1 per pound. DU likes to burn so I hope one would use it in oxide form. Being a very heavy metal doing nasty things to biological systems (Uranium Babies are horrendous) and somewhat radioactive, use gloves when handling. Do not inhale. Dispose at specialized municipal waste recycling centers. $\endgroup$ Feb 4, 2019 at 20:57
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2$\begingroup$ @DavidTonhofer, thanks for this, the maintenance techs on the C-5 were "on the clock" when working in proximity to the DU counterweights and had to cycle out after a certain number of hours which I cannot remember... $\endgroup$ Feb 4, 2019 at 23:48
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4$\begingroup$ It's not super radioactive, not that I'd want to handle it all that much. I'd rather have to worry about a block of DU than, say, a radon build up or dust from uranium ore processing. I've read that the heavy metal toxicity of uranium will kill you long before the radiation exposure, chemical toxicity estimates put it on a similar LD50 to DDT and MDMA, not all that lethal but still not something to mess with lightly. $\endgroup$– KaitharFeb 5, 2019 at 3:27
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4$\begingroup$ Indeed. Consider also this C-5A fact: its main landing gear bogies are cast from beryllium, to save weight. this metal is so severely notch-sensitive for fatigue failure that there are NO radii in the structure less than 12" and the entire assembly is coated with a THICK layer of paint. Why? Because the oxides of beryllium, when inhaled, cause berylosis, a deadly disease. For this reason, maintenance techs on the C-5 are on the clock anytime they are in the main wheel wells, to minimize beryllium exposure via scratches in the paint... $\endgroup$ Feb 5, 2019 at 3:40
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2$\begingroup$ @DavidTonhofer - Formula 1 cars used depleted uranium for ballast until sometime around 2001. It was disallowed not because of the toxicity, but because of cost. By the time teams got the depleted uranium, it cost about 7500 (US dollars) per kilogram. A team supporting 3 cars at around 22 kg of ballast per car would end up spending close to 500,000 (US dollars). $\endgroup$– rcgldrFeb 5, 2019 at 15:29
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No. For example, recently-manufactured modern paragliders and hang gliders contain no uranium.
answered Jun 13, 2019 at 13:57
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$\begingroup$ It was once my understanding that the FAA took the position that ultralights weren't aircraft, but later someone pointed out to me that this wasn't really true, even though FAR 103 does avoiding using the term "aircraft". I can't recall more details of the thrust of the argument at the moment but basically it was that ultralights may NOT be considered exempt from regulations pertaining to "aircraft". $\endgroup$ Jun 13, 2019 at 14:00