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What material was/is used on the skin of the Blackbird SR71 and how was it cooled. How was it manufactured to be stronger with age

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Titanium. Only the hottest portions of the fuselage (the chines) were cooled, using the fuel as a coolant. As far as I'm aware, there was no treatment to make the material stronger with age.

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    $\begingroup$ @securitydude5. There's a great story that the Ti pieces made in summer failed structurally, but those in winter were ok. Eventually it was found chlorine was being added to the domestic water supply in summer to stop algae growth. Once they switched to distilled water, they had no problems. See page 11: cia.gov/library/readingroom/docs/… $\endgroup$ – Penguin Nov 23 '17 at 10:41
  • $\begingroup$ They found the heating and cooling caused by flying the aircraft improved the material strength with age. $\endgroup$ – Mark Jones Jr. Aug 28 at 22:52
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Titanium is the only suitable material which can withstand those temperatures. Stainless steel is much heavier. If you want to find out more about this read Ben Rich's book on the Skunk Works.

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    $\begingroup$ Did you mean to say titanium is not the only material? $\endgroup$ – fooot Aug 28 at 15:50
  • $\begingroup$ Sorry it can be misunderstood. Stainless steel is also resistant to those temperatures however it is too heavy for flying at 70000 feet $\endgroup$ – david david Aug 28 at 15:53
  • $\begingroup$ Remember the u2 was built out of aluminium an extremely light material which made it very fragile. The incident with Powers wss caused when a missile's shockwave destroyed the aluminium, proof of how weak it was. $\endgroup$ – david david Aug 28 at 16:17
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    $\begingroup$ So, contrary to your claim, titanium is not the only material that can withstand those temperatures. It might be the only suitable material, but it's not the only material. $\endgroup$ – David Richerby Aug 28 at 17:46

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