Re: SR-71 - and Ti-13V-11Cr-3Al - replace skins?

Message posted by JB737 on March 27, 2007 at 0:32:45 PST:

Are you trying to verify whether it was always the same skin alloy, and/or trying to figure out if they substuted something else later? If they did substitute a different alloy, they'd have to match up some of the properties, especially the coefficient of expansion with respect to temperature changes. Otherwise, the skin would have to stress or pop its fasteners, or failing that, buckle/bow/etc depending on the geometry and stress situation for a given part.

I don't know if you'd consider it skin or structural, but I have, let's just say, "ongoing access to" several of the quartz optical windows (which were fixed to the aircraft as part of its exterior skin, and the spy cameras peered through) and their corresponding metal frames. They are not as light as you would expect. but that is generally true of titanium parts. Yes, they are lighter than steel, but nowhere near as much lighter as aluminum is.

I believe there were ongoing improvements to the design of the window/frame assemblies circa 1964-66, hence I suspect that many window frames last saw service in the 60s.

I've never had the frames analyzed for exact alloy composition (portable x-ray fluorescence spectrometers cost about the same as a midrange new BMW) but I presume them to be a titanium alloy similar the skin, to match the coefficient of expansion.

I think the double-pane quartz window mechanically floats in something resembling a rabbet in the frame, as quartz essentially does not expand with temperature. The alternative would be to make the frame of Invar, and have the frame float in a rabbet-like assembly on the skin/frame of the aircraft. I don't think the latter is true, as it appears the window frame bolts/clamps in rather than floats.


In Reply to: SR-71 - and Ti-13V-11Cr-3Al - replace skins? posted by psiuh88 on March 26, 2007 at 18:10:49 PST:


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