Yesterday (Aug 14) my sister-in-law and her husband took my wife and me to the National Air and Space Museum Annex near Dulles Airport outside Washington DC, which I'd never seen. It has some ordinary displays of stuff that is “lower priority” than the things at the main museum on the Mall, but also some very large exhibits that literally wouldn't fit. The annex was huge, and we only saw about 3/4 of it in the 5 or so hours we were there. The three big deals for me, in roughly this order, were the Discovery space shuttle, the SR-71 Blackbird, and the Enola Gay.
It was neat to be able to see the Shuttle up reasonably close, but of course it is surrounded by guardrails that keep people from touching it. If I recall correctly one of the signs said that NASA kept the main engine, and two of the three auxiliary engines were replicas, but one of them flew 15 missions. The payload bay was closed; the way the shuttle was placed you might not have been able to see in even from the balcony. I was a little disappointed you couldn't go inside, as you could in the Skylab backup at the Mall museum, but that never flew in space; Discovery is a national treasure. The CanadArm was on display beside it.
I don't know how long the SR71 was there but it was front-and-centre as you came in, so it may once have been considered a key attraction until Discovery upstaged it. It was a spy plan that flew at 80,000 feet at Mach 3.2, back before there were spy satellites. The guided tours started there. We decided to wander on our own instead of taking the tour, but one was starting when we got in, so we listened to the docent talk about it. He kept saying "we did this" and "we did that". The first time I just assumed he meant the US, but it turned out he was an actual SR71 pilot.
He talked about some of the missions they ran. The SR71 produced a double sonic shockwave, one from the nose and one from each engine nacelle (any given spot would only be hit by 2 of the 3 sonic booms). Nothing else made that double-boom sound. It was mostly for spy missions, but every so often they'd fly over a prisoner of war camp in North Vietnam (he mentioned the Hanoi Hilton) to say "we haven't forgotten you." Years later he got to talk to some of the POWs and they said it helped keep them going.
Enola Gay took me by surprise; I recognized it from a distance as a World War II bomber, and did guess it was a B29 Superfortress, but didn't realize which one until I saw the name painted on the nose. So close to Aug 6 it had a lot of emotional impact (this year being the 70th anniversary of the Hiroshima atomic bomb).
They're restoring John Glenn's Mercury capsule (first US orbital flight). You can see it from a balcony above the restoration room, which has a half-dozen things being restored right now, including the Gemini 4 capsule used for the US' first spacewalk.
There were a lot of other interesting planes. One was the "bird leader" ultralight plane they used in Fly Away Home. It had a cage around the propeller to minimize the possibility of damage to the birds. I think it was once a real working bird-guide plane. I need to read more about it; I thought the movie made up the concept of leading birds on migrations. They also have the Gossamer Albatross, first human-powered plane to cross the English Channel. Plus a Concorde.
They had a Cessna 150 (a small 2-seater, which I learned to fly on back in 1977), which kids could get in to play with the controls. Also a simulator of some sort; if we had more time I would probably have waited in line to try it out.
I have a little trouble with one hip, but providentially it didn't start to hurt until we were ready to leave. I bought two t-shirts in the museum store and we headed out to brave the rush-hour traffic. All in all, a very fun day.