[Syonyk]

That era of aviation was nuts. I wish I was around for it. Men with slide rules working out the limits of material science, aerodynamics, and everything else, all at once. Because it wasn't enough to just push one limit, you had to push half a dozen others to get things to that first limit. And the rate of advance was just staggering.

The XB70 flew in late 1964. Concorde was doing revenue flights in 1976, cruising at Mach 2, with passengers being served luxury food.

> The Air Force learned that pushing the technological envelope resulted in plane that was difficult to build, difficult to maintain, difficult to fly, and perhaps even more importantly, was incredibly expensive; the program cost nearly 1.5 billion dollars, or around 11 million dollars per flight.

And nothing has changed. Pushing the limits is expensive. Always has been, always will be.

[mandevil]

My favorite bit of design from this era went something like this: "ooohhh, we need something that can handle high heat. How about if we made it radioactive?" and so Mag-Thor was born (https://en.wikipedia.org/wiki/Mag-Thor): Magnesium plus Thorium. It's creep resistant up to 350C! And it's only mildly radioactive! That's not a problem, right?

Actually used on the BOMARC and D-21's ramjet engines- which is why you don't originals of their engines on display anywhere.

[dogma1138]

Mag-Thor is interesting it actually has rather poor overall thermal characteristic compared to most metals since its melting point is only circa 650c pretty much the same as magnesium but it basically shrugs any heat upto 350-400c depending on the alloy so it doesn’t changes its dimensions or becomes susceptible to mechanical deformation (it’s basically as hard at 350c at it is at room temp). So it’s useful but only for very specific applications unlike say titanium. And today we have super alloys like inconel which can hold back heat creep up to 650c and it’s annealing starts at almost 900c.

[retrocryptid]

They tell the most pernicious lies about radiation.

[skhr0680]

Fun fact: The real-life inventor of the neutron bomb, Samuel T. Cohen, loved “Repo Man”!

[slow_typist]

The sheer amount of gas this plane must have carried in order to fulfil its mission…

[Syonyk]

Per Wikipedia, the XB70 carried: 300,000 pounds (140,000 kg) / 46,745 US gal (38,923 imp gal; 176,950 L), on a maximum takeoff weight of 542,000 lb - so about 55% of takeoff weight was fuel.

A 747-8I carries up to 63,034 gallons, or about 400k pounds, on a max takeoff weight of 987,000 pounds, or about 42% of takeoff weight.

Interestingly, the ranges are about the same. The XB70's combat radius (there and back) is 3,725 nm, for a straight line range of 7450 nm, the 747-8I's range is 7730 nm.

High altitude supersonic flight is actually fairly efficient... if you can handle it.

[nocoiner]

Was the XB-70 capable of inflight refueling? On a quick look, I can’t tell if that was the plan, or if it was going to be a one-way trip (optimistically landing in Turkey or something to refuel, but realistically…).

[Syonyk]

I don't believe it was capable of it, which is why it was so massive. The SR-71, which required inflight refueling repeatedly, only held 80k pounds of fuel (about 12k gallons). I don't have any good sense of fuel burn vs speed either, but in general, jets like to run high and fast. The old Lear 23s burned about as much fuel (pounds per hour) idling on the ground as they did at cruise, and I think the SR-71 (which mostly used the turbojets to keep the afterburners lit, at cruise...) fuel economy up high was quite good. Apparently the major problem with performance was keeping it from overspeeding - left to their own devices, the engine (... entire engine assembly, however long it was) was running so efficiently that they just wanted to go.

[mandevil]

The actually built XB-70's- the two prototypes- did not have a refueling receptacle. Production models would have had a boom receptacle just like the B-47, B-52 and B-58 did. It would have gone in the upper fuselage about where the delta wing starts.

[rsynnott]

And not just any gas: https://en.wikipedia.org/wiki/Zip_fuel