Difficult to quantify really - there isn’t much flight test history of the F-111 being tested at M3 because it only had a requirement for a short dash speed at M2.5 so was never tested or built to go over that. Anything over that could be certain death in reality so I don’t believe the guy was that stupid considering it was just a check flight.
Anything could have failed that measured the speed - or a computer getting out of bounds inputs could start putting out rubbish - or a sensor was simply not measuring the temps properly as it had melted .
North American XB-70 Valkyrie (P Davies, 2018)
A primary design consideration was the choice of metals for an airframe that would be subjected to the roasting temperatures of sustained Mach 3 flight. On the aircraft’s first Mach 3 flight in October 1965, skin temperatures reached 576°F
NAA chose a brazed sandwich of PH 15-7Mo molybdenum stainless steel in panels, using a thin honeycomb core with a very smooth steel skin bonded to each side.
The steel had to be formed at 1,200°F or -100°F, and NAA produced large, extremely strong, light panels up to 20ft long and very resistant to temperatures of 600°F.
Windshield temps of 600 degrees F were recorded.
Strength was therefore the key factor in this relatively hollow section that had to bear the aerodynamic loads on the wings as well as the high external skin temperatures, which would reach 600°F on the leading edges of the flying surfaces and the nose, and the internal temperatures
of up to 900°F caused by the engines’ heat emissions.
The choice of metals giving the necessary strength, lightness, and heat resistance was therefore crucial. Titanium frames, steel beams, and spars were covered with titanium skins on their tops and sides and the engine compartment doors were also fabricated from 6A1-4V(STA) titanium
alloy skins to provide strength and resistance to fracturing
The limit on the speed of the pig was not engines. Especially the G model. The limit was materials used to make key parts like the wing leading edge. The pig could keep accelerating until it melted the wings.
That means VNE changes with all sorts of atmospheric conditions and altitude. There was a “sprint” time and speed but I’ve forgotten the actual numbers. I’ll ask. It was “go this fast in an emergency but slow down after X minutes or melt the airframe”. Guess a missile chasing is a case of go fast or go to bits.
You also needed to be fairly “clean”. As a bomb truck you couldn’t go fast due to drag and stores limits.
Bottom line. Mach 3+ is plausible. The pig was fast.
Same with G limits. If you overstress the airframe, it could be tons of repair or permanent grounding when you land. That’s still preferable to getting shot down, though!
If its out of the rest of the war though or a write off that might not be that much different if you have nothing left to fight with - not everyone is the USAF or has resources flowing in to replace these things. The pilot will be fine assuming the aircraft doesn’t break up in mid air or you just black out and crash. Looking at the age of some of the jets in service today geez!
That’s is pretty cool and maybe the G was different I don’t have any source on that. The TOs for the others say like in the article it is time limited over 153dC but has a do not exceed 214dC (or M2.5)
Interesting if it was later flight tested because it isn’t just the aircraft makeup being limited to M2.5 things like directional stability drop off a cliff for jets around M2.
I don’t doubt it has the T/D to get to M3 with the extra thrust but from an engineers POV the actual limit is not a canopy or any thing like that but whatever the USAF specified on whatever document was used to make it to. (also I suppose they are not going to be liable when something goes wrong at M2.7 )
