Re:Boom supersonic jet readies for rollout
by alfalfasprout on Monday July 13, 2020 @02:25PM
(#23823904)
I never said anything about concorde using afterburners "at speed"/in cruise flight. But the mere use of afterburners in the early stages accounted for an extraordinary amount of fuel consumption.
Didn't SR-71's also leak fuel when on the ground?
Yes but that's a separate concern. The engines were not efficient at slow speed / ground levels even ignoring the "leaks until it gets hot enough to seal the pipes" issue, the blackbird was designed to hit peak efficiency above Mach 3 (generally speaking all jets are designed to hit peak efficiency at their cruising speed, and the blackbird was designed for a cruising altitude of mach 3.2).
Re:Boom supersonic jet readies for rollout
by imtringued on Friday July 10, 2020 @07:30AM
(#23790418)
That's only because they decided to not use tanks inside the wings. The wings themselves contained the fuel. You can certainly build a non leaking SR-71 if a higher weight is acceptable.
> That's only because they decided to not use tanks inside the wings.
It's not only that. It's because they didn't have alloys which would handle the thermal constraints without significant expansion, so they had to design for that expansion. And in the same way rail tracks handle expansion by leaving gaps, that's what they did.
Furthermore, due to limited room and systems able to handle the temperature gradients, the fuel acted not just as fuel but also coolant, heat sink and even hydraulic fluid for some propulsion components (e.g. the afterburner nozzles and inlet guide vanes used JP7 as hydraulic fluid).
Concorde didn't use afterburners "at speed". The afterburners were used for takeoff, and to go through the mach wall.
Concorde burned insane amounts of fuel on the ground because turbojets are very inefficient at low-speed. Not unlike the SR-71's really (though the SR-71 also had such extreme high-speed bypass it was basically using ramjets at speed).