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Thanks Brit 312. "Power set" it is, then. I was aware of the '3 reheat' possibility which is decided before T/O depending on T/O parameters ('is this a 3 re-heat day or a 4 re-heat day?').
On the P1 side of the cockpit is a small hinged piece of metal which can be moved to show '3' or '4'. This is set before flight depending on whether 3 or 4 re-heats are the acceptable minimum for take off that day, so if there is a re-heat failure on T/O, a glance at that indicator will show if it's OK to continue with '3 lit' or not. |
Ahhhh... the famous Reheat Capability Indicator. (Yes that was its official title). I seem to remember that before we did the modification to fit the 'RCI' in the late 1970s, the guys used to set an INS CDU thumbwheel as a memo to whether the take-off was a 'go-er' or a 'stopper'.
It seems a million years ago when we fitted this high presicion lump of alluminium. (Hang on a minute, it WAS :p). Best regards Dude :O |
I've read the entirety of this thread with great interest, having never got to see Concorde in flight, but only visited OAG in Seattle. What a beautiful machine!
My question is: disregarding the certified FL600 / M2.04 / 127ºC restrictions, how high and/or fast do you Concorde builders and designers think she could have gone? :) |
Hello skyhawkmatthew!
M2dude gave a good answer on your question in post #1085, so I think I may quote this here again.
Originally Posted by M2dude
As far as the MAX SPEED bit goes, Concorde was as we know flown to a maximum of Mach 2.23 on A/C 101, but with the production intake and 'final' AICU N1 limiter law, the maximum achievable Mach number in level flight is about Mach 2.13. (Also theoretically, somewhere between Mach 2.2 and 2.3, the front few intake shocks would be 'pushed' back beyond the lower lip, the resulting flow distortion causing multiple severe and surges).
The maximum altitude EVER achieved in testing was I believe by aircraft 102 which achieved 68,000'. |
M2Dude
3) A third isentropic fan shock is generated from the progressively curved section of the fwd ramp 5) A terminal shock system is generated by the coalescence of still supersonic and now subsonic air at the upper section of the ramp area. |
What's an isentropic fan-shock? So the lower lip forms a normal shock and the airflow goes subsonic immediately behind it, the supersonic flow above somehow collide and form a shock between the ramps? I understand how the subsonic and supersonic flow coming together would reduce the average velocity -- I'm still surprised the gap between the forward and rear ramps wouldn't act like a divergent surface and cause the supersonic flow to accelerate rather than come down to subsonic speed. |
CliveL
The first bit of the moveable front ramp was carefully shaped to give a sequence of weak shocks that reduced the Mach Number so gradually that shock losses were minimised. This was close to an isentropic process, hence the name. The whole point of the intake geometry was that the purely aerodynamic boundary between main duct and ramp void was infinitely flexible in shape, which made the design very tolerant of flow disturbances. |
Thanks for your reply CliveL and thanks M2Dude and CliveL again for the great
reply with detail about the intake.:D |
Must have been a highly efficient inlet for a Mach 2 plane: Two traditional oblique waves; a fan-shock (also oblique); a shockwave off the lip that is normal and oblique depending on how far you are away from the lip, and a normal terminal shock. So, isentropic would, in this context, mean that no shock-losses occurred at all? |
And a thank you from me CliveL for your superb explanations regarding intake shock structure. It can not be over-emphasised just what an amazing achievement the Concorde engine/intake combo was. I can think of no other design in the world, before or since, civil or military, where a supersonic engine/intake marriage gave such incredidable levels of performance, stability and predictability. I just regard myself as being extremely fortunate to have been able to 'play with' this amazing kit for so many years and see what design excellance really is. (And at least pertly understand it too).
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Power limit to 60kt
I believe that engine #4 was limited to somewhat less than max power until 60kt because of a vibration issue. Did this mean that reheat for that engine could not be selected until 60kt was achieved?
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All 4 reheats were selected 'on' before take off. They wouldn't actually light until the engine was up to a certain power, so the answer is 'no'. The power-limiting ensures no. 4's re-heat doesn't light below 60kts.
Watch a video of Concorde taking off which gives the view from behind. You'll notice no.4 light up marginally after the other 3 (but there's not much in it as it didn't take the aeroplane long to get to 60kts!). |
Not quite right: the reheats ignite if
(At temperatures colder than -35°C the engine control schedule limits the N1 of all engines to 88% or less.)
Originally Posted by Brit312
Up to 60 kts the F/E could reselect a failed reheat so hoping it would be OK by 100kts
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Thaks Quax. So all 4 reheats should light about the same time, then, regardless of power limiting on #4? It does seem that #4 lags a fraction in vids I've seen.
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This might be because the #4 engine accelerates less fast than the others due to the limiter, reaching 81% N1 a little bit later. But this thread is too brilliant for presumptions (don't want to repeat the mistake of my first post...;) ). Let's see what the Concorde-geniuses add.
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Unique design.
I can think of no other design in the world, before or since, civil or military, where a supersonic engine/intake marriage gave such incredidable levels of performance, stability and predictability. Without proper scheduling, disturbances inside the inlet could result in the shock wave being expelled forward--a phenomenon known as an "inlet unstart." That causes an instantaneous loss of engine thrust, explosive banging noises and violent yawing of the aircraft--like being in a train wreck. Unstarts were not uncommon at that time in the SR-71's development, Basically, a relatively small failure within the intake/spike structure of the SR71 engine, was enough to simply tear the airframe apart within seconds of onset. The scale of forces within these structures therefore, must be almost beyond imagination and yet the Concorde design was such that she did not suffer such destructive failures. My admiration for everyone who worked on her is endless. |
there were already several conduits through tank 11, such as hydraulics for the tail wheel, various electrics, and the 'backbone' fuel manifolds, that ended at the fuel jettison port in the tailcone.
A couple of fairly substantial air ducts would only have displaced a few hundred kgs of fuel at the most, out of the more than 10,000 kgs in tank 11. |
M2Dude
I can think of no other design in the world, before or since, civil or military, where a supersonic engine/intake marriage gave such incredidable levels of performance, stability and predictability. 911slf I believe that engine #4 was limited to somewhat less than max power until 60kt because of a vibration issue. |
Jane-DoH
One of the real beauties of the Concorde intake was that it was completely self-startiing, and so unstarts as such were never heard of. Regarding the vibrations thing, here is my post #80: The reason that #4 engine was limited to 88% N1 on take-off was an interesting one, down to something known as 'foldover effect'. This was discovered during pre-entry into service trials in 1975, when quite moderate levels of first stage LP compressor vibrations were experienced at take-off, but on #4 engine only. Investigations revealed that the vibrations were as the result of vorticies swirling into #4 intake, in an anti-clockwise direction, coming off the R/H wing leading edge. As the engine rotated clockwise (viewed from the front) these vorticies struck the blades edgewise, in the opposite DOR, thus setting up these vibrations. The vorticies were as a result of this 'foldover effect', where the drooping leading edge of the wing slightly shielded the streamtube flowing into the engine intake. #1 engine experienced identical vorticies, but this time, due to coming off of the L/H wing were in a clockwise direction, the same as the engine, so were of little consequence. It was found that by about 60 KTS the vorticies had diminished to the extent that the N1 limit could be automatically removed. Just reducing N1 on it's own was not really enough however; some of this distorted airflow also entered the air intake through the aux' inlet door (A free floating inward opening door that was set into the spill door at the floor of the intake. It was only aerodynamically operated). The only way of reducing this part of the problem was to mechanically limit the opening angle of the aux' inlet door, which left the intake slightly choked at take off power. (The aux' inlet door was purely aerodynamically operated, and diff' pressure completely it by Mach 0.93). |
Investigations revealed that the vibrations were as the result of vorticies swirling into #4 intake, in an anti-clockwise direction, coming off the R/H wing leading edge. |
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