911slf
...I have been a Concorde fan since I won a flight on it in 1980...
Lucky devil! I'm glad you enjoyed the flight.
...There appears to be two digital displays per gauge as well as an analogue display...
Only the lower digital counter was actually a display, and was a digital repeater of the total fuel flow information being displayed by the pointer on the dial. The upper digital counter was merely a digital indication of the value to which the internal yellow triangular bug had been set by the F/E using the bug setting knob on the lower right of the gauge.
Very briefly, during the pre-flight set up, the F/E would calculated the expected fuel flows for each engine, during the take-off whilst using re-heats. He would set this on the bug, and this achieved two things.
Firstly, it gave him a good visual indication whether the required fuel flows were being achieved. Too low a fuel flow would indicate a re-heat problem on that engine.
Secondly, it programmed the expected fuel flow into the engine take-off monitor, as this was one of the parameters that had to be satisfied in order for the monitor to illuminate the Green “Clear-to-Go” light.
The Green “Clear-to-Go” light was one of three “Power Management” lights immediately above the N2 gauge for each engine, the other two being an Amber “Configuration” light and a Blue “Reverse” light. Some take-offs would require all four Green lights to be on, other take-offs, depending on ambient conditions, aircraft weight and runway length, might only require three Green lights.
...What was the peak consumption per engine, and why two digital displays on each gauge?...
The maximum peak consumption predicted was 21,700 kg/eng/hr, or 86,800 kg/hr total. This would have been predicted for a re-heated take-off, at +8°C, at an elevation of -1,000 PA.
More typically, on a standard day, at a sea level airfield, 20,700 kg/eng/hr, or 82,800 kg/hr total. You can probably see why we turned the re-heats off fairly quickly!
...accelerating to Mach 2.0 and immediately slowing down again....we only went to 43,000 feet so the sky did not get very dark...
43,000 ft is actually a bit too low for Concorde to be at M2.0, as you may see from
this graph of her Flight Envelope. She would have been limited to around 525 kts / M1.7 at that height, so I suspect you may have been a little higher than you remember, possibly somewhere around 53,000 ft.
Happy New Year
Bellerophon