Concorde question

[EDHL]

Originally Posted by CliveL

It's way out of date but you will get some idea from Fig 5 of Olympus 593 Control System by C E G Payne published in Aircraft Engineering April 1967

Thanks, that's very helpful! It hadn't occurred to me to go looking in the academic literature.

I see from the paper that TLA does not correspond purely to an N2 demand, as I had previously believed. TLA does appear to control N2 at higher power settings, but at lower power settings, it instead more directly controls fuel flow.

To check my understanding, I'll summarize what I think is going on.

As I understand it, a given TLA produces two demands: A direct fuel flow demand and an N2 demand. The N2 demand, in turn, feeds into a controller that compares the demanded N2 against actual N2 and from this produces its own fuel flow demand. The two fuel flow demands - the one derived directly from TLA and the one coming from the N2 controller - are then compared, and whichever of them is higher is used to drive the throttle.

The result of this is that there is a changeover between TLA producing a direct fuel flow demand (at lower TLA) and an N2 demand (at higher TLA), and this changeover can be seen in Figure 5 as a "knee" in the fuel flow curve.

Moreover, the specific TLA value at which the changeover happens depends on altitude. For higher altitudes, the changeover happens later, i.e. at a higher TLA. I presume this is because the fuel flow required for a given N2 reduces with altitude, so the range of TLAs at which the direct fuel flow demand dominates becomes larger with altitude.

Do I have all of this correct?

Some followup questions:

• The engine appears to reach maximum power at around 90% of the throttle lever's range, with no further change in engine parameters beyond this point. I imagine the purpose of this deadband is to account for tolerances in the engine control and ensure the engine achieves maximum power when the throttle is pushed all the way forward?
• I don't see any mention in the article of the engine control schedules (lo, mid, hi, flyover). I assume these were only introduced later in the development programme? Do you have a sense which engine control schedule the graphs in Figure 5 would most closely correspond to?