I guess that the 'countdown' was just a way of focusing the 3 crew members attention for the commencement of a fairly intense few minutes, that required extreme concentration and discipline. (I suppose in hindsight, the event must seem a little melodramatic, for us it was the only way to do it).
In actual fact the 'spool up' thing had not so much to do with afterburner operation, more to do with maximising the runway length available by obtaining as much power from the whole engine in as short a period of time as possible. (Being a pure jet, the handling of the engine did not need to be anywhere as delicate as for a fan engine. However, the N1 & N2 acceleration rates were carefully controlled by the control system, in order to stay within their respective surge margins).
The afterburner in actual fact, itself only contributed about a 17% increase in take-off thrust, and was triggered automatically at 81% N1. (Engine #4 was initially a little 'dimmer' on the take- off roll than the other 3 engines, due to it's N1 being limited to 88% below 60 KTS. This limitation was due to low speed airflow stability issues).
There are a few good Concorde shows doing the rounds at the moment, I've been extremely priviliged to have been involved in one or two. I'm Really glad that you enjoyed the show guys.
Dude
