Since several posters brought up water injected JT9’s on some 747’s I have a few comments.
· Contrary to some above posts the water was injected into the combustion liner via the fuel nozzles.
· There were two water tank configurations. 747-100’s utilised the dry bay in the centre wing box between the front spar and 1st spanwise rib. The dry bay did not exist on 747-200’s so there were 2 tanks, 1 in each inboard wing leading edge.
· Injecting water into the combustion liner caused a thermal shock and metal fatigue and eventually there were instances of the combustion outer case rupturing on take off which blew the cowlings off along with other damage.
· Filling the demin water tank took quite some time as you had the honey truck servicing the mid lav’s, the potable water truck and the demin water truck all trying to get in the same area along with a catering truck at door 2R. On a quick turnaround it was not uncommon to be still pumping demin water in almost up to pushback, the demin water truck usually being the last to get access.
· The 2 operators of water injected 747’s I was familiar with appeared to use the water to lower the EGT in an attempt to prolong the hot section life of the -3A engine. They did not use it for the extra thrust and given the sector lengths they were flying from my location could even have used a derated thrust most of the time. I seem to recall they used water whenever the OAT was above something like 24C. One of the operators only filled the water tank to about 2/3rds of full.
· I have a distant memories of a trans Pacific operator of very early 747-100’s who started to retrofit the water injection system instead of upgrading their -3A engines to -7CN’s (which nearly everyone else did) but quickly changed course and abandoned the water retrofit and upgraded the engines instead. I have memories of seeing at least 1 or 2 of their older aircraft with all the water control panels fitted but inactive (it was over 45 years ago so memory might be playing tricks!!)