I did a search on this topic, and I think it has been discussed before, but I couldn't find what I was looking for. Anyway, I was spotting at LAX the other day and noticed some very nice condensation forming in the engines during the takeoff roll. What causes this effect to occur? Also, why is it much thicker just after the throttle has been pushed up from idle? As the aircraft started to roll the condensation would come and go during the t/o run. Thanks for any help.