Originally Posted by
jlemon
47. According to a United Air Lines system timetable at the time.....
"The MARK IV is United Air Lines' designation of the advanced DC-8 model equipped with more powerful JT-4 turbofan engines."
well ... the JT4A was in fact a two-spool (low pressure and high pressure) engine, but since it was zero bypass (
i.e., all the low flow went into the high system for combustion) it isn't technically a "turbofan"
the JT3D had an enlarged low-pressure compressor (aka "fan") and a bypass ratio of approximately 1.4 ... in other words, approx 40% of the low flow didn't go into the high system