An story on how P&WA
got into building turbofan engines
executive went to a technical conference in which Rolls-Royce made a presentation on the Conway, which was the first turbofan or by-pass engine.
When the P&WA
representative was queried on what the company was doing, he told them that they had planned on having a turbofan engine running in a test stand shortly and everyone would be invited to come see.
On his return the East Hartford, he asked what the h_ll a by-pass engine was?
took a JT3C engine and replaced the first two stages with the first two stages from a JT4A which had a larger diameter. The cases were cobbled up to produce the by-pass and still provide structural support.
When this engine went to test, the thrust and fuel consumption figures demonstrated that there was a lot of promise even though this was not an optimum match.
From this the JT3D engine was developed.
The JT8D has a similar history.
The JT8A engine was developed for the Hound Dog Air to Surface missile as a turbojet throw away engine.
From this came the JT8B, which is the military J-52 used on later Douglas A-4's and Grumman A-6's.
When Boeing came knocking looking for an engine for the 727, P&WA
did studies on a turbofan JT8 and the JT8D was born.