Space needed by high-bypass fans
How much are high-bypass turbofans bigger that 1950-s, 1960-s pure turbojets or low-bypass turbofans, comparing engines of similar thrust?
Also, are they heavier or lighter?
I have heard quite some planes have actually had engines removed and different engines installed - this is sometimes possible. And pure turbojets have more noise than high-bypass turbofans, as well as having more fuel burn per thrust.
Turbofans work by sucking in a lot of air and accelerating it to moderate speeds, compared to a pure turbojet. Does it mean that a high-bypass turbofan will not work well near another turbofan, as they compete for air to suck in? Pure turbojets and low bypass turbofans are sometimes mounted in pairs, inlets practically next to one another, as on B-52, VC-10 and Concorde. Could high-bypass turbofans be mounted near each other?