> Remember that Boeing's original plan was to use the 747 as a freighter.

You have to wonder actually if that is even true (I've heard it as well obviously). Reason being Boeing may have been thinking SST wouldn't work or be practical (after all it wasn't) but it was easier to sell a 747 based on saying it could be used as a freighter primarily. If they had said it was just another long range high capacity plane the project might have never gotten approval because of the 'bet the company' risk.

No-one could say it was just another long range high capacity plane, as there was nothing comparable. And at the time, Boeing was spending a lot of money on a specific Mach 3 SST project - it was only later that it concluded that it wasn't feasible.

The upper cockpit is a huge aerodynamic drag compared to previous designs.

Perhaps the 747 was a hedge (and it turned out to be a good one if so), but the design kind of implies otherwise IMO.

There are, of course, Boeing 747 freighters. [1]

[1] http://www.boeing.com/commercial/freighters/

The form of a 747 is the result of technology studies for the Air Force CX-HLS program

http://www.boeingimages.com/archive/CX-HLS-Transport-Study-2...

Has there ever been a flying wing approach to freight flights?

The trouble with flying wings is the fuselage tends to be too short for carrying a lot of cargo. You can't put heavy cargo outboard in the wings because then it's tough to balance the load and the high rotational inertia makes roll control difficult.

Flying wings work fine for bombers because the "cargo" is very dense and will fit into a short bomb bay.

There have been proposals. Here's the Lockheed Spanloader concept.[1] Never built. The idea comes around again every once in a while.[2]

[1] https://books.google.com/books?id=jWlaIWwcsiwC&pg=PA112 [2] https://books.google.com/books?id=C0gUyoYewhoC&pg=PT183