We are all wondering what the next Airbus and Boeing narrowbodies will look like, but NASA is already looking beyond that - waaaay beyond that, to airliners that could enter service in 2030-35.
The agency is holding a pre-proposal conference in Washington DC on 29 November as a precursor to inviting bids for advanced concept studies of what it calls "N+3 Generation" subsonic and supersonic fixed-wing transports.
Under NASA's revitalised Fundamental Aeronautics programme, N equals Now and is represented by today's CFM56-powered Boeing 737. N+1 is aircraft that could enter service in 2012-15. They would still look fairly conventional. N+2 is aircraft that could enter service in 2018-20. They could look like Boeing's Blended Wing Body, or this...
N+3 is way out there, and no-one yet knows what the aircraft could look like. Well NASA has some ideas, but it is not revealing them. It also has some targets. For a subsonic 160-seater they include noise 81dB below Stage 3, NOx emissions 80% below CAEP 2, fuel burn 50% lower than the 737 - and a 70% reduction in field length to allow access to more runways.
Realistically, NASA doesn't expect all of these targets to be met in a single vehicle. They are what the agency calls the "corners of the trade space" - what could be possible if the design is focused on that target.
There is no "N" for a supersonic airliner, except Concorde, but NASA's N+3 metrics for a 100- to 200-seat airliner include an efficient Mach 2 cruise where supersonic flight is unrestricted and a low-boom Mach 1.6 over land, airport noise 20-30dB below Stage 3 and a 6,000nm range. Far out, indeed.