A couple of recent NASA research papers give a glimpse of the "super-STOL" tactical transport concept Boeing is working on under the U.S. Air Force's Advanced Joint Air Combat System (AJACS) studies. Boeing last year won the Air Force Research Laboratory's Speed Agile demonstration contract to conduct low- and high-speed windtunnel testing of a possible C-130 replacement that could take off and land in 1,500-2,000ft, yet cruise efficiently above Mach 0.80.
This photograph of an 8ft-span low-speed model tested early in 2008 in NASA Langley's 14 x 22ft windtunnel shows an earlier iteration of Boeing's Speed Agile concept. It has a hybrid wing/body design with embedded engines for stealth, and a V-tail with ruddervators for low-speed controllability. For high lift, the design uses upper-surface blowing of the inboard flaps, active flow control on Fowler-motion flaps on the outboard wing, and leading-edge slats.
Since this model was tested, Boeing says, the design has been updated to meet AFRL's latest AJACS requirements, which include a heavier payload and larger payload box - almost identical to the Airbus A400M's - to carry the Army's ever-larger and heavier Future Combat Systems vehicles.
The Air Force-backed AJACS is the fixed-wing STOL candidate for the emerging Joint Future Theater Lift (JFTL) program - the Army-supported Joint Heavy Lift tiltrotor is the VTOL candidate. We have seen Northrop Grumman's all-wing STOL design for AJACS before, but here are a couple of images from recent NASA presentations that give a better idea of the concept:
Artwork: Northrop Grumman
Look carefully and you can see the drawing above shows the ducting that routes engine fan air to the inboard and outboard blown flaps, which can be deflected downwards to 90deg and upwards to 30deg. There are also leading-edge slats on the outboard wing sections.
Photo: Northrop Grumman
Northrop says a flying wing provides low wing loading for relatively short take-off and landing distances and so minimizes the amount of additional lift required for STOL. The centerbody provides a third of the total lift, it says, while the wings with blown flaps provide the remaining two thirds. The company, which has a lot of experience with this planform, also believes it can control the aircraft at low speed without a tail.