Guy Norris/St Louis
McDONNELL DOUGLAS (MDC) and NASA unveiled the once-classified X-36 tailless fighter-agility research aircraft at St Louis, Missouri, on 19 March, revealing a canard-configured design.
The sub-scale remotely piloted X-36 is said to be the first fighter-type aircraft to be designed from the outset without vertical or horizontal tails, and clearly shows the design heritage of the Northrop/ MDC YF-23.
The MDC/NASA team expects the tailless aircraft to be more manoeuvrable, agile and stealthy than any conventional current or near-term fighter.
One of the biggest challenges of the six-month flight-test programme, expected to begin around June, will be evaluating the complex integrated propulsion- and flight-control system (FCS), says MDC X-36 programme manager David Manley.
The aircraft's fly-by-wire FCS will integrate control inputs, using split ailerons and a still-classified thrust-vectoring system to compensate for the absent tail surfaces.
The thrust-vector nozzle will provide the initial control input until its limits begin to be reached, at which point the split ailerons will gradually take over.
Three ailerons are mounted on the trailing edge of the wing, which is sharply "cranked" towards mid-span in the familiar low-observable characteristic of recent stealth designs.
The two outboard sections function independently and split to provide yaw control (using drag), while the inner section acts like a "typical flaperon", for pitch and roll control, says Manley.
Although thrust vectoring is a key element of the X-36 design, the aircraft will still be flyable in the event of a thrust-vectoring-nozzle "lock-up", or other failure. "We are looking for yaw power without a tail and we basically ended up with what the [Northrop Grumman] B-2 team did," explains Manley.
"The B-2 has a lot more span, so we had a tougher job. Instead of the flaps opening symmetrically, the upper and lower surfaces separate or move together as an aileron," he says. He adds that the wing shape was driven by the sweep.
Foreplanes were added to increase pitch-down control authority and move through +10¡ to -80¡ to compensate for the large pitch-up moment generated by the chined fore-body at high angles of attack. "They needed to be large to help destabilise the aircraft," adds Manley.
The thrust-vectoring system, which was hidden from view during the roll-out is based on a design proposed by MDC engineers in 1989, says NASA X-36 programme manager Larry Birkelbaw.
It is understood that the system deflects engine exhaust in the yaw axis only, probably through a set of vertically mounted vanes. The gases exit through a flattened exhaust nozzle, which is recessed slightly beneath the aircraft's broad "beaver" tail.
The first of two X-36s was made in just 28 months, using rapid prototyping methods, at MDC's Phantom Works. Final assembly began in June 1995, some 17 months after MDC and NASA officially embarked on the $17 million programme.
The airframe structure is of machined aluminum covered with largely composite skins. The fuselage is skinned with LTM-10 composite, which does not require curing in an autoclave, while the wings are skinned with IM-7 composite.
LTM-10 is also used to form the bifurcated inlet/diffuser subassembly, which is scaled directly from the F-18E/F design. The intake lips of the scarfed inlet are blunted, having a larger radius to suit the slower operating envelope of the X-36, which will be flown at speeds up to 160kt (300km/h) for initial tests.
Off-the-shelf components are used heavily, to keep costs down. Examples include the 3.2kN (720lb)-thrust Williams International F112 turbofan, developed for the cancelled advanced cruise missile, a single-channel Honeywell flight-control computer.
Source: Flight International
