Special permission is not typically required to walk inside a wooden mock-up of an aircraft, especially when the model lacks wings, engines and even a cockpit.
But the fuselage section behind a small partition inside a normally off-limits hangar belonging to the Brazilian air force's general-command for aerospace technology is not typical. It is the first tangible artefact of Embraer's five-year-old plan to develop a jet-powered rival to the venerable Lockheed Martin C-130 airlifter, which has enjoyed a monopoly on Western demand for a tactical cargo aircraft virtually since it entered production in 1954.
Embraer and the Brazilian air force are gambling billions of dollars that it can carve at least a dent in the C-130's industrial hegemony, and the mock-up is the first glimpse of this concept in three dimensions.
Embraer's KC-390 originated as a jet-powered rival to the Lockheed Martin C-130
Embraer officials have outlined a business case based on a break-even point of 120 orders for the KC-390 in discussions with potential suppliers. According to the company's projections, that represents about 17% of the addressable market for C-130-sized transports, excluding reasonably locked-out markets in China, Russia, Ukraine and the USA.
"I think it's a good idea for them," says Doug Royce, aviation analyst for Forecast International. "They need to find a sector to expand into the military market, and just below the C-130 was a good choice. That's something that Lockheed Martin has been owning and could use a competitor."
The mock-up is a full-scale surrogate representing the KC-390's fuselage section aft of the bulkhead dividing the cargo compartment and the cockpit section. It will help guide Embraer's designers to refine their drawings three years ahead of first flight, and allow the hangar's owner - and the company's launch customer - to start experimenting with how to operate the future workhorse of its airlift fleet.
At the same time, the wooden outlines of the KC-390 reveal how far Embraer's concept has come since it emerged into public view five years ago. Although key elements, including the tail, nose and wing, are missing from the mock-up, one key difference immediately stands out. Beginning slightly aft of the wing box, the top of the rear fuselage rises upward into a bulbous curve.
This is a common feature of modern, jet-powered airlifters, including the Airbus Military A400M and Boeing C-17, because such shaping optimises the rear fuselage for aerodynamic drag in the transonic speed regime. Although not relevant to a turboprop-powered airlifter like the C-130, transonic drag is a key design point for cargo jets.
But this key design feature was absent from the first visuals released in 2007 of what was then called the C-390 - the "K", denoting a tanker mission, was not added until a year later. Accordingly, the C-390 was originally planned to be a fairly straightforward military freighter spin-off of Embraer's successful E-190 regional jet. The goal was not to directly challenge Lockheed's C-130, but offer a low-risk alternative in a slightly smaller size class.
The difference is evident in the evolution of the KC-390's propulsion requirement. Embraer originally studied options in the 17,000-22,000lb-thrust (75-98kN) range, including engines such as the Pratt & Whitney PW6000 and Rolls-Royce BR715.
That was five years ago. Now Embraer is considering two engines for the KC-390 - the CFM International CFM56 and International Aero Engines V2500, with the thrust requirement growing to between 27,000lb and 30,000lb.
All of that extra power is needed after Embraer radically changed the original scope of the programme. As late as 2007, the launch customer for the C-390 was widely expected to be Brazil's Empresa de Correios e Telègrafos - the national postal service. At the time, Correios officials were considering launching a cargo carrier to meet domestic transport markets.
It was also around that time that Embraer's top leadership changed, with Frederico Curado succeeding Mauricio Botelho as chief executive. Whether by coincidence or design, the concept for the C-390 started changing rapidly.
Within a year, the original conventional E-190 tail on the C-390 morphed into a T-tail. It also became clear that the launch customer would not be Brazil's postal service, but the air force.
The KC-390 tanker-transport was formally launched two years ago with a $1.3 billion, five-year development contract from the Brazilian air force. To replace the multitude of functions performed by the air force's C-130 fleet firmly established, the design of the new airlifter grew bigger and more sophisticated than anything Embraer had attempted.
By July 2010, Brazil displayed a full set of performance specifications that offered no doubt about the KC-390's place in the market. While Lockheed offers the C-130J with a maximum payload of 21,770kg (47,330lb), the KC-390 was initially listed with a lifting capacity of 21,410kg. That figure has since been revised downward to 20,865kg, allowing the company's engineers slightly greater margin for overall weight increases. But it is obvious the re-envisaged KC-390 is intended to compete against the C-130J for orders on the world market.
The cargo compartment can support 80 troops
The cargo compartment in some ways offers more flexibility than its rival. Whereas the C-130J's cargo volume is just under 11m (36ft) long by 2.74m wide and 2.74m high, the KC-390 is slightly larger in each dimension. Embraer's payload bay measures just under 12.8m long in front of the cargo ramp by 3.35m wide and 2.9m high, with the height rising to 3.2m aft of the wingbox.
The KC-390's cargo compartment is sized to support a wide variety of potential payloads, including either 80 troops, two M113 fighting vehicles, one Stryker or a modular airborne firefighting system.
Beneath the skin of the KC-390, Embraer is breaking from its original concept to leverage the E-190's technology as much as possible. Instead, the aircraft's size and avionics suite appear poised to allow the company to leverage the KC-390 for its next generation of civil airliners.
New images showing Embraer's cockpit lay-out for the KC-390, for example, show a different system than the one on the E-190. Embraer has embraced the recent trend in avionics displays embodied in the cockpit lay-outs for the Airbus A350 XWB and Boeing 787. The KC-390 will feature five widescreen displays, including one on the centre pedestal, which appears to include a cursor control unit along with sidesticks.
As the KC-390 is designed to take on the full range of missions flown by the C-130, Embraer is building the cockpit to accommodate an additional crew station for monitoring in-flight refuelling and the cargo handling system. There is also a loadmaster station in the bulkhead at the front of the cargo compartment, with a lavatory in the opposite side of the payload bay.