787-8 lessons pay dividends for -9, but risk and caution remain
is understandably cautious when it comes to using the words “promises” and “787'” in the same sentence, but with a little more than three months to go before the start of final assembly of the first stretched version, it is already projecting a far smoother development path ahead for the .
The derivative has hit the 85% design drawing release point while assembly of all the large subassemblies for the first aircraft is beginning. All this is happening as Boeing marks the first anniversary of the initial 787-8 delivery to launch customerand comes as deliveries hit 25 aircraft.
However, Boeing is not fooling itself and knows that both the progress on the 787-9 and the accelerating deliveries of the 787-8 remain silver linings of a dark cloud still hanging over the company and its revenues after years of delays and problems. The bottom line is that deliveries still have a long way to go to match the rising production tempo and that, if the history of the 787 is anything to go by, Boeing would be wise to expect the unexpected when it comes to development of the stretch.
It is due to the hard-won experience on the 787-8, though, that progress on the extended fuselage variant is edging ahead of schedule, says vice president and chief project engineer for the 787, Mike Sinnett. “From a production standpoint, all the major structural pieces are in initial build. In a lot of cases, we're early. It's a significantly different spot we're in than we were with the -8,” he says.
While always intended to be a transformational aircraft for the operators, the 787 has ended up transforming Boeing in more ways than was ever anticipated. Beyond launching it on the path to more electric, more composite aircraft and modular assembly processes, the 787's huge development costs made its leaders gun-shy over opting for the New Small Airplane instead of a reengined 737 in the face of competition from the. Similarly, Boeing's product development office continues to burn the midnight oil over the potentially costly project. Memories of expensive triage for the 787 lurk in the shadows as Boeing weighs pivotal wing and engine decisions for the next generation of its larger sibling.
Industrially, the rescue effort also expanded Boeing's production footprint for the 787 well beyond that originally planned, with unexpected factory acquisitions in South Carolina and Utah. But it is now the same much-maligned production system that is starting to crank out 787s to a build standard that, according to Sinnett, is actively contributing to the better-than-expected performance of the first batch of aircraft to enter service.
“We are getting cleaner aircraft. When we designed it with an all-composite wing and fuselage, we were conservative,” he says. “Then, as we started looking at weight-reduction changes and we rolled in things like the improved wingbox and the results of full-scale fatigue and static tests, this allowed us to be less conservative.” The result is, “we're seeing some level of surprise that it is performing as well as it is. You always want to talk yourself into thinking that something is not quite right, but its performance is basically spot on,” Sinnett adds. “There was a misconception in part because of the weight challenges early on. People expected the initial aircraft would be heavy, and maybe they are by a little bit, but even the early aircraft are performing to specification.”
Structural block-point improvements progressively introduced to the -8 between Line Nos. 7 and 70 are paying dividends, particularly when it comes to the predicted empty weight of the -9, says Sinnett. “We have a very robust baseline and we've learned a lot of lessons. We're ecstatic with where we are with weight. When we hit firm configuration, we locked in on a number and we've just come down on that. As in any new aircraft design, at every turn there's a risk and an opportunity. On the -8, after firm configuration the weight grew, but the -9 is a more stable design that builds on the experience of the -8 in terms of structural static and fatigue.”
The 787-9 is 206 ft. long, or 20 ft. longer than the -8, with two five-frame stretch sections on either side of the wing. Although seating up to 290 passengers in a three-class layout, compared to 250 in the standard version, the -9 is designed to fly up to 8,500 nm, or 300 nm further than the -8. Maximum takeoff weight (MTOW) is just over 50,000 lb. more for the stretch and currently set at 553,000 lb. Boeing has managed to keep the weight target fixed since the firm configuration freeze in 2010, before which the MTOW was around 545,000 lb.
Another advantage the -9 development has over the -8 is that “people are more familiar with the material,” Sinnett adds. Additionally, the results of structural testing following the design improvements to the wing box and side-of-body have built confidence in the underlying capabilities of the composite primary structure. This has allowed Boeing to trim original design margins that Sinnett says now appear to have been somewhat “over-cautious.”
Sinnett also confirms that, contrary to widely published reports this summer, the hybrid laminar flow control (HLFC) system developed to reduce the empennage drag of the 787-9 has not been dropped. The feature, which is the first form of passive HLFC to enter commercial airline service, is “still on the baseline,” he says. Final assembly of the first 787-9 is expected to begin in Everett early in the first quarter of 2013, with first delivery toslated for early 2014.