Weight saving efforts for Boeing Dreamliner might have gone a bit too far

The Boeing 787 ‘Dreamliner’ is a highly anticipated new aircraft with an advertised fuel consumption that is about 20% lower than competitive aircraft. Its designers claim that success based on replacing a large portion of the aircraft’s most weighty components with carbon fiber composite materials that have higher specific strengths – the same strength for less weight or more strength for the same weight – however you want to look at it.

The Dreamliner advanced sales have been strong, with more than 900 orders already in place, even though commercial versions of the plane have not yet flown. One of the plane’s biggest fans is Amory Lovins of The Rocky Mountain Institute. (Aside: I pay attention to some details that others might ignore. The file that underlies the link for Amory Lovins is posted on a Rocky Mountain Institute web site, so it is an internal document with a locally controlled file name. That filename happens to be E06-09_EnergyGuruLovins.pdf. That says something to me about the man and his followers. End Aside)

While listening to his recent speech for the Energy Conversations series in Washington, I heard him praise the plane and its designers and talk about the importance of Ford Motor Company’s 2006 decision to hire Alan Mulally, one of the leaders of the 787 design effort. According to Lovins, he thought that the weight shaving, fuel conservation approach applied to the 787 would be a timely shift for Detroit.

I could not help experiencing a little bit of glee as I read a March 21 Wall Street Journal article announcing that the Dreamliner aircraft deliveries will be delayed – again – as designers increase the size of several of the beams in the center wing box. Builders will add stiffeners to the wing boxes for the first few planes that are already in final assembly. The design changes will certainly add some weight back to the plane, reducing the fuel consumption advantage by some undeclared amount. The other effect of the change, however, may be even more important from a business point of view. The stiffeners and larger beams will be taking physical space inside a major fuel tank, reducing the plane’s fuel storage capacity and licensed range.

For at least one early customer – Jetstar – the limited range of the first few planes off of the assembly line means that they will be unable to fly the routes from Australia to Europe that the company intended them to fly. Since aircraft purchases are big ticket items, I am pretty certain that there was a detailed business case analysis built to support the decision. That analysis would have been specific for the intended routes, the assumed traffic patterns, and the ticket prices that could be charged for a non stop flight. All of those assumptions go up in smoke if the delivered aircraft is not capable of flying the chosen routes.

Once the need for stiffeners is over with the newly beefed up beams, the Dreamliner’s fuel capacity might be closer to the original design, but the overall effect of the weight change will never go away. In other words – the advertised savings that encouraged the rapid early sales may never be achieved. As someone who has read much of the energy related design advice Amory Lovins has been providing the world for the past 30 years, I am not too surprised. In many cases, it seems that he would have been able to provide more useful advice if he had completed either his Harvard or Oxford educations and learned that there are no easy answers to difficult engineering problems.