There are some sharp reality checks in recently published NASA documents for anyone who believes the age of lightweight breakthrough composite airlines is about to begin with the Boeing 787 or the Airbus A350 families.
These papers were released last week as the NASA N+3 studies into the airliners of the 2030s.
They were drawn up without the involvement of publicists, marketing departments or graphic artists with a gift for rakish shark fin tails or dolphin noses.
In short they occupy a bullshit free zone and help flesh out some
clues that have been dropped by Airbus, Boeing and various of their technical and manufacturing partners that the extension of the largely successful use of monolithic composite structures in airliners into thinner, more dynamically stressed places, such as fuselage skins, and even wings, is not travelling as well as promised.
However this article is not about bashing the potential of composite technologies, nor is it a prediction that in the fullness of time Boeing and Airbus will not deliver highly competent airliners that are decisively superior to those more reliant on alloys.
This is about the consequences of letting myth making run ahead of an investment in new designs and their supporting engineering and technology.
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Consider the slide above in the GE/Cessa/Georgia Tech N+3 case for a highly agile 20 seat commuter propjet based on foreseeable technologies usable by 2035.
Then consider the many public record statements made by Boeing about the issues it has addressed with lightning protection (which it took very seriously) and ramp rash among others.
These issues have as the slide indicates eaten the headline grabbing figures about how light the baseline 787-8 would be compared to a jet using the best available alloys in place of woven, laminated, oven baked plies of burned carbon fibre tape, nailed into place with huge numbers of metal fasteners and a significant resort to titanium.
It all seemed a bit like going to extraordinary lengths to make plastic work like metal, by using lots of metal, and devising, one hopes correctly, models for predicting how thin composite laminates will behave under impacts or the stresses of cumulative cycles.
The slide also raises the question as to just what the authors meant by ‘A new approach to environmental protection & damage detection would enable breakthrough weight savings.’
Did they mean, let’s just ignore them, and downgrade the overall safety of the design. Let’s hope not.
Perhaps they meant what Airbus chief operating officer customers John Leahy was referring to when he told me last November in terms of these thinner composite components:
Composites technology in those applications has not in general been getting quite the weight savings that everyone had hoped for, however this may well reflect the limitations of current engineering thinking or trying to use composites in a closely similar manner to alloys, where new design approaches could ultimately realise their claimed potential.
A further slide in the GE/Cessna/Georgia tech presentation, below, looks toward a far more beneficial generation of thin loading bearing composite structures, with a far less metal dependant solution to lightning protection in particular. But before 2035, please!
In current discussions of composite technologies in airliners reference is often made the immense operational experience acquired in military operations.
This is not realistic. Military aircraft do not fly eight pressurisation cycles or takeoffs and landings per day for months on end, on short haul routes, nor do they generally fly for an average of 13.5 hours or more a day on typical long haul operations.
They often only pressurise the cockpit module. They have more opportunities to avoid hail, and dings in ground handling mishaps. They are built for war, not as airliners with survivability requirements in the event of fire or higher G hard landings. Airliners don’t have ejection seats, they have to be ridden to the ground if crippled or threatened by mechanical failure.
What are some of the other clues we have to go on concerning the airliner industry’s current plans for high composite airliners?
Boeing sources have told me, and I’m sure told others as well, that composites are seen as having the more advantages the larger the airliner, so take that as a signal that the all new single aisle replacement for the 737 family will not be as highly composite in structure as the 787 was originally planned to be. And Airbus, in the second interview linked above, says the same thing about its all new A320 sized family of the future, whenever they get around to doing it.
Mitsubishi also said this when it cut, dramatically, the composite usage in its proposed MRJ regional airliner.
The test for the 787 and A350 airliners, at least in their introductory years, will be to convincingly exceed the comparable range/payload performances of the A330 and 777 families. Both of the new families of high composite jets have been sold on their ability to fly long to very long ranges for less fuel and less maintenance.
Show and tell time draws nearer.