September 29, 2023, ©. Leeham News: We are discussing the Detailed design phase of an airliner development program. We have talked about program management methods, development techniques, and tools for Detailed design.
But there is one area that is more important than even the aircraft aerodynamic, structural, and systems design for a new Heart-Of-The-Market aircraft: how to produce it in higher volumes and at lower cost than before.
In new aircraft programs, it has always been stated: “Design for the production is essential.” But this phrase has got a new meaning over the last 10 years.
One major reason Boeing didn’t go ahead with its clean sheet replacement for the 737 15 years ago was that while it had an efficient composite aircraft design, the program realized it hadn’t solved how to produce the aircraft in quantities of 50 or more per month at the necessary cost.
The efficiency and comfort of a new airliner are important, but as important is that it can be priced at the right cost level and generate the necessary margin for the OEM.
Both Airbus and Boeing are doing extensive studies on how to produce a next-generation aircraft with composite structures at lower costs and higher rates.
The Boeing studies expanded in scope over the last 10 years during the NMA programs. Speaking to project people and listening to top management, it was always emphasized: “This new generation is about how we produce it, more than anything else. Our engineering priorities are reversed; first, we must understand how we shall produce the aircraft, then we design it”.
The NMA was never launched, but the work on production methods and how to design for a rational high-rate production continues.
Airbus is running large-scale technology programs on how to produce the next-generation composite aircraft that shall replace the A320/A321.
The composite wing program is called Wing Of Tomorrow (WOT) and consists of Airbus UK and its key suppliers, such as GKN and Spirit Aerosystems. The WOT aims for a 90% reduction in manufacturing time for a composite wing. It involves Resin Infusion Out Of Autoclave (OOA) skins, Thermoplastic ribs, and a building principle where there is no “in-tank” work (work from the inside of the wing).
The fuselage program is an EU-sponsored Clean Aviation program called Multifunctional Fuselage Demonstrator, MFFD. As a fuselage is more complex than a wing and has more interacting parts (systems, cabin, cargo, avionics, landing gear, APU..) the MFFD program is focused on Thermoplastic composites. It can be given more complex shapes through injection molding pre-formes or advanced in-situ consolidated tape placement, and parts can be assembled through welding.
Even if the thermoplastic material is more expensive than thermoset composites, the production cost for a fuselage will be lower and the production rate higher as it doesn’t require resin curing after the composite is formed (for instance, a tape method has already crystallized resin tape, which is heated by the tape layer to join it to previously placed material) and has fewer time-consuming “drill and fill” fastening operations.
The desing methodology for the MFFD is also different. It’s an inside-out design, and it puts together system-stuffed assemblies that are then welded together into pre-stuffed fuselage sections.
The above is a mere glimpse into these technology programs. They have one thing in common. They reverse the desing priority between overall aircraft design for performance and functionality and the following production preparation of what’s designed.
The production technology and methods now precede and influence the overall aircraft design. This has happened before, like when aircraft went from fabric-skinned space-frame constructions to stressed-skin aluminum designs, but it’s the first time in the last 60 years that the design process has been reversed.