Bjorn’s Corner: New aircraft technologies. Part 32. Design for production

By Bjorn Fehrm

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.

Figure 1. The production of an A350 composite airliner. Source: Airbus.

Design for production

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.

A very different approach

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.


22 Comments on “Bjorn’s Corner: New aircraft technologies. Part 32. Design for production

  1. Getting high quality effectivly is key, still lots of traps to fall into. UV light, creep, form tolerances, solvent spills onto structures, fiber position tolerances after thermoplastics injection… Airlines are getting use to flying narrowbodies +12 cycles/day with engines on wing for 15 000 – 20 000 cycles. Hopefully can new aircrafts beat that and require less maintenance as corrosion should be less of a problem.

  2. Fuselage more complicated than a wing…? Really?

    A large simple tube with relatively simple loading and easy-to-access, mostly uniform stringer/frame/skin panels versus a double-curved complex form with complex variable loading, packed with systems, hard to access and no two parts being exactly the same shape? Okay, if you say so.

    (Nose and tail excepted)

    • You talk about complex parts (shapes and stresses etc.) and the relatively few systems a wing has, I talk about the sheer number of interacting parts, including brackets and fittings for a fuselage section. What it is about is how you can get the cost of production down, which to a large degree is about reducing the work hours to complete to a finished state. Once you have installed all systems (which for a fuselage includes flight deck, avionics with coms and antennas, cargo equipment, cabin with monuments, oxygen, water, wastewater, furnishing, interior with lighting, IFE, etc.), your potential for saving work hours with pre-stuffed TPC assemblies, compared to how it is done today, I venture is higher.

      In essence, a material which is weldable (TPC) to join a very large number of parts in a rational way, is more important in a fuselage than a wing.

  3. Another aspect to be considered is what does automation and design-for-producibility and initial high-rate production do to one’s assumptions of the learning curve. Historical based learning curves may not apply. With Spirit reporting that they’ve never made a profit on 787 and currently lose $1 million per s/s, it seems that the standard learning curve assumptions will need to be questioned. Boeing in particular with its method of accounting relies upon learning curve assumptions in its aircraft pricing and financial disclosures. All that uncertainty makes closing the business case for a new airplane and negotiating contracts with Tier I suppliers difficult.

    • my thought is to have a flexible contract that either side kicks in aspects of.

      Boeing putting Spirit into Bankruptcy would make their problems worse (or like Charleston they can buy the problem entity)

      What is not going to work is business as usual, both sides need to benefit and not have it setup as a cage brawl.

    • how did Bair’s three day final assembly for the 787 work out for a learning curve?

      “In a revised look at commercial airplane production, final assembly of the 7E7 is targeted to take approximately three days instead of the 13-17 days that today’s airplanes take.

      “Three isn’t a fixed number,” Bair said, “but it gives you the idea of the magnitude of difference we are working toward with this airplane. It will be dramatically less.”


      • Just verifying all software after all components are installed, loaded with the correct version of its software and then fix any problems takes 3 days…

  4. And if Boeing had gone with the new aircraft, they would be worlds ahead as they have not made 50 a month in how many years?

    A way to sell it is to ensure that the buyers know the risk (mostly engines but the 787 has proven how mucked up you can get).

    As such the trend leaders get new planes and a step up in dealing with them and you cut over as others realize (hopefully) you have a good product.

    There are always ways to improve production.

  5. Björn,

    there is lot of talk about gradially improving airplanes. Similarvto what Airbus did to the 320 series: A320 Enhanced (A320E) with a variety of improvements: new large winglets (2%), aerodynamic refinements (1%), weight savings and a new aircraft cabin and finally new engines or Boeing by re-winging 747 ad 777. Is it practically possible to do a carbon winged 321 now and in a few years upgrade the fuselage to carbon?

  6. ChrisA
    That would require all new global manufacturing infrastructure (for composite fuselage…doors…nose…tail) You might get away with a new composite wing for A321

  7. “Boeing … realized it hadn’t solved how to produce the aircraft in quantities of 50 or more per month at the necessary cost”
    This applies just as much to the engine OEMs, except more so.
    If there’s to be a new generation engine for the ‘mainstream’ airliner, it has to be producible in quantities exceeding 150 per month if it’s only on one of the new airframes, and probably 250 per month if it’s on both airframes.
    This has to be done to a design which will be sustainable for the OEM both in capital and operating expenses, and sustainable for the customer both in terms of acquisition cost, maintenance cost and time on wing between overhauls.
    That’s quite some challenge

  8. thanks for all the comments and answers, however, my question was more going to a different direction: does it make sense to do new wings at one point and a few years later a new fuselage, or is this approach a creep, as the 747-8i was somehow or the 350 version 1 and 2 would have been, meaning you ended up investing a lot and in the end you still have an old airplane.

    So, gradually improving possible or it is better to squeeze out of the existing frame what is possible and do a completely new aircraft once all is in place: tomorrow’s thermoplastics wing, cheaper carbon parts for the fuselage and probably some even better turbines?

    • I seems on gradually replacing key subassemblies, it has been done successfully on the Boeing 707, 727, 737, re-using e.g. cockpit, fuselage sections, tails.

      On the 777x it apparently got ~out of control. Minor changes, needing no new TC, were used to shorten lead time & money for the improved 777. The 77W served as certification base and then replacing the wing, engines, fuel, redoing the fuselages, tail and cockpit..

      After the 737 crashes 2018 and the 777x unexpected airframe rupture in 2019, experts took another look at 777x development certification process, running in parallel with the 737MAX. And its oversight structure.

      Everybody was alarmed by the power of the OE vs regulator and the wild shortcuts in (self-) certification. A more holistic certification approach was reinstated iso of gradual enhancements. Doing a new wing, let alone fuselage became a less attractive option.

      So I feel at this stage the XLR wing iso an new composites wing is more likely for a A322. A new wing could easily take >6 years/ E6B, a “simple” /same MTOW stretch half of it.

      • ‘After the 737 crashes 2018 and the 777x unexpected airframe rupture in 2019, experts took another look at 777x development certification process, running in parallel with the 737MAX. And its oversight structure.’

        There was also rumblings on the floor about a high alpha problem with a tail that was too small that they were going to fixed with software. Perhaps those with some insight might be able to comment on the issue and where it stands?

        I’m thinking that this also played some part in the delay to EIS

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