Bjorn’s Corner: New aircraft technologies. Part 28. Alternative Preliminary design

By Bjorn Fehrm

September 1, 2023, ©. Leeham News: We described the Preliminary design phase of an airliner development program last week. One could say this was the classical way that aircraft projects conduct Preliminary design.

There is a different way that Conceptual and Preliminary design can be run. It’s more along the lines of pre-development of functions, as a reader commented on two articles back.

Figure 1. An alternative new airliner family development plan. Source: Leeham Co.

Alternative Conceptual and Preliminary design

The gaps between new airliner projects the size we are looking at, Heart of the Market or Widebody, are going from 10 to 15 years historically to decades without OEMs like Airbus or Boeing developing a new generation of airliners.

Historically the time between aircraft projects was spent exploring new technologies and their suitability in a next-generation plane project.

However, the extended time between projects and the new possibilities to make detailed digital models of functions and systems makes it possible to develop, test, and then prepare a detailed digital model of candidate functions and systems that can be part of a next-generation airplane family.

Such work can be decoupled from actual airliner projects and will prepare a library of “pre-developed” solutions and systems that can be used in the project.

The Conceptual phase is still preparing different candidates to fulfill the Marketing and Sales department’s specifications for what the airliner family shall achieve in the market. The Preliminary design phase now expands in scope and OEM workforce, Figure 1.

A deeper Preliminary design phase

The preliminary design phase now has the overall architecture of most systems settled, with detailed digital models describing their functionality, performance, and installation consequences (mass, space, hydraulic and electric power, cooling, wiring /piping requirements).

The Preliminary design still sizes the overall aircraft, its aerodynamics, forces, moments, etc., but the availability of detailed digital models of virtually all systems means these can be sized and scaled to fit the aircraft.

Out comes a definition of the aircraft, which is much deeper and more correct as systems have now influenced the overall design of the aircraft with their volume, mass, and power requirements.

The detailed studies with CFD and windtunnel tests for aero and FEM runs for structure are still made but now have more correct systems simulations as inputs.

Ultimately, the digital models of different parts of the aircraft can be put together to generate a “Digital Twin” version of the aircraft, giving a much deeper, more detailed definition of the aircraft to the next phase, which is Detailed design.

Early simulation of key operational processes

With a well-designed Digital Twin, it should also be possible to do airport turnaround and mission simulations that can test the limits of what the design can do. The demands of this aircraft type will be shorter turnaround times with still larger passenger, bags, and cargo streams on and off the aircraft.

Different solutions in the cabin and for systems give different results. It can influence design trades and system choices before the aircraft goes through a successive design freeze so that detailed structure and system design can work against a stable aircraft definition and experience a minimum of changes.

The importance of a stable overall design

Virtually all systems in the aircraft and many structural parts are subcontracted from suppliers, and it’s important for all parties to have a design that doesn’t change once the detailed work packages are contracted to the supply chain.

If the above “pre-developing” of large parts of the aircraft is done successfully, it can shorten the aircraft’s project time in phases downstream of Conceptual and Preliminary design. The Preliminary design phase is expanded both in scope and work packages in this version, so it will not be shorter than the classical version. But it will speed up the total project if done correctly.

13 Comments on “Bjorn’s Corner: New aircraft technologies. Part 28. Alternative Preliminary design

  1. Engineering might start with the best suppliers, but as purchasing gets involved in cost cutting lots of them loose their position and money/politics get involved from sales/governments as they are replaced with cheaper/new ones and it never stops as they might fail in test/delivery/mass and get replaced again together with requirement creep that puts new requirements onto the suppliers that often can charge extra for late changes once firm contracts are signed. You also want multiple manufacturers of many parts to ensure supplier/cost pressure and it requires even more control (just lock at the Super Puma power gearbox story)

  2. At some point it would be interesting to know why the design process (and ultimately EIS) today, despite all of the automation, takes so much longer than what Boeing managed to pull off with the 747, which seemed like a much larger technological leap than say updating a 737.

    • I can think of a few reasons, which are all linked:

      – Technology maturity; back in the day, you were working with relatively new ideas and techniques which meant that every simple improvement led to a significant step forward – now it takes many rounds of development by many engineers in many teams before your much-more-complex part can be considered worth it for application on a new aircraft.

      – Safety increases; aircraft have to achieve higher levels of safety in all sorts of ways compared to the 1960s. More time required to achieve/justify/test to higher standards.

      – Regulatory paperwork; see above – increased paperwork and increased restrictions means more time required to achieve/justify/test to the satisfaction of the authorities.

      – More corporate environment; increased levels of management, more suppliers, more focus on market and profit all makes the whole thing less nimble and more cautious.

      So basically everything’s more complex and there are no easy gains to be made any more. It’s all about grinding and grinding and grinding before you finally get anough improvement to satisfy customers, regulators and managers.

      • The first passenger jets benefited from the early jet fighters and bombers and could use the same suppliers. They quickly become more reliable than the piston powered DC-7, Lockheed Constellations and customers did not expect much more. Today it is different. The Air Forces do not drive the same amount of technology that can be reused by new airliners and the commercial engine/systems/component and fuselage manufacturers have to develop and certify more on their own with partners. Hence the price/reliability pressure is much higher causing it to take much more time and money to make something much better than what is available today. Still with volumes increasing you can spend more just like the car industry does for each new model. Now brand new car models designed for robotic builds are introduced every 3-9 years.

  3. Shorter Turnaround

    Which factors can slow down the boarding process?

    -The number of exit-doors used for boarding.
    Sometime there is one jet-way, sometimes there are two…

    -The width of the aisle.
    A narrow aisle makes it impossible, for passengers to keep boarding, while a person stops to find room for his hand luggage.

    -The size of the overhead bins, on narrow body aircrafts.
    New generation of larger overhead bins, have been installed on different airliners, with a variable degree of success. The best option I have seen is the extra-large overhead bins installed on the A-321 neo. They are great.

    -When passengers find room for their hand luggage easily, the boarding procedure is accelerated, and flawless.

    -A fast boarding makes possible a short turnaround.

  4. Shorter Turnaround
    What affects the speed of boarding?

    -Total number of passengers
    -Type of aircraft
    -Number of doors used for boarding
    -The width of the aisles
    -The size of the overhead bins
    -The time of the flight
    -Proportion of Jet lagged passengers
    -Proportion of elders on board
    -Number of people with reduced mobility
    -Number of families travelling with children
    -The social culture of the passengers
    -How well lit the passengers cabin is
    -The efficiency of the airline staff at the airport
    -The efficiency of the security control, at the airport
    -The airport infrastructures
    -The quality of the IT systems at the airport …

    • I foresee statutory limits on turnaround times being imposed. There are a number of disturbing incidents involving ground personnel being ingested into engines.

      The constant pressure to shorten turnarounds, the shortage of suitable recruits combined with political pressure and lobbying be legacy carriers may well impact that aspect of design.

      • Here are some of the reasons, why some ground staff have been ingested by aircraft’s engines (lately):

        Lack of experience
        Lack of training
        Lack of supervision
        Lack of situation awareness
        Lack of precaution
        Lack of personal maturity
        Lack of prudence

        Short turnarounds has been done by low cost carriers, all over the world for decades

        • WN were the most emulated in this practice but things have evolved in terms of aircraft gauge but the 30 minute (or less) t/a still remains the goal.

  5. “Virtually all systems in the aircraft and many structural parts are subcontracted from suppliers, and it’s important for all parties to have a design that doesn’t change once the detailed work packages are contracted to the supply chain.”

    Let’s think about this statement for a few moments as to what the implications are:
    – For a composite airplane, the technology used for production has been identified and sufficient number of pre-production manufacturing trials have been conducted to ensure that the equipment, which likely has not yet been installed and qualified at this point, can fabricate the geometry with acceptable quality without voids, wrinkles, porosity, and resin loss. And suppliers have been assessed to ensure that they are capable of fabrication at rate.
    – The full certification approach has been identified for both systems and structure, including systems-structures interaction. Novel features which require special conditions by the FAA/EASA have been coordinated and agreed upon for certification requirements. Risks associated with particular certification approaches have been mitigated through developmental tests.
    – Sufficient buffer/margins have been set aside for risks which may manifest themselves in testing for key parameters such as L/D, takeoff field length, approach and landing noise, aircraft weight, etc.

    Let’s not fall for the hype of the digital twins are going to dramatically reduce developmental time. If anything the amount of upfront work to successfully utilize a digital twin for subsequent benefits in low rate production will require more engineering resources and investment, especially by suppliers who may not have finalized contracts at this point.

    • Thanks for this comment, JB, particularly your final
      paragraph. We’ll see how it goes (yet again).

  6. Deeper preliminary design phase:
    Superb article. Make you want to get back to work… May be one important factor for next NMA would be engine performance data interface with nearly all a/c systems : Because of the probable electric hybridation , and a fortiori for an hydrogen aircraft, the data interface of the classic aircraft OEM propulsion team ( engine+ nacelle+pylon ) with almost all the other aircaft systems will be more complex to define: one element leading to this fact is the message from the Airbus CTO explaining that the the relationship between both the “global ” engine and aircraft manufacturer design office is already changing . A lot of ground iron bird test and preliminary flight test will be needed to freeze these data before going ahead with detailed design phase. Exciting

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