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Large Passenger Aircraft


What is a Large Passenger Aircraft and what are the challenges?

Large Commercial Aircraft – or in the Clean Sky lexicon Large Passenger Aircraft, are generally considered to be aircraft carrying over roughly 100 passengers or an equivalent cargo loading across short, medium and long haul distances. This includes today’s “narrow-body” aircraft which are usually designed and configured around the median of 150 seats, twin-aisle aircraft for medium (200 – 300 seats) and large capacity (roughly 300 – 400 seats) for both mid and long range trips; and “very large” aircraft with two passenger decks and generally over 400 seats.

It should be noted that the largest (sometimes stretched models) of regional aircraft might carry the same amount of passengers as the shortened versions of airliners (the Airbus A318, the shortest aircraft in the A320 family, has approximately 100 seats). One point of difference though is the fact that regional aircraft are mainly intended for short haul flights, whereas Large Passenger Aircraft can be for short, medium, and long-haul missions.

The challenges? From a market perspective, there is fierce competition – not just between the main manufacturers and global leaders (such as Airbus and Boeing) but from what are sometimes misleadingly referred to as "emerging markets" - many of which in fact are not "emerging" but are often nations with well-established aerospace industries. Russia and China, for example, have the ability to produce aircraft that are capable of capturing market-share (especially through access to home markets) – albeit with products that technologically are comparable to the legacy level of the global leaders, using conventional configurations. Nevertheless these aircraft can be produced and supplied at very competitive cost levels and the competition for technology and innovation is certain to increase.

The challenge for Clean Sky 2's Large Passenger Aircraft Programme is to further mature technologies developed in Clean Sky 1, such as the integration of CROR propulsion systems (a radical new type of aero-engine without a nacelle that can ingest air and produce thrust more efficiently than today's conventional engines), and to validate other key technologies such as wings and empennages (the aircraft tail), making use of advanced and hybrid laminar airflow wing developments, as well as an all-new next generation fuselage cabin and cockpit-navigation.

It's an approach that builds on the positive experience in the Smart Fixed Wing Aircraft (SFWA) Programme of Clean Sky 1.

For Clean Sky 2, the Large Passenger Aircraft goal is both high-TRL demonstration of the best technologies and development of disruptive technologies for “2035+” applications to accomplish the combined key ACARE goals with respect to the environment, fulfilling future market needs and improving the competitiveness of Europe's aeronautical industries.



The plan for the Large Passenger Aircraft Programme is to develop these new technologies by streaming them into three parallel workload platforms:

  • focusing on new propulsion systems and their integration in future aircraft
  • the future of the fuselage and aircraft systems concepts for possible next generation cabin architectures, and
  • the ‘cockpit of the future’.

These three platforms will include large scale demonstrators, test rigs and flight test demonstration for the first one.



Platform 1: Advanced Engine and Aircraft Configurations

Platform 1 will provide the environment to explore and validate the integration of the most fuel-efficient propulsion concept(s) and new technologies for next-generation short/ medium and long range aircraft.

A major part of the work will be to build and design technology demonstrators implemented in a representative aircraft environment to reach TRL 5 or 6. The maturity and the performance assessment of technologies will be carried out through large scale demonstrations including campaigns of extensive flight testing. This will be accomplished using full size demonstrators mounted on test aircraft and through fullsize ground demonstrators or through sub-scale model validation in Wind Tunnel Tests. Campaigns with sub-scale flight test aircraft is another mode of testing which is under systematic investigation in LPA Platform 1.

LPA Platform 1 is built upon six main pillars of research, each including at least one of the demonstrators listed below.


  1. Propulsion technologies for Short Medium Range Aircraft
    • Technology Enablers for Integrated Open Rotor Design

      Technology Enablers for Integrated Open Rotor Design

    • Boundary Layer Ingestion Technologies

      UHBR Engine Integration for Future Short Range Aircraft, bringing focus to Aerodynamic and Acoustic Fan Integration Simulator

    • Non Propulsive Energy concept analysis & demonstration

      Boundary Layer Ingestion Technologies

    • Non Propulsive Energy concept analysis & demonstration

      Non Propulsive Energy concept analysis & demonstration

  2. Advanced Rear End
    • Advanced Rear End design structural demonstrator

      Advanced Rear End design structural demonstrator

  3. Propulsion technologies for Long Range A/C
    • UltraFan® Flight Test Demonstration

      UltraFan® Flight Test Demonstration

    • Active flow control for UHBR Engine Integration on Wing

      Active flow control for UHBR Engine Integration on Wing

  4. Natural & Hybrid Laminar Flow Control demonstrators
    • HLFC on tails - large scale ground-based demonstrator

      HLFC on tails - large scale ground-based demonstrator

    • Ground-based demonstrator HLFC wing
  5. Hybrid propulsion system concept
    • Hybrid Electric Ground Test Bench contributing to the development of equipment for the E-Fan X demonstrator

      Hybrid Electric Ground Test Bench contributing to the development of equipment for the “E-Fan X” demonstrator

  6. Novel & Radical aircraft configuration concept
    • Scaled Flight Testing

      Scaled Flight Testing

    • Flight test demonstration of active vibration control technologies/noise prediction methods for rear-mounted engines
    • Radical Configuration Flight Test Demonstrator

      Radical Configuration Flight Test Demonstrator


Highlights of LPA Platform activities

Platform 1: “Advanced Engine and Aircraft Configurations”

Propulsion concept

One major part of the scope of work is to provide the development environment for the integration of the most fuel-efficient propulsion concepts into compatible airframe configurations and concepts which target next generation short and medium range aircraft. The propulsion concepts under consideration range from advanced Ultra-High Bypass Ratio (UHBR) turbofan to hybrid propulsion concepts to Boundary Layer Ingestion (BLI).

In conjunction with the work on new engine and system architectures, studies for Non-Propulsive Energy (NPE) generation will be performed.

The challenge to turn performance improvements for novel engine concepts into improvements of the same order of magnitude when integrated in the aircraft is substantial. Integrating very large turbofan engines requires very intricate design work to avoid issues with the aerodynamic flow at the wing, the engine and other aircraft components under virtually all flight conditions. For example, the system and structural design must be modified to account for the needs of the much higher loads in the engine. The “off-take” of power to run all aircraft systems including cabin pressurization and air conditioning - but also providing energy for cabin lighting, passenger entertainment and galley - are all important considerations when developing new high performance engines.

Engines that have a very large engine diameter and short nacelle require new and effective ways of suppressing noise which need to be applied at both engine and aircraft level.

Research and development in respect of all these challenges is a key part in LPA Platform 1, especially as the project transitions towards the large scale tests of future technologies in wind tunnels and flight tests.

Looking beyond these potential improvements, UHBR engines will be mounted to the wing or the fuselage, or eventually, very large engines will be integrated into the aircraft mainframe structure. This is a potential way to avoid adding even larger nacelles and heavy pylons, which would add unwanted aerodynamic drag and weight.

For high performance engines, a key issue to manage is the ingestion of the boundary layer flow close to the airframe. This dramatically distorts the flow at the engine intake. Understanding the principle of Boundary Layer Ingestion (BLI) and how to treat it using an intelligent and integrated aircraft/engine design is another major element of LPA Platform 1.


Scaled Flight testing

A further demonstration is planned for a comprehensive exploration of the concept of dynamically scaled flight testing. The target is to examine the suitability of dynamically scaled testing for technology demonstration with highly unconventional aircraft configurations, to enable flight test demonstrations that are virtually impossible with modified “standard” test aircraft. The scaling of these tests could allow for a substantial reduction in cost and time to design, manufacture and qualify such test aircraft, thereby accelerating the discovery and validation of radical new aircraft configurations. An important option is a modular design of such scaled flight test vehicles, allowing a “plug and play” insertion of different major aircraft modules, such as alternatively designed aircraft wings or bodies. This would add a new opportunity for research into aerodynamics, aero-performance and flight dynamics.


Hybrid Laminarity

Another major aspectof the scope of Platform 1 is the development of integrated flow control techniques for advanced aircraft performance for the entireoperational envelope. The major technologies relevant to this are the Hybrid Laminar Flow Control technology (HLFC) for skin-friction drag reduction and fluidic actuators for high-lift performance improvement. Additionally, the opportunities and limitations of scaled-flight testing will be investigated. It is an overall objective of Platform 1 that all technologies being developed and demonstrated follow consistent aircraft configuration and conceptual objectives, in order to ensure compatibility between airframes and propulsion technologies.

The flow adjacent to the surfaces of large, fast flying aircraft is not “smooth”, i.e. laminar, but erupts into turbulent patterns very easily. Turbulent flow around transport aircraft creates a lot of additional viscous drag compared to the incidence of laminar flow, which must be counterbalanced by additional engine thrust, leading to extra fuel burn and its consequent CO2 emissions.

The phenomenon of laminar to turbulent transition has been widely known for decades, however a technical solution to avoid it for commercial aircraft in everyday use has not been found yet. The technology to remove large areas of turbulent flow at the main areas of the fin, the horizontal stabilizer or the wings by means of a suction system has been revisited and improved over the last two decades, but all proposed solutions were too complex, heavy and not suitable for routine aircraft operations.

Taking recent results of other national and European funded research programs like AFloNext into account, a new approach towards HLFC is being made in LPA Platform 1 with a more simplified suction system embedded in the aircraft structure. This is enabled by new materials, design and manufacturing strategies.

Following the development of a demonstrator for the Horizontal stabilizer, a ground demonstrator for a main part of a wing will be developed and tested.


Platform 2: “Innovative Physical Integration Cabin – System – Structure”

Platform 2, “Innovative Physical Integration Cabin – System – Structure”, aims to develop, mature, and demonstrate an entirely new and advanced fuselage structural concept in full alignment with next-generation cabin-cargo architectures, including all relevant principal aircraft systems.

Platform 2 technologies and innovative design approaches will bring additional value to the equipped fuselage's contribution to the aircraft environmental footprint, removing separation of functions at design stage, minimizing weight, costs of development, manufacturing, installation and maintenance, allowing increased aircraft production rates.

In order to provision for the substantially different requirements of the test programs, the large scale demonstration will comprise three individual major demonstrators, covering:

  • The Next Generation Multifunctional Fuselage, Cabin and Systems Integration The Fuselage with pre-installed Systems and combined functions will be manufactured using innovative processes and involving Future Factory enablers. This will lead to the demonstration of novel design including new thermoplastic materials for the fuselage, integrating novel and highly automated assembly technologies including cabin systems and pre-equipped modules.

    The Next Generation Multifunctional Fuselage Cabin and Systems Integration

    The Next Generation Multifunctional Fuselage Cabin and Systems Integration

  • The Next Generation Cabin & Cargo Functions will develop key enablers for the cabin & cargo of the future. Technologies such as printed electrics, novel customisable passenger service units, an environmentally friendly fire suppression system and a novel concept for a power optimised cabin will be demonstrated.

    The Next Generation Cabin

  • The Next Generation Lower Center Fuselage demonstrator is mainly based on a new architecture for a Body Landing Gear. This means that the Landing Gear is located below the fuselage instead of being attached to the wing, enabling an optimised wing design that leads to Fuel Burn reduction.

    The Next Generation Lower Center Fuselage

These major demonstrators are supported by the maturation of different materials, processes, testing and simulation technologies, in synergy with the Airframe ITD. This will be accomplished by using a number of test rigs and component demonstrators in the integrated architecture definition during the initial phases of the programme. Technology for automated cabin assembly and structure integration will also be developed with a dedicated functional demonstrator.

The platform objective is to accomplish Technology Readiness Level 5+ by the end of the project.


Platform 3: “Next Generation Aircraft Systems, Cockpit and Avionics”

The objective of Platform 3 is to develop and evaluate innovative and disruptive new aircraft cockpit concepts, as the emergence of new digital technologies increase flight safety and operational reliability. Simultaneously this will improve Europe's Aeronautical industry competitiveness through developmental advances as well as through the reduction of production costs as well as minimisation of lead times.

A rethinking towards a “Human Centric” based cockpit to operate the aircraft will be the basis of the investigations, including innovative functions and ergonomic interface technologies required to reduce crew workload, improve situational awareness, and support disruptive and innovative cockpit operations.

In addition, a value-driven end-to-end maintenance service demonstrator will be developed and evaluated, enabling the further deployment of efficient prognostic based preventive and on-condition maintenance regimes.

Although the focus is mainly on the future large passenger aircraft disruptive cockpit demonstrator, innovative enhanced cockpit demonstrators will also be developed for Regional aircraft and business jets.

Platform 3 will bring advances to the cockpit avionics systems, maintenance technologies and services, raising them to TRL5 or 6 by means of 4 major demonstrators:

  • Large aircraft disruptive cockpit ground demonstrator
  • Regional aircraft Active cockpit demonstrator
  • Business jet flight and ground cockpit demonstrations
  • End-to-end maintenance demonstrator

Most of the demonstrations will be performed using ground tests, and some selected technologies will be brought to TRL6 in flight test environments.

As building blocks for the integrated demonstrators, several Avionics functions will be developed with the aim of reducing flight crew workload, improvement of pilot situational awareness, and by providing increased aircraft systems robustness during abnormal or adverse conditions. These innovative functions and technologies will be developed and integrated in line with the prerequisites of each different vehicle category's Concept of Operations, specifically in respect of Large Aircraft, Regional Aircraft and Business Jets.

  • Innovative multimodal Human Machine Interface (HMI) based upon visual, tactile, voice, haptic interactions are developed and integrated

    Innovative multimodal Human Machine  Interface (HMI) based upon visual

  • New Avionics technologies and communications suite will be investigated to deliver the necessary robustness, flexibility and versatility, and to accommodate the new innovative digital functions

    New Avionics technologies

These functions and technologies will be integrated into 3 cockpit demonstrators:

  • A large aircraft disruptive cockpit ground demonstrator, allowing on the one hand to quickly integrate, evaluate and update the new Human Machine Interface (HMI) concepts, and on the other hand to integrate the systems technologies hosting the innovative digital functions

    A large aircraft disruptive cockpit ground demonstrator

  • A Regional aircraft cockpit demonstrator which implements the crew workload reduction functions and technologies into a regional aircraft's physical and operational environments

    A Regional aircraft cockpit demonstrator

  • Business jet ground and flight demonstrations of enhanced Human Machine Interfaces and navigation technologies will be carried out in order to introduce incremental but significant innovations in terms of navigation, sensors and Man Machine Interface (MMI), in existing cockpit concepts

    Business jet ground and flight demonstrations

  • In addition, an end-to-end value driven maintenance services architecture demonstrator will be integrated and evaluated, with the objectives of:
    • Reduction of operational disruption caused by unscheduled maintenance through application of Health Monitoring and Management Solutions
    • Maximisation of airline and maintenance asset utilization through condition based maintenance and maintenance mobile tools solutions
    • Value Improvement through a service-driven end-to-end integration approach and through a collaborative way of working

      In addition, an end-to-end value driven maintenance

The timescale for facilitating the demonstrators to reach their intended TRLs will last between 2020 and 2023, depending upon the use cases.


CS2 Members: List of Participation