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Experimental Subsonic Investigation of a Complete Aircraft Propulsion system Installation and Architecture power plant optimization

Final Report Summary - ESICAPIA (Experimental Subsonic Investigation of a Complete Aircraft Propulsion system Installation and Architecture power plant optimization)

Executive Summary:
In ESICAPIA an aerodynamic characterization of a Green Regional Aircraft configuration comprising laminar-flow technology as well as rear-mounted turbofans was performed by means of wind-tunnel tests, with a special emphasis on innovative solutions for high-lift devices. In order to achieve this a consortium of four partners was build and implemented. These four partners are:
- IBK-Innovation in charge of project management and model design and data post-processing.
- University of Bristol for loads-calculations, data post-processing and dynamic characterization.
- RUAG for developing an engine simulator allowing to simulate the rear-mounted turbofan.
- EUROTECH (replacing the initial consortium member REVOIND).
In order to perform the test-activities specific requirements for the tests and the WT-model needed to be defined. Due to the fact that the model is large (span of 4.9m) all activities needed to be planned with care including logistics onsite in the WT. The WT was chosen to be the RUAG Large-Wind Tunnel in Emmen.
During the project IBK designed a wind-tunnel model with a strong emphasis on reducing time for configurational changes. This included solutions for actuated devices, which could work together with a hinge-moment measurement solution. In order to optimize and de-risk activities the design and manufacturing of the ESICAPIA-Model was done on strong cooperation with the EASIER project thus taking into account acoustic requirements, like
- Different configuration in the WT (dorsal vs. ventral), model needs to be rotated.
- Landing-gear bay to be realized in a way that is representative of real acoustics
were taken into account upfront and did not lead to a design solution that would impact either test.
Due to the replacement of the initial model manufacturer, a project adaptation was necessary. As a result, the model was simplified, thus removing control-device actuation. The model was delivered to the Wind-Tunnel in Emmen in Q4/2016.
After model availability the tests were performed in the RUAG-Wind-Tunnel using a test-matrix, including both powered and unpowered tests, jointly defined together with the Topic Manager. The Wind-Tunnel tests were performed as planned, allowing a characterization of the noise acting on the wing and analyzing the effect of low-noise technologies developed with the GRA-consortium.
As a final outcome the project can present the aerodynamic characterization of the GRA-configuration.

Project Context and Objectives:
Nowadays, the application of the Natural Laminar Flow (NFL) technology becomes more and more attractive since it offers the possibility to match the ACARE requirements in terms of reducing fuel consumption and of pollution at cruise flight condition. The successful application of NLF to general aviation aircraft was primarily the result of two factors:
First, research activities have provided the understanding of the basic flow physics of laminar, transitional, and turbulent flow. This research began in the early days of NACA (mid 1930s) with studies of laminar flow airfoils. A method of designing airfoil shapes to obtain desired pressure distributions was developed. This work led to the development of the NACA six-series NLF airfoils. Typically the concept that was pioneered involved tailoring the airfoil upper surface to maintain a favorable pressure gradient for as long as possible to maintain laminar flow. Current analytical methods extended these early ideas and allow the designer to tailor laminar airfoil design to the expected flight conditions. Also, new classes of laminar flow airfoils have been extensively tested in wind tunnels and in flight.
The second major factor leading to the use of NLF was the advent of very smooth metal and composite aircraft surfaces which provide the necessary smoothness to prevent disturbances causing premature transition to turbulent flow. General aviation aircraft such the Cessna Citation Jet, the Citation X, the Cirrus single engine pusher propeller light aircraft, the Piaggio P180 pusher aircraft, and the Glasair single place light aircraft are just some examples of successful modern general aviation aircraft designed specifically with natural laminar flow airfoils.
Application of NLF concepts to large commercial subsonic and supersonic aircraft has been studied theoretically and experimentally; however, no application has entered, up to now, the commercial market. An outstanding example of research directed towards large transport applications was the 757 wing noise and laminar flight tests conducted in the 1985 time period.
Later, several aeronautics programs were launched in Europe to investigate the laminar flow technology. Dassault Aviation studied at transonic conditions the NLF concept by designing a laminar wing element mounted on the upper part of a Falcon 50 aircraft fin, which was truncated for this purpose. In Germany, flight experiments were conducted on the VFW 614/ATTAS (ATTAS: Advanced Technologies Testing Aircraft System) research aircraft with a special glove installed on the right wing. The European Laminar Flow Investigation (ELFIN) funded by the European Commission has been initiated in 1989. Beside the improvement of computational methods for transition prediction, it was focused on the development of laminar flow technology for application to commercial transport aircraft. This effort included transonic wind tunnel evaluation of a HLFC concept on a large scale model and NLF flight demonstration on a Fokker F100 aircraft. For the flight tests, a full-chord, partial-span glove was bonded to the original wing surface. Depending on the Reynolds number, on the angle of attack and on the yaw angle, transition was triggered either by TS or by CF instability. The results have been carefully analyzed in subsequent European projects such as ELFIN II or EUROTRANS.
A renewal of interest on laminar flow technology, in particular on NLF, is illustrated by several projects funded by the European Commission. Transonic problems are investigated within TELFONA (TEsting for Laminar Flow On New Aircraft) and NACRE (New Aircraft Concept REsearch), as well as in some of the ITD programs (Smart Fixed Wing and Green Regional Aircraft) of the Clean SKY JTI, while supersonic aspects have been considered within SUPERTRAC (SUPERsonic TRAnsition Control) and HISAC (environmentally friendly HIgh Speed AirCraft).
The improvements of the theoretical models for transition prediction and of the optimization tools for the design of swept laminar wings allow performing multi-objective optimization. It is expected to improve the performance of laminar swept wing not only in cruise conditions but also in off-design condition. In fact, although the laminar flow technology offers great benefits in cruise condition it has some critical issues in landing and takeoff conditions. These arise from the need to have a clean leading edge and by the fact that a trailing edge high lift system is not able to ensure the ClMAX for landing and take-off conditions. Another aspect that can negatively affect the laminar flow coverage is the insect contamination and the icing expected during takeoff and low-altitude operation. The use of a Krueger flap can overcome this problem because it allows obtaining the necessary lift for the landing and simultaneously protecting the leading edge from the contamination of the insects and ice, even if it can limit the laminar flow only to the suction wing side. Today, Krueger flaps are used on several civil transport configurations because they tend to be lighter and simpler. However, Krueger flaps usually have only two positions (cruise and extended) and, as a result, takeoff performance may be somewhat compromised in comparison, for example, to that of three-position slats. An advantage of Krueger flaps over slats is that only the pressure surface of the cruise airfoil is affected by the integration of the leading edge device, and the resulting surface steps and gaps, into the cruise wing. The lack of surface discontinuities on the suction surface has made the Krueger flap the leading-edge device of choice for laminar flow wing designs as illustrated by the study of Moens and Capbern. Another aspect that can affect the extension of the laminar flow on the wing is the location and the installation of the engines. In particular, the installation with under wing engines may present some problems from the laminar flow point of view, because the flow that invests the wing leading edge will interact with the nacelle and the pylon and this can generate disturbances that are swallowed by the boundary layer triggering premature transition. For the laminar wing, a very efficient installation of the propulsion system could be the aft-engine arrangements, because this solution excludes any type of interference between the laminar boundary layer on the wing, the pylon and the nacelle. The advantages of such choice are:
➢ Greater CLmax due to elimination of wing-pylon and exhaust-flap interference, i.e. no flap cut-outs.
➢ Less drag, particularly in the critical take-off climb phase, due to eliminating wing-pylon interference.
➢ Less asymmetric yaw after engine failure with engines close to the fuselage.
➢ Lower fuselage height permitting shorter landing gear and airstair lengths.
➢ Last but not least - it may be the fashion.
But this engine installation could present also several disadvantages such as:
➢ The center of gravity of the empty airplane is moved aft - well behind the center of gravity of the payload. Thus a greater center of gravity range is required. This leads to more difficult balance problems and generally a larger tail.
➢ The wing weight advantage of wing mounted engines is lost.
➢ The wheels kick up water on wet runways and special deflectors on the gear may be needed to avoid water ingestion into the engines.
➢ At very high angles of attack, the nacelle wake blankets the T-tail, necessary with aft-fuselage mounted engines, and may cause a locked-in deep stall. This requires a large tail span that puts part of the horizontal tail well outboard of the nacelles.
➢ Vibration and noise isolation for fuselage mounted engines is a difficult problem.
➢ Aft fuselage mounted engines reduce the rolling moment of inertia. This can be a disadvantage if there is significant rolling moment created by asymmetric stalling. The result can be an excessive roll rate at the stall.
With an aft engine installations, the critical point are the nacelles position that must be placed to be free of interference from wing wakes, so the engine position play an important role for the aircraft efficiency.
Further improvements to the aerodynamic efficiency of a future laminar aircraft can be achieved by reducing the lift-induced drag. The classical way to decrease this drag is to increase the aspect ratio of the wing. This has been done in the past, for example, the A340 wing aspect ratio reaches 9.3. However, wing aspect ratio is a compromise between aerodynamic and structure characteristics and it is clear that for a given technology there is not a great possibility to increase aspect ratios. The alternative is to develop wing tip devices acting on the tip vortex which is at the origin of the lift-induced drag. Many wing type devices have been studied these last years. ONERA, for example, by using CFD approaches and in particular the Euler and Navier-Stokes solvers coupled to the far-field drag extraction technique (allowing accurate drag predictions) have designed several type of devices to reduce the lift-induced drag.
Basic studies have shown that drag reduction can be obtained with variations in planform geometry along a small fraction of the wing-span and with aft-swept configurations.
The Green Regional Aircraft programme of the “Clean Sky” Joint Technology Initiative is developing the future green regional aircraft configuration by using several new technologies able to match the very demanding and critical requirements of the strategic road map stated by ACARE, in terms of a drastic reduction of the environmental impact of air transport by 2020’s noise and gas emission reduction. In order to reduce gas emission, a highly-efficient aerodynamics is mandatory and one of the techniques individuated to reduce fuel consumption and pollution at cruise condition is the Natural Laminar Flow (NLF) wing concept.
The objective of the GRA program is:
➢ To assess technologies able to reduce noise aircraft emission during the approach and landing phases (with engine power at minimum, high-lift devices deployed and undercarriage lowered);
➢ To address technology innovation able to reduce air pollution (CO2 and NOx reduction).
At this end it is necessary to assess and validate the laminar flow methodology used by GRA to design the swept laminar wing both in cruise and high lift condition. As already mentioned, a laminar swept wing has the peculiarity to show low high lift performance. As consequence a leading edge high lift device, such as the Krueger, is necessary and become mandatory to assess and validate the high lift performance of the aircraft. Since the validation and assessment of the cruise performance of the 130 pax geared turbo fan aircraft configuration, with engine rear fuselage mounted, has been planned in the S1MA ONERA wind tunnel, here it is proposed to perform a subsonic wind tunnel test campaign with the objective to validate and to assess the performance of the laminar flow technology in take-off and landing conditions by testing the high lift system, the rear engine aircraft configuration and the T tail configuration.
This is the main motivation of ESICAPIA. This experimental validation was performed by testing a complete powered model at subsonic speed at a significant Reynolds number. In particular, the test campaign focused on the validation of the overall aircraft architecture and of the rear-fuselage power plant integration and on the optimization/development of the:
1. Engine location.
2. Tail plane configuration and empennage sizing.
3. Winglet concepts.
In order to fulfil this, a very complex model was needed. The modelling approach itself had to be innovative in order to make sure that all results could be achieved within a given timeframe and budget.

Project Results:
The following scientific and technical results have been identified:
- ESICAPIA was able to perform the aerodynamic characterisation of the GRA-developed innovative aircraft configuration for next generation GRA Aircrafts. This includes the delivery of test-results usable for deriving aircraft stability and control data.
- ESICAPIA also delivered the comparison of the aerodynamic efficiency of different high-lift devices and two different winglet-devices. ESICAPIA was able to show the aerodynamic influence of the turbofan simulator on the overall results.
The technical results were delivered to the GRA-ITD and support the CS-GRA work performed in CS1 and CS2.
Within ESICAPIA several technical achievements were realised
- The use of actuated devices in the WT is not standard approach nowadays, however, it can improve the use of the WT test-time considerably. In ESICAPIA solutions for this were developed, unfortunately, due to the complex project setup, they were not chosen to be implemented into the final test. These solutions will be used in future R&D projects, in particular they are currently extended for implementation in the project POLITE and will also be candidates for the project WTM-RECYCLE.
- Within ESICAPIA IBK has developed local balances to measure hinge-moments. For the same reason as the actuators this technology could not fully be exploited during the ESICAPIA-campaign, however, the knowledge generated is available and will be used in future projects.
- RUAG has designed a turbo-fan simulator which allows performing WT-tests in turbofan configurations taking into account the effect of the mass-flow through the turbofan on the overall aerodynamic performance. RUAG has demonstrated the performance of the solution successfully through the test in ESICAPIA.
Potential Impact:
Bringing together a complementary, in terms of competencies, set of SMEs, University and Industry, allows for commonalities to be identified and opens the possibility for cross-domain sharing of concepts, methods and tools in order to enable reusable embedded technology development. In addition, the ESICAPIA consortium included one of the largest European Wind Tunnel with extensive experience in mechanical design of aircraft models, the development of hydraulic motors, on the development of equilibrium in the wind tunnel and sensors for measuring the wind tunnel testing. These transversal competences, added to the specific competences of the involved SMEs, enabled the consortium to be extremely confident in solving any critical problem that requires interdisciplinary expertise, thus allowing ESICAPIA to address any technological innovation and/or any new model. This cooperation between partners enriched their knowledge and their capability in design and manufacturing. On the other hand, the development of engine simulators for turbofan increased the capacity of the wind tunnel that can offer this service to all European aeronautical industries. This allowed increasing the competitiveness of the European aeronautical industries in the world.
The impact of this project will work on several different levels:
• Regarding JTI-Cleansky this project will help in solving important questions about the landing and take-off flight conditions. In fact, the project aimed to investigate the high lift devices more appropriate for wings showing laminar flow and their application on future Green Regional Aircraft. On an international level this increases Europe’s competitiveness in the development of the future natural laminar aircrafts, since the landing and take-off flight conditions are strongly affected by these devices. Natural laminar flow technology without appropriate high lift system cannot be used. The optimization of winglets will contributes to further decrease the drag by reducing the induced lift. As consequence both technologies lead to reduced fuel burn by
o Reducing drag (NLF)
o Reducing weight (LC&A)
and are therefore in line with the ACARE-goals
• Apart from an national level each partner that contributes to the project has several advantages:
o Insight into high fidelity test results for an advanced technology aircraft wing
o A reference project that shows competence on an international level as well as successfully working together as a multi-disciplinary team
o All partners in the consortium have the opportunity to further increase their know-how by working in synergy and in an international context. In case of the SMEs this can be further exploited by transferring IP generated in this project into industrial applications. The research facilities strengthen their competence in their field of work.
o The SMEs strongly interacted with one of the largest European Wind Tunnel (RUAG) and this provides a formidable chance to enrich their expertise
o One university is present in the consortium; members such as IBK are giving lectures at universities, too. This allows transferring knowledge achieved in this project to future engineering generations.
• RUAG contributed to the project and will gain several advantages:
o Development and availability of engine simulators coupled to turbofan, for future Turbofan Aircraft testing
o Show-cases for complex model tests. Most tests at RUAG are highly confidential, a complex test-campaign like ESICAPIA (seen to be together with EASIER) allows RUAG to carry out dissemination activities.
This will contribute to increase the competitiveness of the European aeronautical industries because they will have a facility that can also simulate landing and take-off conditions by using engine simulators for turbo fan aircraft configurations.

Socio-Economic Impact/ Wider societal impact:
Due to the strong technical focus of this project the direct socio-economic impact of this project is limited.
Indirect IBK as well as EUROTECH as SME´s are seeing gender equality as one of the relevant topics for their human-resource strategy. Within IBK ~30% of the employees are female (seen over all technical units). Apart from that IBK is very supportive in enabling work-life balance, especially supporting young families with part-time jobs. This helps to keep young and very skilled professionals in the company, provides a good internal climate and a forward oriented mind-set.
Being able to positively support these projects as SME is therefore supporting IBK´s and EUROTECH´s strategies.
All work packages undergo an internal check from each partner for exploitation. The management of knowledge and intellectual property, as well as the establishment of exploitation and dissemination strategies are dedicated
− To manage the generated knowledge and confidentially-related issues.
− To identify the results that can be disseminated (through publications, conferences, workshops, technology transfers)
− To identify results that should be protected (through patents, copyrights or secret) and - if necessary - to achieve an agreement in case of joint ownership.
− To analyse end-user requirements and a potential market as an exploitation strategy.
− Intellectual Property Rights and dissemination of knowledge are not incompatible, provided that they are based on clear principles and rules.
Ownership of results, mutual granting of access rights, IP protection (including patenting) and licensing policy are defined in a Consortium Agreement between the two participants.
Currently the following items have been identified for further exploitation:
- RUAG has developed solutions for designing, manufacturing, operating and testing turbofan simulators. This strongly improves their service portfolio and will be directly exploited by them.
- IBK has developed solutions for quick model changes and tested them up to prototype level. Due to the complex management issues arising during the project the ESICAPIA-model was simplified, thus not allowing to test these features. However, the design was matured at IBK and IBK will exploit this in future projects.
- IBK has designed component balances for all movable devices. Similiarly to the model actuation activities those were not used during the tests, however, considerably knowledge at IBK was developed and will be exploited.
- In ESICAPIA there was a need to quickly rotate the model after the aerodynamic test campaign to implement it into the acoustic configuration. This was realised in cooperation with RUAG in a very efficient way, reducing the WT-blocking time and improving in total the output.

List of Websites:
no public website
Coordinator contact:
Stephan Adden
IBK-Innovation GmbH & Co. KG
Butendeichsweg 2
21129 Hamburg

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