Final Report Summary - REMFI (Rear Fuselage and Empennage Flow Investigation)
Business needs are placing an ever-increasing demand on the aeronautics industry to develop and manufacture aircraft at lower costs, with improved flight capabilities and a reduced impact on the environment. Hence, a primary objective for the aerospace industry is to offer products that not only meet the operating criteria but also significantly reduce the direct operating costs. Furthermore, research effort with respect to an improved understanding of the flow physics around fuselage / tail combinations remains limited. A successful design approach towards the development of modem transport aircraft has to include the empennage as well. This has to be seen in the light of the fact that performance guarantees for future aircraft have to be granted earlier and with higher accuracy as compared to former developments.
The primary objective of the REMFI project was to provide the European aerospace industry with a mechanism to exploit substantial advances made on the research side in the area of design, modelling / simulating tails aerodynamic. The complete and accurate investigation of (at industrial level) new and highly optimised empennage designs has a direct future impact on aircraft design aiming at less fuel consumption due to reduced weight, improved flight trajectories and positive impact on environmental issues. Moreover, it will enable the European aircraft industry to keep a leading role in international competition.
In order to cope with the current aeronautics industrial, an integrative approach was proposed. This can be achieved by pushing the state-of-the art tail designs to its utmost level of performance. REMFI thus focused on three main aspects:
(1) the better understanding of the tail flow physics;
(2) improved computational prediction capability for fuselage / tail configurations; and
(3) analysis and improved experimental techniques for tail flow investigations.
This aims at providing means to:
- increase the empennage aerodynamic efficiency and reduce loads;
- improve empennage performance and weight for optimised gaps effects, including Re number effects;
- investigate sting mounting arrangement effects on empennage wind tunnel measurements;
- enhance the current scaling methodologies to free-night conditions;
- reduce fuel bum;
- novel design concepts for integrated fuselage / empennage designs;
- shorten the design cycle;
- reduce the cost of the aerodynamic design of tail and fuselage and reduce the maintenance costs.
Two main approaches characterise the project's philosophy:
Approach 1
By means of a precise numerical simulation for tail flow phenomena. Besides experiments, which are often the backbone for numerical investigations and in many cases serve for validating codes and models, CFD itself is now a mature instrument in design which means it is becoming a tool in early design stages. At the upstream edge, CFD is also used for complex geometries and flow situations both supporting experiments and providing absolute answers on flow behaviour, including absolute figures for, say, force coefficients.
Approach2
By means of detailed experimental study. Wind tunnel tests contribute to the build-up of physical understanding of the different tail flow phenomena. The testing envelope covered several conditions for Mach number, Reynolds number, tail settings, elevator and rudder settings variations as well as empennage measurements close to true flight Reynolds numbers. Two test facilities were used for conducting the necessary tunnel measurements, the ARA tunnel and the now operational European Transonic Wind Tunnel.
The work breakdown structure of the project is divided into five work packages (WPs).
- WP1 was dedicated to the management of the project.
- WP2: Empennage improved control surfaces efficiency
The main objectives of WP2 was to:
- understand tail flow physics in order to improve prediction capabilities and accuracy of tempennage performance including hinge moments, and transition effects;
- develop the ability to correctly simulate gaps effects on the capability of reliable scaling of sub-scale wind tunnel data to full-scale flight conditions; and
- understand and improve the capability for the accurate simulation of tail stall mechanism.
- WP3: Sting mounting arrangement investigation
The twin-sting measurement technique has been introduced to reach a minimised interference of the model support with the rear end. However, there remains an influence of the support on the fuselage pressure depending on the distance of the twin booms from the model centre line. Other influences include the wing twist due to the rear fuselage pitching moment and the alteration of the wing flow owing to the booms and thus the general flow characteristics. The aim of this task was to clarify the impact of the lateral wing-sting boom spacing on the empennage performance employing the state of the art Navier-Stokes example simulations. Activities in WP3 focused mainly on the following aspects:
i) accurate simulation of twin sting booms location and shape effects on the empennage performance, efficiency and aerodynamic loads, including Reynolds number effects;
ii) develop a methodology for the prediction of wing deformation caused by twin sting mounting arrangement and
iii) define a suitable criterion for the selection of the position of the gap for live rear end measurement techniques;
iv) estimate drag causes and interference effects due to cross flow through gap.
- WP4: Experimental verification study
Two test facilities have been selected. For the first time comprehensive tail plane measurements were conducted in the European Transonic Wind Tunnel. This facility, established and jointly funded by four European nations, offered the capability to obtain aerodynamic data at true flight conditions, where the flow is able to withstand more severe pressure gradients. The exploitation of this capability is crucial not only to better understand the Reynolds number effects on tail-plane performance but also for the qualification of the CFD methods to predict these flows. The second test campaign was carried out in the ARA wind tunnel. This facility has been selected since ARA is specially suited for testing in the lower Reynolds number regime, and the same model used in the ETW can be employed with only minor adaptation needed. Due to easy access to the test section (ambient environment), model configuration changes can be performed quickly. The planned test series therefore focused on those investigations, which require time consuming model changes (gap effect / transition effect tests). The policy to use one and the same model in both wind tunnels not only avoids a duplication of model costs but also supports a dependable data comparison to assure consistency in the results.
All test campaigns were conducted with a twin-sting support. This type of support allows the precise measurement of forces directly at the rear end of the model. For this purpose, the rear fuselage section of the model was mechanically separated from the main body and equipped with a live-rear-end balance. This balance is specially adapted featuring a relatively high stiffness to minimise tail movements without compromising measurement accuracy. Some further effort is needed on the twin-sting support to minimise the interference effects between the support booms and the empennage. In REMFI, three different boom positions were tested. The target was to gain knowledge on the (positive) impact of an increased spacing and, moreover, to generate validation data for the CFD tools to predict the sting effects. The model also received a rear-end motorisation, i.e. a remotely controlled motorised horizontal tail plane. The motorisation allows quick and easy HTP angle settings. The employment of the remotely controlled HTP was expected to boost productivity rate and thus will give ETW an important competitive advantage. The employment of this technology was therefore critically important for the success of the ambitious test schedule. The main objectives of this work package was to: i) improve the knowledge on control surface efficiency and hinge moment behaviour; ii) control surface gap effects;
iii) scale effects on tail flow characteristics up to flight-scale Reynolds numbers and
iv) establish an experimental tail-specific data base for the assessment / improvement of the prediction tools.
- WP5: Innovative fuselage and empennage design
This work package focused mainly on the investigation of innovative novel aerodynamic design solutions, which are not yet realised at current conventional designs but are very promising to enhance the aerodynamic performance of future aircraft. In the past, the aerodynamic design of wing belly fairings has been handled independently from the design of the front / rear-fuselage and empennage parts, because the extension of the belly was limited to the cylindrical part of the fuselage and it was assumed that the interaction with the other parts was negligible. The main objectives of this work package were:
i) to evaluate the improvement potential of integrated designs of the front / rear fuselage and belly fairing and identify the impact of these solutions on the empennage design;
ii) to improve the evaluation accuracy of the boundary layer characteristics in the very rear part of the fuselage for a more precise prediction of the flow conditions for an improved design of the APU air intake and exhaust and
iii) ssess and improve the capability to predict the effects of small geometry changes on the flow characteristics, especially on drag.
The primary objective of the REMFI project was to provide the European aerospace industry with a mechanism to exploit substantial advances made on the research side in the area of design, modelling / simulating tails aerodynamic. The complete and accurate investigation of (at industrial level) new and highly optimised empennage designs has a direct future impact on aircraft design aiming at less fuel consumption due to reduced weight, improved flight trajectories and positive impact on environmental issues. Moreover, it will enable the European aircraft industry to keep a leading role in international competition.
In order to cope with the current aeronautics industrial, an integrative approach was proposed. This can be achieved by pushing the state-of-the art tail designs to its utmost level of performance. REMFI thus focused on three main aspects:
(1) the better understanding of the tail flow physics;
(2) improved computational prediction capability for fuselage / tail configurations; and
(3) analysis and improved experimental techniques for tail flow investigations.
This aims at providing means to:
- increase the empennage aerodynamic efficiency and reduce loads;
- improve empennage performance and weight for optimised gaps effects, including Re number effects;
- investigate sting mounting arrangement effects on empennage wind tunnel measurements;
- enhance the current scaling methodologies to free-night conditions;
- reduce fuel bum;
- novel design concepts for integrated fuselage / empennage designs;
- shorten the design cycle;
- reduce the cost of the aerodynamic design of tail and fuselage and reduce the maintenance costs.
Two main approaches characterise the project's philosophy:
Approach 1
By means of a precise numerical simulation for tail flow phenomena. Besides experiments, which are often the backbone for numerical investigations and in many cases serve for validating codes and models, CFD itself is now a mature instrument in design which means it is becoming a tool in early design stages. At the upstream edge, CFD is also used for complex geometries and flow situations both supporting experiments and providing absolute answers on flow behaviour, including absolute figures for, say, force coefficients.
Approach2
By means of detailed experimental study. Wind tunnel tests contribute to the build-up of physical understanding of the different tail flow phenomena. The testing envelope covered several conditions for Mach number, Reynolds number, tail settings, elevator and rudder settings variations as well as empennage measurements close to true flight Reynolds numbers. Two test facilities were used for conducting the necessary tunnel measurements, the ARA tunnel and the now operational European Transonic Wind Tunnel.
The work breakdown structure of the project is divided into five work packages (WPs).
- WP1 was dedicated to the management of the project.
- WP2: Empennage improved control surfaces efficiency
The main objectives of WP2 was to:
- understand tail flow physics in order to improve prediction capabilities and accuracy of tempennage performance including hinge moments, and transition effects;
- develop the ability to correctly simulate gaps effects on the capability of reliable scaling of sub-scale wind tunnel data to full-scale flight conditions; and
- understand and improve the capability for the accurate simulation of tail stall mechanism.
- WP3: Sting mounting arrangement investigation
The twin-sting measurement technique has been introduced to reach a minimised interference of the model support with the rear end. However, there remains an influence of the support on the fuselage pressure depending on the distance of the twin booms from the model centre line. Other influences include the wing twist due to the rear fuselage pitching moment and the alteration of the wing flow owing to the booms and thus the general flow characteristics. The aim of this task was to clarify the impact of the lateral wing-sting boom spacing on the empennage performance employing the state of the art Navier-Stokes example simulations. Activities in WP3 focused mainly on the following aspects:
i) accurate simulation of twin sting booms location and shape effects on the empennage performance, efficiency and aerodynamic loads, including Reynolds number effects;
ii) develop a methodology for the prediction of wing deformation caused by twin sting mounting arrangement and
iii) define a suitable criterion for the selection of the position of the gap for live rear end measurement techniques;
iv) estimate drag causes and interference effects due to cross flow through gap.
- WP4: Experimental verification study
Two test facilities have been selected. For the first time comprehensive tail plane measurements were conducted in the European Transonic Wind Tunnel. This facility, established and jointly funded by four European nations, offered the capability to obtain aerodynamic data at true flight conditions, where the flow is able to withstand more severe pressure gradients. The exploitation of this capability is crucial not only to better understand the Reynolds number effects on tail-plane performance but also for the qualification of the CFD methods to predict these flows. The second test campaign was carried out in the ARA wind tunnel. This facility has been selected since ARA is specially suited for testing in the lower Reynolds number regime, and the same model used in the ETW can be employed with only minor adaptation needed. Due to easy access to the test section (ambient environment), model configuration changes can be performed quickly. The planned test series therefore focused on those investigations, which require time consuming model changes (gap effect / transition effect tests). The policy to use one and the same model in both wind tunnels not only avoids a duplication of model costs but also supports a dependable data comparison to assure consistency in the results.
All test campaigns were conducted with a twin-sting support. This type of support allows the precise measurement of forces directly at the rear end of the model. For this purpose, the rear fuselage section of the model was mechanically separated from the main body and equipped with a live-rear-end balance. This balance is specially adapted featuring a relatively high stiffness to minimise tail movements without compromising measurement accuracy. Some further effort is needed on the twin-sting support to minimise the interference effects between the support booms and the empennage. In REMFI, three different boom positions were tested. The target was to gain knowledge on the (positive) impact of an increased spacing and, moreover, to generate validation data for the CFD tools to predict the sting effects. The model also received a rear-end motorisation, i.e. a remotely controlled motorised horizontal tail plane. The motorisation allows quick and easy HTP angle settings. The employment of the remotely controlled HTP was expected to boost productivity rate and thus will give ETW an important competitive advantage. The employment of this technology was therefore critically important for the success of the ambitious test schedule. The main objectives of this work package was to: i) improve the knowledge on control surface efficiency and hinge moment behaviour; ii) control surface gap effects;
iii) scale effects on tail flow characteristics up to flight-scale Reynolds numbers and
iv) establish an experimental tail-specific data base for the assessment / improvement of the prediction tools.
- WP5: Innovative fuselage and empennage design
This work package focused mainly on the investigation of innovative novel aerodynamic design solutions, which are not yet realised at current conventional designs but are very promising to enhance the aerodynamic performance of future aircraft. In the past, the aerodynamic design of wing belly fairings has been handled independently from the design of the front / rear-fuselage and empennage parts, because the extension of the belly was limited to the cylindrical part of the fuselage and it was assumed that the interaction with the other parts was negligible. The main objectives of this work package were:
i) to evaluate the improvement potential of integrated designs of the front / rear fuselage and belly fairing and identify the impact of these solutions on the empennage design;
ii) to improve the evaluation accuracy of the boundary layer characteristics in the very rear part of the fuselage for a more precise prediction of the flow conditions for an improved design of the APU air intake and exhaust and
iii) ssess and improve the capability to predict the effects of small geometry changes on the flow characteristics, especially on drag.
