Design, Analysis, and Testing of a Scaled Propeller for an Innovative Regional Turboprop Aircraft

This paper describes the design, numerical analyses, and wind tunnel tests of the scaled model of a propeller serving as a propulsive element for the experimental tests of an advanced regional turboprop aircraft with engines installed on the horizontal tailplane tips. The design has been performed by complying with the thrust similarity from the full-scale aircraft propulsive requirements. Numerical analyses with a high-fidelity aerodynamic solver confirmed that the initial design made with XROTOR would achieve the expected performance. Finally, a strengthened version of the propeller has been manufactured via 3D printing and tested in the wind tunnel. Test data include measurements of thrust as well as propeller normal force at different angles of attack. Good agreement between numerical and experimental results has been observed, enabling the propeller to be used confidently in the aircraft wind tunnel powered test campaign

Numerical aerodynamic analysis on a trapezoidal wing with high lift devices: a comparison with experimental data

The aerodynamic analysis on the DLR-F11 high lift configuration model has been performed on the supercomputing grid infrastructure SCoPE of the University of Naples ???Federico II???. The model geometry is representative of a wide-body commercial aircraft, which experimental investigations at high Reynolds number have been performed at the European Transonic Wind-tunnel (ETW) for the 2nd AIAA High Lift Prediction Workshop. The commercial CAE package Star-CCM+ has been used to solve the Reynolds-averaged Navier-Stokes equations. Inviscid, viscous incompressible, and compressible analyses have been performed with mesh refinement. The inviscid calculations have been used to assess how far is the eulerian prediction from experimental data. Viscous and compressible calculations have been realized using the Spalart-Allmaras turbulence model at 0.175 Mach number and 15.1 million Reynolds number. Results show that the simple Spalart-Allmaras turbulence model can predict quite accurately the stall and post-stall behaviour, getting the angle of stall and underestimating the maximum lift coefficient by less than 5%. Comparisons among numerical and experimental pressure coefficients at several sections are also shown. Finally, the stall path is described

An improved preliminary design methodology for aircraft directional stability prediction and vertical tailplane sizing

This work deals with the development of a new preliminary design method for aircraft directional stability and vertical tail sizing. It is focused on regional turboprop aircraft because of their economic advantage over regional jets on short routes, for the increasing oil price, and because of the market needs of new airplanes in the next 20 years. The focus on aircraft directional stability is due to the significant discrepancies that classical semi-empirical methods, as USAF DATCOM and ESDU, provide for some configurations, because they are based on NACA wind tunnel tests about models not representative of an actual transport airplane. This work exploits the CFD to calculate the aerodynamic interference among aircraft parts for hundreds configurations of a given layout, providing a useful method in aircraft preliminary design. A wind tunnel investigation involving about 180 configurations has validated the numerical approach. The innovation of the work concerns the numerical and experimental parametric study on the static directional stability of a model representative of the regional turboprop aircraft category and the direct measurement of the vertical stabilizer aerodynamic forces in the wind tunnel, in addition to the force and moments acting on the whole model. In this way, useful data about aerodynamic interference have been extracted from experimental tests, which are in good agreement with the results of numerical simulations

An improved preliminary design methodology for aircraft directional stability prediction and vertical tailplane sizing

This work deals with the development of a new preliminary design method for aircraft directional stability and vertical tail sizing. It is focused on regional turboprop aircraft because of their economic advantage over regional jets on short routes, for the increasing oil price, and because of the market needs of new airplanes in the next 20 years. The focus on aircraft directional stability is due to the significant discrepancies that classical semi-empirical methods, as USAF DATCOM and ESDU, provide for some configurations, because they are based on NACA wind tunnel tests about models not representative of an actual transport airplane. This work exploits the CFD to calculate the aerodynamic interference among aircraft parts for hundreds configurations of a given layout, providing a useful method in aircraft preliminary design. A wind tunnel investigation involving about 180 configurations has validated the numerical approach. The innovation of the work concerns the numerical and experimental parametric study on the static directional stability of a model representative of the regional turboprop aircraft category and the direct measurement of the vertical stabilizer aerodynamic forces in the wind tunnel, in addition to the force and moments acting on the whole model. In this way, useful data about aerodynamic interference have been extracted from experimental tests, which are in good agreement with the results of numerical simulations

Benchmark of different aerodynamic solvers on wing aero-propulsive interactions

Distributed electric propulsion is a fertile research topic aiming to increase the wing aerodynamic efficiency by distributing the thrust over the wing span. The blowing due to distributed propulsors shall increase the wing lift coefficient for a given planform area and flight speed. This should bring several advantages as wing area, drag, and structural weight reduction, which in turn reduce fuel consumption, allowing airplanes to fly more efficiently. However, there are no consolidated preliminary design methods to size a distributed propulsion system. Numerical analysis is then performed at early stage, where many design variables have not been fixed yet. Therefore, the design space is vast and exploring all the possible combinations is unfeasible. For instance, low-fidelity methods (VLM, panel codes) have a low computational time, but usually they do not account for flow separation and hence they are unable to predict the wing maximum lift. Conversely, high-fidelity codes (CFD) provide more realistic results, but a single drag polar sweep can last days. This work provides a benchmark of different aerodynamic solvers for a typical regional turboprop wing with flaps and distributed propulsion, to better understand the limits of each software in the prediction of aero-propulsive effects

Development of new preliminary design methodologies for regional turboprop aircraft by CFD analyses

Since 2011 the aerodynamic research group of the Dept. of Industrial Engineering of the University of Naples "Federico II" makes use of the University's computing grid infrastructure SCoPE to perform parallel computing simulations with the commercial CAE package Star-CCM+. This infrastructure allows Navier-Stokes calculations on complete aircraft configurations in a relative short amount of time. Therefore, the software and the above mentioned infrastructure allow the parametric analysis of several configurations that are extremely useful to the correct estimation of aerodynamic interference among aircraft components and to highlight some useful trends that could indicate how a specific aerodynamic characteristic (i.e. the drag of a component, the wing downwash or the directional stability contribution of the vertical tail) is linked to aircraft geometrical parameters. Thus, with the choice of a specific set of test-cases it is possible to make a deep investigation on some aerodynamic features and, from the analyses of results, it is possible to extract and develop ad-hoc semi-empirical methodologies that could be used in preliminary design activities. In this paper, two investigations are presented: the aerodynamic interference among aircraft components in sideslip and the aerodynamic characteristics of a fuselage, focusing on typical large turbopropeller aircraft category

An Investigation on Vertical Tailplane Design

The paper presents a deep investigation on the methodologies to design a vertical tailplane. Nowadays the most used methodologies in preliminary design to estimate the contribution of vertical tailplane on aircraft directional stability and control are: the classical method proposed by USAF DATCOM (also presented in several aeronautics textbooks) and the method presented in ESDU reports. Both methodologies derive from NACA world war II reports of the first half of the ’900, based on obsolete geometries, and give quite different results for certain configurations, e. g. in the case of horizontal stabilizer mounted in fuselage. As shown in literature, the main effects on the side force coefficient of the vertical tail are due to the interactions among the aircraft components: the fuselage acts like a cylinder increasing the local sideslip angle, the wing position and aspect ratio have an influence on the airflow near the tail zone and the horizontal tail, depending on position and size, can act as an endplate increasing the side force. In order to better highlight these effects, a different approach using the RANS equations has been adopted. Several CFD calculations have been performed on some test cases (used as experimental database) described in NACA reports and used in the past to obtain the semi‐empirical methodology reported in USAF DATCOM, to verify the compliance of CFD results with available experimental data. The CFD calculations (performed through the use of a parallel supercomputing platform) have shown a good agreement between numerical and experimental data. Subsequently the abovementioned effects have been deeply investigated on a new set of propeller transport aircraft configurations. The different configurations that have been prepared differs for wing aspect ratio, wing‐fuselage relative position (high‐wing/low‐wing), vertical tailplane aspect ratio (vertical tail span versus fuselage radius) and horizontal tailplane position respect to the vertical tailplane (in particular investigation the effect of fin‐mounted T configuration, typical of regional turboprop transport aircraft). For all configurations the computational mesh has been carefully analyzed and prepared. All the CFD analyses will be useful to obtain new curves to predict the above-mentioned effects and to have a more accurate estimation of vertical tailplane contribution to aircraft directional stability and control

Design Evolution and Wind Tunnel Tests of a Three-Lifting Surface Regional Transport Aircraft

This paper deals with the experimental assessment of the aerodynamic characteristics of an innovative large turboprop aircraft. The configuration is a three-lifting surfaces airplane with rear engine installation at tail tips, conceived to carry up to 130 passengers and targeting a minimum economic and environmental impact, which is competitive with regional jets on short and medium hauls. The three-lifting surfaces layout is the output of previous research made by the authors, and it has been selected to fully comply with the market and design constraints. An experimental test campaign was required to validate the aerodynamics, stability, and control of this innovative configuration. From the results of the first campaign, it appeared that the aircraft had insufficient longitudinal and directional stability. Thus, the authors worked to improve these characteristics, updating the design and executing a second wind tunnel test campaign. The evolution of the design is described in the first part of the paper. In the second part, the authors discuss the aerodynamic interference effects among aircraft components, detailing how the combined downwash coming from both the canard and wing, as well as their wakes, affects the empennage aerodynamics. Experimental tests have revealed a significant reduction of the longitudinal stability due to canard additional downwash, especially at low attitudes. Furthermore, it was found that the canard generates a non-linearity on the aircraft directional stability derivative at moderate sideslip angles because of its tip vortex impinging on the vertical tail. Despite the detrimental interference due to the canard, the updated aircraft proved to be statically stable with sufficient margin at the most rearward center of gravity. Lessons learned in this research may be useful to aerodynamicists and aircraft designers facing similar issues

Directional Stability Issues of a Three Lifting Surface Aircraft

This paper deals with the evaluation of the interference effects among aircraft components in a three lifting surface configuration, an innovative layout for a high-capacity turboprop (130 pax), which is supposed to be competitive with respect to short/medium haul regional jets. The feasibility study of such a configuration is framed within the Innovative turbopROp configuratioN (IRON) project. An experimental wind tunnel test campaign has been performed on a 1:25 scaled model at the main subsonic wind tunnel facility of the Industrial Engineering Department of the University of Naples Federico II. Beside the well-known detrimental effects of the angle of attacK on the sidewash, the experimental tests have highlighted a strong directional stability reduction due to the canard interference with both the fuselage and the vertical tail. Results have shown that the canard increases the fuselage instability of about 14%. The canard wake displacement also affects the aircraft directional stability. Results collected in this work have been useful to perform a redesign of the aircraft empennage and to schedule numerical high-fidelity analyses as well as a second wind tunnel test campaign on the updated aircraft model to get further insights on the aerodynamic interference, including propulsive effects

A comprehensive review of vertical tail design

This work deals with a comprehensive review of vertical tail design methods for aircraft directional stability and vertical tail sizing. The focus on aircraft directional stability is due to the significant discrepancies that classical semi-empirical methods, as USAF DATCOM and ESDU, provide for some configurations, since they are based on NACA wind tunnel tests about models not representative of an actual transport airplane. The authors performed RANS CFD simulations to calculate the aerodynamic interference among aircraft parts for hundreds configurations of a generic regional turboprop aircraft, providing useful results that have been collected in a new vertical tail preliminary design method, named VeDSC. Semi-empirical methods have been put in comparison on a regional turboprop aircraft, where the VeDSC method shows a strong agreement with numerical results. A wind tunnel investigation involving more than 180 configurations has validated the numerical approach. The investigation has covered both the linear and the non-linear range of the aerodynamic coefficients, including the mutual aerodynamic interference between the fuselage and the vertical stabilizer. Also, a preliminary investigation about rudder effectiveness, related to aircraft directional control, is presented. In the final part of the paper, critical issues in vertical tail design are reviewed, highlighting the significance of a good estimation of aircraft directional stability and control derivatives