Browse Topic: Aircraft tails
This SAE Information Report contains definitions for hydrogen fuel cell powered vehicle terminology. It is intended that this document be a resource for those writing other hydrogen fuel cell vehicle documents, specifically, Standards or Recommended Practices.
The empennage of a helicopter is largely responsible for its stability in forward flight. Its performance is mainly determined by its aerodynamics. In this paper, the empennage of a CoAX 2D ultralight research helicopter is analyzed in detail. For this purpose, the helicopter was equipped with flow measurement devices and flight tests were performed, covering different flight conditions. Measurements from a nose boom as well as the pilot’s control inputs and helicopter's position are available for evaluation. For the empennage in particular, seven-hole flow probes were mounted on it and various cameras were used to record the movement of the surface tufts.
A 1/5th scale powered coaxial rotor and propeller system has been developed and tested in the National Full Scale Aerodynamic Complex (NFAC) 40x80 ft Wind Tunnel. Test conditions include airspeeds in excess of 250 kts, the highest recorded for a rotor in edgewise flight at the NFAC. The system was studied in four configurations: a powered coaxial rotor, a powered coaxial rotor with a propeller wake rake, a powered coaxial rotor with a powered propeller, and a bare hub rotor with a propeller wake rake. The high-quality data from the test included propeller, fuselage and main-rotor performance; aerodynamic-interactions between the rotors, fuselage, empennage, and propeller; acoustics and handling-qualities attributes. These results have been used to validate physics-based rotorcraft modeling tools and enhance the quality of full-scale X2 Technology® aircraft designs. Innovative solutions to test measurement challenges included rotor shaft strain gages, balance thermal control systems, and a dual arm rotating rake to measure inflow at the propeller plane. Main rotor hub and blade system performance trends are presented as functions of speed, thrust, and body attitude. Time-averaged and unsteady pressure measurements on the fuselage, empennage, and propulsor plane characterized the interactions between the fuselage, rotor hubs and blades, empennage, and propeller over a wide range of operating conditions.
ABSTRACT Within the framework of NACOR project in CleanSky 2 AIRFRAME ITD, ONERA and DLR performed parallel investigations dealing with the RACER high-speed demonstrator, and especially with its tail parts, each partner respectively focusing on vertical fins (ONERA) and horizontal stabilizer (DLR). During this design phase, most of the CFD simulations were steady-state and neglected the effect of the rotor (or rotor-head) and of the propellers. It however turned out that the rotor-head had a significant effect on the vertical fins and that it was essential to take into account its rotation in time-accurate simulations: the wake from the rotor-head, the upper deck and the engine cowlings indeed strongly impacts the left vertical fin because of the clockwise rotation of the rotor-head. It induces strong oscillations on the tail unit loads, and the mean tail unit lateral thrust is also significantly increased. Moreover the main conclusions of this 'aerodynamic interactions' investigation are almost identical, no matter what the computed configuration: rotating rotor-head, rotating rotor-head with actuator-disk, rotating full-rotor or rotating full-rotor with propellers effect.
ABSTRACT Accurate prediction of aeroelastic coupling between rotor wake and structure remains a key challenge to the development of advanced rotorcraft. Limitations of existing analysis tools to predict such aeroelastic interactions, notably empennage buffeting effects, have resulted in costly late-cycle design changes in multiple rotorcraft development programs, including the UH-60A and AH-64A. Aeromechanical phenomena involving interactions of the fuselage and rotor wake are complex, interdisciplinary, and three-dimensional in nature. For this reason, full vehicle CFD/CSD coupled analysis is essential to accurately capture the mutually dependent interactions between the aerodynamic loads and the aeroelastic response associated with these phenomena. The current state-of-the-art in rotorcraft analysis involves CFD/CSD coupled analysis of aeroelastic rotors and wings, but rigid representations of the fuselage and empennage structures (Ref. 1). To address this limitation, an elastic fuselage coupling capability was developed using RCAS and FUN3D. The elastic fuselage CFD/CSD interface has been successfully tested for several demonstration cases and one validation case.
Heavy class attack helicopter development program aims to develop a new generation assault helicopter with high weapon capacity and modern combat technologies. Design requirements lead to a complicated aerodynamic shape. Wind tunnel tests gain importance for validation of aerodynamic design decisions and methodologies. A short test campaign is planned in a high Reynolds number environment which is achieved through pressurization. Generation of aerodynamic characteristics, effect of under-wing stores, effectivity of tail surfaces and main rotor hub interactions construct the base of test plan. Tests are conducted under varying pressure and airspeed combinations starting from 1.1 Bar 100 m/s to 3 Bar 85 m/s. Test results are compared with CFD simulations as a part of validation studies. Reynolds Averaged Navier-Stokes Simulations provide satisfactory results. Improved results are obtained with high fidelity turbulence model, wall modeled very large eddy simulations.
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ABSTRACT T-tail configurations are a promising approach to increase vertical tail efficiency, reduce fuselage download and hub load cycle amplitudes in low speed transition. However, the horizontal tail can be subject to rotor wake impingement in cruise flight which might lead to high dynamic loads and structural fatigue. The involved aerodynamics are in addition highly complex and hence difficult to be predicted by simulation. In this work a simulation approach for empennage structural loads and vibration prediction is established based on free-wake analysis and modal fuselage approximation, focusing on the expectedly most dominant aerodynamic interaction effects at the T-tail. The results are compared to flight test data to evaluate the approach, and sensitivities of the framework are assessed. The results indicate that the motion of the horizontal tail is characterized only by a few modeshapes, predominantly driven by rotor wake influence, rather than rotor loads via the structural load path. At the same time, high sensitivities are associated with these particular modes and are evaluated in this work to identify the driving mechanisms of T-tail vibrations of the investigated configuration. Discrepancies in the structural model are identified against bang test data. Taking these discrepancies into account, the simulation approach yields reasonable results for T-tail vibrations and loads in comparison to flight test data. In the front part of the fuselage, flight test data is significantly underpredicted as expected and attributed to the employed simplifications in the main rotor blade model.
An aeroelastic coupling framework is applied to the UH-60A platform to examine aerodynamic-induced vibrations at four advance ratios spanning the flight envelope. Both one-way and two-way aeroelastic coupling results are examined at each condition. The two-way coupled results are observed to generally predict closer values to measured flight test data on the lifting surfaces of the empennage, and a less pronounced effect is seen in stiffer, nonlifting structure. The effect of aeroelastic coupling subiterations is examined, and they are found to further refine the two-way coupled results, generally improving prediction quality.
The rotor hub asembly is a primary contributor to rotorcraft parasite drag. Reducing hub drag is one mandatory step to enabling future high - sped conventional and compound rotorcraft. The importance of high - Reynolds number testing of rotor hub flows is emphasized by realizing that high - Reynolds number turbulent coherent structures remain strong for long distances downstream up to the long - age wake where they interact with the empennage and tail. Basic research conducted through the Vertical Lift Research Center of Excellence (VLRCOE) at Pen State's water tunnel facilities has provided unique high Reynolds - scale data of rotor hub wakes, providing new data for physical understanding and validation of computa tional fluid dynamics (CFD) methods. A first rot or hub flow prediction workshop was held in June 2016; the present paper focuses on 'blind comparison results' between experimental data and CFD analyses that were part of the second rotor hub flow prediction workshop at Pen State VLRCOE in May 2018. The hub workshops are the result of a collaboration between Pen State and Georgia Tech VLRCOEs with support from the National Rotorcraft Technology Center (NRTC), including participation from academia, industry, and government. They are compelling examples of productive exchange between experimental and computational efforts that advance the community's knowledge about these complex flows that are relevant to efficient and safe vertical lift.
Aerodynamic interactions between the rotor and the empennage can have a significant impact on steady and unsteady loads and often result in challenges in a rotorcraft design phase. In the present work, numerical analysis of rotor-empennage aerodynamic interactions were compared to full-scale flight test data with respect to steady and unsteady interactional aerodynamic effects. The flight tests provided loads for a low-empennage and a T-Tail configuration for various forward flight velocities. For the T-Tail configuration, additional pressure sensors provided validation data for steady and unsteady interaction effects. The numerical analysis was focused on an unsteady panel method, complemented by high-fidelity CFD/CSM-coupling results for a level flight state. Furthermore, a supplemental validation of the unsteady panel method was performed against an isolated wing-vortex interaction experiment. The flight test data revealed a strong asymmetry in mean empennage loads, which increases with forward flight velocity. The numerical analysis showed coherent results with a slight over-prediction in high-speed. The T-Tail configuration is furthermore subject to 3D effects between the vertical- and horizontal tail. These effects influence pressure and load-distributions on the T-Tail, which was captured by both numerical methods. The general characteristics of the unsteady pressure signatures were captured by both methods. The panel method showed slightly better representation of amplitude.
ABSTRACT The challenge of increasing range and speed of a rotorcraft is encountered in the scope of the European CleanSky2 "Fast Rotorcraft" project by Airbus Helicopters with the compound helicopter design RACER (RapidAndCostEfficientRotorcraft) for which the box wing and the tail parts designs are respectively protected by patent. This paper presents the DLR contributions to the RACER development. This includes the aerodynamic design of the wing and tail section as well as an overall assessment of performance and noise. In a first step the aerodynamic properties of the configuration are evaluated both isolated and with consideration of the main rotor and lateral rotor interferences by the use of actuator discs. In the second step, the investigated possibilities to improve the configurations performance are described. These include airfoil design for improved high lift performance of the wing and tail section, an optimization of the box wing circulation distribution on the upper and lower wing. Additionally, the intersection fairings were improved and the efficiency of the trim flaps was evaluated. In this regard, it could be determined for which cases an isolated approach is appropriate and when the rotor interference should be considered. At the end the evaluation of the aero acoustics of the configuration is conducted. The applied configuration shows good aerodynamic characteristics with some further cruise and off design optimization potential.
ABSTRACT The US Army's Aviation Development Directorate (ADD) has successfully collaborated with its industry partners to reduce system parasitic weight for aviation platforms through multifunctional structures technology development. In short, this can be generalized as achieving weight savings by replacing the combination of aircraft structure and an independent, add-on mission enabler with a singular system that performs the functions of both structure and mission enabler. This extensive multifunctional technology development for aviation structural applications has yielded significant weight savings over parasitic designs. Technologies demonstrating this structural multifunctionality for weight reduction include integrally armored helicopter floor, lightweight integrally armored helicopter floor, lightning-protected structure, structural antenna aperture, helicopter empennage antenna structure, combat tempered aft fuselage, blast attenuating aircraft structure, and highly durable floor armor for rotorcraft. The significance of weight savings that can be enabled via multifunctional structures technology development is clear. One case study exercise indicates a platform-level mission enabler weight savings of 17.8%. This significance of weight savings is analogous to other studies showing synergistic benefits from technology integration at the technology and system (platform) level.
ABSTRACT Multi-objective optimization of horizontal tail of a conventional rotor helicopter is achieved using a genetic algorithm, which is coupled with comprehensive analysis tools, Flightlab® and in-house rotorcraft simulation tool TAI Originated Rotorcraft Simulation (TOROS). Genetic algorithm is used to design a tail that improves static longitudinal stability characteristics of the helicopter during autorotation as well as its longitudinal dynamic stability characteristics at high speeds. Another optimization target is to minimize pitch attitude change in transition to forward flight while keeping pitch attitude close to zero at 140 knots in cruise. This study shows a framework of horizontal stabilizer optimization over its aerodynamic lift characteristics, which can be altered either by introducing gurney flaps and/or slats to change lift characteristics, vortex generators (turbulators) to postpone flow separation or simply by changing incidence angle. By solving a multi-objective optimization problem, the aim of this study is to find an optimum lift curve slope, incidence angle and size of the horizontal stabilizer that satisfies performance and handling qualities requirements of the helicopter. It was witnessed that there are always some trade-offs between optimal design alternatives in Pareto Front and therefore selection of optimum horizontal tail configuration depends highly on these requirements. This study shows that multi-objective optimization can be used as a design tool to replace human effort prior to or during the flight tests by tuning aerodynamic configuration and size of the horizontal tail.
ABSTRACT Within the framework of NACOR project in CleanSky 2 AIRFRAME ITD, ONERA and DLR performed parallel investigations dealing with the RACER high-speed demonstrator, and especially with its tail parts, each partner respectively focusing on vertical fins (ONERA) and horizontal stabilizer (DLR). The present paper focuses on ONERA's contribution to the rear part design: both new vertical fins and design recommendations have been provided based on a multi-fidelity approach. A large panel of performance assessment tools, shape modification and optimization strategies have indeed been used. A major shape modification of the vertical fin has first been proposed in order to tackle a flow separation issue. An optimization process then resulted in an optimized vertical fin aerodynamic design, which met all the constraints and achieved all the objectives. This strong cooperation between ONERA and Airbus Helicopters enabled this investigation to be successful, leading the final vertical fins protected by patent today.
ABSTRACT Wind tunnel tests have been conducted to support development of the SB>1 DEFIANT™ Joint Multi-Role Technology Demonstrator. The objective is to provide data to validate and enhance the aerodynamic performance and flight dynamics models and to improve understanding of the aerodynamics of X2 TECHNOLOGY™ configurations. The first model was a 1/11 scale airframe with a powered propeller that was tested in the United Technologies Research Center (UTRC) Pilot Wind Tunnel (PWT) in 2013-2014. The second model was a 1/5 scale airframe with a powered coaxial main rotor that was tested at the U.S. Air Force National Full Scale Aerodynamic Complex (NFAC) in 2016. This model could also be tested with a powered propeller. Measurements included forces and moments on the various components, as well as fuselage, empennage, and blade surface pressures. For the 1/11 model, fuselage-induced flow fields at the propeller and empennage locations were also measured. Application of the experimental results to the State Space GenHel flight dynamics model is described.
A sequence of scale model wind tunnel tests have been conducted to help design the S-97 RAIDER™ aircraft and better understand the aerodynamics of X2 Technology™ rotorcraft incorporating coaxial rigid lift offset rotors, low drag airframes, and a pusher propeller. The tests provided inputs to aerodynamics and flight dynamics simulations, validation data for CFD, and aerodynamic loads for design. The first test obtained high Reynolds number aerodynamic coefficients for airfoil families planned for the main rotor blades. A particular focus was on forward and reverse flow data for a thick single ended airfoil and a double-ended airfoil. A 1/10 scale unpowered airframe was then tested in the UTRC Pilot Wind Tunnel to obtain basic aerodynamic loads, plus flow interaction diagnostics on the fuselage, tail, and at the propeller plane. A hub and sail fairing drag test was conducted to obtain quantitative drag measurements on multiple fairing geometries, and to get insight into the effect of rotation, gaps, and the presence of blade stubs. A diagnostic test using a 1/5 scale model of the X2 Technology™ demonstrator investigated the aerodynamic interaction between the airframe and the propeller, and helped better understand the flight test data. The final tests were of a Mach-scale powered main rotor and fuselage in the National Full Scale Aerodynamics Facility 40x80' test section. The two entries included airframe-only, airframe plus upper rotor, and airframe plus coaxial rotor. The powered model results discussed in this paper will concentrate on the interactions between the main rotor, fuselage, and empennage.
This paper presents an efficient and high fidelity aerodynamic interaction modeling method for effective simulation and analysis of compound rotorcraft as well as aircraft configured with multiple rotors. The methodology is the first-principle based viscous Vortex Particle Method (VPM) whose rotor wake modeling accuracy has been validated through extensive simulation. This research extends the modeling methodology to address modern multiple rotor systems and compound rotorcraft and emphasizes the mutual interaction between the rotors, wings, fuselage, and aerodynamic surfaces of a full rotorcraft. The developed methodology aims to provide an effective modeling tool to support the design and analysis of next generation vertical lift vehicles. In this paper, the mutual aerodynamic interaction between major components of modern rotorcraft configurations (such as the rotor/rotor, the rotor/wing, the rotor/propeller, the rotor/empennage, and interactions) and its impact on the vehicle performance is studied. The simulation results are compared with available measurements and a good correlation with the measurements is obtained for the representative cases evaluated.
In the following work a set of CFD computational cases was calculated in order to obtain the aerodynamic characteristics of I-28 gyroplane in a wide range of sideslip angle. Severe modifications were checked out, and most important on the directional stability components of forces and moments, acting on an airframe, have been shown in aerodynamic coefficient form. A part of these calculations was to test the influence of rudder deflection on baseline gyroplane aerodynamic properties. In order to compare the results with already flying example of gyroplane, with known, good flight characteristics, a geometry was reconstructed with low accuracy, but enough to obtain reasonable sideslip characteristics, especially for high sideslip angle.
A model-scale wind tunnel test was conducted to determine propulsive efficiency and relative vibration levels of a tail mounted propeller in the wake of a powered rotor and generic fuselage. Six-component propeller loads were measured for all test points with a focus on thrust and torque. Propeller and main rotor operating conditions were set to mimic low- and highspeed vehicle flight operations, simulating speeds from 105 kts to 200 kts. A total pressure wake survey conducted without the propeller installed was used to determine the propeller plane inflow characteristics. Propeller operation had no measureable effect on rotor trim whereas the main rotor states significantly altered the propeller performance. All propeller positions showed a propulsive efficiency increase relative to the isolated propeller data when operated in the rotor wake. No position showed noticeable vibration levels higher or lower than another. The highest propulsive efficiency was measured for the mid-height propeller position.
ABSTRACT Many modern aircraft, including rotorcraft, require conformal antennas and fairings to reduce wind drag, ice accretion, lightning strikes, and impact damage. An innovative approach to embedding Very High Frequency (VHF) antenna elements in the leading and trailing edges of a helicopter empennage has been developed. A prototype has been fabricated and tested on a mockup of a helicopter empennage, consisting of the vertical stabilizer (tail), horizontal stabilator, and gearbox. Testing has shown that the design can meet typical communications range requirements. A history of helicopter empennage antennas, the development approach, design features and key innovations, and measured results are presented and discussed. The approach can be replicated on almost any current or future aircraft or rotorcraft.
Vives College University and Kulab (KU Leuven University campus Ostend) in Belgium are undertaking an aeronautical research program for the development of a new UAV aimed at performing scientific missions along the Belgian coastline above the North Sea. The main performance requirement of the UAV, dubbed Litus, is to be electrically powered with a range of 160 km and a payload up to 5 kg.
In addition to providing a comprehensive review and presentation of state-of-the-art experimental and computational efforts concerning rotor hub flows, this paper presents evidence that both experimental and computational capabilities are ready to foster the physical understanding of the long-age unsteady wake due to rotor hubs. A primary asset of this work is to demonstrate that two different rotor hub configurations show common characteristics of the underlying flow physics. The results of the Georgia Tech computations, when correlated with the experimental data from Penn State University, on two very different four-bladed hub configurations imply that the features of these long-age wakes (in the region where the vehicle tail would be located) may be captured with current computational solvers. This has significant implications in the rotorcraft industry's ability to tackle unsteady aerodynamic and aeroelastic phenomena that degrade performance and component life on the empennage of the vehicle. The necessity of experimental evaluations at component supercritical Reynolds numbers is also confirmed, suggesting the need for large wind tunnel or water tunnel campaigns.
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