Browse Topic: Power and Propulsion
This SAE Aerospace Recommended Practice (ARP) establishes design guidance and photometric values for adequate cargo compartment and cargo access lighting systems for ground handling. The adoption of a standard set of illuminance values, found appropriate for the performance of the task in specified areas, should expedite ground handling.
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.
Drain and Fill plugs used on engines, transmissions, transfer cases and front and rear drive axles for class 5 – 8 vehicles.
Helicopter tail shake constitutes a significant limitation to both passenger comfort and aircraft stability. Under powered descent conditions, elevated Angle of Attack (AoA) cause flow separation around the rotor hub and engine cowling, leading to the development of an unsteady wake dominated by large-scale turbulent structures. To support the helicopter tail shake phenomenon investigation, a dedicated Particle Image Velocimetry (PIV) experimental setup was designed in this work, together with four aerodynamic devices aimed at mitigating tail shake. These components were then tested through a wind tunnel campaign with the PIV setup. The proposed aerodynamic components were conceived to either deflect the hub wake away from the tail empennages or to decrease the Turbulent Kinetic Energy (TKE) within the wake. To achieve these objectives, a dorsal fin, a horse-collar, and two spoiler configurations inspired by automotive applications were designed and experimentally evaluated. The devices were tested both as standalone solutions and in combined arrangements on a scaled helicopter wind tunnel model featuring a rotating hub and blade shanks. The vertical velocity component, was used as an indicator of wake deflection, and the Turbulent Kinetic Energy was used as an indicator of wake turbulence. The Horse Collar and the Large Spoiler showed a reduction in both indicators suggesting possible tail shake mitigating capabilities, and additional improvements were achieved when the two devices were deployed in combination.
Emerging technologies in the field of electrified propulsion systems offer a promising solution to reduce the dependence on fossil fuels and improve efficiency. However, the design of high-power density electric machines introduces new challenges, including limited passive cooling potential and the issue of the weight of electric motors. To address these challenges, this paper considers analysis and design methods for high torque-to-weight ratio axial flux motors. A magnetic equivalent circuit model coupled with a lumped parameter thermal network is developed for design space exploration and optimization. This inexpensive analytical model predicts the performance of a single-stator dual-rotor axial flux motor based on geometry, loading condition, and slot and pole pair combination. To enable comparisons against real-world data, the optimization study was demonstrated using the hover mission requirements from the Research Aircraft for eVTOL Enabling techNologies (RAVEN) vehicle to minimize the mass of the motor. In tandem with the analytical model, a higher-fidelity finite element model was also developed, and good agreement between predicted power and efficiency was demonstrated across a range of axial flux motor designs. The lightest weight design that satisfied the hover mission requirements was the 12 pole pair 27 slot (12PP 27S) configuration with a fixed weight of 9.28 kg. The analytic model undersized the output power of the electric motor by approximately 9% across a range of slot and pole pair combinations.
Urban Air Mobility (UAM) concepts require multidisciplinary analyses across multiple modes of operation and often involve discrete architectural differences such as propulsion type, rotor configuration, and mission context. Existing optimization and workflow frameworks support continuous design variables but provide limited mechanisms for handling discrete variants, multi-modal vehicle definitions, and vehicle management for UAM vehicles. This paper presents uam4x, an open-source Python framework that addresses these challenges through a structured problem definition representation, a plugin-based execution engine, integrated version control, and a function-based branching script mechanism for constructing analysis scenarios. The framework provides integration of existing tools including Open Vehicle Sketch Pad (OpenVSP), NASA Design and Analysis of Rotorcraft (NDARC), M4 Structures Studio (M4SS), and Intelligent Cross Section Generator (IXGEN) through unified plugin interfaces. Parameter sweeps, nested analyses, and optimization via OpenMDAO are supported within the same architecture. This paper also presents demonstrations that were created to illustrate the various capabilities and integration efforts of the framework.
Vertical Take-Off and Landing (VTOL) aircraft introduce complex monitoring challenges due to distributed propulsion, lightweight structures, and variable operating conditions. This paper presents advanced Frequency and Orders domain techniques that repurpose existing flight control, propulsion, and structural sensor data to enhance observability without additional instrumentation. By transforming vibration, acoustic, and electrical signals into frequency and order domains, the approach enables detection of harmonics, resonance, and fault signatures tied to rotor dynamics, supporting adaptive control and predictive maintenance. Beyond rotor systems, these techniques are equally effective for monitoring electric motor health, gearbox wear, bearing degradation, and structural coupling effects in composite airframes. They also provide insight into power electronics and thermal management systems by identifying spectral anomalies linked to electrical imbalance or cooling inefficiencies. Aggregated fleet data strengthens prognostic capabilities, enabling early detection of systemic issues and trend analysis. Applications include mitigating ground resonance and modal instabilities, as well as improving reliability of propulsion and structural subsystems. Integration into avionics emphasizes computational efficiency, scalability, and compliance with standards such as DO-160 [1], DO-178 [2], ARP4761 [3] and ARP4764 [4]. Simulation and bench testing confirm feasibility, demonstrating potential to enhance safety, reliability, and lifecycle cost for next-generation urban air mobility platforms.
During helicopter air-to-air refueling the rotor of the helicopter might enter the slipstream of the tanker aircraft's propeller. Based on blade element momentum theory, the impact of the accelerated air within the propeller slipstream on rotor blade aerodynamics (thrust, rolling and pitching moments) can be solved analytically. Also, DLR's comprehensive rotorcraft code has been used with the Pitt-Peters induced inflow plus rotor-rotor interference model. Additionally, DLR's free-wake code was used for both the propeller and the helicopter main rotor, including mutual wake-wake-interactions. The helicopter rotor's collective and cyclic controls needed for disturbance rejection are computed with all these models for a typical air-to-air refueling scenario without and with blade flapping motion. A propeller wake affecting the retreating side of the rotor requires much larger control inputs to retrim than an impingement on the advancing side. The results of all modelling approaches are compared to each other and generally a reasonably good agreement is found, despite their very different levels of complexity and computational effort.
Several efforts have been made to develop Flight Test Maneuvers for Handling Qualities evaluations, aimed at quantifying the effects of vehicle characteristics and assistance systems on a Helicopter Air-to-Air Refueling mission profile. However, these Flight Test Maneuvers have not achieved widespread adoption, likely due to the substantial logistical challenges associated with tanker deployment. Depending on a tanker aircraft not only incurs significant costs but also requires extensive organizational effort and prior testing, before Handling Qualities can be evaluated for the aerial refueling capabilities of a new rotorcraft design. Additionally, these available Flight Test Maneuver setups are not standardized or widely applied to the same degree as Mission Task Elements of the Aeronautical Design Standard, which limits repeatability and comparability. A new approach is proposed to address these limitations by introducing a repeatable, standardized method to reveal Handling Qualities deficiencies considering a worst-case situation of Helicopter Air-to-Air Refueling. This approach involves analyzing drogue motion to create a synthetic, deterministic target forcing function, based on the summation of several sine waves. Resulting laws of motion are applied to a target tracking task replicating a drogue chasing scenario by projecting all required references into the pilots' field of view. Piloted simulator studies conducted at the Air Vehicle Simulator (AVES) of the German Aerospace Center (DLR) demonstrate a high degree of similarity in pilot control behavior between the proposed Flight Test Maneuver and actual simulated Helicopter Air-to-Air Refueling.
This paper presents experimental research aimed at developing novel low lubrication methods for rotorcraft and jet engines, focusing on sustaining minimal lubrication to prevent catastrophic bearing failure during loss of lubrication (LoL) events or to increase fuel consumption performance on once-through, fuel-oil bearing lubrication engines. Utilizing two high-speed bearing test rigs simulating low and high thrust class engine conditions, the study establishes lower bounds for oil flow rates necessary to maintain thermal stability and prevent thermal runaway in hybrid ball bearings. These findings inform the design of the Zulu Pod (ZPod), a passively driven, self-contained oil delivery system that uses engine compressor bleed air to precisely meter lubricant flow. Engine test stand results demonstrate that replacing traditional fuel-oil lubrication with the ZPod system reduces thrust specific fuel consumption (TSFC) by an average of 7%, with up to 11% savings, without compromising engine thrust or bearing health. The ZPod offers a simplified, efficient alternative to fuel-lubricated systems by eliminating fuel diversion for lubrication, enhancing fuel efficiency, and maintaining bearing performance in attritable or single-use engines. Additionally, the study highlights the potential of minimal lubrication supplied by the ZPod to extend operational life during LoL scenarios, enabling safer aircraft recovery. Future work will focus on extending testing to higher thrust classes and optimizing ZPod designs for broader applications.
Hydrogen-electric vertical takeoff and landing (H2eVTOL) (or fuel cell-electric VTOL) aircraft technologies are poised to emerge in the next coming decades and start operating from existing heliports and new vertiports. This paper assesses how key H2eVTOL design features interact with the ground infrastructure and how facility designers can address H2eVTOL specific facility requirements–especially the supply of hydrogen to the aircraft. Vertiport design should maximize compatibility are important to facilitate the accommodation of hydrogen technologies, minimize the need for extensive capital investments, and promote safety and operational efficiency. Considerations should be given to factors such as general aircraft configuration, electric and hybrid propulsion systems, and refueling infrastructure. The definition of notional aircraft concepts representing the evolution of critical VTOL aircraft over the next coming decades can help aviation facility planners and designers understand the type of vehicles they need to account for and also evaluate the future hydrogen demand. The lack of aviation-specific standards, especially when it comes to fire prevention, might adversely impact vertiports. Strategies are proposed for mitigating the effects of hydrogen operations at space-constrained facilities.
Accurate simulation of fluid-structure interactions (FSI) is critical for designing aircraft systems, particularly for applications involving fuel tank sloshing and large deformations. Traditional added mass methods often fail to capture the nonlinear and frequency-dependent behavior of these coupled systems. This study applies the Finite Pointset Method (FPM), a mesh-free computational fluid dynamics (CFD) technique, coupled with an explicit finite element solver, to predict complex FSI phenomena. Validation is performed using benchmark experiments, including a harmonic tank sloshing test and a guided plate ditching scenario, with results demonstrating strong agreement with measured pressures and structural responses. Additional validation on a composite fuel tank drop impact test confirms FPM's ability to model large deformations and rupture under dynamic loading. The findings highlight FPM's robustness and adaptability for aerospace FSI problems, offering a powerful alternative for virtual prototyping and certification workflows where conventional methods are insufficient.
There is a continued and growing need for better analysis and simulation of complex transmission systems with the rise of hybrid electric powerplants coming to future aviation vehicles. In this paper we discuss how reduced order modeling can help to efficiently predict the thermal behavior of gearboxes during operations smartly reusing data from SPH based oil flow simulations. To solve the thermal problem, a dynamic non-linear Reduced Order Model (ROM) is generated to estimate the Gear-Oil heat transfer coefficient (HTC) based on variable gearbox RPM and Oil fill level.
Electrification could improve full-size rotorcraft performance by reducing peak turbine power demand, reducing transmission system weight and complexity, and reducing operating costs. Integrating electric machines with mechanical powertrains requires careful consideration of the system-level weight and efficiency impacts. This paper presents an optimization framework for evaluating parallel hybrid powertrain configurations using Geometric Programming (GP). Both retrofit and clean-sheet vehicle designs are considered. The results show that high-speed electric motors integrated into a parallel hybrid configuration using batteries can reduce the sized gas turbine power, enabling more efficient engine operation at lower power levels. For retrofit designs, with a fixed vehicle gross weight, adding batteries and motors reduces usable fuel, decreasing mission capability. Clean-sheet designs offer additional flexibility to re-size the vehicle and rotor, resulting in energy savings for an equivalent design mission.
The oil cooling fan of a Main Gearbox (MGB) is a mechanically-driven component whose purpose is to force an air flow through an air cooled oil cooler; its performance is crucial in ensuring that the MGB oil temperature does not exceed a predefined threshold, set to alert the crew in case of an abnormal situation. The design and the certification of a cooling fan is a process involving several steps and multiple disciplines; mechanical design, aerodynamic analysis, dedicated tests carried out both on rigs and at aircraft level need to be exploited as complementary tools to assess the correct aero-mechanical behavior of the system. The aerodynamic assessment is associated to performance, measured in terms of MGB oil temperature: considering a comparison between two cooling fans, one outperforms the other if the resultant MGB oil temperature is lower, keeping the same boundary conditions (engine torque, wind speed, ambient temperature, etc.). The correct mechanical behavior is instead associated to multiple requirements that need to be satisfied: target fatigue life, high and low temperature limits, blade loss containment, maximum speed, etc. The process connecting the very first blank page to the certification of the part is usually linear and well defined, and the experience gathered by Leonardo Helicopters over the years has allowed to follow this path easily in most cases. This paper discusses an intriguing situation: the goal of the activity herein discussed was to replace an obsolete oil cooling fan with a new one. The latter was expected to outperform the first both from the aerodynamic point of view (i.e. lower MGB oil temperature) and from the mechanical point of view (i.e. longer life). The preliminary CFD analyses and the rig tests proved that the new fan was able to outperform the legacy one in regards of the aerodynamic requirement; nevertheless, during the last steps of verification carried out at aircraft level, the installation of the new fan resulted in a higher MGB oil temperature. This triggered dedicated troubleshooting: a sequence of investigative tests performed by means of dedicated rigs, targeted at properly identifying the aerodynamic operative point of the cooling fan and at understanding the reason behind the unexpected outcomes obtained. The relevance of this contribution does not lie in the description of the certification process per se, rather in the nonlinear dynamics characterizing the test sequence once the flight activities pointed out an unpredicted behavior.
This paper presents handling qualities (HQs) research findings for electrical Vertical Take-off and Landing vehicles. Testing in the Vertical Motion Simulator (VMS) investigated handling qualities of vehicle configurations having a degraded powertrain. Powertrain components, including batteries and electric motors, can degrade as the vehicle is flown. This paper investigates the impact of low battery charge and high motor temperature degradations on the pilot's ability to execute precise maneuvers. Pilot comments and ratings that were collected from four rotorcraft test pilots in VMS testing are used to quantify the effects that powertrain degradations had on the HQs of the vehicle.
Developed in the frame of the European Clean Sky 2 program, the RACER High Speed Helicopter Demonstrator of Airbus performed its maiden flight on April 25th, 2024. In the continuity of the previous high-speed demonstrator X3 (1st flight in 2010) the RACER is a 7/8t (15000 / 18000 lb) class compound helicopter powered by two SHE Aneto-1X engines, including a wing and two propellers. The tail rotor is removed as the two propellers control the yaw axis by differential thrust. At flight 07, with its initial default settings, it reached a true airspeed of 227 kts in level flight, exceeding its objective of 220 kts.
A regulated hybrid-electric power sharing architecture was developed and tested for VTOL applications. In this architecture, there are two power supply branches and one load. The first branch draws power from an engine-generator, and it has additional components of an AC-DC rectifier, a DC-DC buck converter, and a power diode. The second branch draws power from a battery, and it has additional components of a solid-state relay, a DC-DC boost converter, and a power diode. Any specified ratio of battery-to-engine power can be achieved with this architecture. Testing on the full range of power share ratios was conducted at a low load power of 300W. The key conclusions are that: (1) regulated power sharing is feasible between an AC supply and a DC battery, including the extremes of all engine and no battery to all battery and no engine, (2) a specified power share ratio can be achieved both in steady-state and transient conditions, and (3) there is a delay in achieving a specified power share ratio, caused not by the power plant, but rather by the change in RPM of the rotor.
The Main Gearbox of a helicopter is a crucial component that delivers the desired performance and ensures the highest possible level of safety of the aircraft; it includes several gears and bearings, which require to be continuously lubricated by a pressurized oil flow. Undesired circumstances may cause the oil to leak from the main circuit, hence reducing its pressure and consequently the oil flow rate targeted towards the rotating components; this modifies their friction coefficient, and subsequently leads to an overheating of the parts with the risk of degenerating in a catastrophic failure. During the design of a helicopter drive system, engineers need to take proper precautions and make sure that the MGB is fully equipped with the proper features to cope with a loss of lubrication event; specifically, the drive system is supposed to be able to run at least 30 minutes after the oil pressure drops to zero. A lot of effort has been put over the years at Leonardo Helicopters to find robust solutions to attain the longest performance of the drive system in no-oil conditions: the most important result is the certification of the AW189 for a 50-minutes “run dry” capability. Nevertheless, the dynamic environment typical of the rotorcraft industry pushes towards continuous innovation, and in the last few years the Transmissions Systems Design department of LH has been asked to investigate suitable ways to further augment the no-oil capabilities of the MGB: the main steps followed and entailed results are presented in this paper. The first part of the manuscript discusses the “state of the art” auxiliary lubrication system, currently flying on the AW189 drive system. The second part tackles the approach adopted to meet the novel requirements, unveiling both the methodology and the final design choice: the latter includes a metering element, able to tune the oil flow rate headed towards the component deemed the most critical in order to satisfy the requirement of longer no-oil performance. Numerical and experimental tools are exploited as complementary tools to properly crystallize the obtained results and corroborate the solution.
This paper, explores the design and sizing of a planetary gear-based electronic continuously variable transmission (ECVT) for implementation of a parallel gas-electric hybrid helicopter propulsion system. The ECVT consists of a differential planetary gear transmission (PGT) and an electric motor/generator (MG) unit. The ECVT enables power-flow between engine, motor and helicopter main rotor. The parallel arrangement enables the main rotor speed to varied continuously based on the MG speed while the engine speed can remain constant. The performance benefits enabled by the main rotor speed variation capability are offset by the added weight penalties introduced by the ECVT system. By considering factors such a as gear tooth bending and contact stress, bearing loads, required motor torque, planetary gear kinematics and pitch-line velocity constraints, this paper conducts a minimum mass design study for several PGT / ECVT arrangements. Here, three different single stage PGT/ECVT arrangements are compared along with an improved two stage ECVT. The three single stage ECVT configurations can be summarized as; I) Sun-Engine / Carrier-Motor / Ring-Out, II) Sun-Engine / Ring-Motor / Carrier-Out, and III) Carrier-Engine / Sun-Motor / Ring-Out. Of these three types, it was found that type III was significantly lighter in weight compared with types I and II since type III would have the highest relative motor speed. When sized for a 3000 Hp engine-side power input at 6000 rpm, the minimum mass design for type III was on the order of 100 lbs compared to 400 lbs and 700 lbs respectively for types I and II. Despite the seemingly obvious advantage of design type III, it's drawback is that it is effectively a speed increasing stage with respect to the engine. To address this, a two-stage ECVT with compound planetary arrangement of Type III and II was designed which achieved an overall minimum weight of 219 lbs at the 3000 Hp level while providing 1:0.351 gear reduction form engine to output. The analysis tools developed and sizing results flowing from this study will provide a baseline for evaluating performance benefits and weight penalties introduced by parallel hybrid drive-systems for rotorcraft applications.
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