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An examination of hydrogen fuel cells and lithium-ion batteries for electric vertical take-off and landing (EVTOL) aircraft
No full textThe primary drawback of electric vertical take-off and landing (eVTOL) aircraft is their poor range and endurance with practical payloads. The objective of this paper is to examine the use of hydrogen fuel cells to overcome this drawback through simulation and hardware testing. The paper develops steady state and transient models of fuel cells and batteries and validates the models experimentally. An equivalent circuit network model was able to capture the waveforms and magnitudes of voltage as a function of current, temperature, and humidity. Examination of the results revealed that the transient behavior of batteries and fuel stacks are significant primarily shortly after startup of the fuel stack and at the limiting ranges of high and low power; for a nominal operating power and barring faults, steady state models were adequate. This paper also demonstrates fuel cell and battery power sharing capabilities in an unregulated parallel configuration as well as in a regulated circuit. A regulating architecture was developed that achieved a reduction in power plant weight. Finally, the paper outlines weight models of motors, batteries, and fuel cells needed for eVTOL sizing, and carries out sizing analysis for three progressively longer on-demand urban air taxi missions. The objective aircraft was sized to carry a minimum of 400 lb payload for an on-demand air taxi-like mission with 5 min hover and 15-60 min cruise at 150 mph. This revealed that for ranges within 75 mi, an all-electric tilting proprotor configuration is feasible with current technology if high C-rate batteries are available. Either a battery-only or fuel cell and battery hybrid power plant is ideal, depending on the range of the mission. In particular, a 5700 lb gross take-off weight aircraft with disk loading of 11 lb/ft2 could be sized using a hybrid power plant with fuel cells and 10C batteries to carry a payload of 430 lb for a 75 mi (inter-city) mission. A smaller aircraft of 4000 lb gross weight and a disk loading of 27 lb/ft2 could be sized using a 6C battery only power plant to carry a payload of 490 lb for a shorter 38 mi (intra-city) mission. Research priorities would depend on target mission duration and range. For any mission beyond 40. miles (or 15 minutes at 150 mph) fuel cells appear to be a compelling candidate. Based simply on performance numbers (cutting-edge numbers proven at a component level but not in flight), ease of re-fueling, high w% hydrogen storage due to the short duration of eVTOL missions, and lack of a compressor due to low-altitude missions, fuel cells appear to far surpass any realistic future projections of Li-ion energy levels. However, for missions less than40 miles, improving battery energy density is the priority. All mission lengths require improved battery power density to 6-10 C for 150 Wh/kg batteries
Experimental and numerical investigation of near-field rotor aeroacoustics
No full textThis work presents comparisons between experimental and numerical estimates of near-field rotor aeroacoustics in hover. The experiments took place at the Kazan National Research Technical University named after A. N. Tupolev (Kazan Aviation Institute). A set of rotor blades with NACA-0012 aerofoil sections was used to obtain the sound pressure distribution using a linear array of microphones. It is shown that CFD and experimental results are in good agreement suggesting that the obtained test data can be useful as a validation case for development of CFD tools
Determining a safe-distance guideline for helicopters near a wind turbine and wind park
No full textThe Netherlands Aerospace Centre (NLR) was tasked to support the (former) Netherlands Ministry of Infrastructure and Environment to define a safe distance guideline for helicopters with respect to wind turbine parks. In an exploratory research, based on a relatively simple analytical wake model, a guideline for safe distance for helicopters is determined that can be used to support helicopter operations near offshore wind turbines and wind farms. The paper discusses the wake model, the safe distance criteria and will also consider the influence of the turbulence intensity, the wind turbine shaft height, rotor diameter of the turbine and the safe distance with regards to a multiple turbines in a wind park. A guideline for a safe distance is determined that could support directives for safe offshore helicopter operations near wind turbines
Design of a generic rotor noise source for helicopter fuselage scattering tests
No full textThis paper deals with the activities conducted in the GARTEUR Action Group HC/AG-24 to address noise scattering of helicopter rotors in presence of the fuselage. The focus of the paper is on the design for a generic "tail rotor" noise source used in the fuselage scattering study. The main design criterion is that the generic rotor noise source should resemble the main characteristics of the tail rotor with clear harmonic components. A two bladed simplified tail rotor model is considered. The performance of the tail rotor model in terms of thrust and torque with respect to the advance ratio is calibrated in the POLIMI wind tunnel. Acoustic measurements of the tail rotor model were tested in the DLR Acoustic Wind tunnel Braunschweig AWB. The results of the rotor performance and the rotor acoustic characteristics are described. The spectral variations resulting from unsteadiness of the source are explored in both with and without wind. The noise characteristics such as the spectral content, sound levels at fixed distances, and the time varying nature of the sound field are discusse
An experimental study on the hover performance characteristics of the coaxial propellers configuration for the drone
No full textDrone (or Passenger Drone) is one of hot issues in eVTOL industry present. So many companies such as Ehang, Airbus, Volocopter, Uber, Workhorse, etc. release their new concept taxi drone. In near future (within 2030), this taxi drone will enter commercial market and taxi service company (ex: Uber) will start to enter service only if these drones are commercialized. One of this taxi drone is required at the urban air mobility environment. This request compact sized vehicle operated between urban buildings with heavy payload which need to cover passengers. So, several candidate concept of taxi drone such as E-hang 184, Workhorse Surefly introduce the coaxial propellers design. Also, the more heavier payload with given sized vehicle drive these coaxial propellers drone described in figure1 [1] The purpose of this study is to present reliable performance data by experimental studying coaxial propellers configuration and to identify the characteristics of coaxial propellers to be used at the design, production, and verification and performance evaluation. To do this, experimental device was developed that can test at low Reynolds number(Re?3�105) of coaxial propellers. The experimental device basically constructed the DAQ which can measure torque, rpm, power so that the performance characteristics of the upper and lower propellers can be known. The experiments which composed of the different H/D ratio (0.1~0.8) defined as the ratio of distance of upper / lower propellers divided by its diameter and the different propeller�s diameter�s ratio were conducted. Experiments were carried out on the coaxial propeller after verifying the calibration. As a result of comparing the values with F.M.(Figure of Merit), it was found that the coaxial propeller of the same diameter showed a constant FM at the H/D ratio(0.2~0.3) and the highest value of all conditions tested was achieved when the diameter of the upper part of the propeller was smaller than the diameter of the lower part confirmed
Helicopter engine air intake icing wind tunnel certification test
No full textKorea Aerospace Industries LTD (KAI) contracted the Netherlands Aerospace Centre (NLR) to support an Icing Wind Tunnel (IWT) test campaign with the Korean Utility Helicopter KUH-1 engine air intakes aimed at substantiating the compliance with the applicable military regulations for flight in icing conditions. The icing wind tunnel test was performed in the Large Climatic Wind Tunnel (CWT) at Rail Tec Arsenal (RTA) in Vienna, Austria. The test set-up included a full-scale production engine cowling complete with electrothermal anti-icing system and it was installed on a mock-up of the aircraft upper fuselage. The production cowling was used to ensure an exact match and conformity of the thermal properties of the part. To aspirate the engine intakes, NLR designed a dedicated Engine Mass Flow System (EMFS) that simulates the airflow through the engine air and cooling intakes. Two separate industrial radial fans were installed to individually control the mass flow through the engine air intakes and cooling inlets. A continuous mass flow measurement was provided for both channels by anti-iced Pitot-static probes that were calibrated against orifice plate measurements performed prior to the icing test. The tunnel test conditions were scaled for altitude effects by matching key similarity parameters. The test airspeed was based on either Reynolds number scaling or Weber number scaling, depending primarily on the static air temperature. Inter-laminate and surface temperature measurements and observed ice shapes compared favourably with artificial and natural icing flight test results obtained with the same intake configuration. The IWT testing supplemented the flight test results by providing more stable icing conditions with control over drop size, and covering the corner points of the icing envelope
Active vibration control for the Kazan Ansat
Get PDFThis paper presents a high-level overview of the implementation and the results of LORD's OMNI Active Vibration Control System (AVCS) on Russian Helicopter's Ansat helicopter platform as well as a brief description of principles of the technology. The AVCS is designed so that it can be easily adapted to both existing production aircraft and new aircraft development to actively reduce in-flight vibration levels. Vibration reduction allows for increased crew comfort, reduced equipment fatigue and in certain cases even an increased flight envelope at minimal installation weight versus performance compared to other vibration reduction technologies. The technology is architected with a high degree of modularity to allow it to be adapted to a wide variety of aircraft and customer use-cases. The primary goal on the Ansat was to configure the AVCS to reduce vibration levels at the VIP seats in the aft cabin although cockpit vibration levels were also to be considered. LORD engineers worked with the Russian Helicopters team at the Kazan, Russia facility to integrate and tune the system through simulation and flight test, which resulted in reductions in vibration levels at the VIP seats of up to 84% depending on flight condition. Ultimately, these efforts resulted in two production configurations, which first appeared on a production Ansat in February 2018, making it the first Russian helicopter with LORD's Active Vibration Control technology
Dynamic simulation of a rotorcraft hybrid engine in Simcenter Amesim
Get PDFThis paper assesses a series hybrid propulsion system utilizing a recuperated gas turbine configuration. An adapted engine model capable to reproduce a turboshaft engine steady state and transient operation is built and used as a baseline for a recuperated engine. The recuperated engine presents a specific fuel consumption improvement of more than 15% at maximum continuous rating at the expense of surge margin which is reduced. An Oil and Gas (OAG) mission of a Twin Engine Medium helicopter has been used for assessing the hybrid configuration. The thermo-electric system brings a certain level of flexibility allowing for the recuperated engine to operate for high take-off weight cases. If envisioned 2025 technology is considered the fuel benefit of the series hybrid recuperated configuration for the OAG mission is in the range of 5%. The integrated system models (gas turbine, electric and heat exchanger systems) are built in Simcenter Amesim, a system modelling platform allowing for both steady state and dynamic simulation
Simulation tools for UAV/OPV autorotation performance metrics evaluation
No full textUnder the framework of the US/France Project Agreement (PA) on Rotary Wing Aeromechanics and Human Factors Integration Research, ONERA and AED began to collaborate on helicopter autorotation capability in 2011. In 2017, a new joint task started, dedicated to improving control and guidance capability and defining requirements for implementation on rotary-wing UAV and OPV when operated in autorotation. This three-year program will investigate the enabling systems and technologies from an UAV automatic system to be used in an OPV for autorotation maneuver, thus taking the benefits of a full-automatic system to provide dedicated piloting aid functions. A modeling and simulation framework is proposed for designing, evaluating and testing flight control algorithms for helicopter autorotation flight. A common helicopter model and set of flight controllers have been developed and shared between ONERA and the US Army. Initial studies of the autorotation flare/landing metrics are presented and discussed, with a focus on using these metrics in the future to evaluate purpose-built automated autorotation controllers for UAV/OPV helicopters
Optimisation of differential infrared thermography for unsteady boundary layer transition measurement
No full textDifferential infrared thermography (DIT) is a method of analyzing infrared images to measure the unsteady motion of the laminar-turbulent transition of a boundary layer. It uses the subtraction of two infrared images taken with a short time delay. DIT is a new technique which already demonstrated its validity in applications related to the unsteady aerodynamics of helicopter rotors in forward 2ight. The current study investigates a pitch-oscillating airfoil and proposes several optimizations of the original concept. These include the extension of DIT to steady test cases, a temperature compensation for long-term measurements, and a discussion of the proper infrared image separation distance. The current results also provide a deeper insight into the working principles of the technique. The results compare well to reference data acquired by unsteady pressure transducers, but at least for the current setup DIT results in an additional measurement-related lag for relevant pitching frequencies