Turboprop Aircraft Research Articles

Reducing take-off and landing distances for regional turboprop aircraft

Reducing take-off and landing distances for regional turboprop aircraft

Synchrophasing control of multiple propellers based on hardware in the loop experimental platform

A hardware in the loop experimental platform is established to evaluate the optimal noise reduction prediction and maintenance capability of multiple propellers under high-precision synchrophasing control. This platform incorporates an online propeller noise model and a digital turboprop engine model into a novel integrated measurement system. Firstly, an improved propeller signature theory using CFD simulation's sound pressure signals is proposed to predict the online propeller noise efficiently. It achieves acceptable noise prediction accuracy using a subset of synchrophase angles to predict noise for all synchrophase angles at all receivers. Secondly, a high-priority interrupt method is proposed for the novel integrated measurement system to guarantee precise measurement and ultimate high-precision synchrophasing control. Thirdly, a turboprop engine model based on a component level model and propeller performance maps' CFD data is also established. To enhance the simulation confidence of the system, we compare the dynamic synchrophasing control effects between systems with and without the integration of a turboprop engine mode. The experimental results demonstrate that the high-priority interrupt method effectively reduces the synchrophase angle(θ) error. These approaches reduce noise by 3.62dB at SPL, exhibit a noise variation within ±0.13dB/°, and effectively manage thrust fluctuation within 4.14%. These results indicate that the method meets the control accuracy and noise reduction requirements in a twin-engined turboprop aircraft.

Hybrid electric aircraft design with optimal power management

The aviation industry has continuously improved its fuel efficiency over the last decades with innovations in technology, design and operation. Further improvements are becoming more difficult as current technology reaches complete maturity. Electrification of road vehicles is predicted to completely replace combustion engines in vehicles. As the efficiency and reliability of electric batteries and motors improve, so does the case for electric propulsion systems in aircraft. Jet fuel carries significantly more energy per weight than current state of the technology batteries, making complete replacement of fuel challenging. Hybrid electric propulsion, where both fuel and batteries are used to power propulsion systems could be feasible and improve fuel efficiency. Hybrid electric powertrains use electric power to reduce the power demands from the combustion engine. Electric batteries are discharged and charged during the operation based on power requirements.This paper presents an aircraft design method that includes optimized power management in the design loop. Power management determines battery discharging and charging throughout the design mission to reduce overall fuel consumption. Power management optimization provides the necessary feedback on battery and fuel performance to design battery pack size. This method is applied to regional aircraft, which typically fly the shortest routes of a commercial airline fleet. These short routes have proportionally longer climb and descent segments. These characteristics of regional aircraft routes lead to wider variations in power during operation, where hybrid electric powertrains are the most beneficial.The proposed hybrid electric aircraft design method finds that a serial hybrid electric regional aircraft could achieve significant fuel efficiency improvements to current regional aircraft. This result is in contrast of the current literature, which requires significant improvements to battery energy density, power distribution efficiency and electric motor efficiency to achieve similar fuel performance results. The hybrid electric regional aircraft does not outperform a traditional turboprop aircraft designed with identical objectives. The turboprop aircraft design improves even greater fuel efficiency improvements over current regional turboprop aircraft. This suggests two pathways are possible; the propulsion system of the next generation of regional aircraft could still be non-electric and achieve improved fuel burn improvements considering current technology or serial hybrid-electric powertrains configurations could be adopted in an expanded time horizon if optimistic technology development is done on battery power density to match the possible improvements of the proposed turboprop aircraft.

Modeling passenger comfort in turboprop aircraft using objective measures.

A quantitative comfort model will aid in evaluating comfort levels of various target groups before the actual flight of an airplane. However, constructing the model is always a challenge due to the complexity of the phenomenon. In this paper, we present quantitative comfort models to predict the (dis)comfort of passengers flying with turboprops based on objective measures. Ninety-seven participants took part in two experiments conducted during real flights, during which forty of them had environmental and personal factors recorded using (self-developed) measurement tools. The collected data were analyzed to model the relations between objective measures and subjective feelings. Two preliminary models based on gradient boosting regression were developed. The models were able to predict the changes in comfort and discomfort of individual passengers with an accuracy of 0.12±0.01 and 0.21±0.01 regarding normalized comfort and discomfort scores, respectively. Additionally, contributions of different factors were highlighted. The outcomes of the models show that we took a step forward in modeling the human comfort experience using objective measurements. Anthropometry (including age), seat positions, time duration, and row (noise) emerged as leading factors influencing the feeling of (dis)comfort in turboprop planes.

Cooling of 1 MW Electric Motors through Submerged Oil Impinging Jets for Aeronautical Applications

Electrification of aircraft is a very challenging task as the demand for energy and power is high. While the storage and generation of electrical energy are widely studied due to the limited specific energy and specific power of batteries and fuel cells, electric machines (power electronics and motors) which have years of experience in many industrial fields must be improved when applied to aviation: they generally have a high efficiency but the increase in power levels determines significant thermal loads which, unlike internal combustion engines (ICE), cannot be rejected with the exhaust. There is therefore a need for thermal management systems (TMSs) with the main objective of maintaining operating temperatures below the maximum level required by electric machines. Turboprop aircraft, such as the ATR 72 or the Dash 8-Q400, are commonly used for regional transport and are equipped with two gas turbine engines whose combined power is in the order of 4 MW. Electric and hybrid propulsion systems for these aircraft are being studied by several leading commercial aviation industries and start-ups, and the 1MW motor size seems to be the main option as it could be used in different aircraft configurations, particularly those that exploit distributed electric propulsion. With reference to the topics mentioned above, the present work presents the design of a TMS for a high-power motor/generator whose electrical architecture is known. Once integrated with the electrical part, the TMS must allow a weight/power ratio of 14 kW/kg (or 20 kW/kg at peak power) while maintaining the temperature below the limit temperature with reasonable safety margins. Submerged jet oil is the cooling technique here applied with a focus on diathermic oil. Parameters affecting cooling, like rotor speed and filling factor, are analysed with advanced CFD.

Application of a climate impact evaluation methodology to compare turboprop and jet aircraft

Application of a climate impact evaluation methodology to compare turboprop and jet aircraft

Multi-channel ANC System with Online Secondary Path Modeling for Turboprop Aircraft Cabin

Multi-channel ANC System with Online Secondary Path Modeling for Turboprop Aircraft Cabin

Validation of a turboprop cabin demonstrator

Turboprop aircraft should be improved as they are more environmentally friendly aircraft compared to turbojet aircraft but noise and vibration are often too high for passengers. A simple and uncomplicated way to carry out experiments is using a demonstrator. To determine whether the demonstrator represents the reality, it must be validated. In this project, real flights were first conducted in a turboprop aircraft. During two 70-minute flights, 94 subjects answered questions about symptoms, mood or comfort levels related to noise and vibration, among other things. In the next step, investigations will be carried out in the demonstrator under the same conditions as the real flights. Both results will be compared with each other. If the data from the demonstrator corresponds to that of the real flights, the demonstrator is considered to have been successfully validated. The requirement for this is that the demonstrator data lies within the confidence intervals of the results from the real flights. The aim is to validate a full-scale on-ground demonstrator of a regional turboprop aircraft cabin that will be used for multiple tests like subject tests and comfort evaluation, composite materials and structures, systems and energy consumption.

Prediction of environmental benefits introducing hybrid-electric propulsion on regional aircraft

The objective of this paper is to assess the environmental benefits arising from the introduction of hybrid-electric propulsion on regional and commuter turboprop aircraft. A great focus is put on the propulsion based on a turbine engine coupled with batteries, combining mature technologies. The introduction of novel propulsion architectures on aircraft deployed on regional and commuter networks allows a substantial reduction of the fuel needed by airlines. In this work, scenarios based on real airline networks are presented, in order to quantify the reduction of greenhouse gas emissions possible considering the expected technological advancement for 2035 and 2050. This analysis is conducted by retrofitting the hybrid-electric propulsive system onto existing aircraft that can carry 19 passengers (Dornier DO228) or 70 passengers (ATR72-600). For the 19-seat class, a clean sheet design is also considered to overcome some limitations of the reference aircraft. A precise assessment of the peculiarities linked to the chosen propulsive configuration shows that networks that have shorter flights are better suited to the introduction of this technology, as the restriction on the design payload is less stringent. The proposed propulsive architecture allows a reduction of the operators’ yearly fuel budget of up to 50% in 2035 and 80% in 2050. At last, the taxi phase is of particular importance for regional aircraft that perform several rotations a day, therefore a further analysis of this phase is carried out. The result shows that the considered aircraft are capable of completing a full Landing & Take-Off (LTO) cycle without resorting to the thermal part of the propulsive system, reducing considerably the impact of the aircraft on the airport area.

A Sensitivity Analysis on the Range Equation of Hybrid-electric aircraft

This paper carries out a sensitivity analysis on the recently proposed hybrid-electric range equation [1]. The proposed hybrid-electric range equation is based on an efficiency-based definition of the degree of hybridization and the efficiencies of respective drivetrains on the range estimation of the hybrid-electric aircraft. The ATR 72 turbo-prop aircraft is chosen as the case study for the sensitivity analysis. The sensitivity analysis done in this paper shows the effects of parameters such as lift to drag ratio, efficiencies, energy densities, payload weight, etc. on the aircraft range. It was observed that variation in aircraft range due to each parameter was distinct and unique. The analysis also depicted the implications of the changes in the above-mentioned parameters from an aircraft designer’s viewpoint. The changes were carried out using the predictions for the year 2050. The sensitivity analysis performed in this work successfully narrowed down the parameters that had the maximum impact on the aircraft range.

Long wave infrared signature of swept back leading edges in aircraft frontal aspect

PurposeIn recent years, increased use of all-aspect infrared (IR)-guided missiles based on the long-wave infrared (LWIR; 8–12 µm) band has lowered the probability of aircraft survival in warfare. The lock-on of these highly sensitive missiles is difficult to break, especially from the front. Aerodynamically heated swept-back leading edges (SBLE), because of their high temperature and large area, serve as a prominent LWIR source for aircraft detection from the front. This study aims to report the influence of sweep-back angle (Λ, based on the Mach number [M∞]) on aerodynamic heating and the LWIR signature of SBLE.Design/methodology/approachThe temperature along SBLE is obtained numerically as radiation equilibrium temperature (Tw) by discretizing the SBLE length into “n” number of segments, and for each segment, emission based on Tw is evaluated. IR radiance due to reflected external sources (sky-shine and Earthshine) and radiance due to Tw are collectively used to determine the IR contrast between SBLE and its replaced background in the LWIR band (icont-SBLE,LWIR).FindingsThe results are obtained for low subsonic turboprop aircraft (Λ = 3°, M∞ = 0.44); high subsonic strategic bombers (Λ = 35°, M∞ = 0.8); fifth-generation stealth aircraft (Λ = 40°, M∞ = 1.6); and aircraft with supercruise/supersonic capability (Λ = 50°, M∞ = 2.5). The aircraft with supersonic capability (Λ = 50°, M∞ = 2.5) reports the maximum LWIR signatures and hence the highest visibility from the front. The results obtained are compared with values at Λ = 0° for all cases, which shows that increasing Λ significantly reduces aerodynamic heating and LWIR signatures.Originality/valueThe novelty of this study comes from its report on the influence of Λ on the LWIR signatures of aircraft SBLE in the frontal aspect for the first time.

Development of Electronic Flight Bag Application for Small Turboprop Aircraft Weight and Balance Calculation

Nowadays, many airlines in modern aviation utilize an Electronic Flight Bag (EFB) during flight to replace traditional paper-based systems. Considering the importance of aircraft weight and balance calculation to flight operations, the flight mission of X-123 (a small turboprop aircraft) and the current EFB market, research on weight and balance application development of X-123 on EFB in Indonesia is conducted. The research aimed to develop the application according to Indonesian regulations and to examine the weight and balance characteristics of X-123 through several simulations in a programming language, Python. Furthermore, Staff Instruction 8900 - 3.3 is analyzed to identify the factors that should be considered in EFB development. The global architecture design and substantial features are, then, proposed as an initial EFB development. In the global architecture design, the utilization of a gateway becomes important as a connection between the EFB developer and the client, providing aircraft data changes flexibility to the client. Moreover, the calculation formula is completely discussed in the calculation modules as a substantial feature and implemented in the simulation. According to simulation results, the payload weight and payload distribution changes can affect significantly the CG location. It is recommended to weigh and assign the payload before flight to ensure flight operation safety. In addition, the proposal of the architecture design and substantial features can be used as a reference and further developed by the Indonesian aviation companies.

Analysis of noise sources in the cabin of a passenger aircraft and methods for combating them

This paper examined the problem of noise in the aircraft cabin and ways to solve it. Through observations, the following causes of noise were identified: the power plant (acoustic and mechanical vibrations, turbulent boundary layer and others), the location of the engine relative to the airframe, the noise of the propeller (if it is a propeller power plant), the propeller of the power plant itself, the air conditioning system, and so on the same operating device in the cabin. There is a comprehensive way to solve the problem of noise in the aircraft cabin: for aircraft with turbojet engines, measures aimed at changing the design and use of sound- absorbing materials can be effective. For a turboprop aircraft, it is necessary to create low-noise propellers and synchronize the rotation of the propellers. For air conditioning elements, reducing duct and exhaust velocities allows for satisfactory acoustic performance of these sources. The reduction in “cabin noise” is achieved by changing the manufacturing technology of various noisy units. It should be emphasized that the possibility of reduction in the cabin and the aircraft is, in principle, laid down when designing the units and the aircraft as a whole. It is worth noting sound insulation, vibration insulation, as well as the rational location of noisy units, including the power plant, relative to the passenger cabin of the aircraft. From the study on sound insulation, we conclude that it is best to use 2 sound insulation options. Reducing noise is a feasible task and its greatest progress is achieved even at the design stage itself

АНАЛІЗ АКУСТИЧНИХ СИГНАЛІВ ЗАСОБІВ ПОВІТРЯНОГО НАПАДУ

This paper analyzes the acoustic signals of aerodynamic aerial attack weapons used by the Russian Federation during a full-scale invasion. These include strike unmanned aerial vehicles, cruise missiles, jet and turboprop aircraft, and helicopters. It has been established that the time for observing an acoustic signal is limited by the speed of the vehicle. For high-speed targets (cruise missiles, airplanes), it averages 10 s, and for slower targets, 40-50 s. The Welch periodogram method was used to extract the spectral characteristics of acoustic signals. It is shown that the acoustic signal of propeller-driven vehicles is the sum of harmonic and noise-like broadband components, and that of turbojet-powered vehicles has a predominantly noise-like structure with several narrowband components. It was found that at the moment of maximum convergence, the signal spectrum has the greatest width. The characteristic change in the frequency of harmonic components associated with the Doppler effect is investigated. It can be used to estimate the parameters of motion and identify the vehicle. By correlation analysis of acoustic signals, it was found that broadband components have a noise-like structure. An acoustic signal for the case of simultaneous over flight of different types of vehicles was formed by adding records of different acoustic signals. It is shown that the characteristic spectral characteristics of all objects are preserved on the frequency-time plane. The results of the analysis can be used to build mathematical models of acoustic signals and to develop methods for processing signals of aerial attack weapons in an acoustic airspace monitoring system. Keywords: aerial attack weapons; acoustic signal; spectrogram; acoustic monitoring system; harmonic component.

Simulation Research on Active Noise Control in Turboprop Cabin with Complex Sound Field Environment

This article summarizes the research work on the complex sound field environment in the cabin of a certain turboprop aircraft, the construction of multi-channel noise active control system and the verification of noise reduction effect were carried out. On the basis of spectrum analysis and distribution characteristic analysis of the measured data in the cabin of this turboprop, taking the key peak frequency as the target frequency, a multi-channel noise active control system with 16 inputs and 16 outputs that meets the requirements of noise reduction indicators is built. And a comprehensive verification platform for the noise reduction effect of turboprop aircraft similar to the real environment was built in a semi-anechoic chamber to verify the real environment was built in a semi-anechoic chamber to verify the noise reduction effect of the system. The result show that the system can reduce the sound pressure level at key frequencies by 14.9 dB(A), the system noise reduction effect is significant and effective.

Aerodynamics and bird ingestion characteristics of a bulge-adjustable turboprop engine inlet

Turboprop aircraft plays an important role in the field of regional airliners and military transport. During take-off or landing, turboprop aircrafts frequently encounter bird flocks that can be ingested into the engine inlet, thereby posing a significant threat to flight safety. Consequently, the aerodynamic characteristics and bird ingestion characteristics of turboprop inlet are investigated in this article. An unsteady computational fluid dynamics (CFD) approach has been proposed to calculate bird ingestion characteristics in a turboprop inlet with different bulge heights under propeller interference by combining a self-developed collision-rebound model with the overset mesh method and 6-degree of freedom (6-DOF) motion method. Considering the characteristics of bird strikes, a parameterized controlled bulge of turboprop inlet with a scavenge duct has been designed. Moreover, the trajectory characteristics of the bird, bird-inlet coupling flowfield characteristics and the aerodynamic characteristics are analyzed in depth. The bulge of the inlet plays a positive role in preventing the bird object from entering the engine duct at a 23° incidence angle. The bird rebounds from the upper bulge and is discharged through the scavenge duct at MaAIP=0.45. The results show that the growth of inlet bulge height has the minimal influence on the total pressure recovery coefficient σ, with only approximately 0.3% variation within the bulge height range of interest. However, it significantly affects the total pressure distortion DC60 with an increase up to 84%.

Including Blade Elasticity into Frequency-Domain Propeller Whirl Flutter Analysis

Whirl flutter as an aeroelastic instability can be a limiting factor in the design and certification of turboprop aircraft configurations, especially for the engine suspension. Whirl flutter prediction for these configurations is currently done in the frequency domain using rigid propeller aerodynamic derivatives. Blade flexibility is neglected in this process, although it is known to have an impact on whirl flutter predictions. This paper uses frequency-domain transfer matrices for the propeller hub loads identified from a time-domain multibody simulation model of an isolated turboprop propeller and included into a frequency-domain flutter analysis to study the impact of blade elasticity on propeller whirl flutter. Results demonstrate a significantly stabilizing effect of blade elasticity on propeller whirl flutter due to a reduction of the destabilizing pitch-yaw cross-coupling moment. The method demonstrated in this paper is applicable to arbitrary time-domain propeller models and compatible with standard frequency-domain flutter processes, allowing for increased fidelity in the flutter prediction process.

Comparison of cabin noise of turboprop and turbofan aircrafts

Turboprop aircrafts are typically used for transporting cargos and for low-capacity short-haul air transport between regional cities. The new designs of turboprop aircrafts tend to focus on noise and comfort level of the aircrafts. Although turboprop aircrafts are known to have relatively higher cabin noise, there are limited reported studies in the open literature examining the actual cabin noise level in commercial flights. In this study, the cabin noise of the ATR 72-500 turboprop aircraft was examined and compared with that of the Bombardier CRJ 900 turbofan aircraft during actual commercial flights. Both are passenger planes which are designed to carry fewer than 100 passengers and are deemed to be a more compatible comparison. Both are single isle aircraft with two seats on each side of the isle. The Bombardier CRJ 900 is found to have a lower cabin noise in terms of both dBA and dBC for both taxing and cruising. As the average equivalent continuous sound pressure level (Leq) for cabin noise is found to be well below 85 dBA, there is no risk of exceeding the daily exposure to noise of 85 dBA for eight hours under the National Institute for Occupational Safety & Health (NIOSH) regulation. However, as many reported studies have shown that prolonged exposure to low frequency noise may lead to disorders, discomfort, sensitivity to and irritability from noise, annoyance, hearing loss, and cardiovascular diseases, there may be a need to carry out a more detailed study of the effect of low frequency noise on passengers.

Off-Design Performance Analysis of a Parallel Hybrid Electric Regional Turboprop Aircraft

Hybrid electric propulsion is one of the alternative solutions for reducing fuel burn and lower emissions while keeping a reasonable battery mass for regional turboprop aircraft operating on short routes. Most studies reporting fuel burn reductions evaluate the aircraft on the design mission, although regional transport aircraft rarely operate under these conditions. Therefore, considering its off-design performance is essential for providing a more complete understanding of aircraft capabilities under various operating conditions. Under these flight conditions, the multi-energy management aspect of hybrid propulsion and the fixed size of the batteries could have a significant impact on the system robustness in off-design operation. In this study, the off-design performance of an existing regional turboprop aircraft retrofitted with a parallel hybrid electric powertrain is assessed. Fuel burn benefits are evaluated on the payload–range diagram for an initial hybrid design and compared to the baseline aircraft. Then, using a novel sizing approach, considering a typical mission operation, this study shows an average improvement of percentage point on fuel burn benefits relative to the initial hybrid aircraft, creating a more robust design.

Features of vortex trace propagation for aircraft with propellers

The article presents the results of a study of the characteristics of the wake vortex of aircraft with turboprop engines. Using the example of the An-12 aircraft, it is shown that rotating propellers make a noticeable contribution to the propagation of the vortex trail behind the aircraft. This is proved by some studies, as well as numerous observations. It also describes a technique for studying the wake vortex of aircraft with propellers. The method is based on the method of discrete vortices. The relevance of such studies is due to the growing interest of carrier companies in aircraft with turboprop engines. It has been proven that when transporting passengers and cargo on such vessels over distances of 700–800 km, maintenance and fuel costs are reduced by about 30–40%. Therefore, the fleet of turboprop aircraft, such as An-22, An-70, An-12, as well as Tu-95, Il-38, C-130, etc., has been preserved so far. New turboprop aircraft are being developed and put into operation: A-400M, Il-114, Il-112M. The vortex trail behind such aircraft also poses a danger to other aircraft flying behind. A feature of the propagation of the wake vortex behind aircraft with propellers is the interaction of vortices coming off the airframe and vortices from the propellers. As a result, due to the rotation of all the screws in one direction, symmetry is broken in the propagation of vortices descending from the right and left halves of the wing. Therefore, it is important to understand how differently the vortices that descend from the airframe of an aircraft with turboprop engines behave. For the convenience of the study, the method of accounting for the effect of vortices from screws is integrated into a special calculation and software package, also based on the method of discrete vortices. In it, when calculating the characteristics of the wake vortex, the flight weight, speed and altitude of the aircraft, its flight configuration, atmospheric conditions, proximity of the earth, axial velocity in the core of the vortex and some other factors are taken into account. This complex has passed the necessary testing and state registration. A number of measures were carried out to validate and verify the developed complex, confirming the operability of the programs included in it and the reliability of the results obtained from it. The results of the study of the characteristics of the wake vortex behind the Antonov-12 aircraft in the form of vertical velocity spectra and fields of perturbed velocities at various distances from it are presented. It is shown that propellers noticeably affect the propagation of the wake vortex behind turboprop aircraft. This circumstance must be taken into account by the crews of aircraft flying behind such aircraft.