Search Results (12)

High payload capacity multi-rotor aerial vehicles are typically configured with multiple propellers to achieve the required aerodynamic lift. However, this design approach often results in an increased overall dimensional envelope, which introduces significant operational limitations in confined spatial environments such as urban airspace. By utilizing a limited overlap rotor configuration, the spatial utilization rate of an aircraft can be greatly improved, ensuring a sufficient thrust of rotor while simultaneously reducing the size of the aircraft. However, the slipstreams of two rotors overlap, which may create a significant aerodynamic interface. This paper utilizes numerical simulation based on the unsteady RANS (Reynolds-averaged Navier–Stokes) method to analyze the influence of parameters such as distance, blade distance, and rotation direction on the interference flow field of overlapping rotors. Research indicates that aerodynamic interference only affects the overlapping area between two rotors at the inner blade, leading to the offset of loading distribution on the blade, which can be explained by the slipstream effect, suction effect, and induced effects generated by two rotors. As the axis distance between two rotors decreases, the strengthening of the slipstream and suction effects leads to a rapid decrease in the aerodynamic efficiency of the two rotors. When the blade between the two rotors increases, the weakening of the suction effect and induced effects causes the load on the lower rotor to translate to the upper rotor. Moreover, the variation in the spatial distribution of the blade tip–vortex leads to blade–vortex interaction, which causes a change in the spanwise distribution of the load on the lower blade. Full article

Both propeller slipstream and flap jet flow can significantly increase the aircraft lift coefficient. To establish design principles for efficient lift enhancement via jet flow under the influence of slipstream, wind tunnel experiments are conducted on a wing with propeller slipstream and jet flow. Force measurements using a balance and flow field measurements using hot-wire anemometry are employed to investigate the effects of different jet flow distribution methods on lift enhancement. The results indicate that the coupling of slipstream and jet flow effects can significantly increase wing lift. The stronger the slipstream effect, the more pronounced the lift enhancement under the same momentum coefficient. At the same thrust coefficient, a higher momentum coefficient is required in the slipstream-affected region to suppress airflow separation. Under the same jet flow rate, increasing the momentum coefficient in the slipstream-affected region can significantly improve lift enhancement. At the thrust coefficient of 0.46 and the momentum coefficient of 0.1, the optimized jet flow distribution method achieved a 52.6% greater lift enhancement compared to the spanwise uniform jet flow distribution method. Full article

Electric short takeoff and landing (eSTOL) aircraft utilize the slipstream generated by distributed propellers to significantly increase the effective lift coefficient and reduce the takeoff and landing distances. By utilizing the blown lift, eSTOL UAVs can achieve similar takeoff and landing site requirements as electric vertical takeoff and landing (eVTOL) UAVs, while having lower takeoff and landing energy consumption and thrust requirements. This research proposes a high-peak-power distributed electric propulsion (DEP) system model and overload design method for eSTOL UAVs to further improve the power and thrust of the propulsion system. The model considers motor temperature factors with the throttle input, which is solved through three-round iterative calculations. The experimental and simulation results indicate that the maximum error of the high-peak-power propulsion unit model without considering temperature is 19.52%, and the maximum error when considering temperature is 1.2%. The propulsion unit ground test indicates that the main factors affecting peak power are the duration of peak power and the temperature limit of the motor. Finally, the effectiveness of the propulsion system model is verified through ground tests and UAV flight tests. Full article

Considering the large-deformation and multi-propeller characteristics of very flexible aircraft, propeller effects are introduced and accessed in the wing static and dynamic aeroelastic analysis and different propeller distributions are utilized to obtain more aeroelastic benefits. The propeller–wing aeroelastic interactions are innovatively modeled in the paper. For propeller–wing aerodynamic interaction, propeller-induced velocities are considered and added in the nonplanar steady and unsteady vortex lattice methods. For propeller–wing structural interaction, the conversion of loads and displacements between attached propellers and the large-deformation wing is derived. Static aeroelastic cases indicate that thrust can reduce structural deformation and slipstream can cause considerable lift increment. Dynamic cases indicate that thrust can reduce the wing’s maximum response to gust and bring an improvement of 9.4% in the wing’s critical velocity, while slipstream can reduce the gust response amplitude. In addition, using smaller and more propellers is recommended instead of an individual larger propeller. Decreasing and increasing propeller speeds toward the wingtip is more beneficial for cruise status and gust alleviation, respectively. Full article

Over twenty Solar-Powered Unmanned Aerial Vehicle (SPUAV) designs exist worldwide, yet few have successfully achieved uninterrupted high-altitude flight. This shortfall is attributed to several factors that cause the actual performance of SPUAV to fall short of expectations. Existing studies identify the propeller slipstream as one of these adverse factors, which leads to a decrease in the lift–drag ratio and an increase in energy consumption. However, traditional design methods for SPUAVs tend to ignore the potential adverse effects of slipstream at the top-level design phase. We find that this oversight results in a reduction in the feasible mission region of SPUAVs from 109 days to only 46 days. To address this issue, this paper presents a high-fidelity multidisciplinary design framework for the energy/propulsion systems of SPUAVs that integrates the effects of a propeller slipstream. Specifically, deep neural networks are employed to predict the lift–drag characteristics of SPUAVs under various slipstream conditions, and the energy performance is further analyzed by evaluating the time-varying state parameters throughout a day. Subsequently, the optimal solutions for the energy/propulsion systems specific to certain latitudes and dates are obtained through optimization design. The effectiveness of the proposed design framework was demonstrated on a 30-m wingspan SPUAV. The results indicated that, compared to the traditional design method, the proposed approach led to designs that more effectively accomplished closed-loop flight in designated regions and prevented the reduction of the feasible mission region. Additionally, through the targeted retrofit of the energy/propulsion systems, SPUAVs exhibited enhanced adaptability to the solar radiation characteristics of different mission points, resulting in a further expansion of the feasible mission region. Furthermore, this research also explored the variation trends in optimal solutions across different latitudes and dates and investigated the reasons and physical mechanisms behind these variations. Full article

Distributed electric propulsion (DEP) with four propellers distributed along the rear edge of the wing (pusher DEP configuration) promote aerodynamic interactions to a higher level. To study the aerodynamic performance of DEP with the rear wing through simulations and experiments, the multi-reference frame (MRF) with sliding grid is combined with wind tunnel tests. The obtained results demonstrate that the lift and drag of DEP increase with the angle of attack (AoA) and are related to the relative position of the propellers and wing. The propeller has no significant effect on the lift of the wing, and the lift and the AoA remain linear when the AoA is less than 16°. By contrast, the lift coefficient is much higher than the baseline (isolated wing), and the lift is greatly improved with the increasing drag when the AoA is greater than 16°. This is because the flow around the wing of the pusher configuration remains attached due to the suction of the inflow of the propeller on the trailing edge vortex. In addition, the acceleration effect on the free flow improves the kinetic energy of the airflow, which effectively delays the separation of the airflow in the slipstream region. Full article

A conceptual framework is presented to determine the improvement in the aerodynamic performance of a canard aircraft fitted with distributed propellers along its main wing. A preliminary study is described with four airframe–propeller configurations predominantly studied in academic and commercial designs. The leading edge–based tractors and trailing edge–based pushers are identified as configurations of interest for the main study. Subsequently, a Navier–Stokes solver is used to simulate the flow using two numerical approaches–a modified steady-state actuator disk and an unsteady rotating propeller profile. Moving meshes with rotating sub-domains are used with a hybrid RANS-LES-based turbulence model while the actuator disks are modified to include viscous swirl effects. The preliminary study shows a local minimum in the change in $C_L$ and $C_D$ at 10${}^{\circ }$ for the pusher and tractor configurations. The main study then demonstrates the outperformance of the pushers over tractors quantified using $C_L$ and $C_L/C_D$. There is a clear preference for the pushers as they increase the lifting capacity of the aircraft without disproportionately increasing the drag due to the flow smoothening by the suction of the pusher propellers over the main wing. The pushers also delay the separation of the boundary layer whereas the tractors are unable to prevent the formation of the separation bubble despite injecting momentum through their slipstreams into the flow. The results from the two numerical approaches are then compared for accuracy in designing DEP configurations for an airframe. Full article

Distributed electric propulsion technology has great potential and advantages in the development of drones. In this paper, to study the slipstream effect of distributed propellers, the actuator disk method was used to verify a single propeller, and the calculated thrust was in good agreement with the test results. Then, based on the actuator disk method, the influence of different installation positions on the slipstream effect was studied, and the distributed propeller layout was optimized by a genetic algorithm to improve the low-speed performance of the unmanned aerial vehicle (UAV) during the take-off phase and increase the cruise duration. The analysis results showed that the lift of the wing will be larger when the propellers are higher than the wing. The wing lift and drag of the counter-rotating are less than those of the co-rotating. Compared with the original layout, the lift coefficient of the optimized distributed propeller layout is significantly increased by 30.97%, while the lift/drag ratio is increased by 7.34%. Finally, we designed the test platform and qualitatively verified the calculated results without quantitative verification. Full article

A large part of small-sized UAVs that are used for surface scanning, video- and photography, or other similar applications are of the multirotor type. These small aircraft perform mainly in hovering or nearly hovering flight mode, and the endurance of these vehicles depends greatly on the efficiency of their motors and the aerodynamic efficiency of their thrust-generating systems, including propellers, ducted fans, etc. Propellers may therefore work in different regimes: in a regime where the propeller performs work to move the vehicle through the air, and the static or hovering regime, in which standing air is accelerated. In both cases, the concept of efficiency can be used to describe the propeller’s performance. There have been several previous studies on static and advancing propellers’ performances. In these studies, when determining the efficiency of a static propeller, the thrust and power coefficients are most commonly compared to evaluate the propeller’s performance. Sometimes, the inducted velocities are calculated via the momentum theory. As small-scale propellers work on very low Reynolds (Re) numbers below 500,000, the flow type transition and boundary layer separation make it very hard to predict the actual efficiency of the propellers in static mode. Therefore, the aim of this paper is to introduce a method to determine the static efficiency of small-scale propellers directly and empirically via a comparison between the output and input power, wherein the output power is determined via the measured thrust and mean induced velocity. The used method combines thrust, torque, and angular velocity measurements with slipstream monitoring. The performed tests showed a decrease in efficiency, with the Re number rising in spite of the rising values of the thrust coefficient. This study led to two main conclusions: thrust and power coefficients are not always the key parameters to determine the efficiency of a propeller; the role of the Re number in the propeller’s efficiency is not yet clear and requires further investigation. The presence of Re number effects has been proven in numerous works, but the impact of those effects seems to not be as trivial as the claim that the lower the Re number, the weaker the propeller’s performance. Full article

Hybrid-Electric Propulsion (HEP) could be part of the solution to decrease emissions associated with regional commercial aviation. This study presents results for the aircraft level fuel reduction potential of a regional turboprop concept with an HEP architecture and Entry-Into-Service (EIS) in 2035+. The configuration specifically tackles the elaborated challenges of introducing an additional electrical energy source to the configuration by employing a twofold electrical assistance to a turboshaft engine in combination with an innovative thermal management concept. Relevant components and disciplines were modeled and incorporated into an integrated aircraft design environment. The behavior and interaction of the HEP architecture with the aircraft was thoroughly investigated. A best-performing configuration was derived and compared with a conventional reference configuration following a State-of-the-Art (SoA) reference aircraft approach. For a typical mission with 200 nmi range, a block fuel reduction of 9.6% was found. However, the assumed battery performance characteristics limited the reduction potential and led to a fuel burn increase for the 600 nmi design mission. Furthermore, sourcing the non-propulsive subsystems directly from the on-board battery was detrimental. The innovative Thermal Management System (TMS) located in the propeller slipstream showed a synergistic effect with the investigated configuration. Full article

A numerical investigation on propeller-induced flow effects in tractor configurations on a Zimmerman wing-fuselage using the cambered thin airfoil is presented in this paper. The Reynolds number based on the mean aerodynamic chord was 1.3 × 10⁵. Significant aerodynamic performance benefits could be found for a propeller in the tractor configuration. The numerical results showed that the propeller slipstream effect on the wings was highly dependent on the size of the propeller, and the major slipstream effect was working at 60% inboard wingspan, whereas less effects were observed towards the wingtip. The propeller slipstream increased the local angle of attack on the up-going blade side. This effect simultaneously augmented the section lift. The unsteady Reynolds-averaged Navier–Stokes (URANS) simulations helped to improve understanding of the interaction of the propeller wake and the wing-fuselage, which is an important aspect to guide the design of future efficient and controllable micro air vehicles. The results indicated that, in MAV designs, the slipstream from the propeller had a significant effect on the wing aerodynamics, regarding both performance and stability of the vehicle. Full article

Airfoil selection procedure, wind tunnel testing and an implementation of 6-DOF model on flying wing micro aerial vehicle (FWMAV) has been proposed in this research. The selection procedure of airfoil has been developed by considering parameters related to aerodynamic efficiency and flight stability. Airfoil aerodynamic parameters have been calculated using a potential flow solver for ten candidate airfoils. Eppler-387 proved to be the most efficient reflexed airfoil and therefore was selected for fabrication and further flight testing of vehicle. Elevon control surfaces have been designed and evaluated for longitudinal and lateral control. The vehicle was fabricated using hot wire machine with EPP styrofoam of density 50 Kg/ ${\mathrm{m}}^3$ . Static aerodynamic coefficients were evaluated using wind tunnel tests conducted at cruise velocity of 20 m/s for varying angles of attack. Rate derivatives and elevon control derivatives have also been calculated. Equations of motion for FWMAV have been written in a body axis system yielding a 6-DOF model. It was found during flight tests that vehicle conducted coordinated turns with no appreciable adverse yaw. Since FWMAV was not designed with a vertical stabilizer and rudder control surface, directional stability was therefore augmented through winglets and high wing leading edge sweep. Major problems encountered during flight tests were related to left rolling tendency. The left roll tendency was found inherent to clockwise rotating propeller as ‘P’ factor, gyroscopic precession, torque effect and spiraling slipstream. To achieve successful flights, many actions were required including removal of excessive play from elevon control rods, active actuation of control surfaces, enhanced launch speed during take off, and increased throttle control during initial phase of flight. FWMAV flew many successful stable flights in which intended mission profile was accomplished, thereby validating the proposed airfoil selection procedure, modeling technique and proposed design. Full article