Forward Flight Speed Research Articles

Three-Dimensional Numerical Investigation on the Dynamic Stall Behavior of the Helicopter Rotor Blade at Forward Flight Speeds

Three-Dimensional Numerical Investigation on the Dynamic Stall Behavior of the Helicopter Rotor Blade at Forward Flight Speeds

Numerical Simulation and Experimental Study on the Aerodynamics of Propulsive Wing for a Novel Electric Vertical Take-Off and Landing Aircraft

The electric vertical take-off and landing (eVTOL) aircraft offers the advantages of vertical take-off and landing, environmental cleanliness, and automated control, making it a crucial component of future urban air traffic. As competition intensifies, demands for aircraft performance are escalating, including forward flight speed and payload capacity. The article presents a novel eVTOL design with propulsive wings and establishes methodologies for propulsive wing unsteady numerical simulation and wind tunnel experiments, analyzing its aerodynamic characteristics and lift enhancement mechanism. The results indicate that the cross-flow fan (CFF) provides unique airflow control capabilities, enabling the propulsive wing to achieve remarkably high lift coefficients (exceeding 7.6 in experiments) and propulsion coefficients (exceeding 7.1 in experiments) at extreme angles of attack (30°~40°) and low airspeeds. On the one hand, the CFF effectively controls boundary layer flow, delaying airflow separation at high angles of attack; on the other hand, the rotation of the CFF induces two eccentric vortices, generating vortex-induced lift and propulsion. The aerodynamic performance of the propulsive wing depends on the advance ratio and angle of attack. Typically, both lift and propulsion coefficients increase with the advance ratio, while lift and drag coefficients increase with the angle of attack. The propulsive wing shows significant advantages and prospects for eVTOL aircrafts in the low flight velocity range (0–30 m/s).

Aerodynamic interference and unsteady loads for a trimming intermeshing rotor compound propeller helicopter at level forward flight

Traditional trim methods for isolated rotor helicopters are not suitable for intermeshing rotor compound propeller helicopters (IRcPHs) due to inherent structural differences. This study aims to establish a novel trim method for an intermeshing rotor with an auxiliary propeller. First, the relationship between the rotor cyclic pitch and the flapping response in the fully articulated rotor system with hinged extension is derived. The study then formulates the equilibrium state equations and the corresponding flight conditions for trimming the IRcPH in level forward flight. In addition, the unsteady vortex lattice method is employed to calculate the periodic averaging states on the rotor disk and correct for induced losses in flight dynamics. Finally, the paper focuses on the aerodynamic interference, blade–vortex interaction, and harmonic load patterns of the IRcPH, serving as a guide for rotor active control systems. Results show that the positions of the mutual aerodynamic interference occur constantly at 160° and 340° azimuths on the intermeshing rotor disk, serving as the phase basis for suppressing vibration. Moreover, the propeller enters the comfort zone as the forward flight speed increases, and the loads only have frequency orders of (2/nw)/rev with respect to the main frequency of the intermeshing rotor.

Propeller Ceiling Effect in Forward Flight

The study extends the investigation of the fixed-pitch small-scale propeller in the ceiling effect to forward flight conditions at different propeller incidence angles. Force-based experiments, phase-locked particle image velocimetry (PIV), and surface oil flow visualization were conducted on two APC propellers at the University of Dayton Low Speed Wind Tunnel. For propellers in edgewise flight, the power required at constant thrust decreases at small advance ratios for each h/D and then increases with a further increase in the advance ratio. Tilting the propeller forward reduces the ceiling effect benefits in both thrust and power, particularly at higher advance ratios. Performance similarity in the propeller ceiling effect at different h/D is observed, and a performance prediction method is proposed. Phase-locked PIV showed an increase in the propeller inflow angle in the ceiling effect at small advance ratios, resulting in higher thrust generation. This effect reduces with an increase in the advance ratio due to minimized interactions with the ceiling plate. Hence, the measured propeller in-ceiling-effect (ICE) propeller performance cannot represent the propeller ICE performance at a higher forward flight speed. Additionally, PIV and surface flow visualization indicated the presence of a stagnation point on the ceiling plate near the trailing side of the propeller disk at higher advance ratios, leading to a reduction in propeller thrust generation.

Effects of kinematic parameters and corrugated structure on the aerodynamic performance of flexible dragonfly wings

The effects of unsteady motions of flapping flat plates and corrugated structures in different parameters are studied using fluid–solid coupling and overlapping grid methods. Based on the dragonfly’s right forewing and right hindwing model, these actions include sweeping and pitching, take-off acceleration, and tandem wings cruising in the reverse phase at 180°. The results show that when the advance ratio J=0.36, the “inflow deflection” improves the aerodynamic force in two degrees of freedom compared to simple flapping. When considering only the impact of flexibility, the aerodynamic forces of flexible flat plates and corrugated structures are better than those of the rigid wing models. Considering the effect of corrugated structures, the lift of flexible corrugated wings diminishes, but more thrust is generated. From the perspective of vortex street, vortex rings materialize only in the downstroke stage, while the attachment effect of leading-edge vortices is noticeable in several models. In the same phase flapping, the two wings combine to form a giant wing, which generates significant forward flight momentum. In out-of-phase flapping mode, the series wings generate two lifts and two or three thrust peaks to attain the required forward flight speed while sustaining a high lift.

Research on transition corridor of distributed tilting power configuration

For a distributed tilt-power configuration aircraft, the transition corridor was studied based on limited conditions such as wing lift characteristics and propeller power requirement. By establishing the dynamic model of each component and balancing according to the balance equation, the boundary of the transition corridor of distributed tilting dynamic configuration is determined. The results show that the minimum forward flight speed required for a low Angle of attack is less than that for a high Angle of attack; the wing lift characteristic high-speed boundary and the propeller power limit boundary together form the high-speed boundary of the transition corridor.

Design and Optimization of Low Impact Shift Control Strategy for Aviation Transmission Power System Based on Response Surface Methodology

The utilization of a variable-speed power system significantly improves the forward flight speed and cruising range of the helicopter. Nevertheless, the shock of speed and torque during the shift process brings stability and safety problems that cannot be ignored. Thus, swift and stable shift control is a key issue in the research on aviation power systems. This study focuses on the design and optimization of low-impact shift control strategies for a variable-speed power system, which involves multiple control variables, long adjustment times, and uncontrollable risks due to the nonsteady state. A comprehensive power system model that integrates the engine, a two-speed dual-clutch transmission system, and the main rotor was proposed. By selecting the engine fuel flow, friction clutch hydraulic pressure, and rotor pitch angle as input signals, regression fitting models between the input signals’ starting time points and speed or torque shock were obtained using Response Surface Methodology (RMS). The interaction effect of multiple time series was analyzed, and four kinds of low-impact nonlinear programming multi-objective optimized models for speed or torque are proposed. The results indicate that the P values of the RMS fitting models at upshift and downshift are less than 0.0001 and 0.05, respectively, which are highly significant and can effectively predict the shift dynamic response; under the optimized upshift and downshift control strategy, the speed and torque shock are reduced by 5–10%.

Rotor cross-tilt optimization for yaw control improvement of multi-rotor eVTOL aircraft

Manned multi-rotor electric Vertical Takeoff and Landing (eVTOL) aircraft is prone to actuator saturation due to its weak yaw control efficiency. To address this inherent problem, a rotor cross-tilt configuration is applied in this paper, with an optimization method proposed to improve the overall control efficiency of the vehicle. First, a flight dynamics model of a 500-kg manned multi-rotor eVTOL aircraft is established. The accuracy of the co-axial rotor model is verified using a single arm test bench, and the accuracy of the flight dynamics model is verified by the flight test data. Then, an optimization method is designed based on the flight dynamics model to calculate an optimal rotor cross-tilt mounting angle, which not only improves the yaw control efficiency, but also basically maintains the efficiency of other control channels. The ideal rotor cross-tilt mounting angle for the prototype is determined by comprehensively considering the optimal results with different payloads, forward flight speeds, and rotor mounting angle errors. Finally, the feasibility of the rotor cross-tilt mounting angle is proved by analyzing the control derivatives of the flight dynamics model, the test data of a ground three Degree-of-Freedom (3DOF) platform, and the actual flight data of the prototype. The results show that a fixed rotor cross-tilt mounting angle can achieve ideal yaw control effectiveness, improving yaw angle tracking and hold ability, increasing endurance time, and achieving good yaw control performance with different payloads and forward speeds.

Numerical Calculation and Analysis of Water Dump Distribution Out of the Belly Tanks of Firefighting Helicopters

Helicopters are more and more widely used for water dumping in fire extinguishing operations nowadays. Increasing attention is being paid to improving helicopter firefighting efficiency. Water distribution onto the ground from the helicopter tank is a key reference target to evaluate firefighting efficiency. Numerical simulations and calculations were carried out concerning water dumping out of the belly tank of a helicopter using the VOF (Volume of Fluent Model) model and mesh adaptation in ANSYS Fluent, and the effects of two parameters, the height of the tank above the ground and the wind speed, on the wake flow and water distribution were discussed. The results showed that for forward flight, the higher the forward flight speed, the less the average water depth on the ground. Similar results were obtained for flight height. The average water depth was one order of magnitude less than in the cases of the corresponding hovering helicopter for a given wind speed. As for hovering flight, the higher the wind speed, the less the average water depth on the ground. The simulation results were basically consistent with the conclusions of water dump tests of fire-fighting equipment carried by helicopters. For example, when the helicopter flew at a forward flight speed of 15 m/s and the tank bottom was 30 m above the ground, the area covered by the dumped water would be 337.5 m2, and the average water depth accumulated per square meter would be 0.3 cm. This result was close to the 0.34 cm obtained under Hayden Biggs’s test condition with a forward flight speed of 70 km/h and a height above the ground of 24 m.

Development of a plant protection UAV and evaluating its efficacy in managing rice leaf folder (Cnaphalocrocis medinalis Guenee.)

Drones (Unmanned Aerial Vehicles, UAV) have revolutionized agriculture by optimizing the use of several farm operations and through reducing input costs. The present study aimed at designing a plant protection UAV and evaluating its efficacy against rice leaf folder. A hexacopter drone was designed by Acharya N G Ranga Agricultural University and designated as “ANGRAU Pushpak-01” with certain specifications and Payload Data suitable for plant protection spraying in rice. Field studies were taken up during kharif seasons (rainy seasons) of 2020 and 2021 in farmers fields of Guntur district of Andhra Pradesh, India on transplanted rice. The test insecticide used in the present study was flubendiamide 480 SC (39.35% W/w). The UAV hexacopter was optimized for its forward flight speed, height of aerial spraying for delivering spray width and for obtaining maximum spray width using standard protocols. Field studies involved five treatments (four replications), a) 100% RDP (recommended dose of pesticide) with UAV, b) 75% RDP with UAV, c) 50% RDP with UAV, d) 100% manual spray with human back pack motorized spray, and e) water spray using UAV in a RCBD fashion. Nursery was raised during both seasons of study and 30-days-old seedlings were transplanted into main fields and treatments were imposed with flubendiamide spray at 60 days after transplanting (DAT). Leaf folder damage was assessed at prior to flubendiamide spray treatment-wise, then periodically and finally at 10 DAS (Days after spray). Grain yields were harvested replication-wise, pooled and assessed treatment wise for both the field studies in successive years. Our results on optimization of spray technology indicated that aerial spray with UAV at a height of 0.6 m above canopy was ideal in delivering maximum spray width. Further, at this height, there was good amount and uniform distribution of flubendiamide as evaluated by HPLC. The flubendiamide at 75% UAV spray could yield uniform deposition on rice canopy (top, medium, and bottom), and is equally effective compared to 100% UAV spray of flubendiamide. Further, UAV sprays at both these concentrations are more effective in terms of droplet distribution compared to 100% UAV spray with human back pack motorized spray. Field studies indicated that leaf folder damage was effectively reduced with flubendiamide sprays at 100% and 75% RDPs with UAV with no significant differences. However, these treatments were significantly superior to 100% RDP of spray using human back pack sprayer. Similarly, grain yields were significantly superior in 100% RDP and 75% RDP-UAV sprayed plots with no significant differences between them. Further, both these treatments were significantly superior to 100% RDP spray using human back pack sprayer in grain yield enhancement. Overall, our results suggested the efficacy of “ANGRAU-Pushpak-01” UAV hexacopter in reducing leaf folder in rice and enhancing grain yields when sprayed with flubendiamide at 75% RDP, thus offering scope for reduced pesticide costs compared to spraying with 100% RDP of flubendiamide using human back pack motorized sprayer under the conditions evaluated.

Aerodynamic Modeling and Performance Analysis of Variable-Speed Coaxial Helicopter

In this paper, the variable-speed coaxial helicopter is modelled by the blade element method, non-uniform inflow method and empirical function method, and the aerodynamic performance analysis method is proposed. To ensure the accuracy of this method, a flight test of the verification aircraft has been performed, and the rotor speed and required power under different forward flight speeds have been obtained. By comparing the experimental results with the calculation results, it is ascertained that the rotor speed trim error of this method is less than 6%, and the required power calculation error is less than 5%, which demonstrates the accuracy of this method. Finally, when the rotor diameter, hovering collective pitch and hovering rotor speed are equal, the required power of variable-speed coaxial helicopter and variable collective-pitch coaxial helicopter is compared through this method. The comparison results show that the variable-speed coaxial helicopter has low required power when it is less than the forward flight speed corresponding to the hovering rotor speed. When the forward speed is higher than that corresponding to the hovering rotor speed, the variable-pitch coaxial helicopter has lower required power.

Dynamic Stability and Flight Control of Biomimetic Flapping-Wing Micro Air Vehicle

This paper proposes an approach to analyze the dynamic stability and develop trajectory-tracking controllers for flapping-wing micro air vehicle (FWMAV). A multibody dynamics simulation framework coupled with a modified quasi-steady aerodynamic model was implemented for stability analysis, which was appended with flight control block for accomplishing various flight objectives. A gradient-based trim search algorithm was employed to obtain the trim conditions by solving the fully coupled nonlinear equations of motion at various flight speeds. Eigenmode analysis showed instability that grew with the flight speed in longitudinal dynamics. Using the trim conditions, we linearized dynamic equations of FWMAV to obtain the optimal gain matrices for various flight speeds using the linear-quadratic regulator (LQR) technique. The gain matrices from each of the linearized equations were used for gain scheduling with respect to forward flight speed. The reference tracking augmented LQR control was implemented to achieve transition flight tracking that involves hovering, acceleration, and deceleration phases. The control parameters were updated once in a wingbeat cycle and were changed smoothly to avoid any discontinuities during simulations. Moreover, trajectories tracking control was achieved successfully using a dual loop control approach. Control simulations showed that the proposed controllers worked effectively for this fairly nonlinear multibody system.

Effects of forward-flight speed on plume flow and infrared radiation of IRS-integrating helicopter

To address deeper understandings about the aero-thermal performance of an integrating infrared suppressor under more realistic situations, a numerical investigation is motivated in the current study, concerning the effects of forward-flight speed on exhaust plume flow and infrared radiation of the Infrared Suppressor-integrating (IRS-integrating) helicopter, wherein the forward-flight speed is changed from 0 m/s (hover state) to 100 m/s, while both the engine exhaust parameters and the main-rotor operation parameters remains unchanged during different forward-flight velocities. The results show that the interaction between forward-flight flow and downwash flow alters the exhaust plume development and the internal flow inside the IRS-integrating rear fuselage more complicatedly, tightly dependent on the forward-flight speed. Of particular concern is the situation where the forward-flight flow has nearly the same level as the downwash flow, the hot mixing flow could possibly interacts with the helicopter rear fuselage to play a local heating effect. With the increase of forward-flight speed, the ejection coefficient is generally increased and the average exhaust temperature of mixing flow is decreased, leading to a reduction of the infrared radiation intensity of exhaust plume in 3–5 μm band. However, the influence of forward-flight speed on the overall infrared radiation intensity of IRS-integrating helicopter is conjectured not monotonous due to the complicated interaction between forward-flight flow and downwash flow. Under high-speed forward-flight states, the overall infrared radiation intensity of the IRS-integrating helicopter in 3–5 μm band is reduced with the increase of forward-flight speed. With respect to 3–5 μm band, the forward-flight speed has little effect on the infrared radiation in 8–14 μm band.

Design, Development, and Testing of Package Delivery Quadrotor Biplane Tail-Sitter

This Paper explores the development of a novel hybrid air vehicle for package delivery called the quadrotor biplane tail-sitter. This vehicle uses differential thrust to effect body attitude changes like a traditional quadrotor, ensuring full transitional control between hover and forward flight modes. This method of control also allows the vehicle to remain mechanically simple. A vehicle was designed with a 1 lb (0.45 kg) payload, resulting in an 8 lb (3.63 kg) gross takeoff weight. The vehicle can hover using 15 in. (0.381 m) diameter proprotors and has two wings that span 3.35 ft (1.03 m), which provide lift in forward flight. Sensors were implemented onboard the vehicle to monitor individual dc brushless motor revolutions per minute, body attitude angles, electrical power consumption, and airspeed relative to wind. Stable hover was demonstrated with package delivery, and it was found that 18% less power was used when hovering with no payload compared to full payload. Package delivery was also successfully demonstrated after transitioning from hover to forward flight and back. In forward flight mode with no payload, the power consumption at a forward flight speed of () was seen to be 50% less than the power consumed in hover.

Disturbance Observer Enhanced Neural Network LPV Control for a Blended-Wing-Body Large Aircraft

The problem of trajectory tracking control for a blended-wing-body (BWB) large aircraft with model parameter uncertainties and unknown disturbances is considered. A linear parameter-varying (LPV) model is derived from the nonlinear dynamics of the BWB aircraft from which a robust linear parameter-varying controller is designed to track a desired trajectory. Using a single quadratic Lyapunov function (SQLF) and an infinite number of linear matrix inequalities to be evaluated at all vertices, a pair of positive definite symmetric matrix solutions are determined via Lyapunov stability theory and linear matrix inequality technique. Furthermore, a disturbance-observer is designed to process the unknown disturbances. Considering the plant exists some model errors except for disturbances, a radial basis function neural network approximation is embedded into the SQLF LPV controller to improve tracking performances, and a composite disturbance-observer based neural network single quadratic Lyapunov function (NNSQLF) controller can realize desired trajectory tracking of the linear parameter-varying system through regulating performance weighting functions. The closed-loop system of trajectory tracking control is proved to be asymptotically stable by using Lyapunov theory. Simulation results of forward flight speed and altitude tracking control of the BWB aircraft show that the proposed disturbance-observer based NNSQLF control can robustly stabilize the LPV system and precisely track the desired trajectory by comparing with conventional SQLF control and parameter-dependent Lyapunov function control, even in unknown exterior disturbances and model uncertainties.

Aerodynamic performance assessment of a ducted fan UAV for VTOL applications

The aerodynamic performance of a recent developed ducted fan Unmanned Aerial Vehicle (UAV) was experimentally assessed by means of force, pressure and PIV measurements. Experiments were conducted on the UAV for both hover and forward flight configurations. Particular attention was given to the in-ground-effect which is important for the take-off and landing modes of the UAV during flight. Variations included rotational speed of the contra-rotating fan, incident angle, forward flight speed and the exit-to-ground distance were examined, allowing a comprehensive understanding of the overall aerodynamic characteristics of the ducted fan UAV. Wind tunnel measurement has successfully defined an initial operation region of the ducted fan UAV. The inlet velocity distortion at the inlet of the UAV during forward flight can significantly influence the inlet circumferential pressure distribution and therefore in principle affect the overall aerodynamic performance. The presence of the ground during take-off and landing can enhance the total lift generation with slightly sacrificing propulsive efficiency. In addition, when the UAV flies in proximity of the ground the back pressure at exit will be increased and thus alleviates the lift production by the duct lip. The outcomes can provide essential information in design and optimization of ducted fan type flight vehicles.

Practical Endurance Estimation for Minimizing Energy Consumption of Multirotor Unmanned Aerial Vehicles

The practically applicable endurance estimation method for multirotor unmanned aerial vehicles (UAVs) using a battery as a power source is proposed. The method considers both hovering and steady-level flights. The endurance, thrust, efficiency, and battery discharge are determined with generally available data from the manufacturer. The effects of the drag coefficient related to vehicle shape and payload weight are examined at various forward flight speeds. As the drag coefficient increases, the optimum speed at the minimum required power and the maximum endurance are reduced. However, the payload weight causes an opposite effect, and the optimal flying speed increases with an increase in the payload weight. For more practical applications for common users, the value of S × Cd is determined from a preliminary flight test. Given this value, the endurance is numerically estimated and validated with the measured flight time. The proposed method can successfully estimate the flight time with an average error of 2.3%. This method would be useful for designers who plan various missions and select UAVs.

Helicopter rotor noise prediction using a convected FW-H equation in the frequency domain

In this paper, high-speed impulsive noise radiated from helicopter rotors in hover and forward flight is computed by using a convected FW-H equation in the frequency domain with a rotating permeable data surface. Compared to the time-domain formulations, the frequency-domain formula avoids retarded time computation and flow data interpolation with respect to the retarded time. In addition, the complicated emission surface construction is obviated, while a supersonic rotating data surface is chosen to account for quadrupole sources outside the sonic cylinder. The selection of a rotating data surface close to the rotor blades improves noise source resolution and thus ensures noise prediction accuracy at a low computational cost, compared to a stationary data surface approach. Besides, the use of a rotating data surface for hovering helicopter rotors enables noise source identification by a steady flow simulation. Application of the methodology to hovering and forward-flight helicopter rotors has shown good agreement with experimental data, thus indicating that the approach is an accurate and efficient computational tool for noise prediction of helicopter rotors operating at high tip Mach number. Since the formula is derived in a moving medium frame, the effect of forward-flight speed on the radiated noise can be explicitly taken into account.

Numerical simulation for three-dimensional rotor icing in forward flight

Icing will occur when helicopters pass through clouds containing supercooled droplets. The ice accreted on rotor blade affects the safety of helicopter. A numerical simulation method of helicopter rotor icing in forward flight is presented, and the icing characteristics of rotor are studied. The flow field is calculated based on the overlapping grids, and the Eulerian model is applied in the droplet trajectory calculation. The unsteady method is used to calculate rotor flow field and droplet trajectory. The icing model considering the effect of centrifugal force is adopted to simulate the ice shapes of rotor in forward flight. The average ice growth rate is compared with the ice growth rate at each azimuth angle, and the effects of blade pitch and forward flight speed on the droplet impingement and icing characteristics are summarized. Finally, the influence of time step on the calculation results is analyzed. The calculation results show that the droplet impingement characteristics and icing characterist...

Conceptual Design and Non-Linear Analysis of Triphibian Drone

Drones are increasingly used to replicate human presence and are extremely capable whether it is in terms of delivering aid to war torn areas or carrying reconnaissance missions beyond borders. Due to their increasing demand in all forms, an arsenal of drones has to be maintained and there is a need to make existing drones capable of maneuvering wherever the need be. Design of drone with land, water and air affinity is proposed along with non-linear analysis of drone structure. Physical contacts in the drone structure and gravity is accounted for and simulated. Weight carrying capacity of the drone is measured by increasing the weight of the components in each simulation run till the point of failure. Landing capability, structural integrity and stress is studied to ensure the structure doesn't collapse. Effective visualization tool for variable thrust, rpm and forward speed of the drone is developed, which is able to generate real time data regarding the drone's flight by plotting a three dimensional surface plot of varying thrust, rpm and forward flight speed. Model of the drone is used to study the flight plan of the drone with gravity considerations in non-linear analysis.