Helicopter Performance Research Articles

Performance of Quiet Helicopter

Abstract Noise generated by helicopters is one of the main problems associated with the operation of rotorcrafts. Requirements for reduction of helicopter noise were reflected in the regulations introducing lower limits of acceptable rotorcraft noise. A significant source of noise generated by helicopters are the main rotor and tail rotor blades. Radical noise reduction can be obtained by slowing down the blade tips speed of main and tail rotors. Reducing the rotational speed of the blades may decrease rotor thrust and diminish helicopter performance. The problem can be solved by attaching more blades to main rotor. The paper presents results of calculation regarding improvement of the helicopter performance which can be achieved for reduced rotor speed but with increased number of rotor blades. The calculations were performed for data of hypothetical light helicopter. Results of simulation include rotor loads and blade deformations in chosen flight conditions. Equations of motion of flexible rotor blades were solved using the Galerkin method which takes into account selected eigen modes of the blades. The simulation analyzes can help to determine the performance and loads of a quiet helicopter with reduced rotor speed within the operational envelope of helicopter flight states.

A shape memory alloy torsion actuator for static blade twist

Active blade twist is an option to increase helicopter performance, for instance moving its condition from hovering to cruise. Shape memory alloys give the possibility of realizing compact devices, with high energy density. Several devices have been proposed in literature, showing limitations in terms of effectiveness and necessary room. In this article, the capability of a shape memory alloy torque tube to induce a certain twist law along the blade, while preserving its integrability within the structure, has been exploited. The study refers to a complex theoretical model, made of different specialized modules. In detail, transmitted twist action by the shape memory alloy actuators, aerodynamic effects caused by the induced geometrical change, inertial impact following the motor system integration, and system layout influence on the blade response have been taken into account. Through this model, a parametric investigation has been organized to highlight the importance of selected design variables. Tube thickness, mass, and length have been considered. Two different configurations have been initially taken into account, distinguished for the twist transmission mode and their outline. In the first hypothesis, a pre-stressed wire system converts tensile stress into a rotary action. In the second sketch, a pre-twisted solid tube connects two different stations of the blade, transmitting relative rotation. After the first trade-off, the second architecture has been selected for further analysis, focusing on its performance in terms of net transmitted twist, aerodynamic effects, while paying attention to a proper mass balance. In the chosen approach, the actuator has been installed at the torsion center. A finite element model has been used to validate the assessed analytical representation and has permitted establishing the applicability domain. Apart elastic forces, acting both in the shape memory alloys and the blade components, centrifugal forces have been taken into account by considering an increased stiffness of the reference structural element. Aerodynamic forces have been evaluated after the target configuration has been reached; helicopter trim has been considered to this purpose. The researchers aim at developing this concept by integrating the reverse action of the aerodynamic field and evaluating the importance of the actuator position along the chord. The research herein presented has been carried out within the SABRE project, project ID 723491, gratefully funded by the European Union within the Horizon 2020 program.

Experimental Study of Rotor Flow Separation Control using a New Type of Dielectric Barrier Discharge Plasma Actuator

Flow separation occurring on rotor blades is an important limiting factor for helicopter performance. This paper presents a new type of dielectric barrier discharge (DBD) plasma actuator for rotor blade flow separation control called bipolar DBD plasma actuator. The bipolar DBD plasma actuator’s connection mode differs from traditional plasma actuators and eliminates reverse discharge between electrodes. The experiments in this work were carried out by smoke-wire flow visualization and PIV technology in the open test section of a low speed wind tunnel, and solved the problem of high voltage electricity supplied to the plasma actuator while the rotor rotated. In this experiment, the rotor, camera, and laser were synchronized to obtain results. Smoke-wire results and PIV results illustrated that the flow separation weakened with increasing rotor speed; the separated flow area was large at a rotating speed of 300 r/min and gradually became smaller at the rotating speed of 600 r/min, the flow separation disappeared at the rotating speed of 1200 r/min. When the plasma was active, both smoke-wire results and PIV results showed the flow separation area was greatly reduced at the rotating speed of 300 r/min and disappeared at the rotating speeds of 600 r/min and 1200 r/min, the rotor flow separation at high angles of attack could be effectively controlled by the new DBD plasma actuator.

Rotor aerodynamic shape design for improving performance of an unmanned helicopter

In order to improve the effective load of an unmanned helicopter, a new blade shape with a new airfoil section, non-linear negative twist, varied chord length and double-swept blade tip was designed by employing a CFD method coupled with an optimization method. Firstly, a new airfoil is designed with improved aerodynamic characteristics. By comparing the numerical data, the new airfoil has better lift-drag ratio, i.e., the maximum lift-drag ratio increases from 63.03 to 66.29 at Mach number of 0.3 and from 70.17 to 72.13 at Mach number of 0.4, compared with the original NACA8H12 airfoil. In addition, a new blade shape is designed based on the new airfoil. By comparing the numerical data, the CT of the design rotor increases from 4.79×10−3 to 5.07×10−3, and the maximum FM increases from 0.67 to 0.72 at the design state. After that, a verification test is performed in hovering flight. The test data indicated the a maxumu thrust increase of 3.18% at the design state. Meanwhile, the FM of design rotor is improved about 3.41% compared with the original rotor.

Analysis of Co-Flow Jet Effect on Dynamic Stall Characteristics Applying to Rotor Airfoils

The performance of helicopter is limited by the phenomenon of dynamic stall. Dynamic stall is attributed to the time-varying angle of attack (AOA) of blade element resulting from blade flapping cyclic pitch inputs and wake flow. Co-flow jet(CFJ), as a novel flow control technique proposed by the joint research team from University Miami (UM) and AFRL has shown great improvement on lift enhancement, drag reduction due to its strong circulation improvement and turbulent mixing effect. Focusing on dynamic stall characteristics, this paper studies the effect of co-flow jet technique applying to rotor airfoil OA309. Numerical simulations show that CFJ can remove dynamic stall phenomenon occurring on rotor airfoils but the momentum coefficient should be carefully chosen so as to obtain high-efficient control effect.

Influence on Aerodynamic Performance of a Compound Helicopter by Wing Incidence Angle

This paper investigates the influence on aerodynamic performance of a winged compound helicopter due to change of the lift share ratio between a rotor and a wing through a numerical simulation. The lift share ratio is defined by the wing incidence angle. A compound helicopter model is constructed with the UH-60A helicopter rotor and the fuselage configuration, which is based on the JAXA scaled down model. The fuselage model combines the body with a rectangular wing of an aspect ratio of 10. Flight condition at a cruising speed corresponding to an advance ratio of 0.703 is simulated, where the rotor speed is reduced to 75% RPM. Numerical simulation results show that the aerodynamic performance degrades significantly by rotor/wing aerodynamic interaction, where a decreasing wing lift relates to a rotor thrust increase. To minimize the aerodynamic drag caused by the rotor/wing interaction, it is found that the wing should be installed at an incidence angle of the highest lift to drag ratio, and the wing area should be adjusted to satisfy the optimal rotor/wing lift ratio.

Trajectory Optimization and Finite-Time Control for Unmanned Helicopters Formation

A safe and rapid formation generation is of great importance for the cooperation performance of the multiple unmanned helicopters. The trajectory optimization and control is the key problem in the process of the formation generation. To achieve this goal, a novel safe formation generation strategy is proposed through trajectory optimization and tracking control. First, the rapidly-exploring random tree (RRT) algorithm is applied to obtain the initial guess to satisfy the requirement of rapid solution. Then, the Gauss pseudospectral method is used to transform the optimal control problem to the nonlinear programming (NLP) problem and the sequence quadratic programming (SQP) method is utilized to gain the optimal trajectory combined with the initial guess. Second, a finite-time sliding mode controller is proposed to ensure the finite time trajectory tracking in the presence of model parameter uncertainties and unknown external disturbances. Finally, the numerical simulation is provided to show the effectiveness of the proposed formation generation strategy for unmanned helicopters formation.

“Defiant”, a Today Unique Helicopter in the World

You do not see helicopters like this every day. Sikorsky-Boeing SB1 in his first demonstration flight showed that it is much more than just a fancy design on paper as he could initially think, with a first relevant flight demonstration. The initial flight lasted less than 30 min, enough time for to prove he can climb and descend easily, move back and forth and turn left and right with extraordinary ease and maneuverability. Companies have described this action as a low-speed flight maneuver and a short film has revealed that the helicopter can also operate in the area of about 10 to 20 m of land successfully. His first start in the inaugural flight test was held at a Sikorsky airport in West Palm Beach, Florida. SB1 has an unusual design that instantly conquers you. If most helicopters have one main rotor for vertical lifting, Defiant has a pair of coaxial rotors, one rotating clockwise and the other rotating trigonometrically (counterclockwise) to achieve a balancing the dynamics of the couple - that is, to prevent it from overturning one side or another. This means that the aircraft no longer needs the standard rotor at the helicopter tail. Instead, it has a new, distinctive, rear-wheel drive, which has the role of getting Defiant's zoom along the high-speed horizontal flight. Defiant is designed to fly at almost twice the speed of classic helicopters while maintaining the best low speed and hover performance of conventional helicopters. Coaxial design can also be found in some Russian military helicopters but without a propeller. Sikorsky used the project earlier (with the propeller) in the experimental X2 helicopter and the next S-97 Raider. The Project is considered by the United States Army for the Future Lift Vertical program, which intends to find a replacement for many of the US military helicopters used today (Finally, as in the early 2030s, where Defiant's rival in that area is the Bell V-280 Valor, which is not a helicopter, but rather a V-22 Osprey-like tiller-like aircraft used by US marines. The V-280 has been able to improve flight quality since its first flight in December 2017). The Sikorsky-Boeing team will then analyze the flight data recorder and film on this first demonstration flight with the aim of establishing a plan for several Defiant test flights in the coming weeks and months to confirm other important features of the new helicopter, before making a complete presentation, for massive future production orders. Sikorsky and Boeing have long been working on this high-speed military helicopter project and have released the first images of what is expected to become a very efficient utility helicopter of the United States Army sometime in 2030. SB1 is a technology demonstrator with Future Lift technology, built around the Sikorsky X2 platform, using two counter-rotating blades at the top of the plane to eliminate the problem of a 150 km/h traction rotor (~ 240 km/h).

Performance improvement of variable speed rotors by Gurney flaps

Gurney flaps are used for improving the performance of variable speed rotors. An analytical model able to predict helicopter rotor power is first presented, and the flight data of the UH-60A helicopter is used for validation. The predictions of the rotor power are in good agreement with the flight test data, justifying the use of this tool in analyzing helicopter performance. A fixed Gurney flap can enhance the performance of variable speed rotors and expand the corresponding flight envelope, especially near stall and high speed flight. A retractable Gurney flap at 1/rev yields more power savings than a fixed Gurney flap or a retractable one with a higher harmonic prescribed motion. At a speed of 200 km/h, the retractable Gurney flap, actuated at 1/rev, can obtain 3.22% more power reduction at a rotor speed of 85% nominal rotor speed, and this value is 8.37% at a speed of 220 km/h. The height corresponding to the minimum power increases slowly in low to medium speed flight, and increases dramatically in high speed flight. With increasing take-off weight (i.e. rotor thrust), the retractable Gurney flap at 1/rev can obtain more rotor power savings.

Extendable chord for improved helicopter rotor performance

Extendable blade sections are investigated as a method for reducing rotor power and improving helicopter performance. A validated helicopter power prediction method, based on an elastic beam model is utilized. The static extendable chord can deliver a rather small power reduction in hover, and significant power savings at high speed flight, however, the cruise power is increased. In hover, the active chord is best deployed in the middle part of the blade, and just inboard of the tip at high speed flight. The increase in chord length can lead to power savings at high speed flight but the benefits decrease in other speeds. The 1/rev dynamically extendable chord can lead to an overall power reduction over the speed range of a helicopter. The best deployment location is at the blade tip, which is different from the statically extendable chord. It is best extended out in the retreating side, and retracted back in the advancing. The power reduction by the 1/rev dynamically extendable chord increases with the increase in the length of the chord extension and take-off weight of the helicopter. Generally, a lower harmonic extendable chord can save more power than one actuated at higher harmonics. The dynamic chord can reduce more power than the corresponding static chord.

Study on the Mechanism of the Variable-Speed Rotor Affecting Rotor Aerodynamic Performance

The variable-speed rotor has proven to be a promising means to improve helicopter performance. Previous investigations on the aeromechanics of the variable-speed rotor are scarce. This work studies the mechanism of the variable-speed rotor affecting the rotor aerodynamic performance by means of dimensionless parameter analysis and reveals the various effect mechanisms under the various flight speeds and take-off weights. The current work shows that, during hover, the variable-speed rotor improves the rotor aerodynamic performance by reducing the blade dynamic pressure, while the non-uniform thrust distribution is attributed to the reduced rotor speed suppresses the performance improvement. In slow forward flight, the blade dynamic pressure reduction improves the rotor aerodynamic performance. In cruise and fast forward flight, both the blade dynamic pressure and advancing blade tip compression loss reductions improve the rotor aerodynamic performance. The study also shows that in forward flight, the rotor loading is smaller, and the effect of reducing the advancing blade tip compression loss through the variable-speed rotor is greater.

A Novel Strategy for Improving the Aeromagnetic Compensation Performance of Helicopters.

An aeromagnetic survey is an important method in magnetic anomaly detection and geophysical prospecting. The magnetic field is typically measured by optically pumped magnetometers (OPM) installed on the aircraft. The measurement accuracy of the OPM is easily affected by the platform-generated magnetic fields. Therefore, aeromagnetic compensation is necessary. The traditional compensation model only considers the permanent, induced, and eddy current interference magnetic field of the aircraft platform. However, the interference field produced by the avionics system, and the relative motion between the aircraft and the magnetometer, are still not taken into account. To address this issue, we proposed a novel strategy to eliminate the additional interference of the platform with two OPMs. Among them, the OPM located farther away from the aircraft serves as a sensing magnetometer, whereas the near OPM serves as a reference magnetometer. The coherent noise suppression method is used to process the residual magnetic field interference after compensation. By establishing the interference magnetic transfer function between the two sensors, the interference field can be suppressed. The results of the experiments demonstrate the effectiveness of the novel strategy, and the standard deviation of residual interference drops from 0.065 nT to 0.045 nT.

Flow Control on Helicopter-Rotor Blades Via Active Gurney Flap

Abstract The Active Gurney Flap (AGF) is a small, flat tab cyclically deployed and retracted at lower surface of the rotor blade near its trailing edge. It is expected that the device may improve performance of modern helicopters. The main goal of presented investigations was to develop research methodology and next to use it in studies on phenomena occurring in the flow around helicopter-rotor blades equipped with AGF. Conducted CFD simulations aimed at validation of the developed methodology as well as at significant supplementing and extension of results of experimental research. Simplified sensitivity analysis has been conducted aiming at determination of geometric and motion-control parameters of the AGF, optimal from point of view of helicopter-performance improvement. Fully three-dimensional simulations of the rotor flight aimed at determination of flight conditions, in which the use of Active Gurney Flaps could significantly improve the rotorcraft performance.

The Influence of Wing Position on Hovering Performance of a Winged Helicopter

The Influence of Wing Position on Hovering Performance of a Winged Helicopter

The Concept and Definition of Integrated Flight Performance for a Small Remotely Piloted Helicopter

The concept and definition of integrated flight performance for a small remotely piloted helicopter are introduced to obtain real operational values in performing a flight mission.

Neural network fuzzy control for enhancing the stability performance of quad-rotor helicopter

Recently, the quad-rotor helicopter has gained increasing attention owing to its very good flexibility, its ability to execute various flight missions even in harsh environments. The quad-rotor helicopter can implement different fight attitudes, which is attributed to the effective control of the motor speed about four propellers. In order to make the quad-rotor helicopter can better finish flight mission, the performance of flight stability then becomes particularly important. A neural network fuzzy control algorithm is proposed in this paper so as to guarantee the stability performance of the quad-rotor helicopter. The proposed algorithm is based on the neural network, which keeps the self-organization and self-learning ability, besides this, it utilizes the strong impression ability of constitutive knowledge as to the fuzzy logic. The proposed control scheme aims to implement good abilities such as describing qualitative knowledge, strong learning mechanism and direct processing about quantitative data of the quad-rotor helicopter. In the practical flight process of the quad-rotor helicopter, while the deviation of position and attitude information become larger, fuzzy control is adopted so as to shorten the overshoot and adjustment time. On the other hand, if the deviation of position and attitude become relatively smaller, neural network PID control will be used so as to reduce the error. Experimental results show that the proposed neural network fuzzy control algorithm exhibits good performance in the flight process of the quad-rotor helicopter.

Aerodynamic performance evaluation of basic airfoils for an agricultural unmanned helicopter using wind tunnel test and CFD simulation

There is growing interest in unmanned aerial pesticide application, which is a new farming paradigm aimed at reducing labor and improving production stability. To alleviate the difficulties being experienced by operators and pilots, researchers are focusing on the lack of lift and are trying to enhance lift by improving rotor airfoil. In this study, with the objective of enhancing the rotor performance of agricultural unmanned helicopters, the performance of basic airfoils was evaluated in a wind tunnel and via computational fluid dynamics simulation. The lift and power characteristics of rotor blades were also evaluated. As airfoil design steps to improve the lift of unmanned helicopter, the characteristics of lift, drag, and power were analyzed via wind tunnel tests for the 400 mm section models of two airfoils, specifically a thick airfoil (V1505A) with blunt nose and a thin airfoil (V2008B) with drooping nose. The V1505A airfoil is appropriate for the inboard region, which requires stable aerodynamics at a high angle of attack. On the other hand, the V2008B airfoil is ideal for the outboard region of the rotor because it has a relatively high dynamic efficiency. Therefore, it is expected that a transitional airfoil blade with a negative twist angle can solve the problems of unmanned aerial pesticide application.

Helicopter gas turbine engine performance analysis: A multivariable approach

Helicopter performance relies heavily on the available output power of the engine(s) installed. A simplistic single-variable analysis approach is often used within the flight-testing community to reduce flight-test data in order to predict the available output power under various atmospheric conditions. This simplistic approach often results in unrealistic predictions. This paper proposes a novel method for analyzing flight-test data of a helicopter gas turbine engine. The so-called “Multivariable Polynomial Optimization under Constraints” method is capable of providing an improved estimation of the engine maximum available power. The Multivariable Polynomial Optimization under Constraints method relies on optimization of a multivariable polynomial model subjected to equalities and inequalities constraints. The Karush–Khun–Tucker optimization method is used with the engine operating limitations serving as inequalities constraints. The proposed Multivariable Polynomial Optimization under Constraints method is applied to a set of flight-test data of a Rolls Royce/Allison MTU250-C20 gas turbine, installed on an MBB BO-105 M helicopter. It is shown that the Multivariable Polynomial Optimization under Constraints method can predict the engine output power under a wider range of atmospheric conditions and that the standard deviation of the output power estimation error is reduced from 13 hp in the single-variable method to only 4.3 hp using the Multivariable Polynomial Optimization under Constraints method (over 300% improvement).

Performance and Loads Study of a High-Speed Compound Helicopter

Performance and Loads Study of a High-Speed Compound Helicopter

Variable-speed tail rotors for helicopters with variable-speed main rotors

ABSTRACTVariable tail rotor speed is investigated as a method for reducing tail rotor power, and improving helicopter performance. A helicopter model able to predict the main rotor and tail rotor powers is presented, and the flight test data of the UH-60A helicopter is used for validation. The predictions of the main and tail rotor powers are generally in good agreement with flight tests, which justifies the use of the present method in analysing main and tail rotors. Reducing the main rotor speed can result in lower main rotor power at certain flight conditions. However, it increases the main rotor torque and the corresponding required tail rotor thrust to trim, which then decreases the yaw control margin of the tail rotor. In hover, the tail rotor may not be able to provide enough thrust to counter the main rotor torque, if it is slowed to follow the main rotor speed. The main rotor speed corresponding to the minimum main rotor power increases, if the change of tail rotor power in hover is considered. As a helicopter translates to cruise, the induced power decreases, and the profile power increases, with the profile power dominating the tail rotor. Reducing the tail rotor speed in cruise reduces the profile power to give a 37% reduction in total tail rotor power and a 1.4% reduction to total helicopter power. In high-speed flight, varying the tail rotor speed is ineffective for power reduction. The power reduction obtained by the variable tail rotor speed is reduced for increased helicopter weight.