Leading-edge Control Surfaces Research Articles

Roll Maneuverability of Transonic High-Aspect-Ratio-Wing Aircraft with Flared Folding Wingtips

This paper investigates the roll maneuvers of a very flexible, transonic high-aspect-ratio-wing aircraft with flared folding wingtips, representing a potential future commercial transport configuration. The computational study leverages a fully coupled nonlinear aeroelastic-flight dynamics framework for simulating roll maneuvers commanded by deflecting control surfaces inboard or outboard of the flared folding wingtip hinge. Releasing the flared folding wingtips during flight makes the aircraft roll faster only when deflecting outboard-of-hinge leading-edge control surfaces. However, the achieved roll angles and rates are much lower than the ones obtained by deflecting inboard-of-hinge trailing-edge control surfaces, whose roll control effectiveness is not impacted or even degrades when releasing the flared folding wingtips. These trends are explained by analyzing the role of sweep-induced washout effects in the very flexible, transonic high-aspect-ratio wing, revealing physical mechanisms not identified in previous studies on straight or swept wings with moderate flexibility. Higher wing out-of-plane bending stiffness increases the effectiveness of flared folding wingtips in enhancing roll maneuvers at low dynamic pressure but plays a slight role at high dynamic pressure. This study highlights the need to consider the impact of washout effects for different flight conditions and levels of wing flexibility when assessing the ability of flared folding wingtips to enhance the roll maneuverability of transonic high-aspect-ratio-wing aircraft.

Exploring the Impact of Rapidly Actuated Control Surfaces on Drone Aerodynamics

This study investigates the use of rapidly actuated leading-edge and trailing-edge control surfaces to improve the control authority of small fixed-wing drones. Static and dynamic characteristics were investigated and presented in two separate papers. In this paper, the focus is on the dynamic effects observed from rapidly actuated 30% chord leading- or trailing-edge hinged control surfaces affixed to two flat-plate airfoils. Forces were resolved from surface pressure measurements and are augmented by PIV measurements, smoke flow visualization and analyses. The static study revealed that trailing-edge control surfaces exhibited higher effectiveness in producing time-averaged CL compared to leading-edge control surfaces. However, leading-edge control surfaces exhibit significantly less fluctuation in pressure and lift coefficients at fixed angles of attack and control surface deflections, indicating better stability. Unsteady aerodynamic effects of the airfoil at α=0∘ and “ramp” deflections of trailing- and leading-edge control surfaces from 0∘ to 40∘ with variations in actuation rates showed that CL peaks are approximately three to four times greater than static values for the case of the leading-edge control surface. This has significant implications for fixed-wing drone maneuverability and countering the effects of atmospheric turbulence.

Low Reynolds number aerodynamics of leading-edge and trailing-edge hinged control surfaces: Part I statics

The use of a leading-edge hinged control surface, as opposed to a traditional trailing-edge hinged control surface, is investigated in the context of improving control authority of fixed-wing Micro Air Vehicles when subject to gusts. Static and dynamics forces are considered in two separate papers (Part I and II). In Part I we document the static lift characteristics of two flat-plate airfoils, having either a 30% chord leading- or trailing-edge hinged control surface, resolved from surface pressure measurements captured at angles of attack ranging from 0∘ to 30∘ and control surface deflections from 0∘ to ±45∘. The lift response of the airfoil with the leading-edge control surface was complex with a reversal in lift noted beyond specific control surface deflections (for e.g., at α=0∘, CL reversed beyond ψ=±20∘). The use of a trailing-edge control surface was found to be more effective than the leading-edge control surface. Analysis of the CP and CL fluctuations at fixed α and control surface deflections revealed the fluctuations were significantly less with leading-edge control surfaces than trailing-edge control surfaces. Furthermore, a simple potential flow model exhibited good correlation of CL against experimental results at small angles of attack and control surface deflections.

Transonic flutter suppression for a three-dimensional elastic wing via active disturbance rejection control

The paper presents an error-based active control law for the transonic flutter suppression of a three dimensional elastic wing in a wide range of Mach numbers and dynamic pressures. The extended state observer is the key issue for the presented controller and provides the observed output signal and the observed total disturbance signal at the same time. The observed output signal obtained via the extended state observer enables one to design a feedback control law for adjusting the output errors, while the observed total disturbance signal linearizes the controlled system and guarantees the anti-interference of the proposed controller. To demonstrate the performance of the proposed controller system for transonic flutter suppression, the transonic aeroservoelastic behaviors of a three-dimensional elastic wing with both leading-edge and trailing-edge control surfaces are illustrated as the test cases. During the numerical simulations, only the tailing-edge control surface is used as the control input and the leading-edge control surface is fixed. The numerical results show that the active control law can effectively suppress the transonic flutter at a wide range of Mach numbers and dynamic pressures. Moreover, the controller system has robustness with respect to certain measurement noises and time delay.

Numerical study on influence of single control surface on aero elastic behavior of forward-swept wing

In order to study the influence of elastic forward-swept wing (FSW) with single control surface, the computational fluid dynamics/computational structural dynamics (CFD/CSD) loose coupling static aero elastic numerical calculation method was adopted for numerical simulation. The effects of the elastic FSW with leading- or trailing-edge control surface on aero elastic characteristics were calculated and analysed under the condition of high subsonic speed. The result shows that, the deflection of every single control surface could change the aero elastic characteristics of elastic FSW greatly. Compared with the baseline model, when leading-edge control surface deflected up, under the condition of small angles of attack, the aerodynamic characteristics was poor, but the bending and torsional deformation decreased. Under the condition of moderate angles of attack, the aerodynamic characteristics was improved, but bending and torsional deformation increased; When leading-edge control surface deflected down, the aerodynamic characteristics was improved, the bending and torsional deformation decreased/increased under the condition of small/moderate angles of attack. Compared with the baseline model, when trailing-edge control surface deflected down, the aerodynamic characteristics was improved. The bending and torsional deformation increased under the condition of small angles of attack. The bending deformation increased under the condition of small angles of attack, but torsional deformation decreases under the condition of moderate angles of attack. So, for the elastic FSW, the deflection of trailing-edge control surface play a more important role on the improvement of aerodynamic and elastic deformation characteristics.

Adaptive control of a nonlinear aeroelastic system

Aeroelastic two-dimensional wing section with both trailing-edge (TE) and leading-edge (LE) was investigated in this paper through numerical simulation in time domain. Structural stiffness and damping in pitch degree of freedom were represented by nonlinear polynomials. Open-loop limit cycle oscillation (LCO) characters of two examples were studied, and flutter boundaries with initial conditions were obtained. Parametric uncertainties in both pitch stiffness and damping were considered in the design of adaptive control laws to depress LCOs. Firstly an adaptive controller based on partial feedback linearization was derived for the wing section with a single TE control surface. Secondly a structured model reference adaptive control law was designed for the aeroelastic system with both TE and LE control surfaces. The results show that the designed control laws are effective for flutter suppression, and that considering damping uncertainty has positive effect on flutter control. It may reduce convergent time or increase flutter speed.

Transient response study on rolling effectiveness of multiple control surfaces

A study of the effectiveness of trailing- and leading-edge control surfaces has been made for a rolling wing-fuselage model. An experimental model and wind tunnel test are used to assess the theoretical results. The theoretical model includes the inherently nonlinear dry friction damping moment that is present between the spindle support and the experimental aeroelastic wing model. The roll trim equation of motion and the appropriate aeroelastic equations are solved for different combinations of leading- and trailing-edge control surface rotations using a reduced-order aerodynamic model based upon the fluid eigenmodes of three-dimensional vortex lattice aerodynamic theory. The focus is on the transient response of the system. The present paper provides new insights into the transient dynamic behavior and design of an adaptive aeroelastic wing using trailing- and leading-edge control surfaces.

Overview of the DARPA Smart Wing Project

The recently completed DARPA/AFRL/NASA Smart Wing program, performed by a team led by Northrop Grumman Corporation (NGC), addressed the development and demonstration of smart materials based concepts to improve the aerodynamic and aeroelastic performance of military aircraft. This paper presents an overview of the program. The program was divided into two phases. Under Phase 1 (January 1995 to February 1999), the NGC-led team developed adaptive wing structures with integrated actuation mechanisms to replace standard hinged control surfaces and provide variable, optimal aerodynamic shapes for a variety of flight regimes. An important limitation of the Phase 1 effort, the low bandwidth achievable in Shape Memory Alloy (SMA)-based actuation, was addressed in Phase 2 (January 1997 to November 2001). Under Phase 2, a 30-percent scale full span wind tunnel model of an NGC Uninhabited Combat Air Vehicle (UCAV) design was developed. For the Phase 2 first wind tunnel test, completed in March 2000, SMA-actuated, hingeless, smoothly contoured, flexible leading and trailing edge control surfaces were incorporated on one wing of the model and conventional trailing edge control surfaces actuated using electric motors on the other. This test provided baseline steady-state data at Mach numbers ranging from 0.3 to 0.8. The test also demonstrated the benefits of the smart leading edge control surface to compensate for loss of aileron effectiveness with increasing dynamic pressure. The second test, performed in May 2001, demonstrated a hingeless, smoothly contoured, structurally compliant, trailing edge control surface actuated using piezoelectric motors. Spanwise and chordwise shape control was demonstrated for the smart trailing edge control surface at deflection rates of up to 80°/s. Performance improvements in terms of increased rolling and pitching moments and lower control surface deflections were quantified. The work performed under this program has demonstrated the feasibility of developing smart control surface designs to provide optimal aerodynamic performance at a wide range of flight conditions.

Aerodynamic Performance of the Smart Wing Control Effectors

This paper presents and discusses the wind tunnel results obtained during Phase 1 and Phase 2 of the Smart Wing program. A series of four tests was conducted, two in each phase. The purpose of the tests was to evaluate the performance of smart material based control effectors in representative aerodynamic environments. In Phase 1, wing twist using a Shape Memory Alloy (SMA) torque tube and smoothly contoured trailing edge surfaces enabled by SMA wires were evaluated on a semi-span, 16% scale model of a typical fighter wing. The focus of Phase 2 was to address the design and demonstration of a high-frequency, large-deflection, and smoothly contoured trailing edge control surface capable of a spanwise variation in deflection. The actuation system for this control surface was based on piezoelectric (PZT) ultrasonic motors. A smoothly contoured leading edge control surface was also built and tested using SMA wires. These designs were evaluated on a 30%, full-span model of a representative Unmanned Combat Air Vehicle (UCAV). In each wind tunnel entry comparisons were made to the performance of conventional control surfaces. Successful results included: improved aileron effectiveness at high dynamic pressures; demonstrated improvements in lateral and longitudinal control effectiveness with smoothly contoured control surfaces over conventional hinged control surfaces; continuous spanwise shape control; and, large deflections at rates over 80°/s, which is well within the desired deflection aileron rates for control of fighter aircraft.

Control of a Nonlinear Wing Section Using Leading- and Trailing-Edge Surfaces

The control of nonlinear aeroelastic response of a wing section with a continuous stiffening-type structural nonlinearity is examined through analytical and experimental studies. Motivated by the limited effectiveness of using a single, trailing-edge control surface for the suppression of limit-cycle oscillations of a typical wing section, improvements in the control of limit-cycle oscillations are investigated through the use of multiple control surfaces, namely, an additional leading-edge control surface. The control methodology consists of a feedback linearization approach that transforms the system equations of motion via Lie algebraic methods and a model reference adaptive control strategy that augments the closed-loop system to account for inexact cancellation of nonlinear terms due to modeling uncertainty. Specifically, uncertainty in the nonlinear pitch stiffness is examined. It is shown through simulations and experiments that globally stabilizing control may be achieved by using two control surfaces.

Aeroelastic Wing with Leading- and Trailing-Edge Control Surfaces

It is well known that the effectiveness of a trailing-edge control surface can be substantially diminished due to the elastic twist of an airfoil or wing. This aeroelastic phenomenon is known as control surface reversal when the lift or roll rate vanishes at a sufficiently large ratio of flow dynamic pressure to wing stiffness. However, a leading-edge control surface can be used to counteract control surface reversal, and indeed, in principle, a leading-edge control surface may entirely cancel the tendency of the trailing-edge control surface to undergo reversal. Moreover, analysis shows that by using a simple control strategy one can use a combination of leading- and trailing-edge control surface rotations to maintain lift and roll effectiveness and minimize control surface rotations. The beneficial effects of leading-edge control surfaces on control surface reversal are known to practioners. However, the present simple model makes these especially transparent and suggests an advantageous strategy using a combination of leading- and trailing-edge control surfaces.

Experimental and Theoretical Study on Rolling Effectiveness of Multiple Control Surfaces

It is well known that the effectiveness of a trailing-edge control surface can be substantially diminished due to the elastic twist of an airfoil or rolling wing. This aeroelastic phenomenon is known as control surface reversal when the lift or rolling rate vanishes at a sufe ciently large ratio of e ow dynamic pressure to airfoil or wing stiffness. However, a leading-edge control surface can be used to counteract control surface reversal, and, indeed, in principle, a leading-edge control surface can entirely cancel the tendency of the trailing-edge control surface to undergo reversal. Moreover, analysis shows that by using a simple adaptive control strategy, one can use a combination positive and negative control surface rotations to maximize lift and rolling effectiveness or minimize control surface rotations. In the present work, a theoretical ‐experimental study of the effectiveness of trailingand leading-edge control surfaces has been made for a rolling wing ‐fuselage model. An experimental model and wind-tunnel test are used to assess the theoretical results. The theoretical model includes the inherently nonlinear dry friction damping moment between the spindle support and the experimental aeroelastic wing model for the rollingdegreeoffreedom.Athree-dimensionalvortexlatticeaerodynamictheoryisemployed.Newinsightsintothe behavior and design of an adaptiveaeroelastic wing using trailing- and leading-edge control surfacesare provided. Nomenclature c = wing chord length K® = torsional stiffness km, kn = numbers of vortex elements on the wing in x and y directions, respectively kmm = total number of vortices on both the wing and wake in the x direction L = total lift on the wing Llocal = local lift along the span