Roll Trim Research Articles

Global strength assessment in oblique waves of a large gas carrier ship, based on a non-linear iterative method

At the ship's design, the first step of the hull structural assessment is based on the longitudinal strength analysis, with head wave equivalent loads by the ships' classification societies’ rules. This paper presents an enhancement of the longitudinal strength analysis, considering the general case of the oblique quasi-static equivalent waves, based on the own non-linear iterative procedure and in-house program. The numerical approach is developed for the mono-hull ships, without restrictions on 3D-hull offset lines non-linearities, and involves three interlinked iterative cycles on floating, pitch and roll trim equilibrium conditions. Besides the ship-wave equilibrium parameters, the ship's girder wave induced loads are obtained. As numerical study case we have considered a large LPG liquefied petroleum gas carrier. The numerical results of the large LPG are compared with the statistical design values from several ships' classification societies’ rules. This study makes possible to obtain the oblique wave conditions that are inducing the maximum loads into the large LPG ship's girder. The numerical results of this study are pointing out that the non-linear iterative approach is necessary for the computation of the extreme loads induced by the oblique waves, ensuring better accuracy of the large LPG ship's longitudinal strength assessment.

가로축 자동비행시스템 개선에 관한 연구

전투기는 공대지 및 공대공 전투임무를 위한 다양한 외부 무장형상으로 운용된다. 무장발사로 인한 비대칭 무장형상에서는 조종사가 롤트림 입력을 인가하여 수평비행을 유지한다. 그러나 외란이 있는 실제 비행 중에는 수평비행을 위해 정확한 롤트림 입력을 인가할 수 없다. 이러한 상태에서 자동비행시스템 인가 시에는 부정확한 롤트림 명령의 영향으로 롤자세각 오차가 발생하여 롤축 자동비행시스템의 성능을 저하시킨다. 본 논문에서는 이러한 문제를 해결하기 위해 롤축 자동비행시스템 명령 단에 적분기를 설계하여 롤자세각의 정상상태 오차를 제거하였다. 또한, 롤자세각 오차량을 제한하는 제한기를 비행영역에 따라 스케줄링하여 초기 과도응답을 개선하였다. 시뮬레이션 평가한 결과, 설계된 비행제어법칙은 부정확한 롤트림 상태에서 자동비행시스템을 운용 시에 롤자세각 추종 성능을 개선함을 확인할 수 있었다. The fighter aircraft uses several different loading configurations for air-to-surface and air-to-air combat missions. To maintain wings-level flight with an asymmetric weapon configuration, a pilot controls a roll trim system. However, it is difficult to apply an accurate roll trim input for wings-level flight in the actual flight under disturbance. The inaccurate roll trim input degrades the performance of the roll autopilot system. In this paper, to solve this problem, an integrator was additionally designed in the command part of the roll autopilot system. The initial transient response was improved by scheduling the limiter to restrict the roll attitude error. As a result of the evaluation of the simulation for the designed flight control law, the roll attitude following performance was found to be improved in the autopilot system operation under the inaccurate roll trim condition.

Inviscid Analysis of Extended-Formation Flight

Flying airplanes in extended formations, with separation distances of tens of wingspans, significantly improves safety while maintaining most of the fuel savings achieved in close formations. The present study investigates the impact of roll trim and compressibility at a fixed lift coefficient on the benefits of extended-formation flight. An Euler solver with adjoint-based mesh refinement combined with a wake propagation model is used to analyze a two-body echelon formation at a separation distance of 30 spans. Two geometries are examined: a simple wing and a wing-body geometry. Energy savings, quantified by both formation drag fraction and span efficiency factor, are investigated at subsonic and transonic speeds for a matrix of vortex locations. The results show that, at fixed lift and trimmed for roll, the optimal location of vortex impingement is about 10% inboard of the trailing airplane’s wing tip. Interestingly, the improvement in drag fraction is relatively robust in the vicinity of the optimal position. Over 90% of energy benefits can be obtained with a 5% variation in vertical and 10% variation in spanwise positions. Control surface deflections required to achieve roll trim reduce the benefits of formation flight by 3–5% at subsonic speeds and 9–11% at transonic speeds. Overall, simulations show peak induced drag saving for the trail aircraft are 54% in subsonic flow and 35% in transonic flow while accounting for trim.

Vortex Dynamics of Free-to-Roll Slender and Nonslender Delta Wings

Experiments were conducted on various free-to-roll delta wings with sweep angles in the range of 40―70 deg in a wind tunnel. For low sweep angles, nonzero trim angles are observed until the wing stalls after which the trim angle becomes zero. The magnitude of the roll trim angle decreases with increasing sweep angle and almost disappears for the most slender wing. In a certain range of sweep angles, and just before the stall, large amplitude self-induced roll oscillations with nonzero mean were observed for thin wings with sharp leading edges for which separation point is fixed. Two different regions of angle of attack with free-to-roll oscillations were found for certain sweep angles. Velocity measurements suggest that the oscillations are initiated by the increasing proximity of the shear layers as the angle of attack is increased. Possible mechanisms of the self-induced roll oscillations based upon the phase-averaged velocity measurements have been proposed, incorporating varying vortex size and strength as well as the movement of the shear-layer reattachment locations. Hysteresis and time lag effects are significant even though typical dimensionless frequencies are very low.

Further analysis of self-induced roll oscillations of a non-slender delta wing

AbstractIn low-speed wind tunnel tests at α = 25 and 30º of a 45º delta wing with semicircular leading edges limit cycle oscillations occurred around the 50º roll trim angle. In some cases the oscillations were highly regular, in other cases, highly irregular. An analysis of the observed roll-oscillation dynamics has shown that several viscous flow phenomena are involved, which depend strongly on the leading-edge geometry, and whose relative importance can vary dramatically with the existing Reynolds number in critical flow regions. The possible role of surface roughness in modifying the viscous flow/motion coupling to cause these dramatically different test results is examined.

Ideal Aerodynamics of Ground Effect and Formation Flight

The theoretical induced-drag benefits are presented for ideally loaded wings flying in formation and ground effect. An optimum-downwash approach using a vortex-lattice implementation was used to study formations of wings loaded optimally for minimum induced drag with roll trim. An exact approach was also developed to examine the drag of elliptically loaded wings in formation. The exact approach allows for decomposition of the benefits by considering the mutual-interference contributions from different pairs of wings in a formation

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.

Multiple Control Surface Utilization in Active Aeroelastic Wing Technology

This study investigates the use of multiple control surfaces to effect roll trim of aircraft. Analytic models of a rectangular wing and a e ghter aircraft are used as examples for steady aeroelastic and antisymmetric trim analyses. The e nite element method is used to calculate structural deformations caused by steady aerodynamic input forces, which are generated by a linear panel method. Values of control surface effectiveness, calculated from the e exible rolling moment stability derivatives, are used to determine which control surfaces are most effective in achieving a desired roll maneuver. The roll trim equation of motion is solved for multiple control surface dee ections using an iterative technique that minimizes the control effort to achieve a specie ed roll rate. Roll trim utilizing multiple control surfaces, including leading-edge surfaces, is examined over a range of dynamic pressures. Aircraft models with reduced wing stiffness are investigated to determine if roll performance requirements can be achieved through the use of multiple control surfaces. The results of utilizing multiple control surfaces on e exible wings are examined to determine if weight savings can be achieved while maintaining a desired level of roll performance.

Multiple-function digital controller system for Active Flexible Wing wind-tunnel model

A real-time multiple-function digital controller system was developed for the Active Flexible Wing program, which demonstrated through wind-tunnel tests that digital control can be used with great versatility to perform a multifunction task such as suppressing flutter and reducing loads during rolling maneuvers. The digital controller system (DCS) allowed simultaneous execution of two control laws: 1) flutter suppression and 2) either roll trim or a rolling maneuver load control. The DCS operated within, but independently of, a slower host operating system environment, at regulated speeds up to 200 Hz. It also coordinated the acquisition, storage, and transfer of data for near real-time controller performance evaluation and both open- and closed-loop plant estimation. It synchronized the operation of four different processing units, allowing flexibility in the number, form, functionality, and order of control laws, and variability in selection of sensors and actuators employed. Most importantly, the DCS enabled successful demonstration of active flutter suppression to conditions approximately 26% (in dynamic pressure) above the open-loop boundary in cases when the model was fixed-inroll, and up to 23% when it was free-to-roll. Aggressive roll maneuvers with load control were achieved above the flutter boundary. The purpose of this article is to present the development, validation, and wind-tunnel testing of this multiple-function digital controller system.

Static aeroelastic tailoring for oblique wing lateral trim

Due to its asymmetrical configuration, an oblique wing aircraft may exhibit a roll-trim imbalance. To correct this imbalance, control surfaces, such as ailerons, might be deflected or built-in twists might be added. This paper explores an alternative method of achieving oblique wing roll trim. This is the concept of applying composite tailoring to the oblique wing for lateral trim. The practical use of this concept to trim an oblique wing is demonstrated through analysis of a realistic wing by a static aeroelastic computational procedure. The computational method includes the full-potential transonic aerodynamic code FLO22 and a Ritz structural plate program that is used to model the stiffness created by symmetrical, but unbalanced, advanced composite wing skins. Analysis results indicate that asymmetric composite tailoring reduces the aileron deflection needed for roll equilibrium of the oblique wing. Furthermore, the use of aeroelastic tailoring for lateral trim can reduce control surface hinge moments and drag, resulting in performance benefits when compared to an untailored wing. At the same time, however, wing-skin stresses are greater when tailoring is used, leading to potential design tradeoffs. As such, an integrated design approach would be required to evaluate the true impact of aeroelastic tailoring on the overall performance of an oblique wing.

Integrated structure/control concepts for oblique wing roll control and trim

The integrated design problem posed by the need for oblique wing aircraft aeroelastic roll trim at subsonic airspeeds is examined. It is shown that the need for roll trim is reduced when structural tailoring with advanced composite materials is used, but there is a maximum oblique wing sweep angle above which tailoring is ineffective. A formula for this sweep angle is developed. The need for a combination of asymmetrical aileron input and aeroelastic tailoring of a laminated wing structure is also examined. The design tradeoff between structural tailoring, to reduce the need for ailerons for roll trim, and aileron control surface effectiveness to provide roll trim is illustrated using an example configuration. Tailoring the aileron size so that the aileron reversal dynamic pressure and the static aeroelastic divergence dynamic pressure of the restrained oblique wing are identical is also discussed.

Selection and Design of Heuristic Procedures for Solving Roll Trim Problems

This paper discusses the selection and design of heuristic procedures for solving one-dimensional roll trim problems. These are well-defined combinatorial problems which are too large to optimize. Five different roll trim problems from the paper and film industries are described along with the heuristic procedures that have been used successfully to improve the quality of the solutions generated. The paper concludes with some general guidelines for developing “industrial-grade” heuristic problem solving procedures.

Type A V/STOL Propulsion System Development

Design and performance considerations associated with the development of a unique Type A V/STOL fourturbofan propulsion system concept are described. This propulsion system uses fixed horizontal nacelles with thrust vectoring nozzles installed for achieving lift, a coaxial fan flow reaction control system for pitch control and trim, and a reaction control system for roll and yaw control and engine-out roll trim. The turbofan engine is specially designed to provide continuous compressor bleed flow for the reaction control system during vertical flight while achieving low specific fuel consumption during conventional flight modes. Critical propulsion system sizing conditions are identified, and the sensitivity of aircraft takeoff gross weight to changes in control criteria requirements, engine cycle parameters, and engine rating schemes are discussed. In addition to having competitive performance characteristics, the propulsion system concept described herein has zero single-point failures, low development cost and risk, and good reliability /maintainability.