Showing papers on "Landing gear published in 2010"

Aircraft landing gear

Abstract: An aircraft landing gear comprising: a shock-absorbing main leg having a sprung part for attachment to an aircraft and an un-sprung part including a slider and an axle carrying at least one wheel, the wheel having a toothed ring gear; a drive transmission mounted externally on the sprung part, or on the un-sprung part, of the main leg, the drive transmission having at least one motor and a drive pinion for meshing with the toothed ring of the wheel; and an actuator for lifting the drive transmission into and out of driving engagement with the toothed ring and for maintaining the driving engagement as the landing gear deflects during a ground taxiing operation. Also, a method of operating the aircraft landing gear.

Experimental assessment of low noise landing gear component design

Abstract: Landing gear related airframe noise is one of the dominant aircraft noise components at approach, so continued research efforts to reduce landing gear noise are essential. This paper describes further development of an advanced low noise main landing gear that was previously designed and tested in the European SILENCER project. The work was carried out under the current European co-financed TIMPAN project (Technologies to IMProve Airframe Noise) using a 1/4 scaled landing gear model that was tested in the German-Dutch Wind Tunnel. A variety of gear configurations were tested including a new side-stay design and various modifications to the bogie inclination, wheel spacing, bogie fairings with different flow transparency, leg-door configurations and brake fairings. The farfield noise data from the tests are compared with results from a landing gear noise prediction model, transposed to full scale flight conditions and compared with the full scale test data obtained for the original SILENCER advanced A340 s...

Experimental study on Noise Generation of a Two-Wheel Main Landing Gear

Abstract: This paper deals with results of noise measurements for a 40% of two-wheel type aircraft main landing gear in lowspeed wind tunnel experiments. In order to accurately assess a noise source location and far-field characteristics during the approach phase, scale model with complex geometry which was equipped with small components such as link mechanism, hydraulic tubes and electrical wiring as well as a tire, a cylinder, a piston, doors, and a sidebrace was used. Model geometry was based on LEG (Landing gear noise Evaluation Geometry) which was designed by a gear manufacturer assuming 100-PAX class regional jet airliner. Experimental results obtained in two kinds of wind tunnels, which were 2m by 2m lowspeed wind tunnel in JAXA and large scale anechoic facility of Railway Technical Research Institute of Japan, showed dominant noise sources around a tire, a sidebrace, some parts of the door and also the junction between the cylinder and the sidebrace. Among these prominent noise sources, the tire and the sidebrace were large contributor to the total of noise level. It was found that noise characteristics around 1kHz was important not only in the amplitude but also in directivity for an actual aircraft scale. Representation of small components and geometry of an actual landing gear even in a scale model seemed to be effective of several decibels in noise level.

A Hybrid Lattice-Boltzmann/FW-H Method to Predict Sources and Propagation of Landing Gear Noise

Abstract: A hybrid approach to predict the far-field noise generated by an airplane nose landing gear is presented in this paper. The approach consists of a Lattice-Boltzmann Method (LBM) for the calculation of the flow-field around the fully detailed geometry of the landing gear which provides the input for a Ffowcs Williams – Hawkings (FW-H) solver to calculate the far-field noise. Both parts have been validated independently. The method is applied to the nose landing gear of a Gulfstream G550 business jet, for comparison with experimental results obtained in the University of Florida UFAFF wind tunnel. The near-field flow simulation using the LBM method showed good correlation with the PIV measurements of the flow field as well as surface microphone measurements, up to frequencies of about 4kHz. The comparison to experimental far-field results shows good agreement in the midfrequency range of 1-3kHz. At both low and high frequencies the simulations underpredict the measured results more strongly than the near field and surface measurements would suggest, which may be due to experimental limitations. A comparison between the solid and porous formulation of the FW-H solver shows that both method provide nearly equivalent results. However, inclusion of additional surfaces such as part of the fuselage is critical to achieving good results with the solid formulation. The effects of resolution of the near-field simulations are also investigated and show the expected lower cut-off frequency for lower resolutions for both the near-field and the far-field. No differences between the cases with different resolutions are observed up to 1 kHz in the near-field and up 2-3kHz in the farfield.

Theoretical Framework for the Simulation of Transport Aircraft Flight

Abstract: This contribution presents a novel simulation theory for a complete fixed-wing aircraft. Novel methods are presented for flight mechanics (fuel planning), turbofan engine simulation (in direct and inverse mode), thermo-physics integration (tire temperature on the ground and fuel temperature in flight) and aircraft noise. At the fundamental level, the framework presented addresses a shortfall in multi-disciplinary integration in aircraft flight, including economic operations, preliminary design and environmental emissions. Validation strategies are introduced for component-level analysis and system integration. Results are presented for geometry models, specific air range and optimal cruise conditions, payload-range performance, fuel temperature of a wing tank, tire heating during normal take-off, aircraft propulsive (jet/nozzle) and non propulsive (landing gear) noise. Selected results are shown for the Boeing B777-300 and the Airbus A380-861.

Reduction of Landing Gear Noise using Meshes

Abstract: Acoustic and resistance measurements were performed in NLR's Small Anechoic Wind Tunnel on a large number of meshes intended for landing gear noise reduction. The meshes were tested on generic bluff bodies which simulated single and combined landing gear struts. An out-of-flow microphone array was used to localize and quantify the noise sources on the model. It is found that the meshes yield a drastic broadband noise reduction for a wide range of mesh materials and mesh shapes. The noise reduction occurs for all tested angles of attack and for all tested models. For the combined bodies it is found to be sufficient to treat only the upstream component with a mesh.

Helicopter Landing Ship: Undercarriage Strength and the Role of the Human Factor

Abstract: We address, using probabilistic modeling and the extreme-value-distribution technique, the helicopter undercarriage strength in a helicopter-landing-ship situation. Our analysis contains an attempt to quantify, on the probabilistic basis, the role of the human factor in the situation in question. This factor is important from the standpoint of the operation time that affects the likelihood of safe landing during the lull period in the sea condition. The operation time includes (1) the time required for the officer-on-ship-board and the helicopter pilot to make their go-ahead decisions and (2) the time of actual landing. It is assumed, for the sake of simplicity, that both these times could be approximated by Rayleigh’s law, while the lull duration follows the normal law with a high enough ratio of the mean value to the standard deviation. Safe landing could be expected if the probability that it occurs during the lull time is sufficiently high. The probability that the helicopter undercarriage strength is not compromised can be evaluated as a product of the probability that landing indeed occurs during the lull time and the probability that the relative velocity of the helicopter undercarriage with respect to the ship’s deck at the moment of encounter does not exceed the allowable level. This level is supposed to be determined for the helicopter-landing-ground situation. The developed model can be used when developing specifications for the undercarriage strength, as well as guidelines for personnel training. Particularly, the model can be of help when establishing the times to be met by the two humans involved to make their go-ahead decisions for landing and to actually land the helicopter. Plenty of additional risk analyses (associated with the need to quantify various underlying uncertainties) and human psychology related efforts will be needed, of course, to make such guidelines practical.

Bifurcation Analysis of Nose-Landing-Gear Shimmy with Lateral and Longitudinal Bending

Abstract: This work develops and studies a model of an aircraft nose landing gear with torsional, lateral, and longitudinal degrees of freedom. The corresponding three modes are coupled in a nonlinear fashion via the geometry of the landing gear in the presence of a nonzero rake angle, as well as via the nonlinear tire forces. Their interplay may lead to different types of shimmy oscillations as a function of the forward velocity and the vertical force on the landing gear. Methods from nonlinear dynamics, especially numerical continuation of equilibria and periodic solutions, are used to asses how the three modes contribute to different types of shimmy dynamics. In conclusion, the longitudinal mode does not actively participate in the nose-landing-gear dynamics over the entire range of forward velocity and vertical force.

Systems and methods for mounting landing gear strain sensors

Abstract: A strain sensor device for measuring loads on aircraft landing gear. This is done by measuring strains in the lower end of the strut, by which we infer the loading in the entire landing gear structure. These strains can be very large (as high as 10,000 microstrain) and can be imposed in numerous random directions and levels. The present invention includes a removable sensor assembly. An electromechanical means is presented that can accommodate large strains, be firmly attached to the strut, and provide good accuracy and resolution.

Initial RANS and DDES of a Rudimentary Landing Gear

Abstract: Results of RANS and Delayed Detached Eddy Simulation (DDES) are presented for a new research model of landing gear. The design is as simple as that of Lazos but a primary motivation for it is a weak and well-understood Reynolds-number dependence. The simplicity should allow essentially grid-converged RANS-LES solutions now or within a few years, but it preserves some physics, which challenge CFD, in a manner meaningful to noise-prediction capability for landing gear. The initial simulations presented in this work parallel an experimental study launched recently at NAL (India). A major goal of the simulations is to verify the potential of the RLG geometry in terms of CFD validation and to attract the attention of the turbulence and airframe noise communities to the experimental database, which will be available in the near future. The principal early challenge to CFD is to predict the wall-pressure fluctuations. Far-field noise will be addressed later.

Aircraft landing gear

Abstract: A landing gear for an aircraft, having mounting means fitted to the fuselage of the aircraft; at least one wheel; and at least one supporting arm having a first end portion connected to the mounting means, and a second end portion opposite the first end portion, and to which the wheel is suspended. The first end portion of the supporting arm has a seating portion fitted in rotary manner to a pin connected to the mounting means and extending crosswise to the supporting arm; and an electrically controlled actuator is fitted to the seating portion, and is activated selectively to rotate the supporting arm, about the pin, between a first and second operating position defining a stowed in-flight configuration and a lowered landing configuration of the landing gear respectively.

Influence of Tire Inflation Pressure on Nose Landing Gear Shimmy

Abstract: This work investigates shimmy oscillations in the nose landing gear of a passenger aircraft and studies how they depend on changes in the tire inflation pressure. To achieve this, a mathematical model of a landing gear is considered that includes the influence of the tire pressure via different tire properties, such as cornering force and contact patch length. Experimental data obtained from two radial tires are used as a basis for modeling the influence of inflation pressure on tire properties. Bifurcation analysis of the mathematical model is then performed. It yields stability diagrams in the plane of velocity and vertical force for different values of the tire inflation pressure. Specifically, two-parameter bifurcation diagrams for five different inflation pressures are presented. This allows the conclusion that for the type of tires considered, the landing gear is less susceptible to shimmy oscillations at higher than nominal inflation pressures.

Control of landing gear noise using meshes

Abstract: In previous investigations of aerodynamic noise from landing gears, solid fairings have been used to shield components from the flow so as to reduce the farfield noise. Larger noise reductions have been achieved by designing advanced low noise gears, and in recent studies further reductions of advanced landing gear noise have been achieved by using flowporous fairings. In this study, the application of porous fairings to conventional landing gears is considered to investigate whether their noise reduction potential can be achieved without the potential penalties of re-designing the landing gear with noise as an additional design constraint, as was done for the advanced gears. The results show that porous fairings can provide significantly greater noise reductions than solid fairings, and that porous material wraps can provide useful attenuation of noise with minimal weight penalty.

Identification and Attenuation of a Tonal-Noise Source on an Aircraft's Landing Gear

Abstract: Aircraft landing gear noise is a major contributor to the overall airframe noise during the landing approach of a commercial aircraft. Fairings covering geometrically complex areas of the gears have proved to be very effective in noise reduction. However, in tests on an A340’s main landing gear, the overall benefit of the fairings was offset by both a slight increase in low-frequency broadband noise and a strong tonal noise. In this study, the identification and attenuation of the tonal-noise source has been carried out using a one-quarter-scale A340 main-landing-gear model. Aeroacoustic and aerodynamic tests were conducted in a closed-section wind tunnel, using a phased microphone array on the ceiling of the test section, flush-mounted pressure transducers on the model surface, and the particleimage- velocimetry technique. Far-field noise tests were then taken in an open jet aeroacoustic facility, using far-field microphones to verify the wind-tunnel test results. The experiments demonstrated the tonal-noise mechanism and a number of different control methods.

Nonlinear analysis of lateral loading during taxiway turns

Abstract: determined by the maximal lateral loading conditions identified in published studies of instrumented in-service passenger aircraft. The performance of the turn can be assessed over the entire operational range in terms of the actual loads experienced at individual landing gears. Recent studies by the Federal Aviation Administration of instrumented aircraft have been limited to investigating the lateral loads experienced at the aircraft’s center-ofgravity position. The results presented here show that this information is insufficient to predict the actual loads experienced by individual landing gears, especially for the nose gear, which is found to experience considerably higher lateral loads than predicted by the corresponding loads at center of gravity. These findings are shown to be robust with respect to changes in the aircraft’s mass and the criterion used to define the limits of the operating regions.

Effects of Local Flow Variations on Landing Gear Noise Prediction and Analysis

Abstract: This paper discusses a study on the local flows in the vicinity of aircraft landing gear. Local flows for various aircraft types at various operation conditions are extracted from a computational fluid dynamics database and analyzed to reveal parametric trends of the local flows. It is shown that, for wing-mounted gear, the circulation around the high-lift wing induces a flow under the wing in the opposite direction to the freestream flow and, hence, makes the local flow velocity lower than the freestream velocity. For fuselage-mounted gear, the trends are opposite; the local flow velocity for nose gear is usually slightly higher than the freestream. For all gear, it is shown that the local flow velocity is a decreasing function of the aircraft angle of attack. Based on these features, a simple reduced-order model is developed, which correlates the local flow velocity to the freestream velocity, the aircraft angle of attack, the maximum aircraft takeoff weight, and the distance from the aircraft. All these parameters are readily available in practical applications, rendering the simple model suitable for landing gear noise prediction. Discussions are given on the effects of the local flow features on landing gear noise analysis and prediction with practical examples.

Modeling and Sensitivity Analysis of the Meridian Unmanned Aircraft

Abstract: This paper describes the modeling and sensitivity analysis of an unmanned aerial vehicle in development for glacial ice research. The Meridian UAV is a single-engine research aircraft with fixed landing gear designed by engineers at the University of Kansas. Linear state space models are developed for both longitudinal and lateral dynamics of the UAV in a large range of airspeeds. The modeling and simulation of the Meridian were done using Advanced Aircraft Analysis and Athena Vortex Lattice software. Stability and control derivatives are estimated for use in a 6-DOF simulator for pilot training and mission planning. A sensitivity analysis is performed evaluating the effect of changing Clβ, Cnβ, and Cyβ on aircraft dynamics to investigate the effects of eight flat plate antennas attached below the wings. Conclusions are drawn from analysis of vehicle dynamics to consider precautions and special preparations for flight test operations.

Device and method for a rotation of the wheels of the landing gear of aircraft

Abstract: The invention concerns a device and a method to cause the rotation of at least one wheel of the landing gear of aircraft, according to which between the supporting structure (12) of the landing gear and the brake group (19, 20) of the wheel is placed at least an actuator element with variable geometry (35, 38, 40, 42) controlled and managed to develop such a force in order impose an intermittent angular rotation of the wheel when the brake group is operated.

Modeling and simulation of tricycle landing gear at normal and abnormal conditions

Abstract: This paper presents the development of a tricycle landing gear simulation model including several classes of system failures such as component degradation and jamming. The model is integrated with the dynamics of a business jet aircraft within a Matlab/Simulink ® simulation environment aimed at providing tools for the design and analysis of fault tolerant control laws, landing gear development, and flight simulation for use in an academic environment. The formulation of the models at normal and abnormal conditions is presented in detail along with simulation results for representative cases.

Fuselage mounted landing gear

Abstract: A landing gear for an aircraft. The landing gear may have a wheel/truck assembly, an oleo strut/support frame for supporting the wheel/truck assembly, and a retraction assembly attached to the oleo strut/support frame, the retraction assembly for moving the landing gear between a deployed position and a retracted position. The retraction assembly may have a pivoting trunnion brace attached to the oleo strut/support frame and to a fuselage of the aircraft for positioning the wheel/truck assembly, the oleo strut/support frame and the retraction assembly at least substantially fully within the fuselage of the aircraft in the retracted position.

Retractable helicopter landing gear

Abstract: A retractable helicopter landing gear has a suspension structure supporting one wheel, and is movable between a withdrawn position, to reduce drag on the helicopter, and a lowered position for landing and takeoff of the helicopter. The landing gear also has a skid, which is located between the axis of rotation of the wheel and the periphery of the wheel, is diametrically opposite the suspension structure, and is connected to the suspension structure by a connecting device having a torsion bar.

Amphibious large aircraft without airstairs

Abstract: An amphibious large aircraft without airstairs is provided. The fuselage (7) of the amphibious large aircraft is flat, and the shape of its bottom is rectangular. The longitudinal cross-section of the fuselage has a shape of the cross-section of a win, so the lift can be generated by the fuselage during flight, and the flight efficiency is increased by 30-40%. The fuselage has only one floor, wherein the passenger cabin (6) is set in the front of the fuselage, and the cargo hold (21) is mounted above the rear. The wings (8) are suspended towards two sides from upper side of the fuselage. A jet engine (30) is mounted above the rear of the fuselage and adjacent to the tail wing. Because landing gears (4, 9) can be lifted vertically and the landing gear wells (3, 10) mounted in the fuselage are provided with fore-and-aft sliding doors (32, 33), the fuselage can stop close to the ground. It is no need for the passenger to go on and off the aircraft via the airstairs and escape from the aircraft via the inflator slide in en emergency. It can be more convenient for the cargo to enter or exit the aircraft when the aircraft is used as a freight aircraft. Because the fuselage is flat, the gliding capability and the ground effect of the aircraft are better, and the aircraft can takeoff, land and cruise on the wide water. The full-length, wingspan and height of the aircraft are all reduced by 25-30% compared with the current aircraft of the same scale, thus the floor space and the investment of the manufacturer, the maintenance factory, the garage and the aerodrome are all reduced.

Prediction of Landing Gear Noise Reduction and Comparison to Measurements

Abstract: Noise continues to be an ongoing problem for existing aircraft in flight and is projected to be a concern for next generation designs. During landing, when the engines are operating at reduced power, the noise from the airframe, of which landing gear noise is an important part, is equal to the engine noise. There are several methods of predicting landing gear noise, but none have been applied to predict the change in noise due to a change in landing gear design. The current effort uses the Landing Gear Model and Acoustic Prediction (LGMAP) code, developed at The Pennsylvania State University to predict the noise from landing gear. These predictions include the influence of noise reduction concepts on the landing gear noise. LGMAP is compared to wind tunnel experiments of a 6.3%-scale Boeing 777 main gear performed in the Quiet Flow Facility (QFF) at NASA Langley. The geometries tested in the QFF include the landing gear with and without a toboggan fairing and the door. It is shown that LGMAP is able to predict the noise directives and spectra from the model-scale test for the baseline configuration as accurately as current gear prediction methods. However, LGMAP is also able to predict the difference in noise caused by the toboggan fairing and by removing the landing gear door. LGMAP is also compared to far-field ground-based flush-mounted microphone measurements from the 2005 Quiet Technology Demonstrator 2 (QTD 2) flight test. These comparisons include a Boeing 777-300ER with and without a toboggan fairing that demonstrate that LGMAP can be applied to full-scale flyover measurements. LGMAP predictions of the noise generated by the nose gear on the main gear measurements are also shown.

Device for controlling trapdoors closing the hold of aircraft landing gear

Abstract: The invention relates to a device for controlling at least one trapdoor (4a, 4b) of the hold of aircraft landing gear, the device comprising a permanent mechanical link (20, 23, 24, 25a, 25b) between the trapdoor and the landing gear. According to the invention, the permanent mechanical link is arranged so as to transform a movement of the landing gear between a stored position and an extended position, or vice versa, into a to-and-fro movement capable of causing the trapdoor to open and then close during the movement of the landing gear between said positions.

Computational Analysis of the Eect of Bogie Inclination Angle on Landing Gear Noise

Abstract: Airframe noise and in particular main landing gear noise is a major noise source during the approach phase. Wind tunnel tests have shown a strong relationship between the inclination angle of the bogie and the noise radiation of a main landing gear. Using Computational Fluid Dynamics, this paper investigates the ow features around three dierent congurations of a simplied four wheel main landing gear. The three congurations consist of a horizontal, 10 toe up and 10 toe down bogie inclination angle. The unsteady CFD results have been used as an input to a FW-H solver to determine far eld noise levels. The results show that strong vortices are generated when the ow separates from the front wheels. The interaction of these vortices with the solid landing gear surface is the main mechanism of noise generation. The results from the simulations show a clear relationship between the bogie inclination angle, the location of the strong vortex cores and the far eld noise levels.

Stochastic optimal control of flexible aircraft taxiing at constant or variable velocity

Abstract: Active control landing gears are used to alleviate vibration during aircraft taxiing. A nonlinear stochastic dynamics model is established, considering the aircraft body pitch movement and elastic vibration excited by the random runway. The equivalent linearization method is adopted to ensure the model linearity near the balance point, and the Gaussian random process of the runway is generated from the Gaussian white noise using a shape filter. Based on the stochastic optimal control theory, the LQG controller is designed along with weighted quadratic performance index for a better ride comfort, shock absorption, road holding and least energy expenditure. The algebraic Riccati and Lyapunov equations are solved to obtain stationary response while taxiing aircraft at a constant velocity and the differential Riccati and Lyapunov equations are solved to obtain the nonstationary response while taxiing aircraft at a variable velocity. The aircraft dynamic responses are obtained through the runway random process modeled by Monte Carlo method. Simulation results show that active control landing gear can give a better ride comfort, shock absorption and road holding performance no matter whether taxiing is at constant or variable velocity.

Airframe Noise–Landing Gear Noise

Abstract: Noise originating from flow around aircraft landing gears is one of the major components of aircraft noise in the approach phase. Owing to the complex structure of landing gears, they represent a cluster of aerodynamic noise sources that are difficult to deal with for the purpose of noise reduction. Moreover, a variety of safety and operational constraints must be considered. Landing gear noise intensity increases proportionally to the 6th power of flow velocity while the sound frequencies increase linearly with the velocity. Through wind tunnel tests on full-scale gears, typical noise characteristics (spectrum and directivity) and the noisiest gear components can be identified. On the basis of this knowledge, both noise prediction models and add-on noise reduction fairings can be developed. Such fairings, to protect complex gear structures from high-speed inflow, provide the only limited noise reduction potential. Much higher noise benefits can be achieved for new landing gears of future aircraft, when aeroacoustic constraints are introduced as an additional design criterion, thus enabling a low-noise design of both the overall gear architecture and of individual gear components. On top of that, both passive and active flow control means can be applied locally to gear components for further noise reduction. Keywords: airframe noise; landing gear noise; add-on gear fairings; low-noise gear design; flow control

Touchdown dynamic modeling and simulation of lunar lander

Abstract: In this paper, the key influences of lunar lander landing model are illuminated systematic. Then the touchdown dynamic model of lunar module is built. And the simulation model for lunar landing described on ADAMS is discussed. As an example, one kind of lunar module model with four cantilever truss style landing gear is built by ADAMS and the simulations are focused on the influences on landing by the characteristics of buffers in primary and secondary struts of the landing gear. The conclusions can be used for the design of lunar lander.

Shrink shock strut locking mechanism for retractable aircraft landing gear

Abstract: A shrink shock strut assembly for retractable aircraft landing gear is disclosed which includes an elongated strut cylinder, an elongated strut piston coaxially mounted for reciprocal movement within the strut cylinder between a shrunk condition when the landing gear is retracted into a wheel well of an aircraft and a fully extended condition when the landing gear is deployed from the wheel well for landing the aircraft, and a blocking mechanism operatively associated with the strut cylinder and mounted for movement into a blocking position with respect to the strut piston, when the landing gear is retracted within the wheel well, to prevent axial movement of the strut piston into the fully extended condition within the wheel well.