Showing papers on "Landing gear published in 1998"

Automatic Landing System Design Using Fuzzy Logic

Abstract: A fuzzy logic system is developed for automatic landing control of a transport aircraft. A linear longitudinal aircraft model, with landing gear and flaps deployed at the sea level, is employed for fuzzy logic controller design of automatic landing system including the two landing phases - the glide-path capture and the flare maneuver. In addition, the fuzzy control system is tested using different values of fuzzy controller scaling factors on a six degree of. freedom nonlinear aircraft model. It is shown that the simple tuning fuzzy controller with altered scaling factors is well suited for controlling the trajectory of the aircraft in the landing phase which requires simultaneous control of engine thrust for the velocity and elevator for the pitch attitude in order to change altitude with a constant airspeed.

Prediction Method for Aerodynamic Noise from Aircraft Landing Gear

Abstract: The continued development of quiet engines is now giving rise to situations where airframe noise is comparable with engine noise at approach. The landing gear is a major contributor to airframe noise, and this paper outlines the development of a prediction model for these components. The fundamental scaling laws for aerodynamic noise generated by solid bodies in a flow are well understood and so the essence of the new model is to refine the geometrical description of the landing gear and to take better account of such factors as the local flow velocity over individual components. The prediction model comprise four fundamental sources for various types of components on the landing gear, and included a number of directivity effects. It was used to predict flyover data for the A320 and A340 aircraft. The accuracy of both predictions was excellent around the overhead position, but was significantly reduced in the far forward and rearward arcs. This discrepancy arose from significant differences in the directivity of the flyover and wind tunnel data sets, the source of which is still unclear.

X-34 Vehicle Aerodynamic Characteristics

Abstract: The X-34, being designed and built by the Orbital Sciences Corporation, is an unmanned sub-orbital vehicle designed to be used as a flying test bed to demonstrate key vehicle and operational technologies applicable to future reusable launch vehicles. The X-34 will be air-launched from an L-1011 carrier aircraft at approximately Mach 0.7 and altitudes to 250,000 feet. An unpowered entry will follow, including an autonomous landing. The X-34 will demonstrate the ability to fly through inclement weather, land horizontally at a designated site, and have a rapid turn-around capability. A series of wind tunnel tests on scaled models was conducted in four facilities at the NASA Langley Research Center to determine the aerodynamic characteristics of the X-34. Analysis of these test results revealed that longitudinal trim could be achieved throughout the design trajectory. The maximum elevon deflection required to trim was only half of that available, leaving a margin for gust alleviation and aerodynamic coefficient uncertainty. Directional control can be achieved aerodynamically except at combined high Mach numbers and high angles of attack, where reaction control jets must be used. The X-34 landing speed, between 184 and 206 knots, is within the capabilities of the gear and tires, and the vehicle has sufficient rudder authority to control the required 30-knot crosswind.

Control system for electrically-operated trailer landing gear

Abstract: A powered landing gear drive system for a trailer for selectively extending and retracting the landing gear legs of the trailer. An electric motor is powered by a battery carried by a tractor or by the trailer and provides the power for an electric motor. A control system is provided as a security measure to permit limited, coded entry access to the system, and motor operating parameters are sensed to prevent exceeding operating limits of the system. The powered landing gear system can be provided as original equipment, or it can be retrofitted to existing trailers to permit powered landing gear operation.

Integrated Display System for Low Visibility Landing and Surface Operations

Abstract: This report summarizes the software products and system architectures developed by Lockheed Martin in support of the Low Visibility Landing and Surface Operations (LVLASO) program at NASA Langley Research Center. It presents an overview of the technical aspects, capabilities, and system integration issues associated with an integrated display system (IDS) that collects, processes and presents information to an aircraft flight crew during all phases of landing, roll-out, turn-off, inbound taxi, outbound taxi and takeoff. Communications hardware, drivers, and software provide continuous real-time data at varying rates and from many different sources to the display programs for presentation on a head-down display (HDD) and/or a head-up display (HUD). An electronic moving map of the airport surface is implemented on the HDD which includes the taxi route assigned by air traffic control, a text messaging system, and surface traffic and runway status information. Typical HUD symbology for navigation and control of the aircraft is augmented to provide aircraft deceleration guidance after touchdown to a pilot selected exit and taxi guidance along the route assigned by ATC. HUD displays include scene-linked symbolic runways, runway exits and taxiways that are conformal with the actual locations on the airport surface. Display formats, system architectures, and the various IDS programs are discussed.

The application of a smart landing gear oleo incorporating Electrorheological fluid

Abstract: The objectives of this paper are to outline the use of Electrorheological (ER) fluid within an aerospace system. The advantages of ER fluid-based systems are given followed by design considerations which include those related to the non-linear behaviour of an ER fluid subjected to oscillatory shear. A control strategy is outlined for the use ofa smart landing gear (LG) oleo incorporating ER fluid. The paper also considers the issues associated with airworthiness requirements and ER fluid devices. For airw orthiness approval a smart oleo based LG system must primarily be shown to be safe and as such has to be fault tolerant. A major failure for this application would be if the control strategy failed and the oleo damping coefficient was consistently too low: a backup system is therefore incorporated into the design and other potential modes of failure considered. A semi-active control strategy applied to a variable damping coefficient LG oleo has specific requirements, partly due to the fact that for the take-off and landing phases of flight they are different. A semi-active control strategy is outlined based on the requirements for the alteration of damping coefficient according to the phase of an aircraft's flight. The strategy is the focus of current work to estimate the effectiveness of semi-active vibration control as applied to an undercarriage.

Aircraft nose landing gear

Abstract: An aircraft nose landing gear installation that utilizes a single piece pin inserted through the gear fittings and into the two piece, fail safe support structure without requiring mechanical retention on the outside of the wheel well.

Landing gear operator

Abstract: An operator for lowering and retracting two or more landing gear on an aircraft with a single motor. The output of the motor is modified by a reduction gear assembly, then rotates a drive shaft of each drive, there being one drive for each landing gear assembly. Output of each drive shaft turns a universal joint, then a screw shaft fixed to the universal joint. The screw shaft is arranged to turn in a threaded collar fixed to a tubular stabilizing strut connected to the main strut of the landing gear such that rotation telescopically extends and contracts the paired strut and screw shaft when the latter rotates. Two opposing landing gear are driven by mirror image drives of the operator. Optionally, a third drive shaft and screw shaft lower and retract the nose wheel or tail wheel of the aircraft.

Nonstationary Random Parametric Vibration in Light Aircraft Landing Gear

Abstract: In this work, a new approach for analysis of random vibration in light aircraft landing gear for a given duty cycle is developed and studied. The aircraft is modeled as a linear, single-degree-of-freedom oscillator with random properties, including nonstationary damping and random nonstationary load. Note that this type of problem is dife cult to analyze efe ciently using most conventional techniques. Two approaches to analyze the random vibration of the system are examined: a new variant of the random matrix approach, a statistical random vibration analysis method developed previously by the authors; and a hybrid Monte Carlo technique containing a spectral representation approach and a variant of Latin hypercube sampling. Random response results are shown for two light aircraft landing on three different terrain types using each method, and comparisons are offered. These results show that Monte Carlo analysis cannot compute accurate solutions for this problem. It is anticipated that the proposed random matrix technique could be used in conjunction with current fatigue analysis methods so that accurate landing gear fatigue information may be computed.

Aircraft landing gear absorber

Abstract: A method and apparatus for eliminating aircraft landing gear fore-and-aft vibration is provided. The method includes using a tuned mass absorber attached to the landing gear. The gear walk motion has a peak amplitude motion and a pre-peak amplitude motion. The tuned mass absorber includes a mass and a spring, with the mass being oriented to move in a fore-and-aft direction at a frequency and amplitude that counterbalances the gear fore-and-aft vibration. The mass in one embodiment is of an amount in the range of 1 to 2 percent of the effective landing gear mass. In one embodiment, the tuned mass absorber is attached to a landing gear strut near the strut's distal end. The motion of the tuned mass absorber mass moves at a frequency and amplitude that counterbalances the gear walk pre-peak amplitude motion. Therefore, the absorber mass is of an amount less than the mass required to counterbalance gear walk peak amplitude motion. The tuned mass absorber thereby eliminates the gear walk motion in its formation.

Interdisciplinary Landing Gear Layout for Large Transport Aircraft

Abstract: One major task of an aircraft landing gear is the absorption of vertical energy which will mostly result either from the landing impact of from overrunning bumps and other ground irregularities. The necessity to limit the applied landing gear loads at the high stroke velocities at touch-down leads to damping characteristics which provide only lillte damping action at less vehement movements. Aircraft with high fuselage flexibility are therefore prone to vibration and resonance phenomena. The vonventional approach of developing the landing gear separetely from the airframe with only simple models to represent the aircraft ground dynamic properties seems no longer appropriate. Multibody system simulationis proposed as the basic software tool of an interdisciplinary development process which takes into account the elastic interaction between the aircraft components. The multibody system technique is aimed towards the simulation of the dynamics of a technical system in its entity, thus forming a core element of computer aided engineering software. Bi-directional interfaces to other software packages allow the integration of modeling and analysis data from a broad range of engineering disciplines. A case study demonstrates the optimization of a large transport aircraft landing gear layout in a multidisciplinary design environment. The aim is to improve the aircraft ride comfort on uneven runways without loss of landing impact absorbing qualities. Two landing gear concepts are considered: a conventional passive landing gear and a semi-active landing gear.

Safety forced landing device

Abstract: PROBLEM TO BE SOLVED: To make soft landing possible of an aircraft without extending a landing gear at landing time. SOLUTION: In a safety forced landing device, an air bag 2 and a carriage 4 are used to serve as a principal constitutional element. In a lower part of the carriage 4, wheels 5 are mounted. Needless to say, a quantity, position and a structure of the wheel are determined so as to endure weight of a jumbo aircraft and a shock at landing time. The air bag 2 has strength resisting against kinetic contact friction of an aircraft 1, to be made by, for instance, waterproof cloth, wear resistant sheet, etc. While watching by a driver a mirror 10 in an upper part of a driver's room 7 provided in a tip end of the carriage 4, its speed and running direction can be matched with that of an approaching aircraft. The running direction is determined by a steering wheel 8. Propulsive force of the carriage is obtained from each engine 6 connected to each wheel 5 through a propeller shaft. The air bag 2 may be formed as a water bed method water pillow type.

Multibody Simulation in the Integrated Design of Semi-Active Landing Gears

Abstract: The paper presents a technique for an integrated aircraft-landing gear design using multibody simulation (MBS). The MBS technique is aimed at the simulation of the dynamics of a technical system in its entity. It has proven to be a well balanced compromise between the requriement of "fast", "robust", and "exact" simulation, thus assisting the process of virtual prototyping. An aircraft model is set up using SIMPACK, DLR's prime MBS tool. The aircraft model presented is based on a large civil aircraft consisting of a finite element structure for fuselage and wings, landing gear models from CAD, control structures from a control design tool, and measured input data for sevral runway profiles. The objective is to achive an optimal landing gear design with respect to the aircraft as a whole. Therefore, a multi-objective optimization loop is used to optimize landing gear parameters using criteria covering both the landing and rolling performance, i.e. resulting loads, stress and comfort at several locations at the aircraft structure. In addition to the conventional suspension design, this method has been used to propose a control strategy for semi-active damping of the nose landing gear that reduces runway induced vibrations of fuselage and wings, thus increasing comfort and minimizing airfram loads.

A Study of aircraft lateral dynamics & ground stability

Abstract: The stability of an aircraft on the runway is dependent on many factors. In this thesis, a mathematical model is developed that allows the ground stability and lateral dynamics of an aircraft to be analyzed while it is in the process of taking off or landing. Only two degrees-of-freedom will be considered: lateral displacement and angular rotation. Equations of motion for the model are developed using Newtonian mechanics. The major components of the aircraft that are included in the model are the main landing gear, the vertical tail, and the tail wheel. The model is developed into both linear and non-linear forms. Comparisons are made between a tricycle gear aircraft and a taildragger. Simulations for both the linear and non-linear model are performed to better understand stability. The results of these simulations are used to comment on the applicability of the linear model.

Nonlinear effects of electrorheological fluids and their application in smart avionic systems

Abstract: Electrorheological (ER) fluids are not yet exploited within the aerospace industry, however, there are systems on an aircraft which would benefit from the use of this type of smart material and its associated technologies. The use of ER fluid within landing gear (LG) systems can be envisaged, for example the control of the passive damping characteristics of a landing gear oleo. This could be beneficial to the airframers by reducing LG weight, to the landing gear systems providers by reducing costs and over design, as well as for the operators by increasing passenger comfort and confidence. The use of ER fluid within an oleo would, however, result in a non-linear damper the characteristics of which would be dependent upon the design, the mode of deformation of the charged fluid and the control strategy. A design strategy is proposed for the use of ER fluid within a LG oleo and the controller design aspects considered.

Method of obtaining information and apparatus for determining the weight of an aircraft

Abstract: An onboard system for use in measuring, computing and displaying the weight and center-of-gravity for aircraft (1), while keeping aircraft movement to a minimum. Pressure sensors (45) are mounted in relation to each of the landing gear struts (3, 5, 7). An onboard pump (38) and reservoirs are attached to each of the landing gear struts and are activated by a computer/controller (25), while landing gear strut pressures are monitored in the determination of strut stiction. The computer/controller calculates the stiction of each landing gear strut and compensates for the pressure distortions caused by landing gear strut stiction. Additional features include reducing strut stiction, measuring landing gear strut fluid levels, monitoring landing gear strut health, weight adjustments for external ice and de-icing fluids, weight adjustments for wind, monitoring aircraft landing gear strut movement.

Boeing 777 pavement load tests

Abstract: The research reported in this paper is the result of a three year test program conducted from July 1994 to August 1996 by the Boeing Company and the Russian airport technology firm Progresstech, Ltd. The program was primarily designed to study the pavement loading characteristics of the six-wheel 777 landing gear but was expanded to include tests to characterize two, four, six and eight-wheel gears under both static and quasi-static loading conditions. The 1996 program also included tests designed to provide an indication of the relative impact of trafficking four and six-wheel gears on the accumulation of surface deflections. For the covering abstract of the proceedings, see IRRD 490713.

Improved landing gear for carrying vehicle

Abstract: The utility model relates to an improved landing gear for carrying vehicles, which is that the landing gear of the tail end of a vehicle body is designed into a center section traffic lane and an end section traffic lane which are formed into integration; the center section traffic lane is jogged with the end section traffic lane which can move in the tail end of the vehicle body; each of the traffic lanes are widened and thickened. Because the structural strength of the traffic lanes of the utility model is strengthened with less possibility for deformation, security when loading vehicles are loaded is improved, and besides, because the number of the traffic lanes is reduced, breakdown maintenance rate of a linkage structure is reduced.

Wheel-type landing gear for helicopters

Abstract: A wheel-type landing gear is disclosed for helicopters with fastening measures on the helicopter which permit a receiving of the wheel-type landing gear on the craft at fittings provided for the fastening of skid-type landing gear without any additional support. The possibility of retrofitting and/or backfitting the helicopter is provided. The main wheels are fastened on rocker arms so that the wheel contact point is situated clearly behind the rearward landing gear fittings.