853 research outputs found
A mathematical model of an active control landing gear for load control during impact and roll-out
A mathematical model of an active control landing gear (ACOLAG) was developed and programmed for operation on a digital computer. The mathematical model includes theoretical subsonic aerodynamics; first-mode wing bending and torsional characteristics; oleo-pneumatic shock strut with fit and binding friction; closed-loop, series-hydraulic control; empirical tire force-deflection characteristics; antiskid braking; and sinusoidal or random runway roughness. The mathematical model was used to compute the loads and motions for a simulated vertical drop test and a simulated landing impact of a conventional (passive) main landing gear designed for a 2268-kg (5000-lbm) class airplane. Computations were also made for a simply modified version of the passive gear including a series-hydraulic active control system. Comparison of computed results for the passive gear with experimental data shows that the active control landing gear analysis is valid for predicting the loads and motions of an airplane during a symmetrical landing. Computed results for the series-hydraulic active control in conjunction with the simply modified passive gear show that 20- to 30-percent reductions in wing force, relative to those occurring with the modified passive gear, can be obtained during the impact phase of the landing. These reductions in wing force could result in substantial increases in fatigue life of the structure
Runway exit designs for capacity improvement demonstrations. Phase 2: Computer model development
The development is described of a computer simulation/optimization model to: (1) estimate the optimal locations of existing and proposed runway turnoffs; and (2) estimate the geometric design requirements associated with newly developed high speed turnoffs. The model described, named REDIM 2.0, represents a stand alone application to be used by airport planners, designers, and researchers alike to estimate optimal turnoff locations. The main procedures are described in detail which are implemented in the software package and possible applications are illustrated when using 6 major runway scenarios. The main output of the computer program is the estimation of the weighted average runway occupancy time for a user defined aircraft population. Also, the location and geometric characteristics of each turnoff are provided to the user
Validation of an Active Gear, Flexible Aircraft Take-off and Landing analysis (AGFATL)
The results of an analytical investigation using a computer program for active gear, flexible aircraft take off and landing analysis (AGFATL) are compared with experimental data from shaker tests, drop tests, and simulated landing tests to validate the AGFATL computer program. Comparison of experimental and analytical responses for both passive and active gears indicates good agreement for shaker tests and drop tests. For the simulated landing tests, the passive and active gears were influenced by large strut binding friction forces. The inclusion of these undefined forces in the analytical simulations was difficult, and consequently only fair to good agreement was obtained. An assessment of the results from the investigation indicates that the AGFATL computer program is a valid tool for the study and initial design of series hydraulic active control landing gear systems
Assessing the Impact of Rutting Depth of Bituminous Airport Runway Pavements on Aircraft Landing Braking Distance during Intense Precipitation
A runway pavement during its useful life is subject to a series of deteriorations because of repeated load cycles and environmental conditions. One of the most common deteriorations is the formation of rutting (surface depression in the wheel path) on the runway surface. Rutting negatively affects aircraft performance during landings and will behave even worse during precipitation or with the existence of fluid contaminations on the surface. This paper aims to develop a model for calculating aircraft braking distance during landing on wet-pavement runways affected by rutting based on dynamic skid resistances generated by tire–fluid–pavement interactions. Intense precipitation, variable rutting depths for a 100 m length step, water film depths (e.g., 1 to 26 mm), and aircraft wheel loads (e.g., 10 to 140 kN) are considered as the boundary conditions of the developed model. The output is a model that can estimate aircraft braking distance as a function of rutting depth and can perform further assessment of the probability of the occurrence of landing overrun. After validating the model with existing methodologies and calibrating it according to the actual landing distance required for each type of aircraft, an Italian airport is simulated using a model with real data regarding the level of service of its pavement surface characteristics
A comparison of some static and dynamic mechanical properties of 18 x 5.5 and 49 x 17 type 7 aircraft tires as measured by three test facilities
The properties were measured during static, slow rolling, and high-speed tests, and comparisons were made between data as acquired on indoor drum dynamometers and on an outdoor test track. In addition, mechanical properties were also obtained from scale model tires and compared with corresponding properties from full-size tires. While the tests covered a wide range of tire properties, results seem to indicate that speed effects are not large, scale models may be used for obtaining some but not all tire properties, and that predictive equations developed in NASA TR R-64 are still useful in estimating most mechanical properties
Shock Absorber Leakage Impact on Aircraft Lateral Stability During Ground Handling Maneuvers
Aircraft braking maneuvers are safety-critical on-ground motions that exhibit complex dynamics and significant dependence on system operating conditions. The fundamental interface between the aircraft and the ground is the landing gear. Among the landing gear components, the shock absorbers may be subject to gas leakage during their lifetime, which is an anomaly that could compromise the lateral stability properties of the aircraft on the operating regimes found during braking maneuvers. In this paper, an explicit link is established between main landing gear shock absorber leakage and aircraft lateral stability. To investigate lateral stability, a high-fidelity multibody nonlinear aircraft simulator is developed in a MATLAB/Simulink framework and validated against experimental data. To generate insight into the problem and to quantify shock absorber leakage impact on aircraft lateral stability, two simple but descriptive analytical models are also developed, each one on a different operating mode of the system. The analysis of the models reveals that shock absorber leakage can have a significant effect on aircraft lateral stability, especially at high velocities and highly damped nose wheel steering conditions. The models developed in this work may be used by aircraft control system designers to come up with more effective lateral stability controllers in the event of main landing gear shock absorber leakage
On the modeling of light aircraft landing gears
International audienceLight aircrafts are designed to be used in both developed and undeveloped areas of a country. Hard landingconditions such as shocks and rebounds may occur. In this context, a good, efficient, robust and easy to maintainlanding gear is vital. Its main role is to dissipate the energy of the impact. The aim of this work is to study aninnovative light aircraft landing gear equipped with a damper. The study includes comparing its dissipationperformance with two traditional light aircraft landing gears: a classical flat spring landing gear and a landing gearwith Sandow cords. These systems’ modeling is carried out through three steps. Firstly, Bush tire is modeled withfinite elements considering tire geometry and material specificities. Secondly, combined finite elements withstructural elements are used to model the different landing gear systems. Thus, stress, deformation and energywithin landing gears components could be obtained. Finally, aircraft rolling simulations are conducted. Systems’transient responses while rolling over ramp are evaluated, as well as the efforts and rebound displacementstransmitted to the aircraft. A dissipation efficiency comparative study between the landing gears is conducted. Inaddition, the influence of simulation’ conditions such as inflation pressure, rolling velocity or runway flatness isinvestigated
Evaluation of two transport aircraft and several ground test vehicle friction measurements obtained for various runway surface types and conditions. A summary of test results from joint FAA/NASA Runway Friction Program
Tests with specially instrumented NASA Boeing 737 and 727 aircraft together with several different ground friction measuring devices were conducted for a variety of runway surface types and conditions. These tests are part of joint FAA/NASA Aircraft/Ground Vehicle Runway Friction Program aimed at obtaining a better understanding of aircraft ground handling performance under adverse weather conditions and defining relationships between aircraft and ground vehicle tire friction measurements. Aircraft braking performance on dry, wet, snow and ice-covered runway conditions is discussed as well as ground vehicle friction data obtained under similar runway conditions. For a given contaminated runway surface condition, the correlation between ground vehicles and aircraft friction data is identified. The influence of major test parameters on friction measurements such as speed, test tire characteristics, type and amount of surface contaminant, and ambient temperature are discussed. The effect of surface type on wet friction levels is also evaluated from comparative data collected on grooved and ungrooved concrete and asphalt surfaces
Landing dynamic simulation of aircraft landing gear with multi-struts
The landing dynamic modeling technology for aircraft landing gear is based on accurate evaluation of the landing gear landing performance. Aiming to study the post landing gear, a model for dynamic analysis of the gear is established based on the analysis of the structure mechanical features and the characteristics of landing dynamic performance. The landing dynamic analysis of strut landing gear is conducted by using LMS Motion software. According to the comparative analysis between simulation and drop test, the dynamic modeling method is accurate and reasonable. To obtain the load distribution of each landing gear, a full aircraft model of multi-strut landing gear is built, and then the dynamic simulation analysis is carried out in different landing process. The study shows that the rear main landing gear bears the highest proportion of load. The initial pitch angle influences load distribution of each landing gear. A lateral force is exerted on the main landing gear tire, when the plane is landing asymmetrically. With landing condition becoming stable, the lateral force is eliminated
Structures and Dynamics Division research and technology plans for FY 1985 and accomplishments for FY 1984
The objectives, FY 1985 plans, approach, and FY 1985 milestones for the Structures and Dynamics Division's research programs are presented. The FY 1984 accomplishments are presented where applicable. This information is useful in program coordination with other government organizations in areas of mutual interest
- …