Search Results

This paper presents the results of a study in which the free rolling behavior of a F-16 tire was numerically modeled. The tire contact patch normal and shear stresses as well as the displacement distributions were obtained from a three dimensional finite element computer program used at the Wright-Patterson Air Force Base, Ohio. It is shown how the predicted deflections are in reasonable agreement with the rated load vs. deformation characteristics, while predicting the effective rolling radius using a theoretical solution. A significant development of this work is the formulation and execution of a finite difference algorithm to evaluate the contact patch slip velocity distribution by methodically manipulating the above computer program results. Slip velocities are then utilized in assessing the rate of slip energy generation at the contact patch, which directly contributes to tire wear. Finally, it is shown how even a low brake slip ratio can increase the contact patch slip energy.

The main objective of this research was to apply an optical technique called fringe projection to quantifying the aircraft tire deformation and strains. The proposed fringe projection technique, using a single light source and a grating, requires no image superposition. Thus, the measurement is not very sensitive to vibration. Three different types of tires in static and dynamic conditions, subjected to different amounts of tire deflections, were tested. A common practice in three dimensional optical measurement is that a fixed reference plane has to be established, from which a fixed reference point is selected. The main technical difficulty in this research is that a tire subjected to an applied load not only moves and rotates, but deforms as well. Therefore, the selected reference point changes its position in three dimensions all the time.

Although there are established methods to measure both tire-pavement friction and pavement texture, friction has not been adequately related to pavement surface texture properties. Therefore, a study has been initiated at the University of South Florida to investigate the dependence of tire-pavement friction on pavement texture. A significant development in the first phase of the study is the formulation of a computer-based methodology that can model the 3-D random roughness of a surface with a given Mean Texture Depth (MTD) as measured by the Grease Patch Test. Examination of synthesized surfaces reveals that the MTD of a random surface is almost an invariant along a given pavement. The same procedure is extended to obtain the frequency spectrum of the generated surface using Fast Fourier Transformation. Finally, the basis of a new analytical approach that can utilize the above frequency spectrum to predict the hysteresis friction of a pavement with random roughness, is illustrated.

A multi-axial dynamic test instrument was designed to perform wear testing of actual aircraft tires as well as tread/carcass composite specimens under laboratory loading conditions which simulate the elements of take-off, landing and taxiing operations. The wear tester consists of a self-spinning abrading head, mounted on the actuator of a servo-hydraulic test system, which faces either (1) the tread surface of a composite specimen clamped by a horizontal stretch frame or (2) the tread region of actual inflated tires. The test concept has been partially proven in the case of tread/carcass composite specimens by building a proto-type test apparatus and operating it successfully. In the current test set-up, the specimen is subjected to static tension to simulate a circumferential load in the tire footprint and the tread surface is in periodic contact with an abrading head under a specific level of pressure.

Knowledge of the tire-wheel interface pressure distribution is necessary for aircraft wheel design and analysis. A finite element code, ANTWIL, has been developed recently which makes tractable the determination of the tire-wheel interface loads from experimentally obtained strains. Motivated by computational considerations, ANTWIL employs an asymmetrically loaded axisymmetric finite element model. Previously reported results have shown numerically that the axisymmetric assumption is well-justified. Data from a strain-roll test conducted at Wright-Patterson Air Force Base for an F-16 Block30 main landing gear wheel were obtained and analyzed via ANTWIL to recover the associated tire-wheel interface loads. Strain comparisons are shown to illustrate the validity of the recovered loads. Comparison of the load profiles for radial and bias ply tires is given and discussed.

Although radial tires have been used in automobiles, they are still in the stage of testing for a possible future use in aircraft. An important consideration is the tire's average life when subjected to various loading conditions. Along with this consideration, tire deformation is one of the concerns. This paper presents a study of deformation comparison between F16 bias and radial aircraft tires subjected to loading conditions against flat plate and flywheel with different percentages of tire deflection and different yaw angles. Optical fringe projection technique is used to determine the three dimensional tire deformation. Like any other similar optical technique, the deformed surface is measured relative to the selected reference point. Therefore, in order to find the absolute geometry of the deformed tire surface, a close-range fiber optic displacement sensor was installed to accurately detect the point's height change in a direction parallel to the wheel axle.

This paper presents an optical technique called fringe projection to measure three dimensional tire deformation subjected to different loads, percentages of deflection and yaw angles. Unlike the well-known Moire method, the proposed technique uses a single light source and a grating, thus requiring no image superposition. As a result, the measurement is not as sensitive to vibration as the Moire method. The fringe projection also differs from the commonly used optical inspection technique in manufacturing industry via line scanning known as structured light, which cannot be applied to dynamic deformation measurements. The recently developed subpixel resolution was employed to accurately locate the optical fringe centers, which in turn improves the accuracy in 3-D geometry determination. A fiber-optic displacement sensor was also placed close to the tire sidewall in order to measure the deformational change of a selected reference point.