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Technical Paper

Phase Change Materials-Current Potential and Future Direction

Phase Change Materials once were an interesting phenomena in search of applications. This is no longer true. Advances in encapsulating phase change materials into microscopically thin shells permits their insertion into a wide varity of host materials. As the technology has developed, new applications are being found in a wide variety of areas. Some applications include temperature controlled suits for firefighters and military personnel, structural panels that absorb transient heat loads, and high heat capacity cooling fluids. This paper will cover the current applications being studied for these materials and propose possible future applications. In many cases, the application of these materials is only hampered by not enough people being aware of their capabilities. This paper will detail the Phase Change Materials (PCM) effort and future directions as developed by the U.S. Air Force Wright Laboratory's Flight Dynamics Directorate.
Technical Paper

Numerical Prediction of Slip Energy of a Straight Rolling Tire

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.
Technical Paper

LAMS B-52 Flight Experiments In Direct Lift Control

This paper reports the results of a limited flight evaluation of Direct Lift Control (DLC) on a modified B-52 aircraft. The evaluation was made in conjunction with concluding flights of the Load Alleviation and Mode Stabilization (LAMS) Program and represents the first flight testing of a blended closed loop DLC system on an aircraft of this size and weight. By allowing the pitch and heave motions in the longitudinal axis to be decoupled, the system provided positive control of altitude displacements while holding pitch attitude constant. In both ILS approaches and aerial refueling tasks, controllability was significantly improved and pilot workload was reduced.
Technical Paper

Dynamic Testing of F-16 Bias and Radial Tire Deformation

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.
Technical Paper

Deformation Comparison Between Bias and Radial Aircraft Tires Using Optical Techniques

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.