recording station in the command center building. (See section "Data Acquisition System" for more information.) Track The ALDF track, as shown in figure 15, has a total length of 2800 ft. The maximum effective jet propulsion distance is approximately 400 ft, and the test section is 1800 ft, which allows for 5 sec of test time during a maximum speed test. The carriage arrestment section is 600 ft. A cross-sectional view of the track is given in figure 16. The track rails are 6 in. square and are welded together forming one continuous rail. Each track rail is supported by chair units which restrain the rail along its length by friction clamping only allowing thermal expansion of the rail at each end. The chairs are spaced 3 to 4 ft apart at random intervals on a pattern that repeats every 81 ft or after 22 chair units. The purpose of this random support spacing is to prevent buildup of harmonic frequencies that could excite the natural frequencies of the carriage. The transfer dolly, shown in figure 17, is located at the end of the track just ahead of the calibration building. It is 72.5 ft long and is used to transport the carriages from the calibration building to the main support building. The same tug which tows the test carriage back to the L-vessel after a run is used to move the transfer dolly holding a test carriage. Arrestment System A photograph of the carriage arrestment system is shown in figure 18 and a schematic of the system is shown in figure 19. The system is located approximately 600 ft from the calibration building at the end of the track. The major components of the system include five independent sets of energy absorbers. Each set of energy absorbers is connected by a cable/tape assembly. The system can routinely absorb 167 000 000 ft-lb of energy which is sufficient energy-absorbing capability to successfully arrest the carriage in the event of a failure of any two sets of energy absorbers. The gantry tower, shown in figures 18 and 19, supports the five cables and is used to position the cable assemblies at the proper elevation for carriage nose block engagement. The gantry is also used to raise the cables above the maximum height of the carriage so that the test carriage can be towed the entire length of the track without interfering with the arrestment system. Each cable assembly spanning the track consists of a steel wire pendant, as shown in figure 20. Each pendant is 1.25 in. in diameter and 100 ft long. Special connectors, shown in figure 20, are used to attach the pendant to the nylon tapes. The tapes which are 8 in. wide, 0.344 in. thick, and 483 ft long are shown after an arrestment in figure 21. The top and bottom edges of each tape are reinforced with extra nylon to accommodate wear and abrasion during the arrestment operation. Each tape is coated with a black resin polymer to resist the degrading effects of ultraviolet radiation and moisture. The cable system has a minimum breaking strength of 150 000 lb. Figure 22 is a photograph of one energy absorber before installation. Each absorber assembly consists of a tub, rotating shaft, and spool. The tub is filled with a mixture of water and glycol as a work medium. Rotor vanes are located between top and bottom stator vanes inside the tub and are connected to a rotating shaft which protrudes through the top of the tub. The spool is connected to the rotating shaft and the nylon tapes are wound about the spool. The energy absorbed in the carriage arrestment process is converted into heat and dissipated into the water/glycol mixture. The arrestment system is equipped with subsystems that pretension the cable assemblies before arrestment such that the catenary deflection does not exceed 6 in. at the center of the track. A safety interlock system prevents the opening of the jet valve unless arresting gear system parameters, such as cable tension and position, and water levels and temperature in each turbine are within allowable limits. Buildings The control room for the ALDF is located on the second floor of the command center building at the propulsion end of the track. (See fig. 6.) The control console graphically displays all facility operational safety interlocks and houses all the controls needed for regulating the operating sequence of the high-speed shutter valve. A process controller checks all safety interlocks just prior to valve actuation to confirm that all systems are ready before a launch. A communications system consisting of a public address system, intercom system, and portable handheld radios is used to secure the area of all but essential personnel prior to and during a test run. The instrumentation room, which is located on the first floor of the command center building, contains the telemetry receiving equipment and all the computer and recording equipment necessary to reduce the data received from the test carriage and test article. (See section "Data Acquisition System" for more information.) The calibration and setup building, identified in figures 5 and 6, is also a storage building for either carriage. A rail system to support the carriage, a test model assembly pit, a massive concrete structure for calibration and drop tests, and an overhead crane are contained in the building. General maintenance service for the carriages and installation of test articles can be performed in this building as well as carriage instrumentation calibration. Data Acquisition System The carriage onboard battery-powered instrumentation system uses signal conditioners with a telemetry system for data transmission. The data system is versatile enough to accommodate a wide range of sensors which are located on the carriage and send analog signals to the signal conditioners. The signals are amplified or attenuated and sent to an analog to digital (A-D) converter and then multiplexed (i.e., each channel is sampled and then sent to one data channel). The multiplexed data are sent to the microwave transmitter and telemetered to the ground station in the instrumentation room. The signal is demultiplexed and sent to a 26-megabyte, 12-bit hard disc computer and to a digital to analog (D-A) converter. The computer processes 28 channels of data directly and can provide output to a printer or multipen plotter. The digital data that goes to the D-A converter is recorded on an FM magnetic tape recorder. Magnetic tape data can be played into a multichannel galvanometer oscillograph system for quick-look purposes of the raw data. The system has a 1600/sec sample rate capability and approximately a 1-percent error on vertical, drag, and lateral load measurements. Speed measurements are accurate within ±1 knot. Forces developed by the test tire are measured by strain gauge load beams that make up the force dynamometer as shown in figure 3 and schematically in figure 23. The dynamometer has five beams measuring the axle loads with two in the vertical, two in the fore-and-aft, and one in the lateral direction. The load transfer between the drag-load beams gives a measure of aligning torque, and the load transfer between the vertical-load beams gives a measure of the overturning torque. Torque links are used to measure the brake torque. Strain gauge type accelerometers are used to measure the axle acceleration along the three axes so that inertial loads can be isolated. Typically 10 channels of data are recorded from the dynamometer. Additional measurements include test wheel vertical displacement, angular speed, and angular acceleration together with carriage position and velocity. Photographic Coverage High-speed motion picture cameras can be placed at various positions around the track, near the propulsion and arresting gear systems, and onboard the carriage to photograph the test articles. The cameras on the carriage are contained in watertight boxes with plexiglass windows. Concluding Remarks The Langley Aircraft Landing Dynamics Facility has been described. This unique facility, which became operational during the summer of 1985, is capable of testing various types of landing gear systems at velocities up to 220 knots on a variety of runway surfaces under all types of weather conditions. The facility has a track 2800 ft long with a test section 1800 ft long, which allows 5 sec of test time at maximum speed. Test articles can be subjected to vertical loads of up to 65 000 lb or sink rates of 20 ft/sec. This facility significantly increases the capability to conduct low-cost testing of conventional and advanced aircraft landing gear systems. The capabilities facilitate testing at speeds and sizes pertinent to large transport aircraft, fighter aircraft, and the Space Shuttle Orbiter. NASA Langley Research Center Hampton, Virginia 23665-5225 August 24, 1987 References Consid 1. Joyner, Upshur T.; and Horne, Walter B.: erations on a Large Hydraulic Jet Catapult. NACA TN 3202, 1954. (Supersedes NACA RM L51B27.) 2. Joyner, Upshur T.; Horne, Walter B.; and Leland, Trafford J. W.: Investigations on the Ground Performance of Aircraft Relating to Wet Runway Braking and Slush Drag. AGARD Rep. 429, Jan. 1963. 3. Durand, W. F.: The Pelton Water Wheel. IDevelopments by Pelton and Others Prior to 1880. Mech. Eng., vol. 61, no. 6, June 1939, pp. 447-454. 4. Durand, W. F.: The Pelton Water Wheel. IIDevelopments by Doble and Others, 1880 to Date. Mech. Eng., vol. 61, no. 7, July 1939, pp. 511-518. 5. Dreher, Robert C.; and Batterson, Sidney A.: Landing and Taxiing Tests Over Various Types of Runway Lights. NACA RM L58C28a, 1958. Batterson, Sidney A.: Investigation of the Maximum 7. Batterson, Sidney A.: Braking and Landing Tests on Some New Types of Airplane Landing Mats and Membranes. NASA TN D-154, 1959. Horne, Walter B.: Experimental Investigation of Spin-Up 9. Horne, Walter B.; Joyner, Upshur T.; and Leland, Trafford J. W.: Studies of the Retardation Force Developed on an Aircraft Tire Rolling in Slush or Water. NASA TN D-552, 1960. 10. Dreher, Robert C.; and Batterson, Sidney A.: Coefficients of Friction and Wear Characteristics for Skids Made of Various Metals on Concrete, Asphalt, and Lakebed Surfaces. NASA TN D-999, 1962. 11. Horne, Walter B.; and Leland, Trafford J. W.: Influence of Tire Tread Pattern and Runway Surface Condition on Braking Friction and Rolling Resistance of a Modern Aircraft Tire. NASA TN D-1376, 1962. 12. Horne, Walter B.; and Dreher, Robert C.: Phenomena of Pneumatic Tire Hydroplaning. NASA TN D-2056, 1963. 13. Horne, Walter B.; Yager, Thomas J.; and Taylor, Glenn R.: Recent Research on Ways To Improve Tire Traction on Water, Slush or Ice. AIAA Paper No. 65-749, Nov. 1965. 14. Yager, Thomas J.: NASA Studies on Effect of Grooved Runway Operations on Aircraft Vibrations and Tire Wear. Pavement Grooving and Traction Studies, NASA SP-5073, 1969, pp. 189–201. 15. McCarty, John Locke: Effects of Runway Grooving on Aircraft Tire Spin-Up Behavior. NASA TM X-2345, 1971. 16. Stubbs, Sandy M.; and Tanner, John A.: Status of Recent Aircraft Braking and Cornering Research. Aircraft Safety and Operating Problems, NASA SP-416, 1976, pp. 257-269. 17. Vogler, William A.; and Tanner, John A.: Cornering Characteristics of the Nose-Gear Tire of the Space Shuttle Orbiter. NASA TP-1917, 1981. |