There are numerous benefits to air launching as an alternative to ground launching: more launch location options, avoiding launch delays from weather, the avoidance of maintenance and operation costs of a ground launch, and preventing acoustic reflections present in a ground launch. The Vertical Air Launch Sled (VALS) method studied in this research is a unique towed air launch concept. The launch platform allows a launch vehicle carried by it to be aerially towed to a preplanned altitude by a mother aircraft using a standard towline. This research aims to study and validate, through ground tests, the scaling effects, longitudinal and lateral stability, and the autonomous tow takeoff phase of flight. The test article is a 1/32 scaled physical model. In order to study the scaling validity, flight test (experimental) data was compared to the theoretically predicted dynamic response of the scaled system, as well as compared to a theoretically predicted dynamic response of the full-scale system. The complete mission cycle of the VALS, as well as the autonomous mission used in the scaled flight test is discussed. Cable mechanics were also studied for integration in the next iteration of the system model. The specific aims are to validate the dynamics/stability of the scaled system, to integrate an autopilot for the ground roll and takeoff operations and to evaluate its effectiveness. Updated dynamic system models are thoroughly analyzed for standard oscillatory flight modes for every configuration in the mission cycle. The towing aircraft used in the test is a 1/11 scale T-28 radio-controlled aircraft, which is manually controlled. The tow-aircraft was deliberately flown off-course several times to test the response of the autopilot in path following. The autonomous navigation and control software parameter setup are detailed for a sample mission that demonstrates the autonomous tow capabilities. Lateral stability, runway centerline following ability, as well as tautness of the tow line are studied as measures of performance. The L1 controller primarily controls demanded lateral acceleration to adaptively approach the target waypoint based on a number of parameters that include the relative distance along the preplanned mission track, the angle between the track and the vehicle, and the angle between the vehicle's velocity vector and the track. There are also two tunable parameters that change the response of the controller, damping and period. The experimental data obtained from the ground roll test verified the need for ground steering capability. While the tow aircraft was able to pull the VALS along the pre-planned path, the rudder servos were saturated in adjusting the trajectory during the mission. Active ground control was integrated into the system for verifying ground control efficacy. Rudder and aileron command signals, GPS recorded path, as well as other system states are analyzed for the duration of the test mission. Results will be provided in the final paper.


Dynamic Simulation and Ground Testing of the Autonomous Vertical Air-Launch Sled Concept

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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