Articulated Landing Gear for Class IV UAS

Description:

TECHNOLOGY AREA(S): Air Platform 

OBJECTIVE: Develop an actively controlled, legged, articulated landing gear which significantly improves rugged landing capabilities of large UAS air vehicle. The articulated landing gear will also support landing under degraded visual environments (DVEs), shipboard landing, and extreme terrain operations. 

DESCRIPTION: Landing safely on uneven ground in unprepared areas and landing safely on a pitching and rolling ship represent two of the greatest challenges faced by rotorcraft conducting military operations today. It is often impossible for UAS operators to know the slope dynamics of the micro-terrain below them when landing in these environments at night, or in DVE. Compounding this problem is on-site, non-aviation ground personnel that may be unaware of landing limitations; or remote operators with limited awareness of landing site topography. Conducting these types of landings is a difficult task even for UAS operators and can lead to air vehicle accidents during military operations. The use of an actively aircraft controlled articulated robotic landing system can mitigate a large portion of the aforementioned risks. These actively controlled legs allow the air vehicle to conform to uneven and sloped terrains and significantly reduce the cognitive loads placed on the autopilot system. Progress has been made towards thedevelopment of such systems, with theoretical and computational models being developed to simulate the rigid body dynamics and controls involved in the design of an articulated landing gear [1-3]. The concept of articulated robotic landing gear has also been successfully demonstrated and flight tested on a small scale (~200 lbs.) unmanned helicopter [4]. An additional benefit of actively controlled landing system is its ability to enhance hard landing survivability. The system can act as a shock absorber with a relatively large stroke, and through active and passive control, can spread impact loads over longer duration times hence reducingactive and passive control, can spread impact loads over longer duration times hence reducing loads seen by the landing gear and the airframe. Studies conducted using rigid body simulation tools have shown that such a system can reduce peak loads by 70 to 90% for particular landing conditions when compared with conventional landing gear [1]. This program will investigate the capability of actively controlled robotic landing gear as a benefit of replacing traditional landing gears with such a system. The focus of the project is on evaluating the capabilities of such a system through design, fabrication, and testing. The end result should be a validated design and simulation package for the deployment of these system to various UAS platforms. Towards the goal of commercialization, the system should be sized for a four-legged Class IV UAS in the 3,000-5,000 lbs. gross weight range and subsequently analyzed using a comprehensive simulation tool set. The program should explore optimization of the design for landing in extreme conditions while maintaining the capabilities of the system as an articulated landing gear and minimizing weight. The program should also define criteria for material selection when sizing the system for various aircraft. The use of advanced materials such as carbon fiber reinforced polymer (CFRP) composites should also be explored. 

PHASE I: The awardee will study a robotic landing system sized for a helicopter or vertically landing Class IV UAS in the 3,000-5,000 lbs. gross weight range and investigate its capabilities to land in extreme environments. Detailed trade studies should be performed including studies on drive system power draws, system weight and volume in various modes, and drag. The study should include stress analysis to prove crashworthiness while optimizing the design for weight minimization. Determine potential automation software, structural, and other failure modes, effects, and mitigations. Also should determine increase in suitable landing zones available for design concepts for various slopes (e.g. % earth with < 7 deg slopes vs. % earth with < 25 deg slope and variations in landing surface quality) and resultant operational impacts that may mitigate weight penalties. An experimental test plan for characterizing and validating the modeling tools used in the design process should also be proposed as part of this effort. The study should address weight savings/penalties over comparable conventional landing gear. Lastly, assess suitability for limited ground mobility. 

PHASE II: The awardee will fabricate a working prototype and experimentally validate its capabilities. Awardee is expected to perform mechanical characterization experiments to calibrate all modeling requirements, predict the systems capabilities, and experimentally validate model predictions. Using the experimentally validated simulation tools, scaling factors and contributing issues will be clearly articulated in the final report with an assessment for scaling up to the 7,000 lbs. and 21,000 lbs. range. 

PHASE III: Integrate prototype into flight test demonstrators as a modular solution which may be added to existing platforms to increase mission capabilities. The system may also be repackaged for commercial UAS operators. Successful demonstration at this scale may provide future opportunities at larger scales as well as for manned rotorcraft/VTOL systems. Commercial opportunities may exist for surveying in areas of rough terrain, autonomous package delivery, and paramilitary and police “perch and stare” surveillance 

REFERENCES: 

1. Kiefet, J., Ward, M., and Costello, M., (2016). “Rotorcraft Hard Landing Mitigation Using Robotic Landing Gear”. Journal of Dynamic Systems, Measurement, and Control. 138(3). 2. Manivannan, V., Langley, J.P., Costello, M., and Ruzzene, M. (2013). “Rotorcraft Slope Landings with Articulated Landing Gear”. In AIAA Atmospheric Flight Mechanics (AFM) Conference (p. 5160). 3. Kim, D., and Costello, M. (2017) "Virtual Model Control of Rotorcraft with Articulated Landing Gear for Shipboard Landing."

KEYWORDS: Robotic, Landing Gear, Crashworthiness, Impact Mitigation, Unmanned Aerial Systems 

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