The private eVTOL/UAM market is rapidly expanding, with many companies and investors betting on the possibility of low-cost-to-operate and zero emissions air taxis and last-mile-delivery sUAS dominating the skies of cities in the near future. While fixed wing and rotary wing aircraft regularly operate over populated areas, the envisioned orders-of-magnitude increase in air traffic increases the risk to those on the ground and in the air. The risk calculus is also altered by the novel designs of some eVTOL aircraft. Many designs have neither significant autorotation nor low-speed-gliding capability to land safely in the event of catastrophic power failure. Ballistic parachute systems (ballistic recovery systems), such as those found in increasing use on general aviation aircraft and small UAS (drones) provide some risk mitigation, but provide no control over the landing location; the aircraft will land wherever the wind blows it. Aviation safety experts have noted that while ballistic recovery systems improve safety and should be included on all UAM aircraft, there are still hazards from a vehicle descending uncontrolled under a parachute. This paper covers the analysis and design of a guided emergency recovery system, which uses bleed-air control and a gliding steerable parachute. The analysis shows that due to the use of a parachute which provides lift, rather than a pure drag device, and the use of lightweight bleed-air control, the overall weight of a guided recovery system can be lower than an equivalent ballistic recovery system. A key feature for an effective guided recovery system is selection of its landing point. The development of a massively parallel probabilistic evaluation method for selecting landing points which provide the best likelihood of avoiding hazards is shown with examples. Simulations of EGRES in New York City Urban Air Mobility, UAS interstate highway inspection, and UAS nuclear power plant inspection scenarios showed that EGRES increased the likelihood of landing in an acceptable area by 2.3, 1.8, and 2.9 times respectively, compared with a ballistic parachute recovery system. Finally, a preliminary design for a Group 2 UAS is presented, along with size and weight estimates.

There is a frequent need to cut lines or rigging on command in airdrop applications, and this is typically done with pyrotechnically driven cut knives. The use of hot wire cutters offers a simple, quiet, low-cost, low-weight alternative. This work provides an explanation of the principals behind hot wire cutters, outlines the design of an example hot-wire cutter system, provides results from experimental testing of this system on a variety of materials typically used in cargo airdrop, and shows results of the use of the system in small-scale airdrop testing. A simple, battery powered, small device was developed which can rapidly cut a wide variety of synthetic ropes including those made from nylon, polyester, Spectra, Dyneema, Vectran, and Kevlar. This device can be used to de-rig payloads from airdrop platforms, detach main parachutes from payloads after landing, and de-reef parachutes.

Guided airdrop systems offer the ability to deliver payloads with accuracy and with a high payload to air vehicle weight fraction. Traditionally, these systems use airborne guidance units with trailing edge control to steer ram-air parafoils in the same manner as a human pilot. Trailing edge control only provides lateral (turn rate) and limited airspeed control. Earthly Dynamics, LLC developed an in-canopy precision guided aerial delivery system that offers both lateral steering and longitudinal glide slope control of a ram-air parafoil. This paper will present the feasible mission CONOPS for this technology as a cargo delivery, spacecraft recovery, or personnel autopilot system. This work then details the flight-proven hardware and software architecture implemented in a 116 ft$^2$ ram-air parachute. Scalability of the design up to 2400 lb payloads is presented. Data and configuration for multiple flight test demonstrations as a cargo airdrop system and a spacecraft recovery system are provided. Finally, this paper concludes with future applications and development plans for this technology.

Impact attenuation is a critical component of cargo airdrop systems, ensuring payload survivability while allowing practical impact speeds. Cardboard honeycomb is the standard material used for this purpose, but this material is far too stiff to function well on small (5 – 50) lb payloads. This work describes an effort to investigate alternative impact attenuation options for small, lightweight payloads. A purpose-built impact test rig was constructed to facilitate rapid testing and enable repeatable impacts at various combinations of horizontal and vertical impact speeds. A computer vision system was developed to track the payloads as they impact to measure actual impact speeds, and custom sensors were used to measure impact accelerations. A variety of different impact attenuation materials were tested using the test rig and instrumentation systems and the results of these experiments are reported.

Articulating landing gear that use closed-loop feedback control are proven to expand the landing capabilities of rotorcraft on sloped and rough terrain. These systems are commonly referred to as robotic landing gear (RLG). Modern RLG systems have limitations for landing on dynamic platforms because their controllers do not incorporate fuselage roll and roll rate feedback. This work presents a proven crashworthy cable-driven RLG system for the commercial S-100 Camcopter that expands static landing zone limits by a factor of three and enables dynamic platform landings in rough sea state (SS) conditions. A new roll and foot-force feedback fused control algorithm is developed to enable ship deck landings of an RLG equipped S-100 without the need for deck lock or advanced vision-based landing systems. Multibody dynamic simulations of the aircraft, landing gear, and new control system show the benefits of this combined roll and force feedback approach. Results include experimental dynamic landings on platforms rolling under sinusoidal motion and simulated SS conditions. The experiments demonstrate, in a limited fashion, the usability of the RLG through ground experimentation, and the results are compared to simulations. Additional simulations of landings of the S-100 with rigid and active landing gear with more challenging landing conditions than experimentally tested are presented. Such results aid in understanding how RLG with this new roll and contact force fused controller prevent dynamic rollover.

Robotic landing gear enhances the landing capabilities of vertical take-off and landing aircraft on sloped, rough, and even moving landing surfaces. This research demonstrates the integration and systematic testing of a robotic landing gear system for the commercial S-100 Camcopter, expanding the aircraft’s landing capabilities to currently inaccessible terrains with slopes at and above 15°. An overview of the mechanical design, sensors, and controller as integrated into the S-100 rotorcraft is provided along with expected landing performance from simulations tools. The system is then demonstrated using ground and flight experiments, and performance metrics are found to match design metrics. An asymmetry in left and right leg landings during flight testing is observed and analyzed. Lastly, cross-coupling of pitch and roll rates induced by the rotor is discussed as a cause of the asymmetry on this three-legged rotorcraft.

In this work a novel crashworthy cable-driven four-bar link mechanism is designed, manufactured, and tested for the development of robotic landing gear for rotorcraft. The paper will demonstrate how combining two such mechanisms through a common driving cable leads to unique advantages in the kinematics of the system and reduced loads applied to the actuators driving the system. The results on the kinematics and static force distributions are presented for such a configuration and show that, for the rotorcraft class under consideration (220-440 lb, 100-200 kg), the leg mechanism can conform to ground slopes up to similar to 20 deg. A novel design, manufacturing, and a drop testing workflow that allows for rapid design and iteration of robotic landing gear are further developed. The workflow includes the design, simulation, rapid manufacturing, and crash-survivability testing through drop testing with a two week turnaround time for a full design iteration. With regard to rapid manufacturing, this work demonstrates the use of three-dimensionally printed acrylonitrile butadiene styrene mandrels for the production of fully functional carbon fiber polymer reinforced components. This paper concludes with actuation experiments to show practical performance capabilities of the final crashworthy robotic landing gear system designed.

Ground contact and force detection sensors are of critical technical importance in the realization of articulated robots capable of navigating unknown or challenging terrains. Current force sensors for robotic ground contact have limitations, including being too heavy, vulnerability to inertial noise, and lacking robustness and redundancy against failure. In this paper, we present the design, laboratory testing, and flight testing of' a novel force sensor which addresses the aforementioned difficulties. The force sensor presented here is based on a custom elastomer dome with an engineered air cavity adhered to a barometric pressure sensor. Uniquely, we may tailor the sensitivity and range of the sensor by engineering the elastomer shape and the air cavity within it. Further, the large deformations incurred by the sensor are exploited to design a sensor enclosure which transfers large loads to structural members rather than onto the force sensor itself. An experimentally validated finite element model is developed to numerically predict the response of the sensor under an applied load. The model is used to perform trade studies on the geometry and material properties of the elastomer dome with a focus on developing design rules for this new type of sensor. With these simple design rules and finite element model, we design, manufacture, and test these new sensors as individuals and within arrays specifically for use on a rotorcraft robotic landing gear.