Browse Topic: Landing gear
With advanced air mobility (AAM) vehicles becoming an increasingly popular topic in aviation, the Eagle Flight Research Center (EFRC) at Embry-Riddle Aeronautical University continues to investigate control strategies that enhance aircraft resilience to total power unit failures. Utilizing a distributed electric propulsion (DEP) quad-heli test bed, the EFRC has explored a variety of control laws and hardware configurations to evaluate their effectiveness under failure conditions, including sustained flight with a completely inoperative rotor. The aircraft utilizes a fractional-order PID (FOPID) controller that has recently been developed and shown to outperform conventional PID controller used previously in both nominal and failure scenarios. The use of a FOPID controller offers improved stability and tracking performance. Another development is the implementation of a split-rotation rotor configuration—where the left-side rotors rotate clockwise and the right-side rotors rotate counterclockwise—which, when combined with a control law leveraging cyclic rotor inputs for yaw control, provides a robust alternative to conventional quadrotor designs. This configuration leverages the redundancy offered by equipping each of the aircraft's four rotors with full helicopter controls, enhancing the potential for sustained flight in the event of two rotor failures while preserving the maneuverability and controllability characteristic of the conventional configuration. Additionally, to support expanded testing and operational capability, the aircraft has been outfitted with a custom-designed landing gear system, designed and fabricated by the EFRC team.
ABSTRACT
Rotorcraft, like most machines, require periodic lubrication tasks to ensure continued safe and reliable operation. Optimal lubrication intervals are desired to maintain system performance while minimizing aircraft downtime and maintenance labor. Boeing and AMRRI conducted a Lubrication Optimization Study (LOS) on the H-47 Chinook helicopter to establish the necessary engineering artifacts to define the grease lubrication intervals for selected Drive, Rotor, and Landing Gear components. Grease samples were collected from these components by H-47 operators from multiple nations and submitted for a laboratory analysis to characterize how wear, properties and contaminants change as time and aircraft hours accumulate. The LOS also revealed opportunities to further evaluate and leverage the data produced in this study, including determining superior performance of specific lubricants within the Mil-Spec designation, testing of greases for compatibility5 when mixed, and enhancing new grease cleanliness to extend component life.
Robotic landing gear (RLG) enhance the landing capabilities of vertical take-off and landing (VTOL) aircraft on sloped, rough, and even mobile landing surfaces. This DARPA funded research demonstrates the design, integration, and ground and flight testing of a RLG system for the commercial S-100 Camcopter, expanding the aircraft's landing capabilities to currently inaccessible terrains with slopes at and above 15°. Lagrange unconstrained and multibody dynamic simulations are elucidated and implemented to design a force feedback controller, state estimation algorithms, and drivetrain components that permit the rotorcraft fuselage to remain level on rough terrain. 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 as arising due to inertial cross coupling inherent to landing with three-legged rotorcraft. Finally, future work and improved RLG controllers are presented.
A high-fidelity engineering simulation model has been developed in FLIGHTLAB for a Sikorsky production helicopter to support future design modifications. The simulation model consists of major subsystems for main rotor, tail rotor, fuselage, empennage, landing gear, flight control system, and propulsion system. As the manufacturer, Sikorsky was able to provide a complete and validated set of model data and a large database of flight test records to ensure the model quality and fidelity. Although the model correlation with test data is satisfactory in most flight conditions including hover, low-speed flight, level flight, and vertical climb, some model-data discrepancies were seen in the forward climb/descent and autorotation test cases. An additional study was conducted at Sikorsky to investigate these discrepancies. Based on the study, a set of model enhancements were developed to improve the model correlation with test data in forward climb/descent and autorotation. These enhancements allow for adjustment of certain semi-empirical corrections to address model limitations at these challenging conditions such as fuselage characteristics and interference at high angles of attack and rotor inflow and interference at low collective settings and near 90-degree wake skew. These enhancements were carefully designed such that the effects were localized so that the model-data correlation was not adversely impacted in other flight conditions. The model-data correlation in forward climb/descent and autorotation were significantly improved by implementing these model enhancements with little to no impact on the other flight conditions resulting in a high-fidelity engineering simulation model validated in the entire flight envelope.
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