Browse Topic: Bearings
A typical helicopter drive system consists of a multi-stage gearbox with highly loaded dynamic components such as gears, shafts, and bearings, crucial for safe flight and landing. Planetary reduction stages are commonly used in the final reduction stage of rotorcraft main gearboxes due to their ability to handle high torques at high gear ratios within a compact envelope. The planet gear, a critical component in this arrangement, is subjected to significant loads on both flanks of its teeth and must meet stringent weight and assembly requirements, leading to a thin rim design with integrated bearing races. This design makes the planet gear susceptible to relevant reduction of its fatigue life. This paper explores analysis methods to evaluate the damage resistance of the planetary stage assembly, focusing on the planet gear. The study aims to assess the "growth" or "no growth" condition of the planet gear against defined flaw defects. An iterative calculation loop determines the critical
Bench-level tribological experiments were utilized to evaluate material, coating, and lubricant formulation effects on the loss-of-lubricant survivability of tapered roller end and cone rib contacts. Cone rib and roller end contacts were simulated using a single rotating roller and rotating flat disk. The applied load and rotational speeds of the roller and disk were controlled to simulate representative rotorcraft gearbox bearing operating conditions. The contacts were lubricated for an initial period before the lubricant supply was shut off, and the supply tube was then removed. Tests continued to run, without additional oil, until the measured friction force reached a predetermined cutoff value. Weibull-based statistical analysis was used to compare the loss-of-lubrication runtimes.
This paper presents experimental research aimed at developing novel low lubrication methods for rotorcraft and jet engines, focusing on sustaining minimal lubrication to prevent catastrophic bearing failure during loss of lubrication (LoL) events or to increase fuel consumption performance on once-through, fuel-oil bearing lubrication engines. Utilizing two high-speed bearing test rigs simulating low and high thrust class engine conditions, the study establishes lower bounds for oil flow rates necessary to maintain thermal stability and prevent thermal runaway in hybrid ball bearings. These findings inform the design of the Zulu Pod (ZPod), a passively driven, self-contained oil delivery system that uses engine compressor bleed air to precisely meter lubricant flow. Engine test stand results demonstrate that replacing traditional fuel-oil lubrication with the ZPod system reduces thrust specific fuel consumption (TSFC) by an average of 7%, with up to 11% savings, without compromising
The paper describes a method for optimal design of a helicopter tail shaft that considers rotordynamic effects from long shaft assembly. The tail shaft transmits power from the main gearbox (MGB) to the tail rotor of the helicopter and operates at high speeds that may exceed 6000 rpm. While higher speeds allow for weight reduction, they also pose risks associated with supercritical operation, necessitating careful design optimization. The objective of the optimization is to maximize the first three transverse natural frequencies with the constraint of the safety parameter (avoidance of the resonance/critical zone) while minimizing the weight of the system. A Non-Dominated Sorting Genetic Algorithm (NSGA-II) is used to obtain the solution to this multiobjective optimization problem, which involves shaft design variables such as length, outer diameter, and wall thickness. In addition, the optimization framework also incorporates system related design variables, including the stiffness of
The Main Gearbox of a helicopter is a crucial component that delivers the desired performance and ensures the highest possible level of safety of the aircraft; it includes several gears and bearings, which require to be continuously lubricated by a pressurized oil flow. Undesired circumstances may cause the oil to leak from the main circuit, hence reducing its pressure and consequently the oil flow rate targeted towards the rotating components; this modifies their friction coefficient, and subsequently leads to an overheating of the parts with the risk of degenerating in a catastrophic failure. During the design of a helicopter drive system, engineers need to take proper precautions and make sure that the MGB is fully equipped with the proper features to cope with a loss of lubrication event; specifically, the drive system is supposed to be able to run at least 30 minutes after the oil pressure drops to zero. A lot of effort has been put over the years at Leonardo Helicopters to find
Wear debris monitoring and analysis is a common practice for the condition assessment of engine and transmission health. Oil debris monitoring (ODM) and electronic chip detectors (ECD) are two common methods deployed for continuous monitoring of oil wetted component health in-flight. This study evaluates the diagnostic performance of the two sensing technologies within controlled rolling element bearing (REB) fault experiments. Progressive visual inspection of the REB spall progression through failure provided a ground truth against which both systems could be compared. Quantifiable metrics of reliability, diagnostic accuracy, provided maintenance interval were defined to create a framework for condition-based maintenance (CBM) program decision making. In summary, it was found that the ODM sensor system provided earlier fault notice, but more so, vastly outperformed the ECD in reliability and avoidance of false positives.
Over 4 decades of research works on the nutating, now pericyclic, mechanical transmission have studied its capability to achieve high power density, low noise, and amplified single-stage reduction ratios of up to 100:1. These analytical efforts have culminated into the fabrication of a 50 HP and 32:1 reduction ratio pericyclic transmission prototype. This work introduces the prototype with highlights of the assembly and alignment procedures validated by static testing evaluation. Then, discussion of the dynamic test stand integration, instrumentation, and lubrication components lay out the framework of the high-speed testing plan. Power transmission data validated the pericyclic reduction ratio model. Accelerometer data demonstrated the transmission's capability to operate at low vibration, with peak amplitudes of 1.2 and 2.5 inches per second on the pericyclic gear train and output shaft respectively. Acoustic emission data captured the first 5 harmonics of the shaft speed as well as
The succession of the BK117 D-2 main rotor concept from the semi-rigid rotor to the BK117 D-3 bearingless main rotor (BMR) system, derived from the H135, held many new and innovative additional benefits in its wake. Although the H135 system is the best on the market regarding maintenance effort and maintenace cost (DMC), it was the purpose to push this benchmark even further. To achive additional benefits, three major improvements needed to be successfully implemented and none of them was a given. First to mention is the concept of the blade being separated in three parts. In case of foreign object damage (FOD), most of the time only the outer part needs to be repaired. In parallel a new possibility to fold the system with a full folding capacity was introduced with the challenge to realize the extremely low DMCs of the H135, in a decisively bigger helicopter and to benefit from the experience of millions of flight hours and thousands of helicopters operated throughout the world
Rolling element bearing failures form one of rotating equipment's most critical failure modes. Vibration analysis has been successfully used for bearing fault detection and diagnostics but does not estimate the spall length of the bearing. An estimate of the spall length would provide insight into the degrading reliability of a drivetrain as the fault propagates. This would improve the timeliness of scheduling a maintenance action. In this paper, a synthetic tachometer signal is generated from the bearing fault itself. It is synchronous to the rolling element, allowing for a time-domain representation of waveform using the time-synchronous average. From this, an estimate of the length of the bearing fault can be determined.
ABSTRACT
ABSTRACT
ABSTRACT
Items per page:
50
1 – 50 of 1216