Architecture for a Light Helicopter HUMS
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DESCRIPTIONHealth and Usage Monitoring Systems (HUMS) have been shown to reduce maintenance cost while increasing availability, improving operational reliability, and enhancing safety. HUMS has been mandated in the United Kingdom on large civil transport helicopter, it was introduced as standard equipment on the Sikorsky S-92 aircraft, it is fitted on the Armys fleet of BLACKHAWK and Apache helicopters, as well as a significant number of Navy helicopters. Despite this success, HUMS is not standard equipment on lighter helicopters and has been largely ignored as a viable retrofit option.It is commonly understood that widespread adoption of HUMS has been hampered by the incremental weight and cost of the systems. The vast majority of light helicopter owners cannot overcome the entry level weight and cost issues to take advantage of the operational and enhanced safety benefits. This paper explores a HUMS architecture that addresses the barriers to the introduction of HUMS in lighter helicopters, specifically: the reduction in hardware and installation time, the reduction in weight, and the reduction in the level of technical support (e.g. the cost of implementing a HUMS, such as threshold setting, information technology infrastructure, training) while maintaining the vast majority of HUMS functions that are currently available in current HUMS equipped fleets.
<p>Architecture for a Light Helicopter HUMSEric BechhoeferNRG Systems 110 Riggs Rd Hinesburg, VT 05461</p> <p>Mike AugustinIVHM Inc 6205 Glengarry CT, Ft. Worth, TX 76180</p> <p>Michael KingsleySikorsky Aircraft Corporation 6900 Main Street Stratford, CT 06615</p> <p>AbstractHealth and Usage Monitoring Systems (HUMS) have been shown to reduce maintenance cost while increasing availability, improving operational reliability, and enhancing safety. HUMS has been mandated in the United Kingdom on large civil transport helicopter, it was introduced as standard equipment on the Sikorsky S-92 aircraft, it is fitted on the Armys fleet of BLACKHAWK and Apache helicopters, as well as a significant number of Navy helicopters. Despite this success, HUMS is not standard equipment on lighter helicopters and has been largely ignored as a viable retrofit option. It is commonly understood that widespread adoption of HUMS has been hampered by the incremental weight and cost of the systems. The vast majority of light helicopter owners cannot overcome the entry level weight and cost issues to take advantage of the operational and enhanced safety benefits. This paper explores a HUMS architecture that addresses the barriers to the introduction of HUMS in lighter helicopters, specifically: the reduction in hardware and installation time, the reduction in weight, and the reduction in the level of technical support (e.g. the cost of implementing a HUMS, such as threshold setting, information technology infrastructure, training) while maintaining the vast majority of HUMS functions that are currently available in current HUMS equipped fleets. Keywords-Health and Usage Monitoring Systems (HUMS); MEMS; Cloud Based Computing; bused sensor systems; smart sensors</p> <p>Current generation systems utilize similar architectures with respect to the installation of analog sensors and point to point wiring necessitated by todays existing technology. The intent of this paper is to review a new framework developed to provide a better value to potential users, especially to those with a few or even a single light helicopter in their fleet. A networked architecture has been developed supporting the application configurable smart sensors in a digital bussed architecture. This new architecture along with innovative packaging, improved algorithms/processing, and simplified system operation has the potential to bring about significant improvements in installed cost and weight, return on investments, and total life cycle cost. The aircraft system and software configuration can be automatically maintained through the systems Cloud based architecture. In addition, the cloud based system allows easy access to the data and the ability to leverage the results from other aircraft of the same type/model without exposure to the loss of proprietary information. The first production lot of the Sensor Processing Modules has been produced and the system installed on a large gearbox used in a wind energy installation. A discussion of the requirements and design considerations is included as well as a review of the data captured recently in this operational system. A helicopter system configuration is outline, addressing the most significant HUMS benefits II. THE BUSINESS CASE FOR MONITORING</p> <p>I.</p> <p>INTRODUCTION</p> <p>The weight, cost, installation times, and in many cases the technical support costs of airborne monitoring systems supporting Health and Usage Monitoring System (HUMS) or Condition Based Maintenance (CBM) have been limited to those cases required by the regulatory agencies or justified by large fleet operations. In general the installation of the systems has also been easier to defend on larger helicopter types due to the current system cost and weight issues. For example the lightest of the helicopter vibration monitoring systems today have an installed weight of 20 or more pounds, with some weighing in at 2 to 3 times higher when including the wiring harness. The systems have been installed to provide enhanced safety and/or economic benefits. The US Army, as an example, is using the systems to derive lifecycle cost benefits such as CBM. Implementation of the systems on light and medium helicopters (aircraft weighing from 4,000 to 8,000 lbs), especially individual fleets of a few aircraft, or even a single aircraft has been limited.</p> <p>Despite the proven benefit of Health and Usage Management systems (see ,, and ), there have been relatively few deployments of systems in commercial or general aviation. Few original equipment manufacturers have offered HUMS as standard equipment for their light or even medium sized helicopters. While there are a number of aftermarket installations, the total deployed HUMS base is small compared to the number of potential installations. The explanation for this low penetration of HUMS into medium and light helicopter market is that owners/operators cannot make the business case: the cost and weight of installing a HUMS has too much impact on their existing margins and future cash flow, potentially the weight increase alone could eliminate the use of a passenger seat. This issues and other where highlighted in . In order to achieve widespread use of HUMS in the helicopter community, both the cost and weight of HUMS must be lowered. Based on these assumptions, a</p> <p>system architecture was developed with the goal of lowering cost and weight while offering primary functionality that the helicopter community has come to expect in HUMS. Incorporating new technologies into the HUMS design that were not available even a few years ago has provided the opportunity for the reduction of cost and weight. As an example, the advent of 5th generation Microelectronic Machines Systems (MEMS) facilitates new ways to think about a HUMS system. For instance, MEMS strap-down inertial measurement units (INU) are less expensive than the cost associated with interfacing with an existing aircraft attitude, heading, reference system (cost such as customizing the software interface, adding a junction box, addition supplemental type certificate requirements, etc). In addition to the reduced cost, there is a weight savings because of the greatly reduced harnessing/junction box, connectors, etc. Other costs borne by the consumer include an aspect of the system called knowledge creation. The concept encompasses the processes required to make actionable decisions based on the HUMS data. This includes: Information technology infrastructure to host and display data, Threshold setting for mechanical diagnostics, Rotor Track and Balance configuration/coefficient development Definition of exceedance parameters, and Training of users and incorporation of HUMS into the maintenance organization/validation during the controlled service introduction. </p> <p>o o o o o o o o</p> <p>Engine (Gas Generator), and the Engine to Main Gearbox input shaft(s) Main Gearbox (Gears, Shafts, and Bearings). Accessory Gearbox Tail Rotor Drive Shaft Intermediate and Tail Rotor Gearboxes Oil Cooler/NOTAR Circulation Control Fan Main Rotor (RTB, swashplate bearing wear indicators) Tail Rotor (RTB, swashplate bearing wear indicators)</p> <p>In addition, CAP753 gives guidance on the required analyses. Specifically, the HUMS should: Process gear tooth indicators, which are capable of detecting gear tooth damage and tooth bending fatigue cracks, Modulation of web tone, indicators which are capable of detecting gear web fatigue cracks and loss of gear support, Indicators capable of monitoring planet gear load sharing and detecting planet carrier damage in the epicyclic gears and that recording of raw data has significant value.</p> <p>Given the desire for lower cost and lighter weight, the system must be designed against a set of functional requirements. The ultimate goal is to design a system where the incremental cost/weight of each added function is small while the user/operator benefit is large. This philosophy defines what the functions HUMS will support. III. SUPPORTED HUMS FUCNTIONALITY</p> <p>While the CAP753 suggests notional HUMS functionality, there are two additional functions, which for little marginal cost give acknowledged benefit to the owner/operator: Exceedance Monitoring and Flight Operations Quality Assurance (FOQA). Exceedance Monitoring identifies, when, and for how long, a parameter threshold defined in the aircraft operations manual is exceeded. Nominally, the pilot is responsible for monitoring exceedances, but HUMS can automate the process and can give a more reliable, accurate and quantitative values for the exceedance. For example, an automated measure of an over torque can greatly simplify maintenance because there is no question as to how long and high the over torque condition existed. Other examples of exeedances include: over speeds, angle of bank/attack/flight envelops, hard landings, etc. Exceedance monitoring also provides asset protection via the monitoring of leased vehicles. Because exceedance monitoring is, in its essence, a pattern recognition problem, the function can also automate the yellow sheet process (e.g flight time reporting requirements such as OPNAV3710/4). The exceedance monitoring algorithm can identify engine starts, taxi/flight condition, and as such, record flight time, rotor turn time, and number of takeoffs/landing. Whereas sensors for RTB and MD must be added to the aircraft, sensors for exceedance monitoring are usually already present (e.g. via signals to the cockpit instruments) in the aircraft. Unfortunately, interfacing to these sensors from a hardware perspective can be complex, adding large recurring cost for each installation and non-recurring engineering cost for each new platform that the HUMS is installed on.</p> <p>A. Maximizing Benefits to Users The functionality supported by HUMS is a balance between cost, weight, and customers needs. While there are no formal requirements for HUMS, the CAP753 (Helicopter Vibration Health Monitoring, ) gives guidance for operators on what capabilities a HUMS should support. The functionality called forth in the CAP753 is primarily concerned with Rotor Track and Balance (RTB) and Mechanical Diagnostics (MD). The document also highlights: The need to acquire and process data in certain flight regimes, That for flights greater than 30 minutes in stabilized conditions, a data set for all components should be automatically collected The monitored components should include:</p> <p>For an analog cockpit, it requires, in addition to a number of discrete inputs, a large number of analog-to-digital converters channels. Further, it may require adding a junction box, which adds weight and cost for the installation (not to mention the costs for drawings, harnessing, etc). For a digital cockpit, while the hardware interface may be easier (e.g. Ethernet or RS-485 based data bus), the software configuration/customization could add considerable nonrecurring costs. FOQA and flight data monitoring (FDM) are fundamentally safety programs that are designed to make commercial aviation safer by providing pilot feedback and training when required regarding operational risk issues . The goal of FOQA is to identify and reduce or eliminate safety risks, as well as to minimize deviation from its regulation, through targeted training. A HUMS capability affords a relatively simple way to acquire aircraft data, since most of this type of data is needed by the exceedance monitoring function. By adding the necessary data logging provisions to HUMS, the owner/operation is provided metrics to train and improve the proficiency of its pilots. The engineering issue for both exceedance monitoring and FOQA are how to add this functionality without the recurring and non-recurring engineering cost associated with hardware and software interfaces with existing aircraft systems. While the four-listed functions do not encompass all possible capabilities of HUMS, it is felt that these functions are of considerable value to an owner/operator. Like any engineering problem, the delivered capability of a light weight/lower cost HUMS will be a balance of functions vs. costs. IV. TECHNOLOGY ADVANCEMENT TO LOWER COST AND WEIGHT</p> <p>Swashplate Bearing Monitor Copilot Uni-axial Accelerometer, RTB Pilot Bi-Axial Accelerometer, RTB (e.g. two channels) For the exceedance monitoring and FOQA functionality, a typical system  would interface into: Altitude and Head Reference System (AHRS) for attitude information Vertical/Lateral Body Accelerometer Altitude and Airspeed Torque (or total engine torque) and TGT Radar Altimeter/Weight on Wheels</p> <p>For a the notional light or medium helicopter, the mechanical diagnostics and RTB functionality would require 16 separate twisted pair runs throughout the aircraft. The exceedance monitoring and FOQA functions would require extensive wiring and interfacing with existing cockpit display (note that for many older aircraft or aircraft with analog cockpits, altitude and airspeed might be pneumatic. Additionally, some aircraft may not actually have some of the inputs needed to support.</p> <p>It has been noted that there has been relatively little penetration of HUMS in the light or medium helicopter market. This could describe aircraft typically weighing from 4,000 to 8,000 lbs. Given the desired HUMS functionality, and this target market, one can notionally define the sensor inputs needed. For a typical HUMS installation on this class of helicopter (Figure 1.) the vibration sensors needed to support the guidance of the CAP753 is: Tail Rotor Radial Tail Rotor Lateral (Used for Tail Rotor Balance and Mechanical Diagnostics) #4 Tail Rotor Drive Shaft Hanger Bearing #3 Tail Rotor Drive Shaft Hanger Bearing #2 Tail Rotor Drive Shaft Hanger Bearing Aft Oil cooler Hanger Bearing Forward Oil Cooler Hanger Bearing Engine Accessory Gear Box Input Gear Shaft Main Case, Port Side Main Case, Starboard Side Main Case, Accessory Drive</p> <p>Figure 1: Typical HUMS Vibration Sensor Location, Medium Helicopter A. Reducing Cost and Weight of HUMS with MEMS MEMS technology can provide a solution strategy to reduce both the cost and weight of HUMS. MEMS technology has been driven by commercial, hand held devices (cameras, smart phones, tablet PCs). This commercial demand has resulted in large supplier base of low cost, light (needs to fit in a cell phone) MEMS accelerometers and MEMS gyros. As an example, the latest (5th) generation of MEMS accelerometers offers performance that in many cases is superior to traditional PZT devices if it is packaged correctly. MEMS accelerometers sense changes in capacitance, based on distance from a reference, instead of charge due to shear. Because of this physically different way to measure acceleration, these devices can measure from DC to 32 KHz. However, since MEMS accelerometers are voltage-loop devices (PZT are current looped and have better electromagnetic noise immunity), they must be packag...</p>
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