POWERPLANT
CS-LURS V.1.0
A reliability program should be provided in order to demonstrate that the product ( engine and powerplant installation ) can ensure a safe operation between the proposed normal inspections or overhauls.
The reliability program should be based on the evidence resulting from the endurance test required by B.LURS.47, the vibration evaluation requested by the AMC for B.LURS.33 and the safety assessment and enhanced design review requested by the AMC for B.LURS.27.
Procedures for in service monitoring ( such as installation of sensors that provide information on the integrity of the in-service engine/powerplant components ) are also recommended in order to support this reliability program
AMC LURS.901(c) Installation
The instructions for installing the engine referred to in CS LURS.901(c)(1) are those required under CS E 20(d) or B.LURS.3.
AMC LURS.903 (a) Engine Type Certification
Engines certificated under CS-E are accepted as complying with appendix B.
AMC LURS.907 Vibration
1 Explanation
Section CS VLR.907 is intended to require the design of the rotor drive system, including the engine, to be free from harmful vibration
The mechanical coupling of the engine to the rotor drive system could lead to a rather complex harmonic response, in terms of torsional vibration, adding resonant frequencies to the engine shaft that otherwise would be absent when the engine is operated on a test bench. In this context the phenomena of torque pulse in compression ignition (diesel) engines is particularly damaging.
Torque pulses produced by reciprocating engines can easily aggravate the relationship between engine and driven equipment in terms of torsional vibration and the resonance that can amplify this vibration to destructive levels. The problem of torque pulse is common to all reciprocating engines but is much more pronounced and is a far greater problem with diesel engines. The problems are compounded by the use of lightweight diesel engines of the type finding their way into aviation use. The problem is significant and can result in the failure of crankshafts, spline shafts, couplings, bearings, gears and seals. The consequence of which will be a
premature failure of the engine or the transmission resulting in a loss of drive to the rotor system, which at a minimum will result in an unpremeditated enforced landing
.
The torque pulses introduce harmonic excitation forces that are not part of the smooth torque output of the engine and do not add to usable power output. However, they can range as high as ten times the engine's normal operating torque, so they can add substantially to the total amount of torque transmitted through
CS-LURS V.1.0
the system and to the rate of wear and damage that results from it. Conducting a vibration survey of the powertrain system will determine the natural frequencies of the system components and the frequencies produced by the engine. Then tuning the system to damp out the vibration and shift destructive resonance speeds away from the engine operating RPM range will contain the problem. This is usually achieved by installing a tuned coupling between the engine and the item it is driving. 2. Procedure
a. In order to determine that there are no damaging effects from excessive vibrational stresses for helicopters powered by spark ignition engines a combination of analytical vibration survey and ground and flight-testing can be used to demonstrate compliance with this requirement. In the absence of an analytical vibration survey substantially more extensive ground and flight-testing can be used.
b. For helicopters powered by compression ignition engines care should be taken to minimize the detrimental effects caused by engine torsional vibration (torque pulses) in all components of the engine, rotor and transmission drive systems - including chain and belt drives, transmission systems and rotor hubs. A combination of analytical vibration survey, coupling selection and ground and flight-testing should be used to demonstrate compliance with the requirements.
c. Before the commencement of the ground and flight test programs the components installed to the rotorcraft and intended to be used for the ground and flight test programs should be identified and their condition recorded, including the dimensions of any part liable to be subjected to wear.
d. At the conclusion of the ground and flight test programs the components of the engine, rotor and transmission drive systems including; chain and belt drives, transmission systems and rotor hubs, should be free of excessive and/or abnormal wear, distortion, cracking and other forms of structural damage.
e. If during the course of the ground and flight test programs, it becomes necessary for any reason to replace any part of the engine, rotor and transmission drive systems including; chain and belt drives, transmission systems and rotor hubs, the Agency should be informed and their advice sought on the continuing validity of that test program.
AMC.LURS.963(e) Fuel Tanks General
1. Explanation
The intent of the requirement is to prevent heating of the fuel due to conditions within the helicopter, beyond a temperature that would normally be reached due to thermal soaking as result of external ambient conditions and above which the helicopter would not be operated. These measures are intended to prevent damage to the fuel tanks, fuel system components and surrounding structure and minimize the risk of potential catastrophic explosion of the fuel tanks due to the fuel exceeding its auto-ignition temperature. The main source of heat is considered to be unused fuel being re-circulated back to the fuel tanks by the engine.
CS-VLR recognizes that compression ignition engines will be used in the class of helicopter catered for by the requirements. Modern compression ignition engines may use very high-pressure re-circulating fuel injection systems that supply a constant volume of fuel in excess of the engine’s needs. The excess fuel is returned to the fuel tanks and because of the pressurization process the fuel is hot. The continuously returning fuel progressively heats up the contents of the fuel tank. If means are not taken to control the temperature rise within the stored fuel then the intent of the requirement cannot be met.
CS-LURS V.1.0
In order to meet the intent of the requirement (particularly when re-circulating type engine fuel distribution systems are used) an assessment of fuel heating within the fuel tanks due to conditions within the helicopter should be made under normal operating conditions. In addition, when re-circulating type engine fuel
distribution systems are used, the most adverse conditions liable to be encountered in service should be considered; i.e. high ambient temperatures, low fuel state, engine running at idle speeds for extended periods of time. If the intent of the requirement cannot be met under these conditions then means should be employed to control and limit the temperature rise within the stored fuel
AMC.LURS.999 Fuel system drains
Reserved
AMC LURS.1011(c) Oil System, General
In assessing the reliance that can be placed upon the means for providing the appropriate fuel/oil mixture to the engine to prevent a hazardous condition, account should be taken of, for example -