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Survivability Improvements for Transmission Loss-of-Lubrication


OBJECTIVE: Provide innovative technologies that can improve the ability of military vehicle transmissions to withstand operation under loss-of-lubrication conditions, specifically in rotorcraft. Extend the amount of time allowable between the loss of primary lubrication and termination of the mission. Technologies must be applicable to rotorcraft main transmissions, although technologies with applicability to other vehicle transmissions are encouraged. DESCRIPTION: Loss of the primary lubrication system in vehicle power transmission systems can result in an immediate or rapid failure of the drive system due to the degradation of tribological performance in the highly loaded gear contacts and reduced heat transfer. Army rotorcraft are currently required to operate for thirty minutes after the loss of the primary oil system, often requiring the addition of secondary emergency lubrication systems which add complexity and weight. To increase vehicle survivability and extend this period to at least half-mission duration, an improved portfolio of technologies is sought to improve transmission performance after the loss of the primary lubrication system. Technologies to achieve this include, but are not limited to: modified gear materials and/or treatments that can better withstand high temperature starved lubrication, lubricant formulations specifically designed for use after failure of the primary system, and specialized delivery implementations to provide adequate lubrication in gear and bearing contacts. Proposers must offer an innovative approach to assuring transmission performance after loss of oil. Slight modifications to existing or well known solutions are not acceptable. Proposals should describe in detail the candidate technology under consideration for improvement of transmission oil-out performance. The most promising technologies will allow the transmission to operate under any conditions within the normal design envelope rather than restricting flight conditions, provide reliable and predictable performance from the initial oil-off event through the end of the mission, be reasonably insensitive to ambient conditions (temperature and altitude), and be scalable to longer required periods of operation beyond 30 minutes to at least 1-2 hours. Any weight, cost, and complexity penalties associated with the proposed technology must be at least 25% better than current fielded technology. Technologies which allow for controlled damage, such as high wear rates, to occur in the transmission during the oil-loss event are acceptable under this topic provided they can be scaled to at least 1 hour. The proposer should select an approach to this problem that requires development of a novel technology such as those listed above. The successful effort would establish feasibility of the technology for rotorcraft transmissions and determine appropriate performance metrics for evaluation. The technology will be demonstrated in a successful Phase II effort and have a clear commercialization strategy providing a pathway toward adoption in military helicopters. PHASE I: Explore the feasibility of the proposed technology for use in a rotorcraft transmission environment. Investigate issues relevant to integration with typical aviation drive systems and establish operational conditions and evaluation metrics to which the concept would be subjected. Conduct analysis and/or bench-level experiment to validate that the tribological performance of the transmission incorporating the proposed technology would be improved. Focus on aspects of the technology that are innovative and result in a commercial product. In the case of a novel lubricant formulation, for example, examine feasibility for its use in typical helicopter transmission application and develop an evaluation plan to optimize the formulation through performance testing. Proposals for Phase I efforts should clearly explain how the proposed effort can provide a robust and predictable improvement in rotorcraft survivability following loss of the primary lubrication system. Offerors should address how the proposed effort would treat tribological phenomena, heat transfer characteristics, material properties, and system-level interactions. They should also address how the technology will be successfully commercialized through sales, licensing, etc. to helicopter OEMs and beyond. PHASE II: Refine the technology developed in Phase I and validate its feasibility through some combination of subscale experimentation and simulation. Verify Phase I assumptions and required performance to design and execute an appropriate evaluation methodology. Examine the vehicle operational envelope to identify critical flight conditions under which the proposed technology will be most vulnerable. Conduct analysis of relevant rotorcraft-class systems to demonstrate that the concept will provide increased vehicle survivability by improving transmission oil-off performance. Determine reasonable endurance estimates for the proposed technology, in terms of aircraft mission endurance after the oil-loss event. Determine limiting physical mechanisms by which the transmission will ultimately cease to function under this operational mode. Identify performance and/or durability tradeoffs resulting from adoption of the proposed technology, including design compromises that may be made. In the example of a technology allowing the transmission to run completely or nearly dry, establish experimental protocols which simulate the high power density and low heat capacity of rotorcraft transmissions to simulate the resulting high temperature. Examine wear and durability aspects of this extreme environment, as well as robustness and tolerance to transient and aggressive flight conditions. Establish estimates of usable life based on the range of expected wear rates. Determine fabrication/production issues and pathways to airworthiness certification. PHASE III: Applications for the technology primarily include powerplant and drive systems for aerospace vehicles. Both commercial and military rotorcraft are clear benefactors of these technologies, as are other aviation propulsion systems such as turboprops and geared fans. Some proposed technologies may also be relevant to wind turbine gearboxes and other industrial power generation equipment. In the example of improved gear materials or coatings/treatments, high performance and specialty transmissions would also benefit from these improved material systems through operation under more severe conditions and at higher power densities. High value mechanical systems might incorporate these material systems to provide additional performance margin. REFERENCES: 1. Handschuh, R., Polly, J., and Morales, W.,"Gear Mesh Loss-of-Lubrication Experiments and Analytical Simulation,"NASA Technical Memorandum 2011-217106, National Aeronautics and Space Administration, November 2011. 2. ADS-50-PRF,"Aeronautical Design Standard, Rotorcraft Propulsion Performance and Qualification Requirements and Guidelines,"U.S. Army Aviation Troop Command, April 1996. 3. Krantz, T. and Kahraman, A.,"An Experimental Investigation of the Influence of the Lubricant Viscosity and Additives on Gear Wear,"NASA/TM2005-213956, ARLTR3126, October 2005.
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