Solutions to Helicopter Blade Erosion Improving Aircraft Availability and Reducing Costs (Safety)
Helicopters engaged in operations conduct a large number of take-offs and landings in “brownout” conditions.
Brownout is a result of surface particles such as dust and sand being stirred up by the downwash from the helicopters rotor blades; causing a cloud which can completely envelop the platform. Flight in these conditions impacts operational effectiveness in several ways including:
• Loss of aircrew spatial awareness when landing which can lead to uncontrolled impacts with the ground;
• Damage to the helicopter from erosion, particularly the engines and rotor blades;
• Scintillation from particle impacts with the rotor blades that creates a light source and reduces effectiveness of night vision devices.
Considerable work has been undertaken in order to develop technological solutions to permit safe operation of the helicopter in brownout conditions, this is continuing with the goal of fielding a robust and affordable solution at the earliest opportunity. Studies also continue to identify enhanced filtration and intake particle separation techniques to provide a higher level of protection to the engines than that previously attainable.
The Materials and Structures Technologies: Science & Technology Centre (MAST STC) sponsored a study with AgustaWestland to quantify the impact of blade erosion damage on helicopter operational availability, to identify mitigations and to propose appropriate short-term solutions for use on the UK battlefield helicopter fleet. If left unprotected the life of a rotor blade in dusty conditions is very short, perhaps no more than 100 hours. Replacement of damaged metallic erosion shields can in general take six months and can only be accomplished in a factory environment and requires several hundred man hours.
Protection technologies have been identified, that can be applied to rotor blades which largely mitigate blade erosion; these are:
These can be effective as long as they are subject to regular inspection and re-application but provide limited protection from impacts from larger sand particles and stones, as they have little or no energy absorbing capability.
These are widely deployed and provide a high level of protection from erosion and scintillation providing they are correctly applied and well maintained. Some of the tapes currently in service do not perform well in precipitation and have been known to break up under these conditions.
These have the potential to provide long operational life with low maintenance, although none are currently available that are able to permanently withstand sand and rain erosion. They require very specialised application and can also be difficult to remove – particularly from composite blades – when damaged and requiring replacement.
All current solutions have pros and cons – none of them are perfect; the study has weighed these up and concluded that blade tape that is maintained effectively is the most cost effective solution for helicopters in service today. This is currently widely exploited across a number of platform types. Application of blade tape can be accomplished in one day at a small fraction of the cost of replacing a metallic erosion shield.
Research continues to explore potential coating technologies that offer significant benefits over existing mitigation measures. A facility to allow assessment of these technologies under representative sand erosion conditions has been established and will support the development of a low maintenance solution in the long term.
Written By: Pat Collins