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Technology to Support Non-destructive Inspection of Helicopter Sling Load (HSL) Slings and Textiles


OBJECTIVE: Develop a technology to non-destructively inspect and test helicopter sling load slings to standards in TM 4-48.09 and FM 3-55.93 DESCRIPTION: Helicopter slings are textiles used to attach a payload (e.g. a truck, howitzer, or container) to the underbody of a military helicopter. This"external underslung payload"is then transported from one location to another. Helicopter slings come in two strengths and sizes. The 2,500 lb capacity sling (NSN for full sling set: 1670-01-027-2902) has a 7/8"outside diameter and is twelve feet long. The 6,250 lb capacity sling (NSN for full sling set: 1670-01-027-2900) has a 1 1/4"outside diameter and is twelve feet long. Each sling leg consists of a nylon rope made from double-braided nylon rope with an eye splice at each end. The outer braid is covered with a vinyl coating. Helicopter slings are exposed to harsh environmental conditions. They are dragged over sand, dirt and cement. They"re exposed to blowing sand and debris under a helicopter during payload hookup and forward flight. The slings can also be sprayed with or submerged in salt water. The salt crystals, upon drying, act as sand as any other foreign particle would and weaken the sling from the inside out. Slings can also be subject to vibrations during flight. There is also UV degradation and decay over time. Manuals TM 4-48.09 and FM 3-55.93 have specific inspection criteria that each helicopter sling load (HSL) component must meet in order to be deemed safe for use. Recent deployments have demonstrated the susceptibility of damage to textile ropes, slings and pendants due to sand penetration in desert environments. During storage, transport and usage, sand has been shown to work its way into the core, strength-bearing fibers of textile slings where the sand can cause microscopic damage to these fibers. This damage leads to reduced strength and safety. The current inspection practices are acceptable for metallic components; however these inspection techniques cannot accurately determine the disposition of the internal fibers of the ropes. Since the current inspection process for ropes, slings and pendants is subjective, it produces different results with different inspectors. In most cases the equipment is removed from service prior to reaching the minimum breaking strength of the double braided rope. This means that the inspection process is generating a false positive result for unserviceable equipment. In other cases the slings break in flight leading to the loss of payload and possible loss of life. About seven years ago, tests were conducted on HSL sling legs in an effort to correlate rope break strength to the visual inspection. The test results were inconclusive as the breaking strengths did not correlate to the external condition of the sling. A visual inspection can only verify the surface conditions while the primary load bearing element is within the sling and not visible. This SBIR proposes to use methods, such as but not limited to electro textiles, sling barrier coats, and/or low stretch fibers to indicate overload conditions that could alert the inspector to significant strength loss, etc., to allow for non-destructive testing and data gathering during testing. This would transform the current subjective inspection process into something quantifiable, significantly advancing the state of the art. This technology, when developed, could be embedded into the Special Patrol Insertion/Extraction System (SPIES), Fast Rope Insertion/Extraction System (FRIES), Helicopter Sling Load (HSL) equipment and climbing/ rappelling ropes. In the cases where personnel are attached to these ropes, the enhanced inspection techniques would also provide a safety improvement. The most successful proposal will present a technology end state of"go/no-go"for a sling based on the proof load values in Table IV drawing 38850-00009"Rope Assy. Sling"(attached) regardless of the type of damage (fiber breakage, UV degradation, chemicals, etc.). This most successful proposal would determine the overall health of the entire sling with reference to the proof load values. While the entire length of the sling must be examined, the areas approximately one inch beneath each eye splice (end of splice taper) are the most likely candidates for damage. The device that will measure/determine the sling health should be portable, use DoD-approved batteries, and have an option for AC and DC power inputs. PHASE I: Develop innovative theoretical approaches to determine and display current break strength of a textile sling or rope without destroying it. Develop an initial concept design and model key elements. Define and develop key component technological milestones. Phase I deliverables include a report detailing theoretical approaches to the research, an initial concept design and modeling key elements, key component technological milestones, a first order prototype design, and a recommended path forward. PHASE II: Design, construct and demonstrate the operation of a prototype that can accurately and non-destructively determine and display the strength of a sling or other textile. Validate accuracy of prototype. Conduct life cycle and environmental testing of prototype. Phase II deliverables include the physical prototype(s) produced, the prototype design (CAD files, technical drawings), and a report detailing Phase II work and a recommended path forward. PHASE III: Refine and improve Phase II prototype design to be more user friendly and size/cost efficient. Manufacture at least one of the refined/improved prototypes. Conduct user evaluations in the field. Write training/operator manual. One specific military application would be to use this prototype for HSL sling inspections prior to a mission. The most likely path for transition to operational capability, in the absence of a formal requirements document, would be for an air assault unit to formally request the ability to non-destructively test/inspect their slings. Potential commercial applications could include helicopter sling load but would most likely center around inspection of crane slings or climbing ropes. PHASE III DUAL-USE APPLICATIONS: Military and civilians using any kind of textile, especially a sheathed one like a sling, are under the same subjective inspection restrictions. An objective strength inspection without pull testing is not currently possible. Therefore, any product that is produced through this SBIR work would be viable in both military and commercial applications (crane slings and rock climbing rope).
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