N211-045 TITLE: Extended Life and Low Maintenance Aircraft Tie Down Fitting
RT&L FOCUS AREA(S): General Warfighting Requirements
TECHNOLOGY AREA(S): Materials / Processes
OBJECTIVE: Develop an extended life, low maintenance, affordable aircraft deck tie down fitting for aircraft carrier applications.
DESCRIPTION: Aircraft securing fittings (commonly refer to as "deck tie-down fittings") as part of flight deck provides an attachment point for onboard aircrafts (i.e., fighter jets, auxiliary planes, helicopters) to prevent movement of aircraft, equipment, or materials due to ship movement and wind. It is essential that the aircraft and equipment be secured in a manner to prevent motion in all directions aboard the ship. Depending on the sea state and weather condition, on average 4 to 12 deck tie-down securing points are used for securing an aircraft. A typical configuration of a deck tie down fitting assembly consists of a crossbar welded onto a fitting cup, which is typically manufactured from heat treatable low alloy steel, and welded onto the flight deck. In aircraft carrier applications, a five-crossbar type tie down fitting is welded directly onto a deck, which is the application of focus under this SBIR topic.
For corrosion protection from marine environment, a coating of military specification grade polyamide epoxy primer is applied on both the crossbar and fitting/deck, post installation; however, due to a constricted access point for paint application and exposure to heavy abrasion during service, the coating is prone to damage. As a result, the corrosion and abrasion of the steel flight deck tie down assembly, especially on the crossbar, has been a persistent issue, leading to severe degradation on ship readiness and increased maintenance burden. A more durable flight deck tie-down fitting needs to be developed for the aircraft carrier application. Durability of the new flight deck tie down fitting must be able to withstand the corrosive marine environment, abrasion and impact from the securing hook and support a significant reduction in maintenance requirements than the current version of the deck tie down fittings to reduce the maintenance burden. The new flight deck tie down fitting must be affordable to support a reduction in total ownership cost during its life cycle. The affordability needs to be addressed both on the material and labor cost front, for the overall economic feasibility.
There are several types of Navy-approved aircraft secure tie down fittings conforming to NAVSEA Drawing 803-1916300 (Hull Standard Drawing Aircraft Securing and Engine Run�Up Fittings). On aircraft carriers, five crossbar fitting Type VIII is installed for providing an additional pull strength for securing aircrafts and equipment aboard the carrier. Type VIII tie down fittings are welded onto the deck, instead of welding onto a fitting cup as previously mentioned. Dimensions and requirements data for deck tie down fittings are covered under the referenced NAVSEA drawing. This NAVSEA drawing is not available on internet on public domain; however, a commercial version of this specific tie down fitting is available through a commercial vendor and their relevant design information [Ref 1]. It is noted that the referenced NAVSEA drawing (803-1916300) supersedes any existing discrepancy on dimensions and design requirements between the two drawings. Replacement of a failed or degraded secure fitting is a significant driver for cost and maintenance burden due to the high number of flight deck tie down fittings installed and the required replacement rate of several hundred tie down fittings for supporting mission operation and readiness.
The Navy is seeking a more durable (e.g., fabricated from a material that is more resistant to corrosion and abrasion than current steel when exposed to seawater and marine environment) deck tie down fitting that would support a form, fit, function replacement of the legacy steel tie down fittings (five crossbar Type VIII version only) on aircraft carriers. This also includes replacement of the two deck lugs installed between the two crossbars for each tie down fitting installed on landing areas of the flight deck with the same corrosion resistance and durable lugs.
The Navy requires tie down fittings that have similar strength as the current fittings (4130 grade steel), are also resistant to corrosion, and wear for a minimum service life of 25 years or more with desirable target of 50 years for supporting entire life cycle of an aircraft carrier. While in service, 100% of the tie down fittings are inspected with a go/no-go gauge per Navy maintenance inspection procedure. The go/no-go gauge is intended to inspect for a reduction in thickness of the crossbar below the required minimum level due to degradation from corrosion and wear/tear while in service.
Dimensions: For this SBIR topic, the only applicable flight deck tie down fitting is five crossbar Type VIII, which is the most common type installed on aircraft carriers. The commercial equivalent of Type VIII and the relevant design parameter is available for access and view online through the commercial vendor�s website. Due to limitation of flight deck configuration, increase or scaling up of the tie down fitting design cannot be supported and will not be considered as a potential solution.
Load: Refer to the flight deck tie down fitting pull test requirements in System Requirements section above.
Shock: N/A as flight deck tie down fitting is considered as a part of the overall ship structure and not subjected to a separate shock requirement.
Vibration: N/A as flight deck tie down fitting is considered as a part of the overall ship structure and not subjected to a separate vibration requirement.
Welding: Cross member material must be compatible to be welded/joined to high strength steel and minimal heat control processing to support in service replacement. In order to meet the minimum heat control-processing requirement, material selection consideration must include a base material/filler metal not subject to heat-affected zone hardenability and hydrogen cracking. Final weld to meet nondestructive testing, such as visual and dye penetrant inspection to acceptance standards, and load testing are requirements for a successful tie down fitting. Minimum requirements for the fabrication and welding design for ship structures are covered in MIL-STD-1689 and provides general welding and inspection requirements for the tie down fittings.
PHASE I: Develop a concept for a corrosion resistant and durable aircraft deck tie down fittings for aircraft carrier application. Describe how the technology will be implemented, provides cost ranges for the systems, and provides notional shipboard implementation. Conduct both literature review and testing of material properties to meet various Navy requirements. (Note: Navy can provide guidance document to selected performers.) Establish feasibility by material testing and/or through analytical modeling. Phase I Option, if exercised, should include the initial specifications and capabilities for the technology to be developed in Phase II.
PHASE II: Produce 15 prototype aircraft securing fittings for delivery and evaluation to determine its capability in meeting the performance goals defined in the Phase II SOW and the Navy requirements specified under NAVSEA Drawing 803-1916300 (Hull Standard Drawing Aircraft Securing and Engine Run�Up Fittings). Ensure that the prototype material can be welded to high strength steel with qualified welding procedures in accordance with the appropriate Navy specific requirements for welding on high strength material. Demonstrate performance through prototype evaluation and testing over the required range of parameters (i.e., accelerated corrosion, wear, weld-ability, and mechanical properties) including numerous deployment cycles to verify test results. For mechanical properties, ensure that the fitting satisfies the pull strength requirement specified in the NAVSEA Drawing 803-1916300 applicable to Type VIII tie down. Using the evaluation results, refine the prototype into an initial design that will meet Navy requirements. Prepare a Phase III development plan to transition the technology for Navy use.
PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the technology for Navy use. Support the Navy for test and validation to certify and qualify the system for Navy use. The technology must be transitioned to the aircraft carrier platform.
This technology may also reduce maintenance and operations costs for commercial ships and aviation. Government and commercial space programs may also benefit from adopting the technology.
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KEYWORDS: Aircraft Secure Fittings; Aircraft Deck Tie Down Fittings; Flight Deck Tie Downs; Tie Downs; Corrosion Resistant Tie Downs; Five Crossbar Type VIII Tie Down Fitting