Rivetless Nutplate Adhesive Bonding for Aircraft
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Solution Overview
Problem
Existing methods for attaching removable aircraft parts, such as nutplates, to airframes using adhesives are inadequate due to low lap shear strength, high failure rates under temperature and humidity stress, and the need for additional holes that weaken the airframe, making riveting the preferred but costly and time-consuming alternative.
Innovation Solution
A method involving the application of specific adhesives, such as 3M DP820 or Ashland Pliogrip 7779, to nutplates, which are then secured to the airframe using an elastomeric fixture and cured before installing bolts, providing a strong and durable bond that withstands torque, temperature cycling, and pressurization forces without the need for riveting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If riveting is used to attach nutplates to airframe, then the attachment strength and reliability are improved, but the manufacturing cost and time consumption increase due to countersinking requirements and additional drilling operations
Solution Approach 1:
The patent replaces the mechanical riveting system with a chemical bonding system using adhesives. The adhesive forms a bonding interface between the nutplate base and the airframe substrate that provides sufficient attachment strength without requiring mechanical fasteners, thereby eliminating countersinking and reducing assembly complexity
Solution Approach 2:
The patent changes the bonding mechanism from mechanical interlocking (rivets) to chemical bonding (adhesive). This parameter change allows the nutplate to be attached through surface adhesion rather than mechanical penetration, eliminating the need for countersinking and reducing assembly time while maintaining reliability
2Reliability
If riveting is used to attach nutplates to airframe, then the attachment strength is improved, but the airframe structural integrity deteriorates due to additional holes that weaken the airframe
Solution Approach 1:
The patent replaces mechanical penetration (drilling rivet holes) with chemical bonding (adhesive application). This substitution eliminates the creation of additional holes in the airframe, preserving its structural integrity while still achieving reliable nutplate attachment through the bonding interface
3Productivity
If adhesive bonding is used to attach nutplates to airframe, then the manufacturing cost and time are reduced, but the bond strength and reliability deteriorate under temperature and humidity stress
Solution Approach 1:
The patent employs a composite adhesive system combining epoxy and polyurethane components that provides both rapid curing for production efficiency and superior environmental resistance. This composite material approach maintains bond strength under temperature cycling and humidity exposure while preserving assembly efficiency
Solution Approach 2:
The patent modifies the adhesive formulation parameters to include specific epoxy-polyurethane ratios and curing conditions that optimize both strength and environmental resistance. By adjusting chemical composition and curing parameters, the adhesive achieves reliable bonding under varying temperature and humidity conditions while maintaining fast cure times
4Strength
If adhesive bonding is used to attach nutplates to airframe, then the need for additional holes is eliminated, but the bond reliability under bolt-fastening torque and pressurization forces is insufficient
Solution Approach 1:
The patent uses a composite adhesive material that distributes mechanical loads across a wider bonding area. This composite formulation provides sufficient bond reliability to withstand bolt-fastening torque and pressurization forces without compromising airframe structural strength, eliminating the need for additional reinforcement holes
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The adhesive method secures nutplates effectively, resisting bolt-fastening torque, temperature fluctuations, and pressurization forces, maintaining structural integrity and eliminating the need for riveting, thus offering a viable alternative to traditional attachment methods.
Implementation Method 1
applying to a bonding surface of a nutplate an adhesive; maintaining the adhesive-coated bonding surface of the nutplate adjacent an interior surface of the airframe
Implementation Method 2
inserting through a hole in the airframe an elastomeric fixture attached to a nut of the nutplate, and pulling the elastomeric fixture to apply tension to the elastomeric fixture
Implementation Method 3
allowing the adhesive to cure
Data Source
AI summary
Methods for attaching a window to an airframe, methods of maintaining structural integrity of an airframe while attaching a window to the airframe, and portions of an aircraft are set forth herein. One method for attaching a window to an airframe comprises the steps of: applying to a bonding surface of a nutplate an adhesive; inserting through an airframe hole a fixture attached to a nut of the nutplate, and applying tension to the fixture to hold the adhesive-coated bonding surface of the nutplate adjacent an interior surface of the airframe; allowing the adhesive to cure; removing the fixture from the nut of the nutplate; and installing a bolt through a hole of a retainer, through the hole in the airframe, and into the nutplate; the retainer being in contact with and securing the window to the airframe. The adhesive is selected such that very specific conditions are met.