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SPECIAL FOCUS MILITARY, AEROSPACE & DEFENCE


BREAKING BARRIERS WITH DRONE MOUNTED AIRCRAFT INSPECTION


Any deviations in external dimensions can interfere with the stealth capabilities of combat aircraft, which could be catastrophic to both plane and pilot. So, Lockheed Martin is investigating the use of a drone-mounted scanner in order to generate fast yet highly accurate results…


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escribed as an all-weather stealth combat aircraft, the F-35 Lightning II has been designed to perform warfare


strike missions and electronic surveillance capabilities at speeds up to 1.6 Mach. Composites comprise 35% of the airframe weight, with the majority being bismaleimide, as well as some carbon nanotube-reinforced epoxy – which has a tensile strength of approximately 100 times greater than steel. However, any deviations in the external dimensions can interfere with stealth capabilities – and at supersonic speeds, this can be catastrophic to both plane and pilot. It is therefore critical that the ‘as built’ metrology is confirmed as ‘near perfect’ to the design. Inspection is currently a manual process at Lockheed Martin’s production facility in Fort Worth, Texas. Here, gantries are assembled above the craft and workers use handheld scanners held at arm’s length. But, not only does this introduces variables, it also puts workers at risk. In order to generate results faster, with


greater accuracy and, of course, more safety, the company realised that digital inspection would be necessary. “For 100 years in aviation we have been using humans for quality assurance, but roughly 75% of my costs come from inspection, and 66% of that requires humans to perform, which involves some degree of subjectivity. But, in our digital future, we need to embrace things in a different way,” commented Chris Colaw, Lockheed fellow, Quality & Mission Success.


INSPECTING LARGE PROJECTS Many devices currently allow for digital measurement of assemblies on a small level. The problem, however, is how to scale up existing commercial equipment to inspect large, completely constructed projects – such as a large-body aircraft, ships and even submarines – while still holding to tight tolerances. An automated metrology solution was


42 DESIGN SOLUTIONS FEBRUARY 2022


therefore needed for Lockheed Martin that could confirm and document measurements to the tightest tolerances in a faster, more accurate, and more repeatable process. The company therefore turned to CAD/CAM


since they presented an opportunity to partner with a scanner company and the University of Texas on drone control. In the spring of 2021, CAD/CAM Services won a Small Business Technology Transfer Research (STTR) award to solve surface metrology issues for the F-35 fighter jet. Its job was to assemble a team of industry-leading suppliers that would deliver to Lockheed Martin a drone-mounted scanner that can accurately (±0.025mm) measure large assemblies, and transmit that data to a system that ultimately creates CAD files for first article inspection or maintenance purposes.


COLLISION AVOIDANCE CAD/CAM Services has provided 3D modelling and CAD conversion services worldwide since 1988 to customers include Boeing, Litton-Ingalls Shipbuilding, and the U.S. Navy and Air Force. Scott Shuppert, CEO, explained: “We are taking various commercial, off-the-shelf components, slightly modifying them, and tying it all together to create a new system to solve a problem that is needed by industry.” The synergistic result started with the


drone and the camera inspection software, which had to actively search for issues such as: dents, cracks, deformations, corrosion, and alignment issues, and then reconcile the measured results to the design model. “Our team decided we needed to have both a


drone and a robot to inspect on the assembly line,” said Shuppert. “The drones will fly above and around the craft, while the wheel-mounted robot will work underneath the plane. For the drones, we went with Airgility because they had most of what we were looking for.” Airgility specialises in integrating AI and autonomy into their unmanned aerial vehicles


(UAV). Their drones met the requirements for manoeuvrability (continuously adjustable tilt motors), control accuracy (ability to hold a flight path to ± 6mm), compliance (NDAA and TAA) and carrying capacity. The guidance and control (G&C) system utilises a multi-loop architecture that computes the error between a desired reference position and the current drone position, and then synthesises the desired 3-axis movements of the rotors at an 80Hz sampling rate. This allows the drone to operate without the benefit of global positioning satellites. “Since GPS signals can’t penetrate a heavily


built aircraft hangar, the drone has to rely on the internal G&C system,” explained Pramod Raheja, CEO and co-founder of Airgility. “This system regulates the angular orientation of the drone via an independent thrust vectoring system so it can follow a 3-D reference trajectory based on the physical dimensions of the aircraft.” According to Raheja, situational awareness is


achieved by an algorithm that incorporates data from numerous, redundant, sensors. This allows the craft to fly in narrow spaces, like over and under a gantry or aircraft wing. Also included in the intelligence is a self-contained on-board AI failsafe mechanism, so if the software crashes for any reason the drone will simply back away, avoid any obstacles, and land itself. Collision avoidance is extremely important


since, in addition to the aircraft itself, the Lockheed Martin factory floor presents numerous physical obstacles including scaffolding, pilot ladders, auxiliary power units, tails, canopies and people. “Before we let a drone fly next to an $80 million


jet, we wanted to test it within a lab environment,” explained Lockheed Martin’s Colaw. This is where Animesh Chakravarthy,


professor of mechanical and aerospace engineering and flight control at the University of Texas at Arlington, was brought in. Chakravarthy’s research in collision avoidance


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