During an aircraft flight, the greater the surface area exposed to rushing air, the bigger the drag. Streamlining and new smooth materials help the plane pass through the air more easily. Engineers have developed a manufacturing process to reduce drag even further. Researchers with the EU-funded HyperDrill project have developed a machine, see photo above, that drills tiny holes in the large titanium plates that make up the body of the plane. HyperDrill was supported by Clean Sky 2's Large Passenger Aircraft Programme.
Little holes in large plates — technical challenges and quality controls
“The main objective of the HYPERDRILL project was to design, manufacture, assembly and test a prototype machine for micro-drilling large titanium sheets at drilling rates higher than 300 holes/second,” outlines Carlos Soriano, project coordinator and head of laser technology at Tekniker, the host company. Developing and perfecting the industrial process to produce the perforated sheets with the necessary precision, uniformity, and in a timely manner, was no easy task. “The prototype machine had to be capable of generating millions of tiny holes (around 0.1 mm diameter) on titanium plates of 1 mm thickness and a working area up to 5 x 2 m2,” explains Soriano. The process and technology needed to be optimised to consistently provide products of desired quality. “One of the biggest challenges was to maintain a uniform hole diameter and hole spacing, with minimal deviation, since the titanium panel deforms slightly as the microdrilling process progresses, mainly due to thermal stresses,” Soriano points out. Using their prototype, the team minimised the number of clogged holes to less than 0.02 %, 2 out of a massive 10 000. Accuracy in diameter is equally impressive with less than 5 µm deviation. In addition, the machine permits different micro-holes distributions like square alignment as well as distances between them. The machine is equipped with various sensors and control systems to monitor the panel treatment and ensure uniformity. “Actually,” he continues, “if something goes wrong, for example, the diameter of the holes starts to deviate from the nominal value, the machine is able to stop, so that the operator can check where the error is, adjust the parameters if necessary, and resume the process in the same position where it stopped.”
Large hybrid laminar flow control suction panels
The microperforated titanium panels will mainly be part of the leading edge of the wings and stabilisers of future passenger aircrafts to bring into action so-called hybrid laminar flow control (HLFC). By means of a suction chamber integrated in the wing structure of the aircraft, this technique enables the boundary layer of turbulent air generated on the surface of the aircraft aerodynamic surfaces in flight to be sucked up through the microperforated skin. The result is a more stable laminar flow, which ultimately reduces the drag of the aircraft and therefore its fuel consumption. “Indeed, HLFC technology can result in a significant reduction of around 10 % in the fuel consumption of civil transport aircraft,” emphasises Soriano, “which in turn reduces CO2 and pollutant emissions.” It is a first prototype and there are promising improvements on the horizon including the integration of new laser sources to improve the surface finish.
HyperDrill, holes, aircraft, drag, prototype, fuel consumption, HLFC, titanium panel, hybrid laminar flow control, laser