Aerodynamic technology continues to progress and develop new designs for airplanes and wings, each with significantly reduced drag. One new technology that has made more recent progress is Laminar Flow Control. There are several forms of Laminar Flow Control (LFC) technology, but their purpose is to prevent turbulence in the airflow over the aircraft surface.
LFC attempts to maintain the laminar boundary layer over a large part of the wing by effectively “sucking” the turbulent boundary layer through tiny perforations in the wing skin or using similar methods.
Figure 1 shows the difference in airflow over an airfoil with and without Laminar Flow Control. The left photo demonstrates the airfoil with an Angle of Attack of 20o and clearly shows a fully separated wake behind the airfoil. The right image shows the same airfoil with the Laminar Flow Control turned on. While the effect of LFC is not absolute, as the right picture shows, it is an improvement.
Figure 1 – Effect of Laminar Flow Control over a Wing Surface
The result of LFC ultimately is that significantly less skin friction drag results through the reduction of turbulent flow from aircraft surfaces. While the gain in fuel efficiency is not significant, it can be notable, as 3 – 5% gains can be achieved with these surfaces. These gains can be cumulative, given that the ultimate purpose of civilian aircraft is to keep flying and building revenue while containing costs. For example, airliners are claimed to be in use between 10 and 13 hours per day.
A primary drawback of Laminar Air Flow methods is that they are active rather than passive systems. This means that additional energy is needed to support these techniques, which lower the pressure inside the wing while drawing in the external boundary layer. Additionally, the perforations on the wing also negatively affect the wing’s structural integrity. The aircraft operators must deal with subtle nuisances, such as cleaning the remains of insects that can clog these perforations, which does reduce system performance. As one can expect, these types of “cleanings” affect aircraft turn-around time, and the efficiencies gained in fuel consumption reduction start to get lost in aircraft availability.
A further enhancement of Laminar Flow Control (LFC) technology is Natural Laminar Flow (NLF). In this case, the idea is more straightforward as it does not require further attachments or structures on an aircraft but requires a redesign. Figure 2 shows that the Port (right-hand side) wing has a new surface, as does the Starboard (left-hand side) wing.
Figure 2 – Application of Natural Laminar Flow Control
Airbus’ Research with NLF
Airbus initiated its own research in 2017, which was focused on further reducing the fuel consumption of airliners and keeping that company and Europe at the forefront of enhancing air transportation’s ecological footprint.
The Airbus research project was designated as project BLADE – an acronym for Breakthrough Laminar Aircraft Demonstrator in Europe. This research utilizes the first-ever A340 jetliner produced by Airbus, with its outboard wings replaced with approximately 10-meter-long laminar wing panels. The panels used represent about two-thirds of the wing size on a short- or medium-range airliner, for which the laminar flow technology is deemed best suited.
Collecting 2,000+ parameters during 150 flight test hours
BLADE is organized through Europe’s Clean Sky aeronautical research program. The BLADE project involves 21 European partners with 500 contributors, including GKN Aerospace which is the designer of the starboard laminar flow wing panel, and Saab the designer of the port wing segment.
Airbus indicated that preparations of the A340 BLADE testbed spanned 16 months, which included integration of the laminar flow wing sections, along with the installation of a highly complex installation of sensors and instrumentation to collect 2,750 dedicated measurements during some 150 flight test hours.
The BLADE research team is comprised of 10 specially-trained pilots, test engineers and flight test engineers.In order to prepare for the A340 BLADE flight evaluations, they all needed to spend time in a simulator and familiarise themselves with the mission equipment – the most technologically advanced test suite to be installed on an Airbus flight test aircraft.
Figure 3 shows the A340 BLADE test aircraft, with the two laminar flow wing panels at the outer edges of the starboard and port wing segments.
Figure 3: Blade Testbed on Airbus 340
Further Notes and Test Results
After collecting data on 2,750 parameters during 150 flight hours, Airbus stated that they had exceeded project expectations. At around Mach 0.75, a 10% drag reduction was achieved. The laminar technology wing also showed promise at higher speeds up to Mach 0.8. Readers will note that Mach 0.8 (981 km/h or 610 mph) is the expected speed for civilian jet aircraft once they have reached cruising altitude.
While the global pandemic halted this project in 2020, Airbus aims to continue more tests with some new ideas dealing with wing attachments. Furthermore, laminar flow is supposedly stabilized over the wing, so new lift enhancement techniques may reveal further fuel efficiency at different flight conditions.
Airbus would also like to test the effects of leading-edge contamination due to rain, snow, and dirt. Contamination is known to change the performance of a wing’s surface; this is expected to affect the laminarity of airflow over the wing.
This story is a continuation of the ideas drawn from the IATA Aircraft Technology Roadmap to 2050.