Wing wavyness was measured with low angle (quasi tangential) reflectometry and steps will be measured with digital Photogrammetry on casted shadows. The combination of both methods allowed dynamic in-flight with no influence on the aerodynamic characteristics of the wing.
Laminar Flow is a key technology to reduce aircraft drag and fuel consumption. As part of the Clean Sky Program the Smart Fixed Wing Aircraft (SFWA) project has designed a new high speed laminar wing. The challenge to have a laminar flow at high speeds is an optimised wing profile with the smallest possible deviation between design and production and the smallest possible degradation during flight.
To test and particularly measure the principles, the outboard 9 meters of the wing of the High Speed Flight demonstrator, an A340-300, was replaced with a new laminar profile wing and equipped with a specially designed measurement system.
However, the measurement method shall not affect the behavior of the wing profile deformation. This is preferably accomplished by a contactless measurement system.
Therefore FTI’s reflectometry methodology was developed to detect any local deformations of the laminar wing surface whilst airborne.
The reflectometry measurement was based on the measurement of the unknown real deformation of a known pattern combined with the as designed, not deformed wing surface. The set-up allowed the installation on an aircraft without affecting its aerodynamic and structural characteristics.
The geometric limitation of the aircraft installation created challenges for the measurement system. The location of the pattern, cameras and illumination required the reflection to be measured under a very shallow angle. The software algorithm must take into consideration that the pattern is already deformed in a defined way by the curved wing surface. As a system with multiple cameras is in use, the software must also be able to stitch picture overlap. An illumination system was also under development to overcome further constraints, such as bright sunlight, highly reflective paint schemes, vibration and so on. As the measurement system was installed on a flying aircraft, it must also conform to requirements concerned with aircraft operation and safety.