Ice accretion on flying surfaces affects the aerodynamic performance and handling qualities of aircraft, and may require different pilot corrective action, dependent upon the surface that ice is accreting onto. The current methodology for ice detection usually relies on an indirect method, normally based on ambient air temperature, and liquid water content. When a pre-set threshold level is reached, the ice protection system is activated, whether or not ice is accreting on
critical surfaces. This method is not cost effective or efficient for an ice protection system. Air Conformal Ice Detection System (ACIDS) obviates these problems by using a 'direct’ method of detection and measurement the presence and thickness of ice. This paper outlines some of the preliminary experimental work done on the optical properties of ice grown in an icing tunnel on the leading edge of an aerofoil leading to the development of a Fibre Optic Direct Ice
Detector sensor (DID) with emphasis. The result of this studies have shown that with suitable processing it is possible to use fibre optic sensors to determine the thickness of ice and texture of the ice accreted in the vicinity of the sensor. In the latter part of this paper basic fibre optic architecture is discussed and together with some preliminary results for representative icing runs.
Conventional aircraft repair techniques employ bolted or riveted metallic reinforcements, which frequently introduce additional stress concentrations leading to further cracking and creating areas difficult or impossible to inspect. Bonded composite repairs (“patches”) result in the elimination of stress concentrations caused by additional fastener holes, improved strength to weight ratio and present a sealed interface. This reduces even further the danger of corrosion and fretting under the repair, gives greater flexibility in design and lessens application time while lengthening fatigue life.
Embedding optical fibres and sensors into the patch, and combining this with advanced data collection and processing systems, creating a so-called “smart patch”, will enable the real-time assessment of aircraft structural integrity resulting in reliable prediction of maintenance requirements for repaired structures. This paper describes the current state of the art in smart patch technology, and includes a detailed description of the measurement problem and of the work being undertaken to solve it, at both the component and system level. An analysis of typical crack behaviour, based on FE modelling is presented and this demonstrates the need for optical strain sensors having a very short gauge length. The paper discusses the advantages and limitations of very short Fibre Bragg Gratings (FBGs) in this context and also provides early experimental data from 1mm and 2mm gratings which have been fabricated for this purpose. The paper also describes the impact of the measurement and environmental constraints on the design of the FBG interrogation system and presents the results of initial trials. The work is being undertaken in the framework of a collaborative project (ACIDS) which is co-funded by the European Commission.
AOS Technology is a UK-based SME which develops advanced optical solutions to challenging measurement and communication problems. Operating across the development spectrum from concept to consumer, the Company manufactures a range of products including a significant portfolio of complete and sub-systems for its clients. Active in the area of smart structures since its inception in 1996. AOS has recently released its GRATIS family of multi-channel, Bragg grating interrogation systems, capable of low drift, high resolution and high accuracy measurements and fast sensor update rates. AOS has also announced a commercial partnership with the FBG manufacturer, AOS GmbH, which will enable both companies to provide turnkey transducer and interrogation system packages.
Given the obvious appeal of a distributed sensing system, it is perhaps surprising that so few distributed fiber optic sensors (DFOS) have so far appeared in the commercial marketplace, especially when considered in the light of the significant research effort that has been expended in this area. This paper describes an extensive review of the commercial prospects for DFOS which has recently been completed. Information on the suppliers and applications of commercially available DFOS systems--dominated by the optical fiber distributed temperature sensor--is presented. This is complemented by a review of the important trials of commercially available DFOS systems.
A review is presented of the development of commercially available fibre optic sensors over the past 10 years,. Whilst the number of companies and sensor types is fairly static , there has been a significant shift from development to product status
This paper presents the results of a survey commissioned by the Optical Sensors Collaborative Association (OSCA) to identify sources and detectors in the wavelength region 250 nm to 5 micrometers , greater emphasis being placed on low cost devices e.g., LEDs and semiconductor lasers, which could form the basis of low to medium cost, general purpose instrumentation. The survey reviews both commercial availability and near term research activities and concludes that while emitters are available across the entire spectral range of interest, and indeed tunable emitters cover the entire range, few low cost devices are currently commercially available. Detectors are available to cover the entire range available, but little novelty was identified except for the inclusion of thermoelectric coolers within device packages and in the area of pyroelectrics.