Fibre-optic measurement of strain and shape on a helicopter rotor blade during a ground run: 1. Measurement of strain

Abstract

Optical fibre strain and shape measurement sensors were deployed on a 5-m long rotor blade during a full-speed (rotation rate 6.6 Hz) helicopter ground run, with real-time data wirelessly streamed from rotor hub-mounted sensor interrogators. In part 1 of a 2-part paper series, the strain sensing capabilities of the two optical fibre-based sensing techniques, optical fibre Bragg grating (FBG) and fibre segment interferometry (FSI), are compared, while Part 2 [1] specifically investigates the blade shape measurement based on the FSI approach. In part 1, the rotor hub-mounted instrumentation is described, and data on the dynamics of the blade obtained from a sequence of controlled pilot inputs are analysed both in the time and spectral domains. It is shown that this can provide insights into the√ aeroelastic properties of the blade. Noise standard deviations of 0.2 n√ ε/ Hz and 30 nε/ Hz for the FSI and FBG-based sensing approaches, respectively, were observed over a strain range of 3500 µε.

Fibre-optic measurement of strain and shape on a helicopter rotor blade during a ground run: 2. Measurement of shape

“…As shown in Part 1 [27], long-gauge length strain sensors interrogated using our range-resolved interferometry (RRI) signal processing technique [28] offer spatially resolved, fast (≫kHz) and highly sensitive (≪nanostrain • Hz −0.5 ) strain measurements using weakly reflecting in-fibre reflectors in an approach termed fibre segment interferometry (FSI) [29], where sensor gauge lengths can range from centimeters [30] to metres [31]. RRI employs an optically simple setup without moving parts, exploiting sinusoidal wavelength modulation through injection-current modulation of robust telecoms distributed feedback laser diodes.…”

“…In this paper, interferometric DFOSS [23] in the rotating frame is demonstrated using a custom-designed interrogation unit. The general setup of the rotor-mounted instrumentation, the wireless data transfer, the technical parameters of the interferometric interrogation unit and FBG-based reflector inscription are detailed in Part 1 [27], while specific aspects relevant to DFOSS are discussed in the following. Figure 1(a) shows the bottom side of the blade with the DFOSS sensing rod attached.…”

“…This paper, the second part of a two part series, details the application of DFOSS to blade deformation sensing. This follows on from Part 1 [27], which instead focuses on the strain sensing aspects of the FSI technology that underpins the DFOSS measurements, comparing the capabilities of the interferometric strain sensing approach with the well-known FBG based strain sensing technology. In this paper, the specific DFOSS sensing configuration is described before experimental results from the helicopter trials are shown.…”

Multifunctional Integration of Optical Fibers and Nanomaterials for Aircraft Systems

“…The optical sensors, which can include optical fiber-based sensors, have also found applications in feeding back real-time measurements of weight distribution, reliable aviation fuel gauging sensors, or even water content detection and online monitoring in aviation fuel. Further, the distributed optical sensors are able to test the structural integrity of the wings and fuselage (following the four SHM levels mentioned), as well as judge the performance of the engines, icing on the wings, loading on the landing gear, and very importantly, the cockpits environment (not only in commercial aircrafts, but also military ones) [ 191 , 192 , 193 ]. In this way, with the continuous development of autopilot systems and flight assistance systems, pilot performance and air safety from the cockpits (temperature, humidity, pressure, and also detecting biological contaminants aboard aircrafts, for example) need to be improved significantly.…”

The use of range-resolved interferometry for multi-parameter sensing in a wind tunnel

“…3,4 Since this signal processing technique can identify individual interferometers from an interferogram of multiple optical cavities, it can therefore be used for interrogating different interferometer designs that are adapted for measuring specific physical parameters. 4,5 Recent work 6 has shown that this processing technique is a reliable, robust approach and would be suited for use in a wind tunnel environment. In this paper, we show that the key parameters of pressure, strain, and vibrational frequency can all be measured on a high-lift wing during a wind tunnel trial, via optical fibre-based sensors, using only the signal processing technique of RRI.…”