Abstract
Fibre optic based sensors are becoming increasingly viable as replacements for traditional flight test sensors. Here we present laboratory, wind tunnel and flight test results of fibre Bragg gratings (FBG) used to measure surface strain and an extrinsic fibre Fabry–Perot interferometric (EFFPI) sensor used to measure unsteady pressure. The calibrated full scale resolution and bandwidth of the FBG and EFFPI sensors were shown to be 0.29% at 2.5 kHz up to 600 με and 0.15% at up to 10 kHz respectively up to 400 Pa. The wind tunnel tests, completed on a 30% scale model, allowed the EFFPI sensor to be developed before incorporation with the FBG system into a Bulldog aerobatic light aircraft. The aircraft was modified and certified based on Certification Standards 23 (CS-23) and flight tested with steady and dynamic manoeuvres. Aerobatic dynamic manoeuvres were performed in flight including a spin over a g-range −1g to +4g and demonstrated both the FBG and the EFFPI instruments to have sufficient resolution to analyse the wing strain and fuselage unsteady pressure characteristics. The steady manoeuvres from the EFFPI sensor matched the wind tunnel data to within experimental error while comparisons of the flight test and wind tunnel EFFPI results with a Kulite pressure sensor showed significant discrepancies between the two sets of data, greater than experimental error. This issue is discussed further in the paper.
Highlights
The field of civil aircraft flight testing presents many instrumentation challenges, including the scale, the environment and the regulatory requirements [1, 2]
extrinsic fibre Fabry–Perot interferometric (EFFPI) sensors have been deployed to measure strain and pressure on a rotor blade in a spin chamber, using a sensor demodulation system mounted in the rotating frame with wireless data transfer [20], and have been evaluated in shock tubes [18] and wind tunnels [21], where it was found that the adhesive used to bond the diaphragm to the fibre ferrule influenced the dynamic response
A fibre Bragg grating (FBG) is a periodic modulation of the refractive index of the core of an optical fibre, which acts to reflect a specific wavelength back along the optical fibre
Summary
The field of civil aircraft flight testing presents many instrumentation challenges, including the scale, the environment and the regulatory requirements [1, 2]. The potential of fibre Bragg grating (FBG) sensors for use in aerospace applications, including wind tunnel and aircraft structural health monitoring [7,8,9,10,11] and wing shape measurement [12, 13], is becoming widely acknowledged. EFFPI sensors have been deployed to measure strain and pressure on a rotor blade in a spin chamber, using a sensor demodulation system mounted in the rotating frame with wireless data transfer [20], and have been evaluated in shock tubes [18] and wind tunnels [21], where it was found that the adhesive used to bond the diaphragm to the fibre ferrule influenced the dynamic response. In-flight, the two instruments are shown to perform well under dynamic and steady state conditions through a g-load range of −1g to +4g, offering the potential for application to larger scale aircraft
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