## 2 Materials and Methods  
### Wing Model with Multiple Flaps and Optical Fiber Sensors  
We developed a 3.6-m semi-spanned wing model with eight flaps on the trailing edge. The wing structure had balsa wood main and aft spars and skin. Woven carbon fiber-reinforced plastic fabrics covered the balsa wood. A 400-mm stainless-steel shaft was inserted from the wing root in the main spar in order to attach the wing model to the wind tunnel base. Figure 1 shows a photograph and a schematic of the wing model. We set the Z axis along the span. We labelled the flaps Flap 1, 2,..., 8 from the wing root. For each wing segment with Flap 1, 2,..., 8, we listed in Table 1 the position Z of the center of the flap, the span-wise length of the flaps, the chord length of the wing measured at the center of the flaps, and the flap width measured in chord-wise. Servomotors (BLS177 SV, Futaba) controlled the flap angles. The movable range of the flap angles was from \(-\)15-15\({}^{\circ}\). The positive angle indicates flap down so that the lift force increases, with zero degrees being the neutral setting. We set eight static pressure-port arrays at the center of each wing segment. For each pressure sensor array, there were 15 pressure ports on the upper side and 8 on the lower side. A total of 184 silicon tubes for pressure sensors were installed and connected to an interrogator (Electronic Pressure Scanners, Pressure System) that was placed out of the wind tunnel. Figure 2 shows the cross-section of the wing model with the locations of the pressure ports and spars. We set the X and Y axes. We labelled the pressure ports on the upper side as u1, u2,..., u15 and on the lower side as l1, l2,..., 18, counting from the leading edge. The normal direction at each pressure port was expressed by \(\theta\). Table 2 listed the geometry of the pressure ports at the wing segment of Flap 1. The geometry was not identical but similar for other wing segments. The distributions of the pressure coefficient, \(C_{p}\), of the wing segment with Flap 1 are shown in Figure 3. The flap position was neutral. We calculated the applied lift loads on each wing segment by integrating the measured static pressures around the airfoil. By dividing the airfoil into segments as labelled U1, U2,..., U15, L1, L2,..., L8 corresponding to each pressure port as seen in Figure 2, we multiplied the measured pressures with corresponding areas of the segments based on the approximation that the pressures were uniform in the segments. By considering the normal direction, we calculated the out-of-plane forces on the wing and defined them as the lift loads. Figure 4 shows the lift coefficient, \(C_{L}\), of the wing model with respect to AoA. The positions of the flaps were neutral. We bonded two optical fibers with inscribed FBGs on the upper side of the wing along the main and aft spars. We used an epoxy adhesive and fully covered the fibers with the minimum possible thickness. We applied a small pre-strain to set the fibers straight before bonding. We inscribed 30 FBGs at 120 mm intervals in individual fibers in order to cover the whole semi-span of the wing. The gauge length of the FBGs was 5 mm and the reflectivity was 70%. We designed the Bragg wavelengths of the 30 FBGs ranging from 1530-1595 nm (in the C- and L-bands) so that we could monitor the individual Bragg spectra in the wavelength-division-multiplexing manner. Figure 5 shows the reflected Bragg spectra from the optical fibers bonded to the main and aft spars. We used FBG interrogation monitors (I-MON 512 USB, [PERSON]) to observe the reflected spectra and observed 30 FBGs in the wavelength domain. The Bragg wavelength intervals were set wider at shorter wavelengths. We aligned the FBGs with shorter Bragg wavelengths closer to the wing root as the wing root was expected to have greater strain variation amplitudes in general, and it was aimed at avoiding spectral overlap. A wind shield was placed at the wing root.