PSI - Issue 58

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Aleksandar Grbovic et al. / Procedia Structural Integrity 58 (2024) 42–47 A. Grbovic et al. / Structural Integrity Procedia 00 (2019) 000–000

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The main goal was to compare the displacements measured in different zones of the wing prototype with those obtained numerically. Displacements were measured at 10 positions, while the strain was measured at 26 separate locations, as shown in more details by Solob, (2021), where it was also shown that the central spar was connected by two pins to a thick steel plate, fixed to the test bench through threaded bolts. Testing was conducted in the following way: once loads along wingspan were calculated for any of the case defined by regulations, they were introduced to wing prototype using whiffle-tree configuration (Fig. 5). The whiffle-tree was used to apply different loads along the wingspan to simulate the nearly parabolic distribution of aerodynamic forces in combination with inertial forces. Since a single hydraulic jack was used to introduce the load, the choice of spreaders and link rods (stirrups) was the best practical solution. As it was decided to apply loads using the whiffle-tree on the ribs’ positions along the wingspan, the whiffle-tree shown in Fig. 6 was designed in Catia v5 software, as shown in more details by Solob, (2021).

Fig. 5. Scheme of the whiffle-tree for wing structure testing. Fig. 6. Designed whiffle-tree system for wing structure testing (CATIA). The moment of external load about the y-axis for each wing segment is calculated using the relation: =−( ∙ )+ ∙ ∙( ∙ + ∙ ) (1) Chord-wise position of the resultant load from the main spar is now calculated using: = =−( ∙ )+ ∙ ∙( ∙ + ∙ ) − ∙ ∙( + ) (2) Here, is the distance of the centre of pressure from the central spar = 0− =0.619− (3) where: =[( ) − ]∙ (4) In the case D (n=6) =0.5308 and =−0.0663, thus the load distribution (lift force minus inertial force) and the moment distribution along the span and chord-wise position of the resultant load from the central spar are given in Fig. 7 and Fig. 8. Since the first rib of the wing prototype is at position =4.54 , and rib number 10 is at position =1.566 (measured from the x-axis), values of − and had to be recalculated for the ribs’ positions (let us not forget that decision was made to apply loads on the ribs in the experiment). For that purpose, polynomial interpolation was used, and values calculated at rib positions are given in Table 1.