The aircraft such as high altitude long endurance unmanned aerial vehicle(UAV) and human powered aircraft(HPA) has high aspect ratio wing for lightweight structure and high lift-to-drag ratio. These wings can be deformed in flight. The displacement information of the deformed high-aspect-ratio wings is needed for the control effectiveness and real time monitoring of the structural responses. It is also needed to adjust the performance of conformal load bearing antenna structures (CLAS) system, which can be degraded because of wing deformation. It is hard to measure the deformed wing displacement directly. Wing deformation is able to be predicted based on the relationship between the strain on the wing skin and the displacement. Because the large wing deformation occur in flight, the displacement prediction considering geometric nonlinearity is required. Generally, the structural behaviors of aircraft wings are assumed as the behavior of beam. However the strain distribution of wings subjected to bending is complex in the chordwise direction. Therefore the deformations can be diversely predicted depending on chordwise locations of the strain sensing lines using the displacement prediction based on the strain-displacement relationship. Hence, the strain correction methods were proposed to improve the accuracy of the displacement prediction, regardless of the chordwise sensing position.
In this paper, the study on the spanwise strain correction are conducted to accurately predict the displacement by using nonlinear displacement prediction algorithm(NDPA). The ratio of the chordwise to spanwise strain, the ratio of the beam and plate strain, and Poisson''s ratio were used to correct spanwise strain. The strain and displacement were calculated by nonlinear finite element analysis (FEA).
The conclusions are as follows,
(1) If the wing structure shape and strain sensing position are chosen, we can conduct nonlinear finite element analysis before flight. Therefore, the strain ratio which are ratio of the chordwise to spanwise strain and coefficients of a quadric equation(a,b,c) to calculate strain calibration coefficient were calculated from FEA. Using these information, the spanwise strain can be corrected to improve accurate of predicted displacement.
(2) As simplified wing model, the plate and beam model were chosen. Considering real aircraft wings, the plate model under uniform and triangular distributed loads and tapered plate model also were chosen to verify the strain correction algorithm. In addition, experiments with the simplified wing model under concentrated load were conducted. The predicted displacement using the strain correction were consistent with those calculated by the FEA and measured by bending testing.
In the future, we expect that the study can be applied to improve the accuracy of the deformation prediction of wings in flight by using the data from FEA beforehand with NDPA that it not only uses minimum number of sensors but also has high accuracy.