# Experimental Validation and Evaluation of a Coupled Twist-Camber Morphing Wing Concept
## 3 Ground Testing
### Estimation of Root Bending Moment (RBM) and Roll Rates  
From the twist and camber distributions obtained and using the expected airfoil cambered shapes data as well as the 2D CL curves for those airfoils from [18], it was possible to correlate the local camber with a local zero-lift angle of attack and local lift slope, therefore, making it possible to analyze the current wing shape using the LLT. Figure 11 depicts an example of the half-spanwise lift distributions for a total lift of 39.22 N, corresponding to a 4 Kg maximum take-off mass (MTOM), and a speed of 12 m/s of the main configurations together with the lift distributions of the maneuvering configurations at the same angle of attack (AOA) as the main configuration.  
Figure 10: Spanwise camber for the selected configurations.  
It was noticed that the main configurations (solid lines) varied from closer to elliptical lift distribution in configuration 1 to increasingly steeper triangular distributions as the overall wing camber was increased from configurations #2 to #6. This was a consequence of the above-mentioned intense negative twist variation induced by the camber increase at the inboard part of the span, which more than overcame the combined effect of camber and twist angle increase caused by actuation at the outboard region of the wing.  
Figure 11: Spanwise lift distributions of the selected configurations.  
The resultant RBM for the different main configurations was therefore significantly affected by the lift distribution, as could be observed from the data in Table 2 below:  
Therefore, the RBM could be significantly reduced if one was able to detect/predict the load increase and change the configuration sufficiently fast. This corresponds to an active load alleviation strategy that could potentially be used to either reduce the structural requirements on the wing structural design, therefore, reducing structural weight, or increase the magnitude of the total load-bearing capability of the structure, therefore, increasing the maximum operational load factor and maneuverability.  
A simplistic quantification of the potential maximum operational load increase stems directly from the RBM variation from configuration #1 to #5, which suggests that this load could increase from 16% up to 49%, depending on the current flight speed.  
Regarding the roll authority of this morphing concept prototype, the rolling moment was obtained by assuming different lift distributions on the right- and left-wing sides (i.e., configurations *.1 and *.2 for main configurations #2 to #5, configurations #1 and #1.1 for main configuration #1 and configurations #6 and #6.2 for main configuration #6) and calculating the difference between RBM for each side.  
Table 3 shows the obtained values for the maximum achievable rolling moment coefficient (CI) for each main configuration for different flight speeds:  
The calculated rolling moment coefficients magnitudes were very modest when compared to what could be obtained with moderate aileron deflections of 15 deg in a Cessna 152 aircraft (0.047), which indicated potential difficulties in attaining high levels of roll authority with this concept.  
Augmentation of roll authority might be achievable by improving the actuation system to provide the configuration with more camber in the first two-thirds of the wing, which would provide both a lift increase in that region and in the last third of the wingspan by means of reducing the negative twist in the *.1 configurations.