Fig. 5. Lift coefficients of spar-and-membrane profile models, with (pro) and without a propatagium (no pro), measured in a wind tunnel at a Reynolds number of 1.2x10⁵, an appropriate value for large pterosaurs (Wilkinson, 2002). Data re-plotted from Wilkinson et al. (Wilkinson et al., 2006). Measurements were nominally made at angles of attack from –2° to 20°, but below 2° the model without a propatagium luffed so severely that readings could not be taken. Above 18° the same model stalled, and again became too unstable for the lift to be measured. For the model with a propatagium, the best performance was obtained if propatagium deflection (pd), measured with respect to the chord line of the cheiropatagium, was increased from 30° to 50° as indicated.