Fig. 5. Comparison of frictional adhesion, JKR and Kendall peel models. We chose parameters such that a 2-D model of a 50 g gecko could adhere to inclined planes from 0° to 180°. Stability regions (shaded) and limits (borders) of each model are plotted in force-space (F_||, F ) measured as a percentage of body weight. (A) Frictional adhesion given by Eqn 4, Eqn 5 and Eqn 6 along with current experimental results from setal arrays and toe detachment angles and previous results for single setae (Autumn et al., 2000). (B) JKR model for elastic spherical asperity in contact with flat substrate. Absolute values for adhesive and shear forces have been increased to comparable levels by assuming an array of contact asperities each contributing to overall adhesion and shear (Peressadko and Gorb, 2004). (C) Kendall peel model for thin adhesive films. Maximum force occurs at 0° (intersection with +F_||-axis) and decreases as peel angle increases (measured below horizontal) towards 90° (intersection with-F -axis), eventually reaching a minimum finite value at 180°. Maximum shear for positive normal force is assumed to be independent of normal force and set at the Kendall peel model limits for 0° and 180°.