Fig. 7. Predicted lifespan (N cycles) over a range of mass specific force outputs for a generalized 1 kg motor that can withstand a maximal force load of 890 N. This curve assumes that a=1 and b=3 in the load-life equation (Eqn 2). Also shown is a curve relating specific load to the observed number of wingbeat cycles for hummingbirds over one day of normal flight (a highly conservative estimate of cycles to failure) and during experimentally imposed maximal loading.