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Fig. 6. Force diagram for unsteady (accelerating) glides. The resultant aerodynamic
force is inclined forward because of the horizontal acceleration. A downward
acceleration indicates that the vertical component of the resultant
aerodynamic force has a smaller magnitude than the weight. M, mass of
the animal; g, acceleration due to gravity; R,
resultant aerodynamic force vector; L, lift; D, drag;
, reference angle between negative velocity (drag) and resultant
aerodynamic force vector.