a
LL
Figure 3-6. Length of strut when fully deployed, stowed and free length of spring
At any instant of time the distance traveled by the plates (Zi) is not equal to the
deflection of the spring and the springs are always at an angle with respect to the
direction of motion. Both these factors together contribute to the non-linear behavior of
the mechanism. According to Newton's second law of motion (F=ma), the force applied
by the springs is always equal to the product of the mass (M) of the vertical member and
its acceleration.
S(Z,)M
K ((Lmax L) +dmin) cos i ( M (3.4)
at2
The force applied by the spring on the mass follows a curve as shown in Figure 3-7.