The forces acting on the latches and rods create a torque from which there arise in the ring additional bending momenta and torque equal to where and are the rigidity of the cross section of the ring during bending and torqie elements of the ring are in a complex stressed state. The absolute values of tension in the cross sections of the ring are usually small, and the dimensions of the basic elements are chosen from the condition of providing the required rigidity. The ring of the APDA has a box-like cross section and protrusions for attachment of the guides; the internal cavity is covered by a detachable hatch which makes it possible to install sensors and the cables which connect them. The presence of a detachable hatch decreases the rigidity of the ring. However, for a sufficient number of screws (in the APDA 72 screws with a countersunk head) the rigidity of detachable and permanent structures, as experiments have shown, are virtually identical. An important element is the connection of the ring with the mechanism which connects the rod and the casing of the latches. Its construction is affected by the choice of kinematics and the force schematic of the latches, and the mechanism for back-up opening (Figure 3.10). The structure created for the APDA has a completely independent mechanism for back-up disengagement; this is achieved by the fact that the casing of the latch is installed on the mechanism which connects the rod in the axis of rotation, and is kept from rotating around this axis by a pyrotechnic bolt. A drawback of this design is that forces on the latch create substantial momentum, bending the ring.
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