Under what condition is a direct tiedown considered effective against forward and rearward forces?

A direct tiedown is deemed effective against forward and rearward forces primarily due to the angle at which it is secured. When the tiedown makes an angle of less than 45 degrees with respect to the load, it maximizes the component of force acting directly to secure the load, thus providing better stability against movement.

This angle helps in effectively distributing the load's weight and counteracting the forces of inertia that arise during acceleration or deceleration. If the angle were greater than 45 degrees, the effectiveness of the tiedown would diminish as the force being exerted would have a larger component pulling away from the load, which could lead to potential slippage or loss of control.

Other factors like the materials used or specific mechanisms can enhance the overall reliability of the tiedown, but the angle itself is crucial in ensuring that it functions properly against forward and rearward movement of the secured item.