Calculations: why tie down placement is important

Assuming that there is 150 lbs. tension in each tie-down Strap and assuming the geometry as shown in Figures 7 and 8.

Front (Figure 8a)

The tie-down tension can be broken down into its horizontal and vertical components:

• vertical(down ) force = 150 lbs. x sin 48 deg.= 112 lbs.
• horizontal force = 150 lbs. x cos 48 deg.= 100 lbs.

The horizontal force can be further broken down into its forward (fore) and lateral components:

• fore = 100 lbs. x cos 47 = 68 lbs.
• lateral = 100 lbs. x sin 47 = 73 lbs.

Rear (Figure 8b)

The tie-down tension can be broken down into its horizontal and vertical components:

• vertical(down ) force = 150 lbs. x sin 67 deg.= 138 lbs.
• horizontal force = 150 lbs. x cos 67 deg.= 59 lbs.

The horizontal force can be further broken down into its rearward (aft) and lateral components.

• aft = 59 lbs. x sin 9 = 9 lbs.
• lateral = 59 lbs. x cos 9 = 58 lbs.

Since the geometry and tension is equal for both front straps the total fore force is equal to 2 times the fore force or 136 lbs.

Since the geometry and tension is equal for both rear straps the total aft force is equal to 2 times the aft force or 18 lbs.

The fore and aft imbalance is 118 lbs. (136 lbs. - 18 lbs.)

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