What is the calculated bend tangent line dimension for the middle of a U channel?

The proper method for calculating the bend tangent line dimension for the middle of a U channel involves understanding the relationship between the midline dimension (MLD), the flange thickness, and the bend radius.

When calculating the bend tangent line dimension, it's important to account for the bends at both ends of the U channel. The correct formula reflects this by subtracting the setback dimensions (SB) from the midline dimension (MLD). The setback represents how far the material is set back from the edge of the bend. Since you have bends on both sides of the U channel, you need to subtract the setback twice from the midline to get the correct tangent line measurement.

Thus, the correct calculation for the bend tangent line dimension considers the midline dimension and subtracts the setbacks from both ends, leading to the established formula: BTLD = MLD - SB - SB. This formula accurately reflects the geometry of the U channel and ensures precise measurements for structural repair and fabrication within the aircraft metalworking field.