NCCCO Boom Angle and Radius Calculations 3

Question 1

A crane boom is 80 feet long and set at a 60° angle from horizontal. What is the approximate working radius?

Accepted Answer

40 feet

Answer

Radius = boom length × cos(boom angle) = 80 × cos(60°) = 80 × 0.5 = 40 feet.

Question 2

When a load chart specifies a radius of 25 feet, from where is that radius measured?

Accepted Answer

From the centerline of rotation (pin)

Answer

Radius is always measured from the crane's centerline of rotation to the center of the suspended load.

Question 3

As boom angle increases from 45° to 75°, what happens to the working radius if boom length stays constant?

Accepted Answer

Radius decreases

Answer

As boom angle increases, cos(angle) decreases, so horizontal reach (radius) decreases.

Question 4

A crane operator notes the load radius is 30 feet and the boom is 60 feet long. What is the sine of the boom angle?

Accepted Answer

0.87

Answer

sin(angle) = √(1 - cos²(angle)); cos(angle) = 30/60 = 0.5, so sin(angle) = √(1-0.25) = √0.75 ≈ 0.87.

Question 5

Which condition causes the greatest increase in effective load radius during a lift?

Accepted Answer

Decreasing boom angle

Answer

Decreasing the boom angle lowers the boom toward horizontal, directly increasing the working radius.

NCCCO (National Commission for the Certification of Crane Operators) Practice Test