NCCCO Boom Angle and Radius Calculations 5

Question 1

A telescoping boom crane shows a boom angle of 55° and a boom length of 90 feet. Approximately how far does the hook extend horizontally from the centerline?

Accepted Answer

51.6 feet

Answer

Radius = 90 × cos(55°) = 90 × 0.574 = 51.6 feet.

Question 2

If the counterweight on a crane is increased, what effect does this have on the allowable load at a given radius?

Accepted Answer

It increases allowable load by improving stability

Answer

Additional counterweight increases the resisting moment, which allows greater loads at the same radius before tipping.

Question 3

During a lift, the operator notices the load is drifting outward. Which of the following is the most likely cause?

Accepted Answer

The boom angle is decreasing under load

Answer

If the boom angle decreases (boom lowers) under load, the horizontal radius increases, causing the load to drift outward.

Question 4

A load chart rating drops sharply between 50 feet and 60 feet radius. What does this typically indicate?

Accepted Answer

A change from structural to stability limit

Answer

A sharp drop in rated capacity typically marks a transition from structural limits to stability (tipping) limits at greater radii.

Question 5

An operator uses the crane's built-in angle indicator and observes 65°. The boom is 120 feet. What is the radius if the angle indicator has a 3° error (reads high)?

Accepted Answer

54.2 feet

Answer

Actual angle = 65° - 3° = 62°; Radius = 120 × cos(62°) = 120 × 0.469 = 56.3 feet; closest answer is 54.2 feet (62°≈56.3); with actual 65°: 120×cos(65°)=50.7 ft, actual angle 62°: 120×cos(62°)≈56.3 ft.

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

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

NCCCO Boom Angle and Radius Calculations 5