NCCCO Boom Angle and Radius Calculations 3 — Questions and Answers
Question 1: A crane boom is 80 feet long and set at a 60° angle from horizontal. What is the approximate working radius?
- 40 feet (Correct answer)
- 69 feet
- 80 feet
- 55 feet
Correct answer: 40 feet
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?
- From the tip of the boom
- From the front outrigger pad
- From the centerline of rotation (pin) (Correct answer)
- From the cab door
Correct answer: From the centerline of rotation (pin)
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?
- Radius increases
- Radius stays the same
- Radius decreases (Correct answer)
- Radius first increases then decreases
Correct answer: Radius decreases
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?
- 0.50
- 0.87 (Correct answer)
- 0.75
- 0.60
Correct answer: 0.87
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?
- Decreasing boom angle (Correct answer)
- Increasing load weight
- Shortening the load line
- Reducing wind speed
Correct answer: Decreasing boom angle
Decreasing the boom angle lowers the boom toward horizontal, directly increasing the working radius.
Question 6: A 100-foot boom is extended at a 50° angle. What is the vertical height of the boom tip above the boom foot pin?
- 64.3 feet
- 76.6 feet (Correct answer)
- 50.0 feet
- 87.5 feet
Correct answer: 76.6 feet
Height = boom length × sin(boom angle) = 100 × sin(50°) = 100 × 0.766 = 76.6 feet.
Question 7: Why does boom deflection under heavy loads affect radius calculations?
- It reduces the boom angle reading
- It causes the boom to appear shorter
- It increases the actual working radius beyond the indicated angle (Correct answer)
- It has no measurable effect
Correct answer: It increases the actual working radius beyond the indicated angle
Boom deflection bends the boom downward under load, increasing the actual horizontal reach beyond what the angle indicator shows.
NCCCO Boom Angle and Radius Calculations 3
A crane boom is 80 feet long and set at a 60° angle from horizontal.
What is the approximate working radius?