FAA Aviation Mechanic General (AMG)Physics, Math and Fluid LinesHard
A technician must apply 100 in-lb of actual torque to a bolt. A torque wrench 10 inches long is fitted with an extension that adds 2 inches to its effective length, making the total length from the pivot point to the bolt 12 inches. What torque value should the wrench scale be set to in order to achieve the correct actual torque at the bolt?
- A83.3 in-lb
- B90 in-lb
- C120 in-lb
- D100 in-lb
Show answer & explanationAnswer & explanation
Correct answer: A. 83.3 in-lb
Using the formula TW = TA × L/(L+A), where TA=100 in-lb, L=10 in, A=2 in: TW = 100 × 10/12 = 83.3 in-lb. This lower wrench reading compensates for the added leverage of the extension.
Why the other options are wrong
- B. This is close but does not match the precise formula calculation.
- C. This incorrectly increases the value instead of decreasing it.
- D. This ignores the effect of the extension on effective torque.
Torque Wrench Extension Formula
When an extension is used with a torque wrench, the wrench reading must be adjusted to achieve the correct actual torque at the fastener.
- TW = TA × L/(L+A)
- L = wrench length, A = extension length
- Extensions increase leverage, so wrench reading must be lower than actual torque desired
Memory trick: Longer arm, lighter squeeze needed on the dial.