2-89. STANDARD PRACTICE - AIRFRAME
2-90. TORQUE WRENCH. Torque wrenches should be checked daily and calibrated by means of weights and a
measured lever arm to make sure that inaccuracies are not present. Checking one torque wrench against another
is not sufficient and is not recommended. Some wrenches are quite sensitive as to the way they are supported
during a tightening operation. Any instructions furnished by the manufacturer must be followed explicitly.
When it is necessary to use a special extension or adapter wrench together with a torque wrench, a simple
mathematical equation must be worked out to arrive at the correct torque reading. Following is the formula to be
used: (Refer to Figure 2-14.)
T = Torque desired at the part.
A = Basic lever length from center of wrench shank to center of handle or an area.stamped on wrench or
listed for that model wrench.
B = Length of adapter extension, center of bolt to center of shank.
C = Scale reading needed to obtain desired torque (T).
The formula: C = A x T
A + B
EXAMPLE
A bolt requires 30 foot-pounds and a 3 inch adapter (one-quarter of a foot or .25) is needed to get at it.
You want to know what scale reading it will take on a one-foot lever arm wrench to obtain the 30 foot-
pounds at the bolt.
C = 1 x 30 or C = 30 = 24 ft.-lbs.
1 + .25 1.25
Remember, the 3 inch adapter must be projecting 3 inches straight along the wrench axis.
In general, avoid all complex assemblages or adapters and extensions of flex joints.
Figure 2-14. Torque Wrench Formula
PIPER AIRCRAFT
PA-28-161 CADET
AIRPLANE MAINTENANCE MANUAL
Issued: FEBRUARY. 28, 1989
HANDLING AND SERV I C I N G
1C19
