The actual power loss due to friction in a gear pair is of significant interest to the transmission community.
This loss impacts fuel efficiency on almost every form of transportation. In aircraft applications, this loss
converts to heat, which must be removed using cooling equipment, inherently detracting from the payload
of the aircraft. Consequently, the impact of gear tooth surface characteristics and lubricant on friction and
frictional losses at the gear mesh is of significant interest to designers of high performance gear boxes.
While a prior paper [1 ] compared the change in losses due to these factors, this effort is intended to
actually evaluate the effective coefficient of friction at the gear tooth flank under the conditions described
below.
By instrumenting the input and output ends of the test box of a four-square, power re-circulating gear test
rig with high-accuracy torque transducers, losses at the meshing gear pair in the test box are measured.
The difference between the readings of the two torque transducers are the losses in the test gear box. By
subtracting bearing and seal losses and neglecting windage losses, the friction losses at the test gear
mesh are obtained. The nominal torque in the four-square loop is known, therefore the “effective
coefficient of friction” at the tooth flank is calculated.

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