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"Mount it upon a shaft, which must be on ball—bearings. Place the propeller in a horizontal position, and it should remain in that position. If a weight of a trifle over an ounce placed in a bolt—hole on one side of the boss fails to disturb the balance, then the propeller is usually regarded as unfit for use." —Barber, 1917

Aeroplane Propeller Balance

"Mount it upon a shaft, which must be on ball—bearings. Place the propeller in a horizontal position,…