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SCHATZ Engineering & Technical Info

SCHATZ Bearing Life Calculations

Load Ratings and Fatigue Life Calculations

Aircraft Control Bearings Load Limit Rating

The Limit Load Ratings listed in this catalog were developed to rate bearings that operate in slow
speed applications such as those encountered in aircraft control applications. For Bearing Life
Calculations, please consult the Schatz Engineering Department.

Basic Dynamic Radial Load Rating Cr

Schatz dynamic radial load ratings are the radial bearing loads that will give a basic rating life
of 1,000,000 revolutions. The basic dynamic load ratings have been determined in accordance
with the methods prescribed by ISO, ABMA, and ANSI.

Bearing Fatigue Life

The fatigue life of a guide wheel bearing is defined by the number of revolutions the bearing will operate before the first signs of fatigue occur.  The L10 life is the basic rating life in hours that 90% of a sufficiently large group of apparently identical bearings will operate before the first signs of fatigue appear.

Use the following formula to calculate L10 life for guide wheel bearings:


Fr = Applied Radial Load
Fa = Applied Axial Load
S = Bearing Speed (RPM)
L10 = Life (hrs.)
Z = Factor
Cr = Schatz Bearing Dynamic Load Rating (See Following Table)

Schatz Bearing Basic P/N
Cr(Lbs.) 500
Z 2.20
Cr(Lbs.) 910
Z 2.50
Cr(Lbs.) 1,740
Z 2.25
Cr(Lbs.) 3,260
Z 2.45
Schatz Bearing Basic P/N Cr(Lbs.) Z
W1 500 2.20
W2 910 2.50
W3 1,740 2.25
W4 3,260 2.45

Life Adjustment Factors

Many life adjustment factors can be applied to the calculated bearing life as stated above.  These factors are simply multiplied by the bearing life to determine the final adjusted operating life of the bearing.
L10 (Calculated) * A1 * A2 * A3 = Adjusted Bearing Life

The three life adjustment factors that Schatz recommends using are:

A1 – life adjustment factor for reliability
A2 – life adjustment factor for material
A3 – life adjustment factor for lubrication

Reliability (A1):
All formulas are based on an L10 life. If a different life needs to be calculated, use the following table for the adjustment factor:

Reliability (%)
90 (L10) 1.00
95 (L5) .62
96 (L4) .53
97 (L3) .44
98 (L2) .33
99 (L1) .21
Reliability (%) 90 (L10) 95 (L5) 96 (L4) 97 (L3) 98 (L2) 99 (L1)
Factor 1.00 .62 .53 .44 .33 .21

Material (A2):
There are several material options for use with Schatz bearings. The following chart shows the life adjustment factors for the materials offered:

Material Type
Factor (A2)
52100 2.2
440-C .6
M-50 4.2
Schatz EMS 138 4.2
Material Type 52100 440-C M-50 Schatz EMS 138
Factor (A2) 2.2 .6 4.2 4.2

Lubrication (A3):
Lubrication and the presence of an elastic-hydrodynamic lubrication film is critical to achieving proper bearing life. Please consult the Schatz engineering department for information on determining the lubrication factor for a specific application.

Visit our Lubrication Options page for grease specifications.

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