Load Capacity Estimation of Foil Air Bearings
A simple 'Rule of Thumb' estimation for the load capacity of foil air bearings
has been developed as a feasibility guide for new Oil-Free turbomachinery.
-
Based on first principles and published data
-
Load capacity coefficient, D, relates load and rotational
speed
The permissible load is a function of design, bearing area and surface
velocity is expressed as:
W = D (L x D) (D x 
)
where:
W is the maximum steady-state
load that can be supported, N (lbs)
D is the bearing load capacity coefficient, N/(mm3
krpm) (lbs/(in3 krpm))
L is the bearing axial length, mm (in)
D is the shaft diameter, mm (in)
is the shaft speed
in thousand rpm (krpm)
Using the non-SI units there is an observed mnemonic aid for design
in that a foil bearing can typically support:
"a pound of load per inch of bearing diameter per square inch of bearing
projected area per thousand rpm."
Experimental data for 'third generation' bearings supports this rule of thumb.
Foil Bearing Load Capacity vs. Speed
From the refernce report:
- Generation I bearings exhibit D of about 0.3
- Generation II bearings have D of about 0.5
- Generation III bearings have D of about 1.0 or higher
Reference Report
- Load Capacity Estimation of Foil Air Journal Bearings for Oil-Free Turbomachinery
Applications,
NASA/TM-2000-209782,
Oct 01, 2000
Responsible NASA Official: Dr. Christopher DellaCorte
Curator: Michelle L. Beagle
Last Update: April 7, 2008
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