Air Bearings: Aerostatic, Foil, Linear, Spindle & Spherical Types
Air bearings support motion on a pressurized gas film. Aerostatic bearings receive externally supplied air; aerodynamic bearings generate supporting pressure through motion. Foil air bearings are a self-acting form used in rotating machinery, not another name for an externally fed precision linear slide.
On this page11 sections ⌄
Aerostatic vs aerodynamic vs foil bearings
The pressure source determines what must be available before the bearing can carry its intended load.
NASA's foil-bearing research explicitly examines solid lubrication for startup and shutdown, when speed is insufficient to establish the hydrodynamic air film. Oil-free running therefore does not mean that every surface is always contact-free. The test conditions in a research report are not a universal operating rating.
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| Type | Supporting film | Important boundary |
|---|---|---|
| Aerostatic | Externally pressurized air passes into the working gap | Air quality, regulation and supply-loss response belong to the system specification |
| Aerodynamic / self-acting | Relative motion generates gas-film pressure | The running film cannot be assumed at zero or insufficient speed |
| Foil air bearing | Self-acting gas film with a compliant foil support construction | Startup and shutdown can involve sliding contact; coating and wear management matter |
Linear, rotary and spherical catalogue examples
PI's published product groups provide concrete examples of the motion categories. Check an individual variant before using any dimensions or ratings.
Precision metrology and CMM axes need controlled linear motion; a spindle needs rotational support, while a spherical platform permits angular motion. None of these names identifies the motor or guarantees an application-specific accuracy. A non-motorized bearing is not a complete servo stage.
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| Example family | Motion or purpose | Useful comparison field |
|---|---|---|
| PI A-101–A-109 | Non-motorized linear slides | Travel, supported load directions and guide accuracy |
| PI A-601–A-607 | Rotary air bearings | Radial/axial load and rotational error motion |
| PI A-651–A-657 | Spherical bearings with three rotational degrees of freedom | Angular freedom, supported centre of mass and restraint |
| PI A-80x | Air preparation accessories | Regulation and filtration required by the chosen bearing |
Porous graphite, orifices and preload are separate choices
Air may be metered through small orifices or distributed through porous media. New Way describes carbon-based porous surfaces; this is not permission to substitute arbitrary graphite stock.
Do not equate supply pressure multiplied by the visible area with usable capacity. The pressure distribution and opposing loads matter. A generic size comparison does not verify stiffness, flow consumption or safe touchdown behavior.
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| Feature | What to distinguish | Record before comparison |
|---|---|---|
| Porous or orifice feed | How air enters the film | Flow characteristics and the supplier's surface requirements |
| Vacuum preload | An opposing force that draws the bearing toward its guide | Vacuum and pressure circuits, load and orientation |
| Magnetic or opposed-pad preload | An arrangement used to load the air film | The complete force balance; not simply bearing footprint |
| Temperature or contamination | Housing, medium and guide can respond differently | Approved operating conditions and cleaning instructions |
What an air-bearing selection must still establish
Use this as a record of missing evidence, not a workshop construction procedure.
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| Requirement | Evidence to retain |
|---|---|
| Stable supply | Specified pressure and flow at the bearing, filtration and moisture/oil limits |
| Loss of supply | Alarm, controlled shutdown and any verified reserve-air provision |
| Guide and mounting | Surface geometry, finish, joints, alignment and preload arrangement |
| Complete motion performance | Load-dependent accuracy, motor/encoder effects and thermal behavior |
What air bearing is commonly used in CMM construction?
Externally supplied aerostatic pads or guides are commonly associated with precision measuring motion. Determine the actual machine's guide and pad arrangement; foil turbomachinery bearings are not interchangeable with them.
Are air bearings maintenance-free and literally frictionless?
Do not turn low-contact-friction descriptions into a whole-machine guarantee. Supply quality, controls, surfaces and abnormal contact still require attention; use the exact system instructions.
Does this include a DIY or 3D-printable bearing design?
No. A reproducible design needs validated geometry, material, feed restriction, loading and test results. This reference does not certify a home-built pressure-supported device.
What the evidence can — and cannot — tell you
| Observation or context | Interpretation to consider | Verification needed |
|---|---|---|
| Precision slide or CMM axis | Often an externally supplied air-film arrangement | Check guide geometry, air quality, loading direction and loss-of-pressure protection. |
| Foil bearing in a blower or turbine | Self-acting gas-film support during running | Confirm startup/shutdown contact, coating and machine operating envelope. |
| Porous graphite surface | A distributed air-feed construction | Obtain the actual material, flow and surface specifications; appearance is insufficient. |
| Air bearing spindle | A rotating support system, not an air-powered motor specification | Identify axial/radial capacity, speed, motor, encoder and cooling separately. |
A practical investigation sequence
Identify and record
Identify the desired motion and supported axes: translation, rotation or angular movement. Record loads and moments at their actual application points.
Check the context
Collect the exact bearing or stage specification, guide surface requirements, air preparation and supply-loss response. Do not copy settings from another series.
Verify before acting
Compare the full assembly, including preload, motor and measurement system. A bearing component alone does not define stage accuracy or positioning resolution.
Keep the decision traceable
Keep accepted conditions and unresolved values in the comparison record. Do not treat a prototype, 3D-printed part or generic porous material as a rated bearing.
Capture the information a model search cannot guess
Keep this checklist with your inspection or comparison. Checking a box only records that you have collected the item; it does not certify the bearing.
0 of 4 information groups recorded.
Technical basis & editorial scope
Original BearingScope workflow, written for catalogue research and comparison. Manufacturer material is used to check principles, not copied as a product endorsement or substituted for model-specific instructions. Reviewed 1 October 2026.
- PI Nelson Air — Air bearing fundamentals — Principles and explicitly named examples only; not an equipment fitment or universal rating. Source reviewed 3 October 2026.
- PI — Air bearing product families and motion categories — Principles and explicitly named examples only; not an equipment fitment or universal rating. Source reviewed 3 October 2026.
- New Way Air Bearings — Porous media and supply considerations — Principles and explicitly named examples only; not an equipment fitment or universal rating. Source reviewed 3 October 2026.
- NASA Glenn — Foil air bearing solid lubrication, NASA/TM-2002-211482 (abstract) — Principles and explicitly named examples only; not an equipment fitment or universal rating. Source reviewed 3 October 2026.
Source addresses and collection status are retained in the internal audit. No unpublished dimensions, torque settings, service intervals or interchange approvals are inferred.