MIL-PRF-7808L Performance Specification - Lubricating Oil, Aircraft Turbine Engine, Synthetic Base

The “MIL-PRF-7808L Performance specifications – Lubricating oil, aircraft turbine engine, synthetic base” standard, a military standard developed by the United States Department of Defense, covers the requirements for two classes of aircraft turbine engine lubricating oils.

Lubricating oil is supplied in the following grades:

• Grade 3 is normally used in most applications and is available on request unless otherwise stated.
• Grade 4 is specified when higher viscosity or greater thermal stability is required.

The requirements are described in this standard as follows:

• Qualification. Lubricating oils supplied under this standard must be products authorized by the qualifying activity to be listed on the qualified products list before the contract is awarded.
• Materials. The composition of this lubricating oil is not limited, except that organometallic compounds of titanium and silicone antifoam agents and known or suspected human carcinogens are prohibited (as defined by "29 CFR 1910.1200 Occupational safety and health standards - Hazard communications"). If the lubricating oil contains a tricresyl phosphate additive, no more than 1 percent of the tricresyl phosphate additive shall be ortho isomer. The engine lubricating oil shall not have an adverse effect on personnel health when used as intended. Recycled base stocks are permitted, but each lot shall be fully tested in accordance with all qualification requirements of this specification. The test methods specified in the standard currently require the use of chemicals that deplete the ozone layer. An acceptable substitute has been determined for each test.
• Chemical and physical requirements. All classifications of finished lubricating oil shall conform to the requirements listed in the tables provided in the standard when tested in accordance with the applicable test methods. Table I contains chemical, physical and performance requirements, Table II contains chemical, physical and performance requirements: elastomer compatibility.
• Bench performance requirements. The bench performance requirements shall be as specified in the “bearing unit” and “gear load-carrying capacity” sections of this standard. The bearing accumulation of lubricating oil shall be determined in accordance with FEDSTD-791, Method 3450. The gear load-carrying capacity requirement shall be in accordance with “ASTM D1947-10 Standard Practice for Installation of Folded Poly(Vinyl Chloride) (PVC) Pipe in Existing Sewers and Drains.” The gear load-carrying capacity requirement shall also be in accordance with “ASTM D5182-19 Standard Test Method for Evaluating the Wear Load Capacity of Oils (FZG Visual Method).” The average of the two determinations by both test methods shall be required to determine the load-carrying capacity.
• Full-scale performance requirements. For engine durability, oils are tested in a turboshaft engine in accordance with this standard to assess their acceptability for turbine engine use. The post-test condition of the engine shall not show excessive deposits, wear, corrosion or other adverse conditions attributable to the test oil.
• Workmanship. The finished lubricating oil shall be clear and uniform in appearance when examined visually by transmitted light and shall be free from turbidity, suspended matter or other deterioration.
• Material safety data sheets. Material safety data sheets are prepared in accordance with the FED-STD-313 standard.

Inspection and testing of lubricating oils are classified as follows:

• Qualification inspection
• Compliance inspection

The qualification inspection consists of testing against all the requirements specified in the tables given in this standard. Additional evaluations (engine testing) on ​​candidate formulations may be required when deemed necessary during the qualification activity.

The conformity inspection of production batches consists of all the tests specified in the table included in the standard. Failure of production batches to pass any of the conformity tests will result in the rejection of the batch.

All tests are performed in accordance with the tables given in the standard.

Major tests include:

• Conformity tests
• Elastomer compatibility
• Corrosion and oxidation stability (Class 3: 200 hours at 96 degrees, Class 4: 220 hours at 40 degrees)
• Trace metal content (ppm, maximum)
• Gear load carrying capacity
• Flash point (degrees)
• Evaporation loss (percentage at 205 degrees)
• Foaming (static) (foam volume, ml, maximum)
• Accumulation
• Lead corrosion (g/m2)
• Corrosion test (at 232 degrees)
• Thermal stability and corrosivity (at 274 degrees)
• Shear stability, viscosity loss (percentage)
• Particle contamination (mg/liter)
• Acid number (mg KOH/g)
• Viscosity (at 100 degrees, 40 degrees and minus 51 degrees, 35 minutes, 3 hours)

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