What hydraulic oil number is specified for use?

The correct specification for hydraulic oil in many aircraft and military applications is MIL-PRF-83282. This is a synthetic, phosphate ester-based fluid that meets the requirements for high-performance hydraulic systems in aircraft. It provides excellent lubrication, fluid stability, and resistance to thermal degradation at elevated temperatures, which is critical for the safe operation of hydraulic systems under high-pressure conditions.

Using a fluid that meets this specification ensures compatibility with materials commonly found in hydraulic systems and helps prevent fluid break down, which could lead to equipment failure. In contrast, the other options listed, while they are indeed specifications for various aerospace fluids, are not designed specifically for hydraulic power systems like MIL-PRF-83282. For instance, MIL-PRF-23699 is primarily used for jet engine lubricants, while MIL-PRF-7808 is typically a lubricant for aircraft engines, and MIL-PRF-7870 is associated with some specific high-temperature applications.