Topic: Hydraulic Fluids in Aviation

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Discussion Overview

The discussion revolves around the use of hydraulic fluids in aviation, specifically comparing Hyjet (used in commercial aviation) and MIL-H-83282 (used in military aviation). Participants explore the properties, standards, and reasons for the differing choices of hydraulic fluids in these sectors.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that MIL-H-83282 has a synthetic hydrocarbon base with additives for viscosity and anti-wear characteristics, while Hyjet is used in commercial aviation for its higher temperature resistance and inflammable properties.
  • One participant suggests that commercial airlines may use fluids similar to MIL specs but at a lower cost, implying that the same fluid could be marketed under different standards.
  • Another participant emphasizes that the two fluids are not the same and highlights the need for different handling procedures, including the use of specific gloves for each fluid type.
  • It is mentioned that Hyjet has a higher auto-ignition point compared to MIL-H-83282, which some participants argue is a key reason for its use in commercial aviation.
  • Participants provide links to external resources for further information on hydraulic fluids and their properties.

Areas of Agreement / Disagreement

Participants express differing views on the properties and applications of the hydraulic fluids, indicating that there is no consensus on the reasons for the differences in usage between commercial and military aviation.

Contextual Notes

Participants reference various standards and specifications but do not resolve the complexities surrounding the definitions and properties of the fluids discussed.

AeroGeek
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Hello,

We all know that, in Commercial aviation, we use Hyjet (SKydrol or 500B4). and in military we use MIL-H-83282 (red oil). what are the main reasons?

MIL-H-83282 has a synthetic hydro carbon base and contains additives to provide the required viscosity and anti wear characteristics, which inhibits oxidation and corrosion. and having a temperature range of -40 Deg C to +135 Deg C, and its a fire resistant fluid.

Why are we not using MIL standard fluid for Commercial aircraft?
What are the defined standards for Hydraulic systems in Commercial and Military? (where can i get that info. CS/FAA-25?)
Difference in Properties of both fluids?

Thanks in Advance.
 
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There are many different standards. You must use the approved fluid. How could you know that two fluids specified in different standards were not the same ?
Anything MIL spec wil be more expensive because the taxpayer pays the bill.
Commercial airlines probably get exactly the same fluid for a lower price, but with a different standard and part number.

https://en.wikipedia.org/wiki/Hydraulic_fluid#Aircraft_hydraulic_systems

http://www.shell.com/business-customers/aviation/aeroshell/knowledge-centre/the-aeroshell-book/_jcr_content/par/textimage_1433441235.file/1445042942924/6c2cb5c8f66a346239c3d2d57412b07f/aeroshell-book-6hydraulics.pdf
 
Thanks for the reply. Actually, the two specified fluids are not the same. I'm working in this area currently. we use red oil for military and hyjet for commercial. Both have different properties, i think. While we handle those fluids, we use different set of gloves for each type and different care. Thanks for the manual info book. i'll dig into that and observe the differences and post back the reasons.
 
The reason why Hyjet is used in commercial sector is because of its inflammable properties upto 1600 C. and its auto ignition point is about 400 0 C. While Red Oil or MIL-5606/83282 has a lower flash point of about 940 C. They use red oil in military sector because of the confidentiality in technologies and gathering information.
 

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