Topic: Hydraulic Fluids in Aviation

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SUMMARY

In aviation, Hyjet (SKydrol or 500B4) is utilized for commercial aircraft, while MIL-H-83282 (red oil) is reserved for military applications. MIL-H-83282 features a synthetic hydrocarbon base with additives for viscosity and anti-wear properties, operating effectively between -40°C and +135°C, and is fire-resistant. The primary reasons for the distinction include cost differences, with commercial airlines obtaining similar fluids at lower prices under different standards, and the unique properties of each fluid necessitating different handling procedures, including the use of specific gloves and seals.

PREREQUISITES
  • Understanding of hydraulic fluid specifications, specifically MIL-H-83282 and Hyjet.
  • Knowledge of aviation hydraulic systems and their operational standards.
  • Familiarity with fluid properties such as viscosity, flash point, and fire resistance.
  • Awareness of military versus commercial aviation regulations and standards.
NEXT STEPS
  • Research the differences in properties between MIL-H-83282 and Hyjet hydraulic fluids.
  • Explore the specifications and applications of MIL-H-5606 and its relevance in military aviation.
  • Investigate the handling procedures and safety measures for different hydraulic fluids in aviation.
  • Review the regulatory standards set by the FAA and CS-25 for commercial aircraft hydraulic systems.
USEFUL FOR

Aerospace engineers, aviation maintenance professionals, and anyone involved in the selection and handling of hydraulic fluids in commercial and military aviation.

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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