Skydrol: What You Need to Know Aviation's Preferred Hydraulic Fluid

Leading Gear in AviationHydraulic fluid plays an important role in your hydraulic systems. It allows you to control specific functions of an aircraft because it is the energy transfer medium in all hydraulic systems. Skydrol is one of the most widely used hydraulic fluids because of its unique properties.

What Makes Skydrol Unique?

Skydrol is a hydraulic fluid that is phosphate ester-based, Eastman explains. Its chemical makeup delivers its most defining characteristic: fire resistance. In fact, Skydrol is the first ever fire-resistant hydraulic fluid in the industry.

Skydrol was developed in the late 1940s because of the risk of fire in aircraft operations. These risks stemmed from potentially leaking high-pressure mineral oil-based hydraulic fluids that were in use at the time. 

Moving away from mineral oil-based hydraulic fluids, the Douglas Aircraft Company and Monsanto, two companies in this joint venture, invested in phosphate-ester technology. When jet aircraft were introduced, phosphate ester fluids needed to be improved to accommodate lower external temperatures and higher altitudes. 

What Are the Properties of Skydrol?

Skydrol is the most advanced hydraulic fluid in use for aviation because of how cutting-edge it is. Some of its properties include:

  • Fire Resistance: Skydrol is most commonly known for its fire resistance. This generally makes it much safer for use in common aviation applications which gives this product enormous popularity in the aviation and aerospace industries. This also makes it much safer than other alternative hydraulic fluids.
  • Chemical Stability: While Skydrol has a reputation as the gold standard among this type of hydraulic fluid, its chemical stability shouldn’t be overshadowed by its fire resistance. High chemical stability means that it can last a much longer time without needing to be replaced. A reduced need for replacements and fluid changes for an extended period makes Skydrol cost-effective for futureproofing. 
  • High-temperature Stability: Skydrol is praised because of how well it handles thermal stability in real-world conditions. Stability at high temperatures allows it to maintain its general properties like viscosity and fire resistance even in extreme conditions. These high temperatures are extremely common in aircraft hydraulic systems, so this reduces the risk of a hydraulic system failure.

What Are the Different Variations of Skydrol?

Skydrol hydraulic fluid has a wide range that was developed for different aviation requirements and needs. Some of these include:

1. Skydrol PE-5

Skydrol PE-5 hydraulic fluid is a breakthrough product solving problems related to the longevity of aviation phosphate ester-based hydraulic fluids. It offers the longest hydraulic fluid life of any phosphate-ester-based product. 

Even under high moisture conditions, this Skydrol hydraulic fluid allows you to have less frequent fluid replacements. Overall, this reduces your environmental impact and gives you a much more cost-effective and operationally efficient hydraulic fluid. 

2. Skydrol 5

Skydrol 5 is a premium hydraulic fluid specifically designed to be extra lightweight. Its design is due to its much lower density compared to other types of Skydrol hydraulic fluid. The idea behind a lighter hydraulic fluid is for you to use less fuel because of lower aircraft weight, which ultimately boils down to saving on fuel costs. 

This doesn’t mean that Skydrol 5 is a second-rate hydraulic fluid. It is the first aviation hydraulic fluid that has erosion resistance at high temperatures. Amazingly, you can have less downtime and maintenance with this Skydrol hydraulic fluid.

3. Skydrol LD 4

Skydrol LD-4 has a high standard among Type IV hydraulic fluids. This particular variant offers low density, deposit control, and valve protection. The Skydrol LD-4 variant can solve the problem of valve erosion. 

Its unique formula has an anti-erosion additive and acid scavenger that reduces valve erosion. This formula has been servicing aircraft for over 35 years with no change in its makeup. 

4. Skydrol 500B-4

Skydrol 500B-4 has the longest service history among phosphate ester hydraulic fluids and for good reason. The Skydrol 500B-4 is a fire-resistant hydraulic fluid, like all other Skydrol variants. However, it also has improved erosion resistance because it contains the same anti-erosion additive and acid scavenger found in the Skydrol 500B-4.

How Is Skydrol Used?

Skydrol has lots of applications in aviation including:

  • Landing Gears: It helps with the operation of the actuators that move the different parts of the gear system through hydraulic fluid. This makes sure that any movement of the equipment is seamless and secure.Landing Gear Runway
  • Flight Control Surfaces: Hydraulic fluid can help to manage the pitch, roll, and yaw movements. It is incorporated into the flight control surfaces such as elevators, ailerons, and rudders to achieve control over the plane.
  • Flats and Slats: Skydrol hydraulic fluid can help to control the hydraulic actuators that power the movement of flaps on an aircraft’s wings. They can also be used to control the movement of the slats found on the leading edge of the wings. Both of these parts contribute to the lift and drag of an aircraft.
  • Thrust Reversers: When landing aircraft, pilots need hydraulic thrust reversers to decrease speed. Skydrol supplies the power to these actuators enabling them to deploy and retract.
  • Brake Systems: For smaller aircraft, the brake systems may be powered by hydraulic fluid to move the actuated components. This is what gives them consistent and reliable performance. 

Is Skydrol Hazardous?

Skydrol is popularly used in aviation, but there is some concern about its safety if proper protocols aren’t followed. Skydrol-to-skin contact may cause irritation, redness, or even chemical burns. This is why it is recommended that you take care when handling hydraulic fluid with the right protective gear. Always follow the Material Safety Data Sheet recommendations. 

Use the Industry Standard Hydraulic Fluid

Skydrol is the go-to option when it comes to hydraulic systems in aircraft due to the many advantages it offers in the aviation industry. Skydrol is highly important in the aviation industry, as it positions hydraulic systems to run smoothly and securely. Its distinct features enable it to be an ideal choice for aircraft hydraulic systems. This contributes to the better safety and performance of the aircraft.

Shop Skydrol and enhance your aviation maintenance!

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