Hydraulic Fluids in Aircraft

Hydraulic fluids used in aircraft are relatively thin compared to industrial fluids. They must also be fire resistant, which is critical when the nearest fire department is five miles below, not a few blocks away. Aircraft hydraulic fluids also differ from industrial applications because they must remain at -65° and up to 275° F. At those temperatures water and vegetable-based oil lubricants will freeze or boil. The primary hydraulic fluids used in military and commercial aircraft depend on the particular application and environment:

Hydraulic System Applications in Aerospace

As mentioned, hydraulic systems are vital to the operation of commercial and military aircraft and space vehicles, including:

• Cargo Doors
• Rudders
• Spoilers
• Landing gear
• Nose wheel steering 
• Primary flight controls
• Emergency generators
• Flap/slat drives

Hydraulic Systems: The Heart and Arteries of Aircrafts

Hydraulic systems are used on aircraft to move and actuate landing gear, flaps and brakes. Larger aircraft rely heavily on these systems for flight controls, spoilers and thrust reversers. These systems are reliable due to using hydraulic fluid that is virtually incompressible and able to transmit high pressures while being lightweight and more durable in comparison to pneumatic systems.

Hydraulic System Components in Aircraft

Though the same basic components are typically used across most aircraft, from a twin engine Cesena to a Boeing 787, hydraulic systems will vary depending on the size of the aircraft and the complexity of the application.

As with many other major industries such as automotive and medical equipment, the tier supplier network in aerospace is comprised of those who provide a variety of essential materials and commodities that are used to manufacture a finished product. There are three primary levels of segregation for tier suppliers; Tier 1, Tier 2 and Tier 3. Each of these tiers plays a significant role in the supply chain to aerospace OEMs and the support of U.S. military readiness. First we need to understand who the OEM is.

U.S. Aerospace & Defense Comprises 5 Major Segments

Commercial Aviation
The general aviation commercial aircraft segment is comprised of private companies that design, manufacture and service commercial aircraft, helicopters, commercial unmanned aerial vehicles, business jets & personal aircraft. 

The U.S. Aerospace & Defense industry is the world’s largest manufacturer of highly advanced aircraft, space systems and defense equipment. For over a century the aerospace and defense industries in America have been pivotal in creating the most superior military on the planet. As the technological leader in design and development the United States’ significant achievements have lead the way for today’s modern communication, transportation and medical achievements throughout the world. The Aerospace & Defense industry continues to be one of the largest employers and serves as the nation’s economic baseline through its vast supply chain; from the world’s largest defense contractors, down through the three primary manufacturing tiers. From major contractors such as General Dynamics, to tier one manufacturers such as little known Inseego’s IoT products and more widely known industrial manufacturers such as Babcock & Wilcox, all the way to local machine shops, the military industrial complex is the strongest segment in U.S. manufacturing. The system is tightly controlled, requiring participants to follow rigorous specifications such as ITAR registration (International Traffic in Arms Regulations), be in good standing on the QPL (Qualified Parts List) and Nadcap accredited (National Aerospace and Defense Contractors Accreditation Program).

What is ITAR?

Throughout the past few years, Brennan has earned many certifications and accreditations—one of these being ITAR (International Traffic in Arms Regulations). All manufacturers, exporters, and brokers of defense articles, services, and data must be ITAR compliant. For Brennan, being ITAR compliant has allowed us to expand our product line and customer base. It requires processes that control the manufacturing, sale, and distribution of defense and space-related articles and provides protection over product, blueprints, and our domestic manufacturing facility.

In April of 2017, Brennan Industries took the first step in entering the Aerospace market and became AS9100C and NADCAP certified meaning our fittings became approved for civilian aerospace applications. Approximately one year later, in June of 2018, we became ITAR compliant which expanded our product line and customer base requiring regulations that control the manufacturing, sale, and distribution of defense and space-related articles. Entering these new markets expands our capabilities and allows us to be a contender in a continually growing and developing industry. 

We’re excited to welcome new National Aerospace/Manufacturing Product Manager, Diane Swencki, to our team at Brennan. She will be working out of Brennan’s manufacturing facility in Euclid, Ohio.

Both flared and flareless fittings are commonly used in the aerospace industry, depending on the application. The AN (Army-Navy) military standard calls for tighter tolerances and defines all fitting types, where the JIC uses AN specifications as the base line for their own standards and covers fewer sizes. 

In the aerospace industry,  O-rings are very popular among equipment designers because of their leak-tight connections, typically using a 90 durometer, Buna-N (Nitrile) O-ring. There are two primary types of O-ring boss fittings: