Understanding the F-35 Air Vehicle

The F-35 is the world’s most advanced 5th Generation fighter that touts capabilities like 360-degree pilot vision and unprecedented situational awareness. These features, of course, only matter if the F-35 can take to the skies.

Keith Rail, Angela Lanier and Adrian Cardenas help the F-35 do just that. The three seasoned engineers all work in Flight Control Actuation on the F-35 Air Vehicle Systems team.

So, What is an Air Vehicle System?

“The air vehicle systems on the plane are what give it life. Without them, it’s just a big piece of metal,” explains Keith, one of the lead systems engineers for Flight Control Actuation. “We make it fly.” Adrian, the Flight Control Actuation Electronics technical lead, adds, “You talk about all of the fantastic things the F-35 can do. You can’t do those things without being able to get there and back—that’s what air vehicle systems do.”

To break it down further, the F-35 air vehicle system includes the flight controls, power system, cooling system, hydraulics, landing gear, air frame, propulsion and the software that controls it all—anything that helps the jet fly. This excludes mission systems and software like the weapons, controls for weapons, radar, Electronic Warfare (EW) and sensor fusion.

“It’s the airplane minus the mission-specific part of it,” says Angela, who works with Electro Hydrostatic Actuators (EHAs) in Flight Control Actuation.

Innovation Brought to Life

During the recent Operational Test-1 (OT-1), the U.S. Marine Corps F-35B conducted vertical landings aboard the USS Wasp. In the midst of a vertical landing, all sorts of doors open, surfaces move and the engine reconfigures to regulate the controlled descent. While we see this happening from the outside, the pilot is not directly controlling every one of those actions. This leaves more time for him or her to focus on actions that are mission-oriented.

The integration of air vehicle systems on the F-35 is even more impressive when we consider that to convert the F-35B to short takeoff/vertical landing (STOVL) mode, the pilot merely pushes a button.

Keith, Angela and Adrian affirm that the F-35B’s STOVL ability is the culmination of all the air vehicle systems seamlessly integrating together –and is hands down the most innovative feature of the jet’s air vehicle system.

“The software and interaction between all the different components are extremely complex on all three variants,” Adrian shares. “In the end, it’s seamless to the pilot.”

Rising to the Challenge

With the F-35’s complex hardware and software, systems need to work seamlessly together in all modes of flight. Keith reveals that, “our biggest challenge changes over time. Problems are solved and new ones are discovered as we push the limits in test.”

Adrian remarks with a smile, “If everything works like it’s supposed to the first time, things get pretty boring for engineers.”

The F-35 is unique in that it is the first time Electro Hydrostatic Actuators (EHAs) are being used as primary flight controls in a fighter aircraft. “Primary flight controls” refer to the rudder, horizontal tail, and flaperon control surfaces that control the jet’s flight.

“Some commercial airliners have backup EHAs, but the F-35 is really the first use of EHAs as primary flight controls,” Angela elaborates.

Angela, who specializes in EHAs, explains that an EHA is a compact, self-contained hydraulic unit. In Legacy fighters like the F-16, a centralized hydraulic system uses pressure to push fluid out to extremities of the aircraft, which in turn moves an actuator—a rod—that controls movement of a specific surface.

However, with this significant tubing running to all ends of the jet comes potential hydraulic fluid leaks and extra weight. Additionally, any type of aircraft maintenance requires full depressurization of the hydraulic system.

In the F-35, each surface is controlled by one EHA unit—no centralized system is needed.

Instead, power from the aircraft is funneled to Electronic Units (EUs) that power individual EHAs to move the flight control surfaces. Adrian explains why this presented a particular engineering challenge.

“The question became: ‘How do we build hardware that will withstand what we’re asking it to do using electrical power driving an actuator that has not been done before?’ Having a large amount of power going in and out of a small box is not something trivial to figure out.”

Since EHAs are self-contained, maintenance only requires the removal or repair of a single unit, say, beneath an F-35 horizontal tail. The potential for hydraulic fluid leaks is minimized and extra tubing weight is eliminated.

EHAs are single units, but they are substantial. In fact, some in the F-35 are as large as a tabletop and weigh 200 pounds. Each EHA must be powerful enough to overcome aerodynamic forces as it drives its surface into the wind flow.

The Sum of Many Parts

Each time an F-35 takes off, we are reminded how Keith, Angela, Adrian and the Flight Control Actuation team rose to meet that engineering challenge. But Keith reminds us that their team is only a small part of the hundreds of folks working in F-35 Air Vehicle Systems.

“All of those systems are an integrated group interacting together to be able to function. No single one stands alone.”

For Angela, the coolest part has been seeing the entire system evolve over the life of the program. Adrian, too, marvels at it.

“You think about all these pieces involved and how complex it is, and then you get the answer from the pilot community saying how easy it is to fly. That is a testament to all the pieces fitting together so well.”