We discovered a few things that would need to change before the aircraft entered production. On the X-35B’s STOVL variant, the doors above the lift fan had a bi-fold arrangement: They folded and slid outward, creating an opening for air to enter the fan. However, when the airplane was slowed to a hover, the air flowing across the top of the aircraft would not on its own make the turn into the fan efficiently; it needed to be guided. On the production F-35B there is a different arrangement: Instead of two doors sliding open, a single door, hinged aft, lifts up and acts like an air scoop, helping to funnel the air into the fan. But the new design of the lift fan cover created additional challenges for the two auxiliary air inlet doors that sit right behind it. Not all the air is channeled into the fan, and at higher speeds, the air that flows around its raised cover is turbulent, causing the open doors on the auxiliary air inlets to vibrate. The hinges on those doors, therefore, had to be strengthened.
Another change that would be required in the production airplane was in the cockpit controls. The cockpit controls for flying in the X-35B were similar to those in the AV-8B. In that and earlier STOVL aircraft, the pilot has a set of cockpit controls for conventional flight and a separate set of controls for the hover. Typically, the hover control is an additional lever the pilot used to control the thrust vector, so as the aircraft transitioned from conventional flight through the hover, the pilot had to use both hands to manipulate stick, throttle, and thrust vector.
The F-35B has a stick and throttle. They work in four regimes: conventional flight, transition to hover, hover, and vertical landing. No longer does the pilot manage the thrust vector with a separate control. It doesn’t matter whether you are in the A, B, or C model or you’re flying at 500 knots or hovering—you use the same inputs to control the aircraft. If you want to go up, pull back on the stick; if you want to go down, push forward. If you want to go forward or go faster, increase the throttle; if you want to slow down or go backward, decrease it.
A variety of sensors, combined with accelerometers, an inertial navigation system, and GPS, make this happen. The pilot inputs commands via the stick and throttle to tell the airplane where he wants to go. The flight control computer (there are three, for redundancy) translates the pilot’s inputs to adjust the engine thrust, thrust vector, and flight controls.
The F-35s we’re flying at Eglin differ from the X-35 in a third way: They have no head up displays. Instead, the displays have been integrated with our flight helmets; we now wear a helmet-mounted display (HMD) system. Tiny cameras inside the helmet project data on the visor. In addition to basic flight information—speed, altitude, attitude—the display continuously provides the status of targets, weapons, navigation, threat, and critical aircraft information. The helmet has a built-in night-vision camera and can also display infrared views from cameras mounted outside the aircraft, so when, for example, you look down at the floor of the cockpit, you see the ground below in the visor display.
Most legacy helmet-mounted displays are monocular. The F-35 HMD is binocular. With a monocular system, one eye is giving your brain information from outside the HMD. With a binocular system, your brain gets what your eyes are seeing in the HMD. The new technology has run into some problems, such as how fast the computers need to process an image and display it to the pilot. The time lag is measured in milliseconds; just how many is the key issue. If the delay is too long and your brain registers the difference, what you see in the display doesn’t match what you see in the real world. Because this is the first use of an advanced system, we have to learn what the human eye and brain can tolerate.
The final difference between the production and test versions of the aircraft has to do with weight. One of the key attributes of a STOVL aircraft is its ability to land vertically with as much weight as possible, so the aircraft can return with unexpended weapons or extra fuel or both. In order to increase the weight the aircraft can land with, the designers must either increase engine thrust or decrease aircraft weight. In the F-35B, the engine thrust was fixed; the only way to achieve the performance the government wanted was to decrease weight. You just get rid of things you don’t really need. But how do you decide what you don’t need? There were numerous meetings, engineering discussions, and emotional debate. As part of the perpetual battle to keep weight down, we lost the pilot’s ability to extend the boarding ladder from the cockpit, which is about 12 feet above the ground. But pilots in other airplanes have lived without it, so we had to let it go.
The first step in becoming a Joint Strike Fighter pilot is familiar to anyone who has learned to fly: ground school. In Marine Fighter Attack Training Squadron 501, ground school consists of academics and simulators that teach the pilots how to operate and fly the aircraft. When I learned to fly the AV-8B, I got a stack of books. I read the books, sat in classes, and practiced in a basic cockpit trainer. My student got a laptop computer with a stick and throttle to plug into it, just like the stick and throttle in the F-35. His classroom is fully electronic. He learns by doing. When we are teaching him about the fuel system, he sees the fuel system, watches the fuel burn down, and views the fuel display on his computer exactly as it appears in the aircraft. When he is in the classroom, his desktop trainer has a touch screen display, a stick and throttle, and a headset and microphone so he can use voice activation to command certain functions—all precisely mimicking the systems in the airplane. After three weeks in the classroom, he graduates to the Full Mission Simulator, an F-35 cockpit that slides into a large dome. Multiple high-definition cameras project on the surface of the dome images of the scenes around the airplane. Although the simulator does not move, it provides realistic video and sound. The simulator is vital, because the F-35 does not have a trainer or two-seat variant. When a student first flies the airplane, he or she is solo.