Navy test pilots are conducting numerous shore-based test landings of the F-35C of the next-generation Joint Strike Fighter in anticipation of its first at-sea landing on an aircraft carrier later this year, service officials said.
The shore landings, taking place at Naval Air Station Patuxent River, Md., are designed to replicate the range of conditions which the F-35C is likely to encounter at sea – to the extent that is possible.
Test pilots are working on what they call a structural survey, an effort to assess the F-35C’s ability to land in a wide range of scenarios such as nose down, tail down or max engaging speed, said F-35 Test Pilot Lt. Cmdr. Tony Wilson, or “Brick.”
Max engaging speed involves landing the aircraft heavy and fast to determine if it is the aircraft or the arresting gear that gets damaged, Wilson explained.
“The whole purpose is to make sure the landing gear and the aircraft structure are all suitable to take the stresses that the pilot could see while trying to land aboard the deck of an aircraft carrier,” Wilson explained.
While recognizing that the mix of conditions at sea on board a carrier cannot be replicated on land, Wilson said the test landings seek to simulate what he called unusual attitudes such as instances where the aircraft is rolling with one side up or descending faster than normal with what’s called a “high sink” rate.
“We’ve done about 90 carrier-style landings,” he said.
High sink rate is reached when an aircraft is descending 21-feet per second, much faster than the typical 10-feet per second descend rate, Wilson explained. The shore landings also seek to replicate an airplane condition known as “yawing” when the body of the aircraft is moving from side to side.
The F-35C is engineered to be larger than the Air Force’s F-35 A or Marine Corps short-take-off-and-landing F-35B because the structure of the aircraft needs to be able to withstand the impact of landing on a carrier. Also, the F-35C has larger, foldable wings to facilitate slower approach speeds compatible with moving ships, Navy officials said.
“In order to withstand the forces experienced during an arrested landing, the keel of an F-35C is strengthened and the landing gear is of a heavier-duty build than the A and B models,” an official with the F-35 Integrated Test Force said.
The wings of the F-35 C are also built with what’s called “aileron control surfaces” designed to provide control power to roll the aircraft at slow approaching speeds, Wilson explained.
At sea, pilots must account for their speed as well as the speed of the wind, the weather or visibility conditions as well as the speed of the boat, Wilson explained.
“The landing area is constantly changing. This is a challenge to structure of the aircraft because there is no way of knowing for certain how hard we are going to hit the deck or at what angle they are going to be at,” he added.
On an aircraft carrier, the ship has arresting wires or metal cables attached to hydraulic engines used to slow the aircraft down to a complete stop within the landing area.
“On an aircraft carrier, the landing area is off about 10-degrees. The boat’s motion itself is moving away from you — so you can’t just aim at the boat,” Wilson said.
The cable is four to six inches above the deck of the carrier and hydraulic fluid controls the pace of deceleration for the aircraft, Wilson said. A hook lowers from the back end of the F-35C aircraft, designed to catch the cable and slow down the plane.
“In order to maintain our stealth configuration, we had to put the hook internal to the airframe. On all the legacy systems, the tail hook sits up underneath the engine externally. We have three doors that open up to allow the tail hook to fall down,” Wilson said.
The aircraft also needs to be able to withstand what’s called a “free flight,” a situation where the pilot receives a late wave off to keep flying after the hook on the airplane has already connected with the wire, he explained.
“We need to be sure that the engine and the aircraft itself can handle the stress of essentially being ripped out of the air by the interaction between the cable and the hook,” Wilson added.
Describing landing as a controlled crash into the aircraft carrier, Wilson explained that pilots look at a light on the ship called the Fresnel Lens in order to orient their approach.
“The whole purpose of the lighting system is to show us where we are in reference to a specific glide slope. What this lens does is it tells us where we are,” he said.
In total, the Navy plans to acquire 340 F-35C aircraft. So far, five F-35Cs have been delivered for pilot training at Eglin Air Force Base, Fla.
Both Wilson and fellow test pilot Lt. Cmdr. Michael Burks, or “Sniff,” former F-18 Hornet and Super Hornet pilots, said flying the F-35C represents a large step forward in fighter jet technology.
Burks referred to the JSF’s touchscreen cockpit display which combines information from a range of sensors, cameras and radars….ect.
“Unlike our legacy aircraft where I might have to look at several different displays – the F-35C’s integrated core processor integrates all the information for the pilot. It very neatly and concisely displays all that information in one location, making tactical decisions much easier,” Burks said.