By Geoff Fein
While General Atomics and the Navy continue to work to prove the ability to catapult aircraft from a carrier using electricity instead of steam, the company is also working to improve how aircraft land at sea, a service official said.
And unlike GA’s electromagnetic aircraft launch system (EMALS) effort, the Advanced Arresting Gear (AAG) is being designed to replace the Mark 7 system currently used on carriers, as well as to become part of the Gerald R. Ford‘s recovery system, Capt. Randy Mahr, program manager for aircraft launch and recovery equipment, told Defense Daily in a recent interview.
Using the Mark 7, the motion of the aircraft is taken out on the flight deck and translated into pistons moving in hydraulic fluid to slow the aircraft down, Mahr said.
“For the first time in roughly 50 years, we will be changing what we do,” he added. “AAG takes that same motion on the flight deck and we translate it and stop it in four different ways.”
While above deck, there will be little if any noticeable change. But below deck, the Mark 7 and its system of several hydraulic power cylinders and cabling will be replaced by different systems integrated to create a new arresting gear, Mahr said.
The first way of stopping an aircraft is using a water brake, Mahr said.
“We translate the motion into…[something] like a centrifugal pump…and we manage the pressure against the pump with how much water [goes] out at any time. So, the faster it turns, the harder it is and we slow [the aircraft] down that way,” Mahr said.
The water break component is used on shore-based arresting gear systems, he added. “All we did was adapt what we did for expeditionary airfields and shore-based systems and size it to fit on the ship.”
The next piece is a mechanical friction brake that wraps around a shaft. Pressure is applied to the break around the shaft and the aircraft is slowed down, Mahr said.
“The third one, we convert it into electrical energy. We have a motor and, as the shaft turns, it spins up the motor and we draw it off with a resistive load, which slows the motor down. The resistive load is then dumped into a bunch of cooling water,” he said.
“So instead of depending on one set of hydraulic pistons, we take it out in three different ways and this gives us redundancy. So on each wire, each of these components…are replicated, one on the left side one on the right side,” Mahr added. “I can lose any one of them and still operate normally. I can have the mechanical brake fail and operate normally. I can have one of the electric motors go down and operate normally.”
The next thing the Navy did was look at how to remove the amount of cable below deck. Back in the 1970s and into the early 1980s, Naval Air Engineering Station, Lakehurst, N.J., experimented with a conical drum and it was very effective, but it turned out not to be needed at the time, Mahr said.
“So we took the conical drum technology and brought it back for this. That allows us to handle a lot more cable in a small area rather than having to run it back and forth across the ship,” he added.
That system, called the Mark 14 arresting gear, was never fielded, Mahr said.
The good thing going forward, Mahr added, is that all of the systems that comprise AAG are relatively proven technologies.
“What we are doing is taking the water brake, the conical drum, the mechanical friction break and taking an electric motor and just putting them together. The challenge on EMALS, there was some technology development,” he said. “The challenge on AAG was taking known technology and integrating it together. This is proven technology, but the integration is what we have been spending our time on.”
Mahr said he has one-half of a system currently being tested at General Atomics in Rancho Bernardo, Calif.
“We are running it up a little over 12 hours a day…now through the beginning of July,” he said. “This is helping us get early reliability data on it.”
AAG wasn’t selected to be either forward fit or retrofit, Mahr noted.
“The way the schedule works out it does happen to go into the Ford first, and then after that CVN-72, the USS Lincoln,” he said. “I’ll have Ford forward fit and then about a year later it will go into Lincoln. It’s just the way the carrier schedules work out.”
Installation of the new arresting gear system occurs during a carrier’s Refueling and Complex Overhaul (RCOH).
“We are spread out roughly through that two-and-a-half year period. But the actual time it takes us is roughly 15 months,” Mahr said. “That includes taking out all of the Mark 7 systems and then putting in all the new ones.”