Sikorsky’s CH-53K King Stallion is a new breed of heavy lifter, in ascension.

By James Wynbrandt

The airframe appears virtually identical, the model designation varies by just a single letter, and even their names are almost interchangeable. But the Sikorsky CH-53K King Stallion, now in development, is a breed apart from the CH-53E Super Stallion it is scheduled to replace, and represents major advances in rotorcraft performance, safety, maintainability, and design process.

It is well known that the Super Stallion is already the largest and undisputed heaviest-lifting helicopter in the U.S. military. So why replace it?

“The straight and simple answer is, the [troop] support equipment has gotten a lot heavier,” says Colonel Hank Vanderborght, U.S. Marine Corps Program Manager for the Naval Air Systems Command’s Heavy Lift Helicopter Program.

“Part of what drove the gear to become heavier,” Vanderborght adds, “was going into Afghanistan and Iraq, and contending with the IEDs (Improvised Explosive Devices).” Today, Humvees, which once weighed as little as 5,500 pounds, can tip the scales at 14,000 pounds. Another impetus for replacement is that the theaters that these helicopters now operate in present high and hot environments for which the original CH-53s were not originally designed.


The Stallion Reborn

Early in the last decade, after concluding life extension or upgrade programs for the CH-53E  could not provide the necessary improvements, Pentagon planners published a new set of specifications. These included a 300 percent increase in payload over the original model, as well as a request for proposal (RFP) for a replacement helicopter. Sikorsky Aircraft based its solution for the new platform on the existing CH-53 configuration.

“Our challenge,” says Dr. Michael Torok, Vice President CH-53K Programs at Sikorsky, “was how do we use new technology conservatively to triple the lift of the Echo, and get additional lift capability in more austere conditions, while still fitting it into the same size box?”

Sikorsky proposed incorporating and integrating technology improvements in four key aircraft systems — the engines, transmission, rotor blades, and use of composites — to achieve program requirements. In 2004, the U.S. Department of Defense awarded Sikorsky a development contract for the new platform, designated the CH-53K, or Kilo model, also known as the King Stallion.


Utilizing three engines, like all CH-53s, the King Stallion is powered by Full Authority Digital Engine Control (FADEC) T-408s. Though roughly the same size as the Super Stallion’s, they produce nearly 7,500 shaft horsepower each versus the Echo model’s 4,380 shaft horsepower. The new engines also contain roughly 50 percent of the parts count, an improvement that is expected to result in increased reliability and lower lifecycle costs.

Sikorsky engineers also redesigned the transmission that delivers this increased power to the rotor, eliminating the Echo’s planetary gear system, which, if scaled up, would have been too big and heavy for the application. To enhance lift, the King Stallion’s fourth generation all-composite rotors incorporate a new blade airfoil, twist, and anhedral tip design, resulting in more performance from the same 79-foot diameter rotor span. Composites, in addition to forming the blades, are used in place of metal throughout the airframe, reducing empty weight and expanding the useful load.

In a first for helicopters, the King Stallion was completely digitally designed. The process required first “decomposing” all mandated performance requirements and specifications into interface control documentation; this allowed the integration of physical and functional elements across all design platforms. Thus, any change introduced to the hydraulics system, for example, reflect its impact on all other aspects of the design. This forward-thinking approach enabled engineers to identify and rectify issues before construction began, and ensured proper fit and functionality from the first test article.


This helicopter’s primary mission is delivering heavy lift, and here the K model, which can lift an external load of 36,000 pounds, proves itself King. The CH-53E is a single-load aircraft, hauling external loads one at a time between ship and drop zones. The new model can carry up to three individual loads, and service three different landing zones in one sortie. “That’s a huge step increase in function, not to mention the 53K has triple the lift capability,” Vanderborght notes. Moreover, specifications call for the aircraft to deliver 100 percent performance in 103-degree Fahrenheit heat at sea level, and at 91.5 degrees F at a 3,000-foot elevation.

Internally, a new high-speed cargo system can accommodate standard U.S. Air Force 463L pallets. (These are too big for the CH -53E, currently requiring loads to be re-palletized after drop-off at forward bases by C-5 and C-17 cargo jets.) Room for the pallets was made by a redesign of the CH-53’s baseline sponson and external auxiliary fuel tank, allowing the cabin to be widened by 12 inches, even as the overall external airframe width has been reduced by 2 inches.

In the cockpit, the Rockwell Collins glass panel and fly-by-wire flight controls support a variety of automated modes. This capability improves stability, enables more precise, efficient, and safe operations, and allows pilots to focus on the mission, rather than on the finer points of flying the helicopter.

Throughout the development process, the emphasis has been on collaboration. Sikorsky and the U.S. Marine Corps created and maintain parallel teams that stay in daily contact. “From systems engineering lead and logistics lead on down, everybody on my team has a Sikorsky counterpart,” says Vanderborght.


A Focus on Maintainability

Improved maintainability was a key design objective. To meet specifications, the U.S Marine Corps established a Design for Maintainers working group, composed of senior level maintainers from the Super Stallion fleet, which met quarterly with the Sikorsky design team at the company’s Stratford, Connecticut, headquarters. There, maintainers provided direct input on design, and the two groups reviewed the evolving K model on computers.

The “hundreds” of resulting suggestions that were incorporated into the King range from the way avionics are mounted in an electronics bay under the cockpit, to a simplified gearbox assembly for the outboard engines’ drive trains. The combined impact of these many changes is a significant improvement in maintainability, Vanderborght says.

The King also requires only half the support equipment — almost 150 fewer pieces — than the Echo, acing the design specifications’ logistics footprint requirements.  Data collection sensors embedded throughout the airframe, avionics, electrical systems and components feed an Integrated Vehicle Health Management (IVHM) system on the aircraft. The data, once downloaded, populates a Fleet Common Operating Environment (FCOE), a derivative of an operating system Sikorsky uses in its S-92 commercial helicopters servicing the North Sea oil field platforms. The information can be leveraged for diagnostics and preventive maintenance across the entire fleet.

Says Torok, “We can monitor the fleet, and if we see in the vibration data that a customer has a seal that’s starting to wear, we can inform them they have a pending fault that might occur in 100 hours, but they have maintenance scheduled in 20 hours, and recommend they change the part then.”

For individual aircraft, the data also can extend the life limits of major components, which are conservative by design and based on worst-case normal wear. “We can now monitor the data and say, ‘You don’t need to take this [component] out at 5,000 hours, you can wait until it reaches 7,000 hours,’” Torok points out.

The system also meets “default isolation requirements,” which mandate that the IVHM system verify the cause for a minimum percentage of system alerts displayed in the cockpit to a single ambiguity group. Contemporary systems typically provide alerts without pinpointing the fault, and sometimes without cause, often requiring maintainers to “hunt and peck” for the problem. As Torok confirms, “It’s time consuming, and it takes good equipment out of service in many cases.”

The Kilo’s default isolation system detects and notes flaws in the maintainer’s log, pinpointing exactly what needs to be fixed. “It saves costs tremendously, eliminating false removals, and also reduces mean time to repair,” says Torok. “When we sell this aircraft to the Marine Corp, we want them to have them available.”


Flight Testing and Service Entry

The first flight of the CH-53K, in October 2015, was more than a year behind schedule, due to a gearbox problem and “other technical issues,” according to Sikorsky. But development continued during the delay, and by that first official flight, a fully flyable test vehicle anchored to the ground had accumulated more than 400 hours of operation.

Those tests helped Sikorsky “mitigate a lot of risks to the flight test program, and resolve a lot of issues,” according to Torok. In the time since, most critical milestones have been achieved, including the U.S. Marine Corps’s initial operational testing of external lift scenarios of 27,000 pounds in hover, and a 12,000 pounds in a 110-nautical mile radius mission. Ground events included embarkation and debarkation of combat-equipped troops, internal and external cargo rigging, tactical bulk fuel delivery system (TBFDS) operation, and MEDIVAC litter configuration.

The CH-53K King Stallion program of record, budgeted at approximately $30 billion, calls for production of 200 CH-53Ks. This includes the first six system development test articles (SDTA), which also will serve as operational evaluation aircraft at the conclusion of the flight test program.

An integrated team from Sikorsky, the U.S. Naval Air Systems Command (NAVAIR), and the U.S. Marines, including active duty test pilots and maintainers, is conducting the final portions of the flight test program at Sikorsky’s Development Flight Center in West Palm Beach, Florida. “This is the earliest [in a flight test program] that active duty Marines have been involved,” notes Vanderborght. As for the maintainers’ role: “Their job is to provide early warning on deficiencies, so we can take action,” he says. “It’s been very valuable in helping prove the concepts of how [the platform] might be supported and maintained in the field.”

Despite these outstanding trials, at the time of this writing, the team was “equally focused on the transition to production,” Torok says. Assuming tests are concluded successfully and the DOD does grants approval, Sikorsky will receive a low rate initial production (LRIP) contract, and commence King Stallion production deliveries in 2020 in parallel with the conclusion of the development program.

“The key to the overall design, if I could sum it up,” concludes Torok, “is taking the latest of technologies and figuring out how to integrate them all together. We’ve had good results so far.”

Adds Vanderborght, “War requires having an upper hand with logistics. That’s why the -53K is such a key enabler.”

Image Credits: 

Image #1 - Photo courtesy Sikorsky.

Image #2 - U.S. Marine Corps pilots maneuver a CH-53K King Stallion as it delivers a 12,000 pound external load after completing a 110 nautical mile mission during the two-week initial operational test (OT-B1) conducted at Sikorsky.  (Photo courtesy Sikorsky).

Image #3 - The helicopter completed its first flight event hovering for 30 minutes at 25 feet while the test team assessed basic aircraft controllability and landing. (Photo courtesy Sikorsky).

Image #4 - The most powerful helicopter in the Department of Defense, the CH-53K is a new-build helicopter that will expand the fleet’s ability to move more material, more rapidly throughout the area of responsibility using proven and mature technologies. Designed to lift nearly 14 tons at a mission radius of 110 nautical miles in Navy high/hot environments, the CH-53K is designed to lift triple the baseline CH-53E lift capability with an equivalent logistics shipboard footprint, lower operating costs per aircraft, and less direct maintenance man hours per flight hour. The USMC’s procurement objective is 200 helicopters. (Photo courtesy Sikorsky).

Image #5 - U.S. Marine Corps aircrew load a High Mobility Multipurpose Wheeled Vehicle onto a CH-53K King Stallion with ease during the two-week initial operational test (OT-B1) conducted at Sikorsky’s Flight Center in West Palm Beach, FL. (Photo courtesy Sikorsky).

Image #6 - Members of the Blue-Green Team pose for group photo in front of an MH-53E during a tour at Helicopter Mine Countermeasures Squadrons (HM) 14 in Norfolk, Va. The team met to tackle mission readiness issues related to H-53 helicopters shared between the U.S. Navy and Marine Corps, such as maintenance processes, procedures, and training. From the left: Lt. Cmdr. Michael Lanzillo, HM-14 maintenance officer; Lt. Col. Enrique Azenon, Marine Aircraft Group (MAG) 29 Personal Support Detachment commanding officer; Capt. Melissa DePriest, Marine Aviation Logistics Squadron (MALS) 29 assistant aircraft maintenance officer; Maj. Paul Herrle, MALS-29 aircraft maintenance officer; Lt. Col. Brian Taylor, Naval Air Systems Command H-53 Heavy Lift Helicopter Program In-Service Integrated Product Team co-lead; Cmdr. Grady Duffey, wing maintenance officer Helicopter Sea Combat Wing Atlantic Fleet; Col. Sean Salene, MAG-29 commanding officer; Cmdr. Derek Brady, HM-14 commanding officer. (Photo courtesy U.S. Navy).