The way it has always been done will not cut it for the future of Army rotorcraft.

Army rotorcraft—helicopters and, someday, Future Vertical Lift—are the workhorse of the Army, capable of transporting soldiers and supplies, firing on enemy forces, reconnaissance and more. Despite the military’s reliance on them and decades of use during war and peacetime, there was not a set military standard to ensure the structures that make up rotorcraft are capable of not only completing the mission but also of protecting soldiers—until recently.

In order to build a fleet that maintains vertical lift dominance over the enemy, the Army must start with structural basics. The U.S. Army Combat Capabilities Development Command Aviation and Missile Center, known as AvMC, has leveraged more than 50 years of experience and innovation to create a Rotorcraft Structural Integrity Program that will ensure the safety and readiness of the warfighter and the success of Future Vertical Lift. Structural integrity is when a structure is capable of performing its intended function.

“Structural integrity is a challenge for rotorcraft, especially when it relates to trying to ensure airworthiness from a structural standpoint,” said Robert Benton, branch chief for Future Attack Reconnaissance Aircraft in AvMC’s Systems Readiness Directorate. “Structural integrity is different from airworthiness, but you need to have structural integrity in order to have airworthiness in a structural sense.”

Best Practices

Experts from government and industry, to include prime contractors, the Air Force and the Navy, began the effort to create a standard practice document for rotorcraft structural integrity in 2013. Co-authored by AvMC employees representing the Technology Development Directorate, which is responsible for the center’s science and technology efforts, and the Systems Readiness Directorate, which oversees airworthiness, the Rotorcraft Structural Integrity Program standard practice was published as Military Standard 3063, or  MIL-STD-3063, in 2018.

“I’ve always seen this military standard as a path to get new technology into the fleet,” said co-author Mark Robeson, structures technical area lead in AvMC’s Technology Development Directorate-Aviation. “The Army has made significant achievements in advancing aviation structures, offering a lot of improved capability. You have to have a path, a framework, to get those improvements into the fleet so that the war-fighter can benefit from the improved capability. This is a way to do that.”

The Rotorcraft Structural Integrity Program provides a framework of requirements and criteria applied during design to ensure structural performance throughout the rotorcraft’s life cycle, to include concerns such as load, strength, deformation, durability, fatigue, fracture, tolerances, mass properties, dynamics and survivability. The result is more reliable, available, maintainable and suitable rotorcraft construction for the warfighter, Benton said, as well as a more consistent process for industry, fewer technical surprises for development programs and a better understanding for partners of what is needed for modification programs.

“This will guide designers in proper planning for structural integrity and also makes it really clear to all people involved what the risks are if certain shortcuts are taken,” said Kit Fry, branch chief for dynamic components with AvMC’s Systems Readiness Directorate, and a reviewer of the document.

Cross-Platform Performance

The military standard applies to all development and modification programs for military rotorcraft.

“We wanted it to be applicable to any type of configuration you could come up with—coaxial rotor, tilt rotor, you name it,” said co-author Bob Arden, a contractor for AvMC’s Systems Readiness Directorate who has worked in Army aviation since 1975. “We didn’t know what [Future Vertical Lift] would come up with, but we tried to make it applicable to them.”

Consistency is a key element of the Rotorcraft Structural Integrity Program, according to reviewer Becca Loper, engineer with the AvMC Systems Readiness Directorate, as it ensures rotorcraft are held to the same standards.

“Every program is different; you could say every aircraft is different. They’re supposed to be coming off the assembly line the same, but some have different features—anomalies that occur. The standard will help ensure that anomalies are enveloped for structural integrity and that requirements are known early in a program,” Loper said. “If the [Rotorcraft Structural Integrity Program] is followed, we will have an aircraft that is structurally sound, airworthy and maintainable, because that’s one thing the military standard also has in it, is the sustainment plan over the lifetime of that aircraft.”

Tough Enough

One of the most impactful components of the Rotorcraft Structural Integrity Program is the incorporation of enhanced safe life and damage tolerance methodologies. With greater demands and expectations on Future Vertical Lift—to include increases in reach, protection, lethality and agility—come a greater need for structural integrity to ensure the rotorcraft won’t just perform on day one but will be able to fly, fight and prevail even after wear and tear. With a bottom-up approach to damage tolerance, aircraft are able to fly extended maintenance-free operations because they are engineered to withstand nicks, dents, scratches, erosion and the like. The result is not only less downtime, but also less cost.

The Rotorcraft Structural Integrity Program is beneficial not only from a government perspective, but also from an industry perspective.

“This really does make a better product—a product that will last in the field and be there and be operational when it’s needed,” said Darryl Toni, a Lockheed Martin senior fellow. “I’m seeing aircraft, designed and validated by test, that are able to disposition damage that occurs in the field, and we are able to give authorization for that aircraft to perform its next mission because it was designed to sustain that damage.”

“This standard is both comprehensive and general,” said Dennis McCarthy, technical fellow for structures design and analysis at Boeing Co. “Comprehensive in that it covers the complete life cycle of an aircraft from preliminary design through fleet support. Changes can be inexpensively made early in the design to comply with acknowledged future requirements. General in that the government’s ‘what’ is defined in [the Rotorcraft Structural Integrity Program], but not necessarily the ‘how.’ This allows industry—and government—to innovate to develop optimum solutions. 

“MIL-STD-3063 allows the U.S. government and industry to better define the total scope of a development effort to avoid requirements creep and unexpected cost overruns.”

Troop Benefits

AvMC’s vision is to be a warfighter-focused valued team of world leaders in aviation and missile technologies and life cycle engineering. Ultimately, it is the warfighter who will benefit most from MIL-STD-3063.

“There will be new opportunities to improve the standard practice as we and our industry partners learn through its implementation with future rotorcraft programs—but at this point, I am grateful for all of the people who have joined together as a team to make the standard practice what it is today,” Benton said.