Sikorsky Envisions X2 Technology as the Helicopter Equivalent of the F-35

Sikorsky shared its concept vision for a future X2 aircraft, interestingly envisioning it as an F-35 Lightning II parallel in the low-altitude domain.

After the cancellation of the Future Attack Reconnaissance Aircraft (FARA) program in 2024, Sikorsky is still actively working on the X2 technology. In fact, this technology is still among the candidates for the next generation helicopter programs of NATO and South Korea.

During the first day of the X2 Technology Demonstration, Luigi Piantadosi, Lockheed Martin’s Director of Future Vertical Lift International, gave a presentation of the company’s vision with the X2 technology and the current status of NATO’s Next-Generation Rotorcraft Capability (NGRC) initiative. For the latter, the company has been contracted, together with Airbus and Leonardo, for a detailed platform concept study.

The X2 concept currently offered by Sikorsky and its parent company Lockheed Martin builds on the work done so far on the X2 technology and the U.S. Army’s Future Vertical Lift program. The X2 concept has the potential to completely change how helicopters are operated, paving the way to new possibilities both in the military and civil sectors, although the focus is currently on the former.

The need for a next-generation rotorcraft

The analysis of the current operational environments, including conflicts such as Ukraine, highlights the necessity for an advanced rotorcraft. In fact, current conflicts have once again highlighted the vulnerability of helicopters, requiring them to fly low and fast to maximize their survivability and make targeting by an adversary more difficult.

Flying low and fast not only makes detection more difficult, but it also gives a shorter reaction time to the adversary and thus less time to aim weapons at the helicopters. Conversely, flying high makes detection easier and gives the adversary more time to react, even if flying at high speed.

Survivability is thus directly linked to altitude and speed. To give some numbers, at higher altitudes, detection rates approach 100%, significantly reducing survivability. However, flying below 500 feet reduces detection rates to approximately 40%, and at 100 feet detection becomes minimal, only 7%, with a substantial increase in survivability.

The primary advantage of the X2 Technology over a conventional single main rotor helicopter lies in its ability to fly faster and lower, while still retaining good agility, says Sikorsky.

The X2 as an F-35 parallel in the low-altitude domain

Sikorsky drew an interesting comparison between the X2 technology and the F-35 Lightning II. The F-35 is well known for its capabilities in the high-altitude air domain, including precision targeting, sensor and data fusion, survivability in highly contested environments and secure communications.

Sikorsky believes the X2 Technology can replicate these advantages in the low-altitude air domain by providing enhanced survivability, fused battlespace awareness, and advanced targeting solutions. After all, Sikorsky is part of Lockheed Martin, the manufacturer of the F-35, and these capabilities would greatly help the armed reconnaissance mission which would have been performed by the now cancelled Future Attack Reconnaissance Aircraft of the U.S. Army.

The comparison makes sense also if we consider what the F-35 achieved in Europe, starting from just a handful of NATO Allies adopting it and now becoming Europe’s most widespread fighter with over 700 expected to be fielded by the next decade. Right now five countries are involved in the NGRC initiative, but more could join, replicating the F-35 cooperation and standardizing also the helicopter fleets across the continent.

Simplicity and modularity imply cost-efficient design

Despite its advanced capabilities, the X2 is fundamentally a simple and modular technology, says Sikorsky. Modularity translates to cost savings, allowing for scalable and adaptable solutions. The MOSA (Modular Open Systems Approach) which we can now find in every new military program is one of the best tools available to keep a platform always up to date with the current scenarios and at a low cost.

For an instance, if a new threat appears on the battlefield, a company – even other than the Original Equipment Manufacturer – can develop an upgraded system to counter it and this can be quickly installed on the aircraft. Many times the upgrade is as simple as replacing a Line Replaceable Unit (LRU), something that can be done quickly even on the flight line, with minimal cost and downtime.

Flight dynamics differences

A key aerodynamic challenge in high-speed rotary flight is the dissymmetry of lift, where the advancing blade generates more lift than the retreating blade, potentially causing instability. The counter-rotating coaxial rotors balance lift across both sides, eliminating the problem at the root.

Also, traditional helicopters need a tail rotor to counteract the torque of the main rotor and for yaw control. The X2 balances the torque between its two main rotors and uses a torque differential for yaw control.

This leaves the tail free for a rear-mounted pusher propeller for additional forward thrust. The propeller gives additional advantages, including a high turn rate capability and high, level body deceleration.

To achieve tight turns, the X2 can add reverse thrust on the pusher prop to decelerate while maximizing load factor. As the aircraft exits the turn, forward thrust is reintroduced to regain speed efficiently. This method allows to reduce the turn radius as much as possible while still exiting the turn at high speed.

When landing in traditional helicopters, the deceleration requires raising the nose, which can reduce visibility in one of the most critical phases of flight, particularly when approaching an unfamiliar landing zone. This also requires to plan the correct time to begin the deceleration, meaning that the helicopter needs to travel at lower speed for a longer distance.

On the other hand, the pusher propeller allows pilots to slow down while maintaining an unobstructed view of the landing area and to lose speed much quicker, reducing the vulnerability. Sikorsky provided a comparison with the UH-60 Black Hawk, with the X2 being able to stop in 34% less distance, or about half a kilometer, even if it started from a higher speed.

Scalability and versatility

As mentioned in the first part of our report about the X2 Technology Demonstration, the original X2 demonstrator flew in 2008. This technology was then scaled up for the S-97 Raider and the similar Raider X, and later further developed into the 14-ton SB>1 Defiant, demonstrating the scalability across different weight classes.

Sikorsky says that multiple countries are evaluating rotorcraft requirements in the 14-15 ton range, though no definitive requirements have been set. The company, however, believes a 12-ton configuration may offer the optimal balance of capability and affordability, providing a cost-effective, sustainable solution for military forces and, eventually, the commercial market.

A key advantage is the multi-role adaptability as, rather than investing in multiple platforms for different missions, a single platform can be reconfigured for various roles, optimizing fleet management and reducing the acquisition costs. For its 12 tons X2 concept, Sikorsky evaluated the possibility to quickly reconfigure the cabin for attack, maritime, air assault, search and rescue, and utility missions.

Autonomy

The X2 integrates an optionally piloted capability as the fly-by-wire system (FBW) simplifies an eventual transition from manned to unmanned operations. In fact, since the FBW system already includes a comprehensive set of sensors and controls, adding unmanned capabilities requires only software modifications and minimal additional effort, compared to conventional aircraft that lack FBW systems.

The unmanned capabilities were already demonstrated through the UH-60 OPV (Optionally Piloted Vehicle) program. In October 2024, Lockheed Martin Rotary and Mission Systems President Stephanie Hill controlled an experimental fly-by-wire UH-60 Black Hawk helicopter which was 300 miles away.

With a tablet and a datalink, she commanded the helicopter, equipped with the MATRIX autonomous flight system,  to autonomously perform take off and hover, before flying a circuit and landing again without input from the safety pilots onboard. This public demonstration follows multiple tests performed since at least 2020.

The system can also supplement pilots with AI assistance, instead of replacing them, helping to prevent controlled flight into terrain, ease navigation in adverse weather and reduce the workload. The main idea is to equip the helicopter with autonomy to help the pilots during complex missions and replace them for routine missions such as resupply missions in remote areas.

Obviously, to do this the aircraft needs to be equipped with multiple sensors and have spatial awareness and Artificial Intelligence algorithms. This way, the system can determine the best flight path based on terrain, traffic, fuel, weather, airspace restrictions and safely perform the task.

Technological advantages

Future technological advancements, such as additive manufacturing and hybrid-electric propulsion, could further enhance X2 capabilities as they mature. These technologies are already available today, but they are not mature enough yet.

The Open System Architecture (OSA) can change the way fleets and capabilities are managed. With the systems broken into components in interfaces that are much smaller, pretty much anything on the helicopter can be removed, replaced, upgraded to meet new requirements.

All the data collected by sensors and computers can also be used to improve operations and maintenance. This would allow to employ the helicopter to the maximum of its capabilities with an efficient maintenance which keeps downtime to a minimum.

NATO Next-Generation Rotorcraft Capability (NGRC)

NATO has identified new operational challenges and gaps, prompting the Next-Generation Rotorcraft Capability (NGRC) initiative. The NGRC is meant to develop the concept for a new medium-multirole rotorcraft for multiple NATO Allies.

The NATO Support and Procurement Agency (NSPA) asked contractors to identify and exploit cutting-edge technologies for potential integrated platform concepts which can meet the NGRC operational and supportability capabilities, as well as seeking innovation in digital design and development processes and advanced materials and manufacturing. In 2024, the NSPA awarded three contracts to Airbus Helicopters, Lockheed Martin Sikorsky and Leonardo to perform detailed platform concept studies.

The NGRC currently involves six participating nations and five studies, of which three are in collaboration with industry and two are internal. Among these are a Novel Engine Study, which concluded that full-electric propulsion will not be viable for another 20-30 years; an Open Systems Architecture (OSA) study, awarded to Lockheed Martin; the Platform Concept Study awarded in 2024 to three OEMs to refine initial requirements.

Joint development

Sikorsky says that a large part of the X2 technology can be co-developed with international partners, with the maximum amount being subject to the U.S. Department of Defense technology transfer regulations. New contract with companies and partners would also help keep the engineering community at work to continue refining the technology.

The possibility of collaborating abroad is not remote, as the global demand for next-generation rotorcraft to replace older types is substantial. In fact, NATO alone is expected to replace over 900 military helicopters from 2035 onward, while South Korea is expected to need 400 helicopters for its next generation helicopter program.

NATO’s official Request for Proposals is anticipated to be released next year, with a dedicated program manager and expert team already in place. Broader market potential also includes paramilitary, law enforcement, and commercial applications, which can also benefit from this technology.