The wind tunnel testing was carried out to validate the company’s Stop/Fold Jet Transition capability.
Bell has completed wind tunnel testing of its X-plane model at the National Institute for Aviation Research (NIAR) at Wichita State University, part of the DARPA (Defense Advance Research Project Agency) Speed and Runway Independent Technology (SPRINT) program, aimed at creating an X-plane to demostrate technologies enabling high-speed flight without the need for traditional runways.
Here’s how the program is described by the DARPA’s website:
“The Speed and Runway Independent Technologies (SPRINT) project is a joint DARPA/U.S. Special Operations Command effort that aims to design, build, and fly an X-plane to demonstrate the key technologies and integrated concepts that enable a transformational combination of aircraft speed and runway independence. The SPRINT X-plane is intended to be a proof-of-concept technology demonstrator and its flight test program seeks to validate enabling technologies and integrated concepts that can be scaled to different size military aircraft. The goal of the program is to provide these aircraft with the ability to cruise at speeds from 400 to 450 knots at relevant altitudes and hover in austere environments from unprepared surfaces.”
In Phase 1A, which started in November 2023, conceptual design reviews were conducted; in May 2024, Bell and Aurora Flight Sciences were down-selected and awarded contracts for Phase 1B with approximately one year to complete preliminary design work for their aircraft.
According to a press release by Bell, the wind tunnel testing comes after successful trials of its Stop/Fold rotor system at Holloman High Speed Test Track in New Mexico last year.
Along with the announcement, Bell has released a rendering of the X-plane along with a rendering of the concept Bell is working on to redefine how aircraft perform in contested environments. The aircraft has two wing-like structures extending outward symmetrically from either side, with compact tilt-rotor nacelles. The concept model also features fold-away rotor blades, suggesting a significant focus on reducing drag and optimizing for high-speed and efficient airflow. The central body appears sturdy, likely designed for stability during high-speed maneuvers or transitions. The aircraft also features two tails canted outwards.
The presence of a C-130-sized plane in the rendering is also interesting.
Triangular spinners? Bell tests stop-fold tiltrotor #X-plane design for #DARPA SPRINT project. Also reveals potential C-130-size operational vehicle with chined spinners that conceal blade fold and pitch mechanisms and reduce drag at high speed. SPRINT aiming for #VTOL and 400kt cruise. #aviation
— Graham Warwick (@theworacle.bsky.social) December 5, 2024 at 8:19 PM
Their Stop/Fold system allows aircraft to fold and unfold rotors as well as rotor blades mid-flight, blending helicopter-like versatility with jet-like speed and, according to the company, the recent wind tunnel tests were critical in proving this concept works. These trials verified the aircraft’s stability and control as it transitions through rotor folding and unfolding during flight. Combined with last year’s high-speed sled tests, Bell has cleared two major hurdles, demonstrating that this groundbreaking technology is ready to move into the flight demonstration phase under the DARPA SPRINT program.
Bell completed risk reduction testing at Holloman Air Force Base in late 2023, showcasing folding rotor, integrated propulsion, and flight control technologies Bell is building on its investment in High-Speed Vertical Takeoff and Landing (HSVTOL) technology and past X-plane experience to inform the X-plane development for this program.
Bell’s HSVTOL technology blends the hover capability of a helicopter with the speed (400+ kts), range, and survivability of jet aircraft. Bell has developed high-speed vertical lift technology for more than 85 years, pioneering innovative VTOL configurations like the X-14, X-22, XV-3 and XV-15 for NASA, the U.S. Army and U.S. Air Force, and continues to build on its proven history of fast flight from the Bell X-1.
Jason Hurst, Bell’s executive vice president of engineering, commented the successful completion of the wind tunnel testing:
“After completing folding rotor transition testing on the sled at Holloman Air Force Base last year, we’re thrilled to have now completed this next phase of testing,” said Jason Hurst, executive vice president, Engineering, Bell. Bell’s advanced Stop/Fold family of systems will revolutionize the speed, range and survivability of vertical lift aircraft to enable operations in contested environments. We are excited to be part of another aviation milestone with this breakthrough technology.”
The DARPA SPRINT program’s goal is ambitious: develop an experimental aircraft (X-Plane) that combines jet speed with the flexibility to take off and land almost anywhere.
For the military, this tech represents a massive leap forward. It gives warfighters the ability to operate with greater payloads and longer ranges from virtually any location. This isn’t just about convenience; it’s a strategic advantage, especially in regions like the Indo-Pacific, where long distances and limited runways make traditional aircraft operations more difficult.
Bell’s scalable Stop/Fold configurations combine modern jet speed with runway independence, offering next-generation capabilities that will transform the battlefield for the nation’s warfighters. The ability to leverage available runways for maximum payload and range, along with robust vertical lift, empowers Agile Combat Employment (ACE) from nearly any location—delivering a clear strategic advantage, particularly in the Indo-Pacific theater. In an environment with limited runways, vast distances, and a contested battlespace, this aircraft provides the essential speed and range to meet mission demands. This unique combination of capabilities is also ideally suited for Special Operations, enhancing speed, reach, and survivability for our most challenging and sensitive missions.
