Bell X-76 tiltrotor for the DARPA SPRINT program
The design of the future X-76 UAV
Bell Textron, commissioned by DARPA, has developed a new experimental aircraft—the X-76 SPRINT tiltrotor. This project has now completed the main development stages, and construction of the prototype is now underway. Within two years, it is planned to undergo testing and make its first flight, after which the tiltrotor will be expected to demonstrate a unique combination of flight and takeoff/landing characteristics.
In the early stages
The SPRINT (Speed and Runway Independent Technologies) program was launched three years ago. On March 1, 2023, the Defense Advanced Research Projects Agency (DARPA) and the U.S. Special Operations Command (US SOCOM) held an official presentation announcing the launch of the new program and revealing its main goals and features.
On March 9, DARPA issued a request for information and opened the call for applications from companies interested in participating in the project. Submissions were accepted for two months, after which the project's stakeholders began reviewing the proposals. Projects for further development were scheduled for selection and award of contracts in the fall.
The goal of the SPRINT program was to create an aircraft capable of achieving sufficiently high speeds without requiring large runways or landing sites. At the prototype stage, the desired speed was at least 400 knots (740 km/h), a range of at least 200 nautical miles (370 km), and a payload capacity of over 450 kg.
Three years ago, it was reported that the program would be divided into three phases. The first involved developing the overall concept of the new aircraft. The second involved fully developing the project and building prototypes. Phase 3 encompassed a full range of ground and flight tests.
Early concepts of SPRINT aircraft
All development stages were planned to be completed by mid-2026 fiscal year, or spring 2026 calendar year. The first flight was planned for 2027, and all flight tests were to be completed by the end of 2028. As has now become clear, the original schedule had to be revised.
Project from Bell Textron
The SPRINT program attracted the interest of Bell Textron Inc., who submitted their application and technical proposal within the specified deadline. This company has been actively pursuing the development of non-standard aircraft in recent years, and their experience could be applied to the new DARPA and US SOCOM program.
In October 2023, the customers approved Bell-Textron's design and funded its further development. For the next several months, work proceeded behind closed doors. However, in late 2024, the company first published a possible design for the future SPRINT product. Using 3D models, they demonstrated the key features of this technology.
In June 2025, Bell Textron's project moved to the next phase. Phase 2 was intended to complete the development and build a prototype aircraft. At that point, it was noted that the project was on schedule, and all subsequent activities would be completed as previously stated.
On March 9, 2026, it was announced that Bell Textron had completed the technical documentation and was beginning construction of a prototype aircraft. The aircraft received the working designation X-76. The "X" denotes the experimental nature of the project, and the numbers refer to 1776—the new project commemorates the 250th anniversary of American independence.
According to current plans, construction of the X-76 tiltrotor prototype will be completed next year. It will then begin preliminary ground tests. The first flight is scheduled for early 2028. A timeline for all necessary tests cannot yet be determined.
Bell Textron's SPRINT manned and unmanned tiltrotor aircraft are 2024 concepts.
New solutions
The X-76 SPRINT project proposes a unique tiltrotor design that aims to achieve an optimal balance of key performance characteristics. It envisages the use of established and proven concepts, as well as several original solutions. The project's key design principles could be scaled up for the development of new, similar aircraft.
The X-76 resembles an unmanned aircraft. It will feature a spindle-shaped fuselage with a pointed nose cone. The center of the fuselage will house a high-mounted, straight wing with engine nacelles. The tail is V-shaped. The fuselage will house control systems, a cargo bay, and other components.
The dimensions and weight of the future tiltrotor have not yet been specified. The customer's specifications suggest a medium size and a takeoff weight of several tons.
The X-76 will receive a unique three-engine powerplant. Two engines of an unspecified model are proposed to be mounted in rotating nacelles on the wingtips. These engines will have two operating modes. During vertical takeoff and landing, hovering, and low-speed flight, they are expected to operate as turboshafts, turning three-bladed propellers. As the aircraft accelerates, the propeller blades will fold along the nacelles, and the engines will switch to jet mode. A further turbojet engine is also planned for the tail of the fuselage.
It is expected that this powerplant, despite its complexity, will deliver the required level of flight performance. Flight speed will reach the target 400-450 knots, range will exceed 200 miles, and so on.
The X-76 prototype will be unmanned. It will feature a control system with an autopilot and remote control. These instruments will allow it to perform simple flight missions necessary to demonstrate its performance characteristics. Installing more complex equipment, including for practical applications, currently appears impractical.
Hypothetical manned tiltrotor aircraft SPRINT
The SPRINT prototype is required to have a payload capacity of at least 1 pounds. During the testing phase, the X-76 will likely carry ballast. However, future tests involving simulated combat payloads and their "use" are possible.
Plans for the future
According to the latest newsBell Textron's X-76 tiltrotor project has completed the development phase, and construction of the prototype is now underway. This process is expected to take approximately eighteen months. Ground testing is expected by the end of 2027, with the first flight scheduled for early 2028.
During flight tests, the X-76 prototype will need to demonstrate the operability of the key technical solutions used in its design. The projected flight, technical, and operational characteristics will also need to be confirmed. Only after this will experiments with practical applications of interest to the Special Operations Command or other agencies begin.
The X-76 project's main innovations affect the powerplant design. A non-standard set of engines with unusual operating modes is proposed. Folding propellers also play a key role in the design. All of this significantly complicates the tiltrotor's overall design, but should improve key performance characteristics.
The current experimental project is expected to demonstrate the potential of these ideas. If positive results are achieved, they can be used in new projects. Plans are already underway to create similar tiltrotor aircraft in manned and unmanned configurations, with different weight and payload parameters, with distinct functions, and so on.
Overall, the SPRINT program has great potential. In the medium and long term, it could significantly impact development. aviation The US military, including Special Operations Command and other agencies, is currently considering these capabilities. However, for now, these are only theoretical possibilities. The SPRINT program has not yet reached full-scale testing, and the prototype technology has not yet demonstrated its real-world capabilities. Full conclusions will not be possible until 2028, when the X-76 takes to the air for the first time.
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