Revolutionizing Air Mobility: How DARPA SPRINT is Developing Fast, Runway-Independent Aircraft to Expand Military Capabilities

Airplanes have revolutionized long-distance transportation allowing  people to cross continents and oceans quickly, safely, and relatively cheaply. They have changed the meaning of warfare and were an important stepping stone into space. However, conventional aircraft require long runways for both take-off and landing are classified as CTOL ( Conventional Take-off or Landing).

Sometimes long runways aren’t available to use and there is a need for an aircraft to use short or no runways at all.  Vertical take-off and landing VTOL technology means aircraft can theoretically take off and land almost anywhere, making them far more flexible. They’re also able to perform various manoeuvres not possible with a conventional plane; a significant advantage for aircraft in combat situations. What’s more, VTOL aircraft, such as drones, that use electric motors are more energy efficient than those using jet engines.

Runway independent aircraft (RIA)

Runway independent aircraft (RIA) are aircraft that are capable of taking off and landing without the need for a traditional runway, using techniques such as vertical takeoff and landing (VTOL) or short takeoff and landing (STOL).

Vertical takeoff and landing (VTOL) aircraft include fixed-wing aircraft that can hover, take off and land vertically, as well as helicopters and other aircraft with powered rotors, such as tiltrotors. The helicopter’s spinning rotors create thrust like a large propeller that is directed vertically, enabling it to lift off. While in flight, a slight tilt in the desired direction pushes some of the aircraft’s thrust and sends the craft forward.

For deeper understanding of STL/VTOL technology and applications please visit: Vertical Take-off and Landing (VTOL) Aviation: Soaring Beyond Horizons

The development and use of RIA pose several requirement challenges, including:

1. Safety: RIA technology requires a high degree of safety due to the lack of runway infrastructure. This includes the development of reliable propulsion systems, advanced avionics, and collision avoidance systems.
2. Efficiency: RIA must be efficient in terms of fuel consumption and performance to ensure their viability for commercial use. This involves designing aircraft with lightweight materials, advanced aerodynamics, and efficient power plants.
3. Infrastructure: RIA require specific infrastructure such as landing pads, maintenance facilities, and navigation systems. These will need to be developed and maintained to support RIA operations.
4. Regulatory frameworks: The development of RIA requires a regulatory framework that addresses safety, certification, and operational requirements. This will require the involvement of national and international regulatory agencies.
5. Cost: RIA technology is still relatively new and developing the technology requires significant investment. The cost of producing RIA will need to be reduced to make it commercially viable.
6. Noise: Some types of RIA, such as VTOL aircraft, can produce significant noise pollution. This can be a challenge in urban environments where noise restrictions are in place.
7. Pilot training: Pilots will require specialized training to operate RIA due to the unique flight characteristics and technology involved.

Overall, the development and use of RIA pose several requirement challenges that must be addressed to ensure their safe and efficient operation. However, the potential benefits of RIA, such as increased mobility and reduced congestion, make it an area of significant interest and investment for the aviation industry.

DARPA SPRINT Program

DARPA  announced an initiative called SPRINT (SPeed and Runway INdependent Technologies) in March 2023, inviting designers to develop aircraft that can fly fast and take off and land without the need for runways. The agency aims to have a demonstration flight within 42 months. SPRINT seeks to create an aircraft capable of cruising at 400 knots (460 mph), faster than Black Hawk helicopters but slower than an F-16 fighter jet. The aircraft should also be able to hover in austere environments like fields or deserts.

The SPRINT X-Plane project will seek to validate technologies and integrated concepts that can be scaled to different size military aircraft. “The objective of the SPRINT program is to design, build, certify, and fly an X-plane to demonstrate enabling technologies and integrated concepts necessary for a transformational combination of aircraft speed and runway independence for the next generation of air mobility platforms,” explained DARPA’s in an official press release.

Runway independent operations are envisioned as the ability to operate and hover near unprepared surfaces, such as sections of damaged runways, remote highways/roadways, unprepared fields with dry grass, parking lots, etc. Runway independent operations are transient operations not meant for continuous operations in one particular spot. Runway independent operations are still meant to be compatible with personnel operations from or near the aircraft. There is no disk loading, downwash or surface hardness limit set for the proposal.

Technical Objectives and Assumptions

The primary technical objectives of the SPRINT X-Plane Demonstrator are aimed at validating the underlying technologies and integrated concepts through flight demonstration:

• SPRINT X-Plane must demonstrate the ability to cruise ≥ 400 KTAS at a relevant altitude and perform basic forward flight maneuvers in a stable manner.
• SPRINT X-Plane must demonstrate the ability to hover and perform hover maneuvers in a stable manner.
• SPRINT X-Plane must demonstrate the ability to transition between hover, forward flight and high-speed forward flight modes in both directions in a stable manner.

The X-Plane will have the following attributes to assist with sizing and meeting technical objectives:

• Sustained flight speed ≥ 400 KTAS at an altitude between 15,000 and 30,000 feet
• Useful payload of ≥ 1000 lbs. in mainly a single dedicated space reserved for flight test instrumentation/avionics or residual capability

SPRINT X-Plane must demonstrate the ability to generate and distribute power in all modes of flight and during transition between these modes of flight

In addition to basic design and performance information the proposer will further highlight the capabilities of the technologies/integrated concept by discussing the following attributes:

• Short Take-off and Landing Capability – Describe ability to take-off and/or land in 300 feet, describe payload range effects or other relevant performance impacts.
• Runway Independent Operations in Austere Environments – Discuss impact of downwash/outwash and engine exhaust environment on operations in austere environments. Discussion should include vertical take-off, hover operations, personnel deployment from aircraft, personnel on the ground.
• Engine Out Operability – Describe advantages or disadvantages of fundamental technologies or integrated concept to land after a loss of power in a vertical mode of operation.
• Mission Applicability – Describe OS design’s ability to conduct infiltration/exfiltration, agile tactical airlift, and aeromedical evacuation missions from a cargo space viewpoint, (i.e., how do the fundamental technologies or integrated concept impact cargo space available).
• Aerial Refueling – Describe whether the fundamental technologies or integrated concept limit aerial refueling capability and efficiency.
• Maneuverability/Nap of the Earth Controllability – Describe advantages or disadvantages of the fundamental technologies or integrated concept ability to maneuver during slow or hover operations, vertical rate of climb or control during nap-of-the-earth operations (comparison to legacy platforms is useful).

Technologies validated by the X-plane testing can be scaled to different sized military aircraft, allowing them to cruise at over 400 knots and hover in harsh, unprepared spaces.

DARPA TTO is planning a 42-month contract to develop the SPRINT X-Plane demonstrator. The first six months will involve conceptual design and review as well as interface definition. It will be followed by simulation, component and subsystem testing, and planning the production and flight test.

The second phase of the project will cover construction, ground test and certification, and the third phase will involve validation in a flight environment.

Airworthiness certification of the X-Plane will occur in Phase 2; however, design and test planning considerations may be applicable to this BAA. Performers are expected to complete all safety/airworthiness reviews and obtain airworthiness certification prior to first flight