Stingray air vehicle T1
Stingray air vehicle T1 positioned with the forward launch and aft holdback bars lowered over the imitation catapult’s shuttle track.

Published in the UAV supplement 2020/2021 – US Naval Air Systems Command is developing the world’s first non-experimental air vehicle designed for carrier-based operations and autonomous aerial refuelling.

A team of aerospace specialists led by Naval Air Systems Command (NAVAIR) and Boeing’s Phantom Works is currently developing a new weapon system, one that’s set to change many of the established cultures of military aviation. Designated the MQ-25A and named Stingray, this 15.5 metre (51 foot) long non-experimental unmanned air vehicle (UAV) is the world’s first designed for carrier-based operations. In addition to catapult launch and arrested landing capabilities, the Stingray will perform autonomous aerial refuelling (AAR) in support of all fixed wing aircraft assigned to the Carrier Air Wing (CVW).

Secondary to that, the MQ-25A has an intelligence, surveillance and reconnaissance (ISR) role afforded by an electro-optical and infrared (EO/IR) sensor. Data will be transmitted at appropriate classification levels to other aircraft, naval vessels, ground forces, and to exploitation nodes afloat and ashore, specifically the Navy’s Distributed Common Ground System.

In official Department of Defense (DoD) parlance, the MQ-25 extends CVW mission effectiveness range, partially reduces the current Carrier Strike Group (CSG) organic ISR shortfall and fills the future CVW-tanker gap, mitigating strike fighter deficit and preserving F/A-18 Super Hornet fatigue life for fleet defence and strike missions.

As the first carrier-based, Group 5 unmanned aircraft system (UAS), the MQ-25 will pioneer the integration of manned and unmanned flight operations, demonstrate mature sea-based UAS command, control, communications, computers, and intelligence (C4I) technologies, and pave the way for future multifaceted multi-mission unmanned air vehicles to keep pace with emerging threats.

The latter is a pointer to follow-on roles for the MQ-25. Certainly the air vehicle’s low-observable stealthy configuration points to the air vehicle being used to drag aircraft in CVW strike packages further from the carrier than ever before: most importantly supporting F-35C Lightning IIs into non-permissive environments.

A likelihood not denied by Captain Chad Reed, MQ-25 programme manager, Unmanned Carrier Aviation with PMA-268 who said: “Right now, even though its configuration is stealthy, there is no low-observable requirement for the MQ-25. Our requirement was for Boeing to use mature technologies in accordance with the accelerated programme goals. It is designed to operate in permissive environments when it enters the fleet, while concepts of operation are explored, and it’s meshed with manned operations. Manned-unmanned teaming is a notable aspect of the programme, one that’s on the cutting-edge simply because other aircraft are not designed to operate in such close proximity to and with manned aircraft: Stingray has a configuration and a new capability unmatched in a current air wing.”

UCLASS and NGAD

MQ-25 requirements are aligned with the initial capability documents for the Unmanned Carrier Launched Airborne Surveillance and Strike (UCLASS) programme, and the Next Generation Air Dominance (NGAD) family of systems. Both documents highlighted the need for carrier-based refuelling and persistent ISR capabilities.

The Joint Requirements Oversight Council’s (JROC’s) guidance set out a requirement for a versatile platform that supports a myriad of organic naval missions such as aerial refuelling and ISR to support the CSG. On 21 July 2017, the JROC validated the capability development document for the MQ-25 Carrier Based Aerial Refueling System (CBARS).

Designed to be sustainable on board an aircraft carrier and from shore bases, the MQ-25 system is comprised of three major architectural segments:

– the air segment includes the MQ-25A air vehicle and associated support and handling equipment including the deck handling system, spares and repair materials.

– the control system and connectivity (CS&C) segment includes the Unmanned carrier aviation Mission Control System (UMCS) and its associated communication equipment; mission support functionality of the Distributed Common Ground Station-Navy (DCGS-N), the Navy’s primary intelligence, surveillance, reconnaissance and targeting system; all network based interfaces and routing equipment required to control the Stingray; and all required modifications to existing networks and C4I system infrastructure.

– the CVN (aircraft carrier) segment comprises the ships’ spaces allocated to unmanned carrier aviation, installed ship systems and modifications necessary for interface with the air and CS&C segments. CVN systems important to the MQ-25 include aircraft launch and recovery systems, data dissemination systems (including radio terminals and antennas), and deck operations systems. Ship installation requires considerable work to re-model nearly 900ft² (84m²) of space on board the carrier to house the UMCS.

As Lead Systems Integrator (LSI), PMA-268 manages all three.

In terms of its operating envelope, the MQ-25 adequately meets the fleet’s current operational needs and achieves the two primary roles. Driving that performance is a relatively low air vehicle empty weight and the fuel-efficiency of the Rolls-Royce AE3007N engine.

Components integrated on the air vehicle to meet mission requirements include a long wingspan for flight stability and endurance; a Héroux-Devtek landing gear system; redundancy systems for safety of flight; Raytheon ALR-69A(V) all-digital radar warning receivers providing 360 degree  coverage; a Raytheon AAS-52 MTS-A multi-sensor imaging system equipped with infrared and CCDTV sensors, laser rangefinder, designator and illuminator; and one Rolls-Royce AE3007N turbofan engine rated at 9,000lb (40kN).

Systems specific to carrier flight deck operations include a tail hook for arrested landings; foldable wings to minimise the air vehicle’s parking footprint on the flight deck; design features that ease maintenance; and on-deck control systems that integrate with systems currently used on Nimitz and Ford-class carriers.

CBARS Competition

Based on the US government’s acquisition strategy approved in April 2017, the MQ-25 programme is an evolution from the previous UCLASS programme.

Concepts for the now defunct UCLASS programme were deemed too difficult and challenging given the number of new technologies involved, all of which required evaluation. Consequently, NAVAIR’s PMA-268 implemented a restart to evaluate the art of the possible for introducing something so new as the MQ-25, and to explore concepts of operation.

In 2016 Congress appropriated PMA-268 a congressional plus-up award for four contractors each capable of developing an UAS suitable for the CBARS requirements; Boeing, General Atomics, Lockheed Martin and Northrop Grumman.

Each contractor presented PMA-268 with ideas about how they were to mature their own technologies and concepts prior to receiving their share of the congressional plus-up award; a means of funding their respective concept development programmes through mid-2018. At that point with details, including the giveaway fuel load and ranges of each of the concepts submitted, PMA-268 conducted a tanker trade study which help conclude its requirements for the CBARS programme.

CBARS programme
An artist impression of the Lockheed Martin proposal for the CBARS programme, shown on a catapult ready for launch.

PMA-268 released the draft air system Engineering, Manufacturing, and Development (EMD) Request for Proposal (RFP) in July 2017 and released the final EMD RFP in early October 2017. Shortly after, Northrop Grumman dropped out of the competition citing an inability to meet the Navy’s specification and deliver a profit.

Less than eight months after receiving qualified proposals, PMA-268 awarded the EMD contract to Boeing Company in August 2018. This was the fastest Acquisition Category 1 (ACAT-1) EMD award of the past ten years.

Under the EMD contract, the first seven aircraft procured by the Navy are four Engineering Development Model (EDM, not EMD) test air vehicles (AV-1, AV-2, AV-3 and AV-4), and three System Demonstration Test Articles (SDTA). In addition, Boeing will also build two more airframes – one for fatigue testing and one for static loads testing.

Part of the requirement was to have a considerable amount of the design already complete prior to contract award; each company had either a prototype or a developmental article ready.

PMA-268 staff conducted a thorough review of each proposal over the next eight months. Boeing’s bid was determined to offer the best value for the government, first and foremost because of its ability to meet the schedule, and the ability to meet the key performance parameters (KPPs). It’s notable that the MQ-25 had just two KPPs. This a consequence of a pilot programme launched by the Chief of Naval Operations, Admiral John Richardson in 2017 that sought to limit the number of KPPs for a new weapon system to no more than three. PMA-268 opted for two; the capability to give away a set amount of fuel to a CVW strike package hundreds of miles away from the carrier, and full integration with Nimitz and Ford-class carriers as they currently operate.

MQ-25 is designated a maritime accelerated acquisition programme because the Chief of Naval Operations, Admiral John Richardson and the Assistant Secretary of the Navy for research, development and acquisition, James Geurts saw the importance of getting the system to the fleet quickly. More specifically to reduce the amount of flight time used up by F/A-18 Super Hornets when conducting the aerial refuelling role. The 6,000-hour Super Hornet service life is being depleted at much faster rates than anticipated. This has forced the Navy to devise and develop a new weapon system to conduct its tanker mission and save Super Hornet service life. This is a primary reason why the Navy switched its plan for a carrier-borne UAS from one programme, UCLASS, to another; CBARS (see below).

The CBARS concept also addresses other tactical aspects of carrier aviation; it helps to counter emerging threats now fielded by potential adversaries. That capability almost certainly points to a need for the MQ-25’s stealthy, low-observable configuration.

T1 and Phase One Testing

Phantom Works, Boeing’s advanced prototyping division, started building air vehicle T1 in 2012.

The design features a blended wing-body-tail air foil with folding, high-aspect-ratio wings and a V-tail. Its configuration reflects the long-endurance mission requirements of the UCLASS programme, particularly the long thin wings. Phantom Works finished the first iteration in 2014 as part of its design proposal for the UCLASS programme.

Air vehicle T1 has the same outer mould line and the same engine to nascent production standard MQ-25s. Consequently, some aspects of testing already undertaken with T1 will not require repeating with a production standard air vehicle.

T1 N234MQ
T1 N234MQ (s/n 00001) on its first wheels-up flight from MidAmerica Airport. The shadow cast shows the air vehicle’s chine, the longitudinal line of sharp change in the cross-section profile of the fuselage.

The objective of the MQ-25 test programme is to evaluate system maturity and technical performance of the aerial refuelling role; both mission and recovery tanking.

Initial ground testing with T1, including communications integration, towing, combined system and taxi, began almost immediately following contract award at Boeing’s facilities in St Louis, Missouri. In April 2019, Boeing trucked T1 to MidAmerica St. Louis Airport in Illinois to conduct the first phases of flight testing. T1’s maiden flight took place there on 19 September 2019. The company chose MidAmerica (the commercial side of Scott Air Force Base) because of hangar, runway, taxiway and air space availability.

As of 20 March, T1 had flown 12 flights and amassed nearly 30 hours during which the team worked through test points designed to evaluate the aerodynamic performance of the air vehicle, altitudes and air speeds, and the performance of the engine. T1 is fully instrumented for capturing flight test data used to evaluate flight and aerodynamic performance.

T1 is currently undergoing a planned modification for the installation of an aerial refuelling store underneath the left wing, specifically a Cobham 31-301-7 buddy store. The modification is required because T1 was originally developed without pylons to carry stores; that was not a requirement of UCLASS. The first series of aerial refuelling flight tests will follow later this year.

Testing with T1 will continue over the next few years to include envelope expansion, engine testing, aerial refuelling store operations, and Joint Precision Approach Landing System (JPALS) functionality testing.

The latter will require T1 to undergo a second modification period to enable the air vehicle to land using the JPALS, a differential, GPS-based precision landing system that guides aircraft onto carriers in all weather and surface conditions up to the rough waters of Sea State 5.

An important mod to evaluate functionality and identify any issue with JPALS before the FY2021 delivery to Naval Air Station Patuxent River of the first EDM test configured air vehicle AV-1.

T1’s involvement in the test programme will culminate with its hoisting aboard an aircraft carrier to test the deck handling and control station systems.

Boeing’s St Louis facility.
Combined system and taxi testing at Boeing’s St Louis facility. This shot shows the fuselage cross section form, the bulges of the wing joints housing the actuators and hydraulically-actuated pins that lock the wings in place, and the pitch of the tail surfaces of the V-tail.

Risk Reducer / Later Test Phases

T1 has already proven beneficial as a risk reducer during initial ground and flight testing. According to PMA-268, T1 is performing as the models projected to give the programme confidence as it moves to EDM standard air vehicle production and test.

Having T1 available for testing years before the first EDM comes off Boeing’s St Louis production line supports early learning and the discovery of any issues much earlier than is typical. Lessons learned and any issues identified can be applied and corrected during the development of the EDM air vehicles. For example, an icing susceptibility issue with the air data probe system has already been identified. To correct the issue, a different air data probe has been designed and will be fitted to all four EDM air vehicles AV-1, AV-2, AV-3 and AV-4, during their production.

Without T1, the test team would not have been able to identify the air data probe problem for several years.

Initial testing of each EDM air vehicle will take place at Boeing’s MidAmerica St Louis Airport facility by an integrated Navy-Boeing test team before delivery to Naval Air Station Patuxent River, Maryland. The Air Test and Evaluation Squadron 23 (VX-23) ‘Salty Dogs’ will lead testing of MQ-25.

Part of the air vehicle’s catapult launch and arrested landing equipment testing will take place at Naval Air Engineering Station Lakehurst, New Jersey, followed by cold soak trials in the McKinley climatic laboratory at Eglin Air Force Base, Florida.

AV-1 will undergo all aspects of a standard flight test programme followed by catapult launches and arrested landings at both Patuxent River and Lakehurst.

Boeing is conducting T1 flights in partnership with PMA-268, whereas EDM flight testing will be conducted by an integrated Navy-Boeing test team led by VX-23.

PMA-268 is overseeing all preparations for the MQ-25’s test programme at Patuxent River. A hangar and laboratory facility are under construction, support equipment is being acquired, and personnel recruited.

AV-1 and AV-2 will be dedicated to flight sciences testing and fitted with similar instrumentation to T1. AV-3 and AV-4 will be dedicated to mission systems and carrier suitability testing, and the air vehicle’s effectiveness to the aerial refuelling role, all planned for the second phase.

The air vehicle’s all-up weight is an incredibly important design parameter for carrier suitability. The MQ-25 must be capable of fulfilling its tanking role despite the constraints imposed by maximum catapult shot weights and arrested recoveries from Nimitz- and Ford-class carriers. All-up weight was also constrained by the requirement for a fuel giveaway of 16,000lb (7,257kg) at 500 nautical miles (925km) from the carrier. By comparison, a Super Hornet holds a giveaway fuel load of 12,000lb (5,443kg) on a two-hour cycle, 15,000lb (6,803kg) on a normal cycle and 25,000lb (11,339kg) on a short cycle.

The MQ-25 will also be tasked with recovery tanking, which involves having a tanker airborne in orbit close to the carrier while aircraft recover. A critical capability at night or when the weather conditions are bad with a pitching deck in heavy seas, such that pilots need to top up the tanks to afford further attempts to land on the flight deck.

Initial Operational Test and Evaluation (IOT&E) is the final phase.

Control System

Designated the MD-5 A/B (ship/shore), the Unmanned Carrier Aviation Mission Control System (UMCS). An MD-5 A/B control station comprises open architecture software, six OJ-845 common display systems, two UYQ-122 common processing systems, one network processing group, one integrated communication system, and network connectivity.

Both the MD-5 and its operating software are being developed by PMA-268, which is also responsible for all modifications required to shore-based and CVN infrastructure. The latter includes integration of NAVAIR-developed software with Boeing’s air vehicle OFP, the network, and the command, control and communication systems that will enable both CVN and shore-based control of the air vehicle.

A PMA-268 team demonstrated the first build of the UMCS using representative shipboard equipment and a simulated air vehicle at Patuxent River on April 11, 2017.

During the demo, the UMCS communicated with a Surface Mobile Aviation Interoperability Lab truck, simulating an air vehicle, and verifying command and control. Connectivity between the UMCS and shipboard network systems was tested and voice trunking (internet protocol to serial) between the air vehicle operator (AVO) and the simulated UAV was verified.

Limited control and data dissemination between the UMCS and simulated air vehicle to include automatic identification system detection, electro-optical/infrared camera operation, and full motion video, pre-planned and dynamic mission re-planning, was also performed.

UMCS 1.0 demonstrated that third party software can coexist with the common control system (CCS) framework, thereby proving the architecture is viable.

This demonstration was the first of a series to demonstrate UMCS capabilities as development of the system progresses.

Integration testing is ongoing at Patuxent River as part of the programme’s first test phase.

UMCS hardware builds on Naval Sea Systems Command’s common display and processing systems from the DDG-1000 Zumwalt-class destroyer and other Aegis-equipped ships.

It also incorporates the Navy’s CCS, a software architecture that features a common framework, user interface, and components designed for use with a variety of unmanned systems.

US Navy documentation lists a requirement for 12 UMCS sub-systems for assembly and delivery to installation sites between September 2020 and October 2027.

Air Vehicle Control

Using mouse and keyboard controls, the AVO commands the air vehicle where it needs to go and what it’s required to do: the system determines how to get there in the most safe and efficient way.

Typical operation involves the AVO maintaining positive control of the air vehicle, including the ability to change speed, direction and altitude, and continuously monitor the machine while in flight.

Flight control software is designed to handle unexpected events such as bad weather or when a change to altitude or the position of its tanking pattern is required.

The AVO, a warrant officer, will use the MD-5 control station housed within the carrier’s Unmanned Carrier Aviation Warfare Center throughout all stages of the mission from the catapult launch to the arrested landing.

Prior to launch and landing, a deck handling operator will use a deck control device to taxi the Stingray around the flight deck. Once the air vehicle is on the catapult, at some point the deck handling operator will hand-off to the AVO. After landing, the deck handling operator will assume control to taxi the air vehicle to its parking spot. This is a similar method to the one used for the Northrop Grumman X-47B demonstrator.

During aerial refuelling ops, the AVO will have the ability to communicate with the receiver aircraft’s pilot. PMA-268 is currently developing a concept of operations for aerial refuelling which will follow the same procedures as currently used by Super Hornets.

Milestone C and Beyond

Since contract award to Boeing, PMA-268 is following a non-standard version of the rigorous Systems Engineering and Technical Review (SETR) process to finalise the design. The DoD tasked PMA-268 to tailor out elements of the standard SETR process as part of the MQ-25’s Military Airworthiness Authority distinction in order to achieve a six-year schedule. MQ-25 milestone names and requirements differ from the traditional convention because of the focus on accelerating development and delivery to the fleet. Work will continue through to the MQ-25 system design review (SDR) later this year to set its baseline design. This will allow production of the EDM air vehicles to begin. SDR is similar to a critical design review used by other DoD programmes.

PMA-268 is pursuing a Milestone C decision for low rate initial production in FY2023 to procure up to 12 MQ-25A air vehicles. Following successful IOT&E, PMA-268 will pursue a full rate production decision for an estimated total of 76 air vehicles. Stingray is expected to achieve its initial operational capability with the fleet in 2024.

by Peter Donaldson

MQ-25 Stingray Characteristics

Wingspan: 22.86m (75ft)
Wingspan folded: 9.54m (31ft 3in)
Length: 15.54m (51ft)
Height: 4.78m (15ft 8in)
Flight deck footprint – no greater than a Super Hornet