Hybrid Air Vehicles HAV 304 Airlander 10

HAV 304 and the LEMV requirement

During the 1990s, British engineer Roger Munk founded a company, Hybrid Air Vehicles (HAV), for the purpose of conducting development and marketing work upon on a large modern hybrid airship concept, referred to early on as Sky Cat. HAV formed a partnership with US aerospace and defense company Northrop Grumman to collaborate and promote the type to various military operators, particularly those of the US. Following the successful demonstration of the HAV-3 small-scale demonstrator, and with Northrop Grumman as the prime bidder, the hybrid airship concept was accepted for the US Long Endurance Multi-intelligence Vehicle (LEMV) project, in preference to the Lockheed Martin P-791 that had also been submitted.

In addition to Northrop Grumman itself, several subcontractors were involved in the LEMV project; these include United Kingdom-based Hybrid Air Vehicles Ltd. (the designer and manufacturer of the HAV 304 platform itself), Warwick Mills (providing fabric engineering and development), ILC Dover (specialised engineering development and manufacturing services), Textron subsidiary AAI Corporation (providing the US Army's OneSystem UAV/surveillance aircraft control & information distribution stations), and SAIC (full-motion video processing). Northrop Grumman were responsible for the integration of the various electro-optical/infrared, signals intelligence, radar and communications relay payloads onto the airship.

Requirements included the capability to operate at 6 km (20,000 feet) above mean sea level, a 3000 km (2,000 mile) radius of action, and a 21-day on-station availability, provide up to 16 kilowatts of electrical power for payload, be runway independent and carry several different sensors at the same time. According to the U.S. Army, the LEMV was to have been a recoverable and reusable multi-mission platform. It could be forward located to support extended geostationary operations from austere locations and capable of beyond-line-of-sight command and control. The developmental prototype emerged as the HAV 304, a helium-filled airship with twin conjoined hulls having a total internal capacity of 38,000 cubic metres. At 91 metres (299 ft) long, it is the longest aircraft in the world today; mid-20th century airships were longer, for example the German Hindenburg-class airships were 245 metres (804 ft) long.

Operationally, the LEMV was intended to be typically flown autonomously or as a remotely operated aircraft; for being transported to theatres of operation or within normal civil airspace, the airship can also be flown by onboard operators. According to Northrop's projections, one LEMV could provide the equivalent work of 15 fixed-wing medium-altitude aircraft.

Airlander 10

Following cancellation of the LEMV project, the deflated HAV 304 was repurchased by HAV, returned to the UK and hangared at RAF Cardington. There it was reassembled, refurbished and modified for a more general role; accordingly, the aircraft was no longer an example of the HAV 304 design, having been rebuilt into the Airlander 10 prototype instead.

Overview

The HAV 304 Airlander 10 is a hybrid airship, achieving lift, and thereby flight, via both aerostatic and aerodynamic forces. Unlike most airship designs, it does not have a circular cross-section, having adopted an elliptical shape with a contoured and flattened hull. This shaping is deliberate so that it acts as a lifting body, contributing aerodynamic lift while the airship is in forward motion; generating up to half of the airship's lift in a similar manner to that of a conventional fixed-wing aeroplane. Buoyancy is also provided by helium contained within the envelope, the pressure from which maintains the airship's unique shape, between 60 per cent and 80 per cent of the aircraft's weight is supported by the lighter-than-air helium.

The Airlander 10 is equipped with a set of pneumatic skids with which it may reportedly land and take off from a wide variety of terrain, as well as from water. On the ground and during takeoff, a reversible hovercraft-style air cushion is employed to manoeuvre on the ground; this facility can also be used to firmly fix the airship in place when grounded, useful when offloading cargo and eliminating the requirement for attaching ropes for anchoring purposes. On the ground, the Airlander 10 weighs approximately one tonne.

The Airlander 10 is capable of staying aloft for five days while crewed, and over two weeks while unmanned. The type had the potential for various civil and military applications; these include transportation purposes, conducting aerial surveillance, acting as a communications relay, supporting disaster relief operations, and various passenger services such as leisure flights and luxury VIP duties. Many of these duties could involve different configurations of the airship's mission module to suit. Northrop also said the LEMV could be used as a cargo aircraft, claiming that it had enough buoyancy to haul seven tons of cargo 3,900 km (2,400 mi) at 50 km/h (30 mph). According to HAV, the design would allow operators to choose between trade-offs between endurance and cargo capacity, carrying up to a maximum of 30,000lb of cargo.

Flight deck and controls

The Airlander 10 possesses a sizable flight deck upon which four large floor-to-celling windows are present, providing for a high level of external visibility. While the airship had originally been envisioned to be unmanned, HAV adopted an optionally piloted approach as a result of customer interest in such operations. In 2015, positions for a single pilot and an observer had been installed in the Airlander 10; HAV intend to adopt a twin-pilot configuration along with a greater prevalence of glass cockpit-style controls and instrumentation in the future. The airship is controlled by a side-stick mounted on the right-hand side, somewhat resembling that of a rotorcraft; there are no rudder pedals, the side-stick being automatically slaved to the vanes instead. Garmin-built avionics furnish the cockpit; the suite includes a closed-circuit television system that enables the pilot to view the otherwise-distant engines.

The propulsion units and flying surfaces are both connected to the flight control system via fly-by-optics, using optical fibre cables to efficiently cope with the vast scale of the vehicle. Inputs from the pilots controls are fed into various potentiometers, which produce digital signals encoded into light pulses and directed to the relevant flight surface or propulsion unit, or element thereof. Transitioning between the airship's multiple modes of flight is regulated directly by the computers of flight control system computers, enabling the type to be operated in a remotely-operated or unmanned configuration. According to HAV, the designing of the flight control regime was eased by the natural pendulum stability of the airship.

Structure

The hull of the airship comprises a skin made of triple-layered combination of composite materials, the skin provides considerable strength and rigidity when inflated, serving to keep in the gas, retain its unique shape, and support the four engines, fins and the flight deck that are attached directly upon it. Materials used include Vectran, Kevlar, Tedlar, Polyurethane, and Mylar; the Mylar layer, enveloped within polyurethane film layers, forms the airship's gas barrier. The Airlander 10 lacks any internal framework; weight from the payload module is distributed across every frame via cables running across and into the hull as well as internal diaphragms. According to HAV's Technical Director Mike Durham, the entirety of the airship's structural strength is derived from being inflated to just above atmospheric pressure with a 4-in. water gauge pressure differential (around 0.15 psi); this strength is due to the huge diameter of the vessel despite the relatively-low pressure differential.

The hull is internally divided by diaphragms into a total of six main compartments with additional sub-divisions; these divisions can be sealed in the event of emergencies, such as battle damage being sustained, allowing for the majority of the airship's helium, and thereby lift capacity, to be retained. Ballonets are housed within these compartments in order to regulate gas pressure; these are inflated on the ground to increase density and reduce lift. Air and helium are not allowed to mix in the ballonets, thus enabling each to be furnished with valves and fans in order to increase and decrease air volume independently; this approach is claimed by HAV to be unique to the airship.

According to estimates performed by Northrop, the biggest foreseen threat to the HAV 304 is adverse weather conditions, such as high winds or thunderstorms, that could buffet the craft. The threat posed by windy conditions is in part due to its vast surface area in comparison to most aircraft; in particular, ground operations are more difficult in such conditions, but not thought to reach the extent of becoming impossible. According to HAV chief test pilot David Burns, the danger from missiles was relatively low as they can pass through the airship without forcing it down. The skin is reportedly capable of handling small arms fire and other causes of tears due a level of built-in redundancy and the relatively-low pressure difference between the inside and outside of the hull.

Propulsion

The Airlander 10 is powered by a total of four Thielert Centurion 325hp V8 diesel engine which drive sets of three-bladed ducted propellers to provide the thrust for both flight and manoeuvring. These engines are positioned in pairs, one set being located towards the rear of the airship, while the other are positioned alongside the sides of the forward fuselage, mounted on stub wings. Each engine is furnished with a 50KW generator, which provides electrical power for the airship and its mission systems. The assembly for each of the side-mounted engines can be pivoted 20 degrees in either direction, vectoring the thrust to provide flight control, particularly during landing and taking off; the rear-mounted engines are fixed. By employing thrust vectoring, the engines can direct their thrust downwards to provide additional lift during takeoff. A series of four triangular-shaped variable vanes are positioned behind the engines to provide further control authority; such as by re-directing thrust from the rear engines over the tail fins.

While cruising at altitude, propulsion can be switched to a more efficient electric drive fed from the airship's central generator. Due to the hybrid aerostatic/aerodynamic lift approach, fuel can be expended without entering a state of positive buoyancy that would necessitate routine helium venting in order to land, a costly weakness present upon conventional airships. Fuel is primarily contained within the 40-ft.-long main fuel module housing up to nine tons of fuel; the main tank is supplemented by separate rear and forward tanks, containing up to 4 tons. To optimise cruising efficiency, the angle of incidence can be adjusted by pumping fuel between the fore and aft tanks.

Payloads

The Airlander 10 can be combined with an array of payloads—including ground moving target indication radar, electro-optical/infra-red sensors, communications relay, blue force tracking, signals intelligence, and electronic countermeasures. The LEMV was to have augmented existing ISR (Intelligence, surveillance and reconnaissance) platforms to provide additional capabilities, providing a possible solution for beyond line-of-sight communications to end users, signals intelligence collection and almost any other type of payload configuration that meets the power, weight and size requirements. By providing this all-source sensor data to existing ground stations, the data would be available to multiple users and analysts. This interoperability with existing tasking, processing exploitation, and dissemination had the potential to improve information-poor situations, mitigating warfighter gaps and existing shortfalls through multi-intelligence sensor integration.

The costs involved in reconnaissance by fixed-wing aircraft flight were estimated in 2010 to be $10,000–20,000 per flight hour, plus an additional $10,000 in recapitalization costs. Helicopters are more affordable than their fighter equivalent, and can intervene like fighters if weapons are needed, but are noisy and vulnerable, have very low endurance, and are not cheap to operate. Hybrid airships can operate, like a helicopter, from small forward bases. Their operating cost is likely to be better than other surveillance options, as is their endurance. According to Alan Metzger, director for airship programmes at Northrop Grumman, the airship's ability to stay in the air for long periods made it perfect for surveillance missions, stating to The Engineer magazine that the LEMV was "going to be the longest endurance UAV in the world. There will be no gaps in the data that gets put down to the war-fighter."

The airship could serve as a steady communications relay, ensuring that groups of soldiers in mountainous areas would never lose contact with one another, even if they do not have direct line of sight to each other. The LEMV could have tracked important convoys, key roadways, or other key infrastructure as semi-permanent overwatch escorts, monitor an urban area of interest to prepare for major battles or enforce security, or focus on shutting down border chokepoints. The LEMV would have enabled the American DoD to fly the most technologically advanced payloads in the near term as they became available. Northrop Grumman designed their system to integrate into the Army's existing common ground station command centers, and equipment used by ground troops in forward operating bases.

The LEMV project and the HAV 304

On 14 June 2010, the agreement for the development of the project was signed between the US Army Space and Missile Defense Command/Army Forces Strategic Command and Northrop Grumman. The agreement also included options for procuring two additional airships. The timeline for LEMV was an 18-month schedule starting in June 2010 that included vehicle inflation at about month 10. Additional operational characterization would have occurred at Yuma Proving Ground, Arizona, in month 16. The project cost between $154 million and $517 million, dependent on all options. The cost included the design, development, and testing of the airship system within an 18-month time period, followed by transport to Afghanistan for military assessment.

Throughout development, technological challenges and multiple delays were encountered. In October 2011, aerospace publication Flight International reported that the LEMV was scheduled to conduct its first flight in November 2011, three months later than originally planned. According to media reports, the first flight of the LEMV was rescheduled in early June 2012; however, unspecified problems again delayed the flight until August 2012.

The LEMV required at least 300 m (1,000 ft) of runway (violating the runway-independent requirement), and a tether point with a 100 m (300 ft) clear flat area around on which to park, which prevented them from operating at most large bases and all small bases.

On 7 August 2012, the LEMV conducted its maiden flight over Joint Base McGuire-Dix-Lakehurst, New Jersey. The flight lasted 90 minutes and was performed with a crew on board, being flown by Chief Test Pilot David Burns. The first flight primary objective was to perform a safe launch and recovery with a secondary objective to verify the flight control system operation. Additional first flight objectives included airworthiness testing and demonstration, and system level performance verification. At this point, the combat deployment of the LEMV to Afghanistan was projected to occur in early 2013.

Two months after the test flight, the US Army stated that it had concerns about sending the airship abroad; these included safety, transportation to the theatre of operations, and the timeline of deployment. The US Army had planned to demonstrate the first LEMV in Afghanistan 18 months after the signing of the contract; at one point, proposals included plans to construct a further five airships following mission completion. In October 2012, the Government Accountability Office (GAO) stated that the LEMV project was 10 months behind schedule due to a combination of factors, including issues with fabric production, foreign components being cleared through customs, and the impact of adverse weather conditions.

On 14 February 2013, the US Army confirmed that it had cancelled the LEMV development effort. In a statement made by a US Army Space and Missile Defense Command spokesperson, the cancellation was a result of technical and performance challenges that had been encountered, as well as resource constrains that had come into effect. Practical and theoretical knowledge gained was redirected from the LEMV to the JLENS program.

Reacquisition and the Airlander 10

The US Army believed that the project's technical data and computer software could be useful for future projects but that selling it would save money. Hybrid Air Vehicles expressed an interest in purchasing the airship, saying they wanted to use it for cold-weather flights and other testing for the development of their proposed "Airlander 50" 50-ton cargo airship. The HAV offer included the basic avionics, mooring masts and spare engines but not the specialist equipment or helium. With this the only offer on the table, in September 2013 the Pentagon sold the LEMV airship back to HAV for $301,000.

The deflated airship was returned to the UK, where it underwent reassembly and modification as the Airlander 10 prototype at RAF Cardington. In April 2014, HAV announced that it was forming an industry team with Selex ES and QinetiQ to develop and demonstrate the sensor capabilities of the Airlander 10, and that a three month demonstration period for the UK's Ministry of Defence has been planned. Selex has stated their future vision for the airship includes its possible use as a mother ship for launching multiple UAVs, such as the Selex ES Falco.

In April 2014, it was announced that both the European Aviation Safety Agency (EASA) and the UK's Civil Aviation Authority (CAA) had approved the necessary permissions for Airlander 10 to return to flight. At one point, HAV had intended for the airship to have completed reassembly and be ready for test flights by December 2014; however, delays were encountered while additional financing from commercial and government entities was being sought. The project received both UK and EU funding to support the airship's further development, totalling £7 million by March 2016. Crowdfunding from members of the general public also raised £2.1 million.

On 21 March 2016, the fully assembled Airlander 10 was publicly unveiled; at this point, HAV announced that the type would be offered for both civil and military use in the future. The Airlander 10 is also to serve as a prototype for an even larger version of the airship, referred to as the Airlander 50. According to reports, several military customers have shown interest in potential uses for the type, including in a projected unmanned configuration. Named the Martha Gwyn after the company chairman's wife, the airship has became popularly known as "the flying bum" for "the resemblance its plump front end shares with a human's back end."

Test flights and crash

On 17 August 2016, the first test flight took place at the aircraft's home base, Cardington Airfield in Bedfordshire, England, and lasted 30 minutes. HAV has stated that they intend for around 200 flight hours of testing to be eventually carried out to prove the airship ahead of performing customer demonstration flights.

On 24 August 2016, at the completion of its otherwise-successful, 100-minute second test flight, the Airlander suffered an accident while in the process of landing at Cardington. The airship came into contact with the ground nose-first and suffered extensive damage to the cockpit. The crew were reported to be "safe and well". The Air Accidents Investigation Branch opened an investigation. It revealed that the accident was influenced by the airship's mooring rope becoming entangled in wires as it approached its mooring mast.

HAV 304

Source:

Airlander 10

Data from hybridairvehicles.com

General characteristics

Performance