Form Follows Function? Bell's Invictus Helicopter Looks Familiar….

Form Follows Function? Bell's Invictus Helicopter Looks Familiar….

Form Follows Function? Bell's Invictus Helicopter Looks Familiar….

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Bell has finally taken the wraps off its contender for the US Army’s Future Attack Reconnaissance Aircraft (FARA) program. The Bell 360 Invictus is as interesting about what it looks like as what it can actually do. Bell’s military offerings of late have been a blend of ‘legacy’ rotorcraft, the highly evolved UH-1 Venom / AH-1 Viper family, and high-technology ‘bleeding edge’ tilt-rotors such as the V-22 Osprey, V-280 Valor (competing to replace the ubiquitous UH-60 Black Hawk in the US Army’s Future Long Range Assault Aircraft (FLRAA) competition) and the striking mock-up of the V-247 Vigilant Tilt-Rotor unmanned escort platform, designed in response to the USMC’s Unmanned Expeditionary Capabilities (MUX) concept study.

But. There’s no getting away from the fact that, at first glance, the Invictus looks a lot like the abandoned, and much lamented, Sikorsky RAH-66 Comanche.

The RAH-66 was sacrificed on the altar of cost savings in the early 2000s when it became clear that the War on Terror was going to be a prolonged fight against relatively unsophisticated opponents. Designed to replace the cheap, but vulnerable, OH-58 Kiowa in the Scout role, the RAH-66 was designed to operate in the high threat environment envisaged in Europe if the Cold War had ever turned ‘hot’. Unfortunately for the Comanche, such survivability came at a huge Dollar price. By the time of cancellation, the program had already consumed $7Bn in development and demonstration funding, with a further cost over $30Bn anticipated for the production of 1200 front line machines. The battlefield the RAH-66 was exquisitely moulded to survive on vanished, for good it seemed, with the end of the Cold War. Questions began to be raised about ‘Peace Dividends’, but the Army stubbornly continued with the Comanche program. The ‘game changer’ was the War on Terror; helicopters were suddenly very important to support campaigns in Iraq and Afghanistan, and in-service types such as CH-47, AH-64 and UH-60 needed upgrades to operate and survive in harsh environmental and extensive ‘low tech’ threat conditions found in both theatres. The Comanche’s expensive attributes – stealth and speed – were adjudged not required – as a Congressional report of 2003 noted that its –

“capabilities and mission requirements were developed in response to a Cold War threat environment that no longer exists”.

The US Army elected to recapitalise the Comanche production funding by updating its legacy fleets, investing in UAVs (militarily ‘all the rage’ at the time…), and by purchasing a new, cheaper, helicopter to replace the OH-58 Kiowa. This latter policy became unglued – quickly. Attempts to buy the ARH-70 single-source from Bell fell apart, and the palliative measure of re-assigning AH-64 Apache to the Scout role was immensely unpopular within the broader Army community; National Guard AH-64 Attack units found their aircraft being reassigned back to the Regular Army and replaced with UH-60 Black Hawk utility helicopters. It was quickly pointed out by vocal critics of the policy that it was absurdly expensive to use a full-up attack helicopter in the Scout role – despite the best efforts of the Army to justify it by attempts to ‘team’ it with Unmanned Air Vehicles under ‘Manned-Unmanned Teaming’ (MUM-T) programs.

So, what’s changed?

Remember that “Cold War threat environment that no longer exists”?

Well, it’s back. And in a big way.

Whilst Western militaries were fighting low light conditions, extreme temperatures and a threat environment characterised by shoulder launched heat-seeking missiles (MANPADS – Man Portable Air Defense Systems), Rocket Propelled Grenades (RPGs) and guns of nearly every calibre, our international competitors were investing hard in radar guided Surface to Air Missiles (SAMs) and advanced anti-aircraft guns.  They have also significantly upped their game in the fields of Electronic Warfare (denying, degrading, destroying, confusing or ‘spoofing’ friendly radars via electronic means), Jamming (radars and GPS) and, finally, Cyber warfare. Coupled with an increasingly confrontational stance from an emboldened Russia, a China keen to assert its place in the world and the proliferation of advanced weapon systems to third parties, including those involved in proxy wars, the ‘threat board’ for rotary wing aviation has spiked dramatically in recent years.

To survive in this “Back to the Future” environment we may well need technologies designed to aid platform protection back in the ‘bad old days’. This is where an aircraft like the Bell Invictus, perhaps inevitably, starts to resemble platforms designed in that epoch. Key design similarities, and their rationale, are;

1.    Angular fuselage shape. This is for two reasons. Firstly, and most obvious thinking about other designs, the angles of the Invictus will have been carefully calculated to minimise the aircraft’s Radar Cross Section (RCS). As with most Low Observable (LO) platforms, the RCS reduction will be optimised from specific aspects. As FARA will be a Scout aircraft, it is reasonable to assume that frontal aspect RCS has been optimised in the design. Secondly, somewhat more prosaic, the shape and packaging of Invictus mirrors the Comanche in reducing to a practical minimum the fuselage size. This makes the Invictus harder to visually acquire, and a smaller target to attempt to hit with ballistic weapons. It is also worth noting that the rotor hub is also shrouded to reduce RCS and, possibly, sun glint. Finally, an arrowhead is considered a very efficient aerodynamic shape – and one that is reflected in the Invictus’ basic form. Therefore, we can suggest that aerodynamic efficiency has also been a key design driver for Bell’s engineers.

2.    Internal weapons carriage. The RAH-66 carried its weapons internally. The Invictus plans to do the same too. Weapons in bays are a fundamental part of LO design – all ‘stealth’ aircraft have them. Missiles, due to their need for seeker heads and guidance fins, are often distinctly ‘non-stealthy’ – indeed, the entire RCS of the Comanche, whilst classified, was rumoured to resemble one Hellfire missile. Not only are missiles non-stealthy, they’re also ‘draggy’ aerodynamically so externally carried weapons not only slow the platform down, but will also increase fuel burn and, therefore, reduce range. Finally, missiles and rockets contain explosive warheads and sensitive electronics. Mounted on a weapons pylon they are vulnerable to both enemy fire (potentially causing a catastrophic daisy-chain detonation) and Electronic / Cyber-attack. Protected and shielded in a weapons bay, missiles are much safer to the host platform. Much like the F-35 in ‘Beast Mode’, the Comanche had a ‘conventional war’ capability with fitting external pylons to boost weapon load when the need for LO characteristics is considered less important. Given that the Invictus already has lift-compounding wings fitted, these may well be stressed and ‘plumbed’ for weapons and fuel tank carriage. It’s not yet clear from Bell whether the gun also stows when not in use, like the Comanche’s did.

3.    Retractable Undercarriage. Although it adds weight and complexity to a helicopter, the use of retractable gear on both the Comanche and the Invictus is consistent with reducing RCS, visual signature and drag.

4.    Shrouded / Tilted Tail Rotor. This is a really clever piece of homage to Comanche. The shrouded rotor, or Fenestron as it is known in Europe, provides significant signature reduction benefits. Firstly, it generates a smaller RCS than a conventional tail rotor. Secondly, it also reduces the acoustic signature, which remains important on the modern battlefield – especially for a Scout helicopter. The tilted rotor helps generate ‘free’ lift in the hover and at low speeds, helping the flight control system to level the aircraft for weapons release and reducing the power required to hover. This gives the pilot a little bit spare power to either enhance platform agility – for example to avoid an RPG – or take an increased payload.

Therefore, to a point, Form does follow Functionality. However, there are a few key differences to the Comanche that the Invictus is displaying in these ‘first look’ images.

1.    The wing. It’s the fundamental difference between the two aircraft. The design speed for FARA is around 200kts. Comanche topped out at around 180kts. The wing provides ‘lift compounding’ to the rotor blades. At high speed they generate enough lift to unload some of the aerodynamic burden from the rotor disk, enabling the Angle-of-Attack (AoA) – the blade angle relative to oncoming airflow – to be reduced. This is important for helicopters as too much AoA at too high a speed can cause the onset of a condition known as ‘Retreating Blade Stall’ which can cause a violent departure from controlled flight. Yet to be confirmed by Bell, but Thrust Compounding also opens the door to slowing the main rotor down. The key benefit of slowing the rotor is that it, naturally, also slows the blade tip speed. On conventional helicopters this tip velocity can reach near supersonic speeds – causing significant drag and vibration issues. High tip speeds are also a major factor in a helicopter noise profile. Therefore, an ability to slow the rotor at high speed is beneficial in performance and signature terms.

2.    IR Signature. Comanche had a complex internal structure that buried the engines and cooled the exhaust gasses internally before they were released into ambient air. This reduced the aircraft’s Infra-Red (IR) signature, making it a harder target to acquire and track either by an Electro-Optic sensor or IR Missile seeker head. At prima facie the Invictus has a more conventional engine exhaust system. Doubtless, there will be IR suppression techniques applied internally, as it appears that the intake and exhaust are on opposite sides, and I would postulate that the engines and transmissions are surrounded by thermal protection blankets to minimise the ‘hot metal’ signature that modern missile seekers can detect.

3.    “Supplementary power”. Bell’s initial press release refers to an intriguing piece of kit they term a supplemental power source. Geared from the main transmission, Bell cite the system as being on call to provide more speed and power when required. The obvious uses for extra power could be to enable a short duration ‘dash’ to evade a threat or improve manoeuvre potential, to facilitate hovering at high altitude or, with one eye on the future, having a power bank for discharging Directed Energy Weapons. This will doubtless be one feature the industry will look at most keenly.

4.    Built to a Cost. The fact that the Invictus is not going ‘full Comanche’ is as much to do with cost as capability requirements. Bell will have listened closely to the Army’s needs, and price control is a key driver – Comanche was cancelled for financial, not technical, reasons. Costs are reduced by having a single engine, the use of less exotic materials and reusing significant elements of the Bell 525 Relentless transmission and rotor system.

The Invictus is an intriguing overall package. As more details are released about the concept, and the broader FARA program, doubtless some of our questions will be answered and new ones raised. However, there is an important larger point; the US Army has consistently failed to field a new helicopter type since the UH60 and AH64 in the 1970s (the UH-72 Lakota was, effectively, a mature civil design painted green with a few military ‘extras’). Programs have been started and been cancelled. While successfully managing upgrades to legacy types, this failure to introduce new platforms has resulted in the wasting of $Billions, and several questions  over the Army’s acquisition process.

With FLRAA and FARA, the US Army has two headline programs underway – surely, this time, ‘failure is not an option’?


This article was written by Paul Kennard from Forbes and was legally licensed through the NewsCred publisher network. Please direct all licensing questions to