Lightweight armour for aircraft and helicopters

Modern composite armour has transformed protection for helicopters by slashing weight and minimising risks from ricochets compared to older heavy steel plates. The CH-47 Chinook’s upgraded kit proves that modern materials boost survivability without endangering performance. Commanders still face trade-offs though: more armour means reduced payload and impacts manoeuvrability, especially in hot, high-altitude zones. Ultimately, effective protection is about striking the right balance between safety and mission success.

The use of armour to protect individuals, equipment and platforms from hostile fire, be it percussive or piercing, is as old as, ahem, ‘knight and day’. Those that could not afford the full suits of armour worn by our heraldic ancestors resorted to the use of small plates or helmets to offer protection to their most valuable and vulnerable areas. In many respects, when it comes to protecting todays’ combat aircraft and helicopters, many of the same considerations apply.

The trade-offs of protection

Full suits of armour indeed made the wearer all but impervious to many types of arrows and slashing weapons. However, they were also extraordinarily expensive and heavy, often restricting the ability of the wearer to bring their own weapons to bear. They also caused issues for their wearer’s horse – more weight equated to less speed and endurance, both reducing combat effectiveness. Moreover, being cocooned in steel also degraded the wearer’s situational awareness (SA) – sight and hearing were both impacted – both key factors in battle. Inevitably, as has been the cycle throughout history, weapons and tactics were developed and employed to counteract the protection afforded by armour – including piercing weapons such as lances, blunt trauma effectors such as maces, and, eventually, firearms. A slower horse was an easier target too, and dismounting a knight from his steed would leave him at a manoeuvre and SA disadvantage as he tried to stand his ground or make good an escape.

Many of the same trade-offs remain relevant today for military aircraft. At what point does the armour become so heavy that it degrades the platform’s ability to execute its mission? At what stage does fitting a comprehensive armour kit result in the platform having to complete two runs instead of one, due to the weight and space limit the armour imposes, thereby exposing itself to more risk of engagement? What parts of the aircraft or helicopter are armoured, to what level of protection? These and many other considerations, are often on the minds of requirements staff, manufacturers and commanders in the field. Ultimately, it is the latter who have to weigh and balance risks based on their understanding of the threat and operational imperative. Sometimes, as experienced by helicopter crews in high-density altitude theatres such as Afghanistan, a decision regarding armour can leave a helicopter poorly placed in the event of a single engine failure – potentially resulting in an increase in heavy landings.

As we would often teach trainees on the Tactics Instructors course, despite it being a hackneyed phrase, it’s important to ‘honour the highest threat’ – and sometimes that’s the natural environment you’re flying through, not the enemy you face.

Understanding the threat

To defend against a threat, you must first categorise it. This article will focus on the use of applique armour, rather than ‘built in’ provision. Therefore, it will not consider those aircraft and helicopters designed to aggressively confront the enemy directly on the battlefield. The AH-64 Apache, for example, is built with ballistic tolerance as part of its core DNA, while the pilots of the venerable A-10 Thunderbolt sit within a titanium ‘bathtub’ shielding them from harm at calibres up to 23 mm. There is no ‘trade’ to be made in such aircraft – they are wheeled out of the factory at a high level of tolerance and protection.

Instead, we will concentrate on those platforms that move through much of the same battlespace as the likes of the A-10 and AH-64, but whose primary task is to deliver people, supplies and equipment – not conducting gun runs and launching Hellfire missiles; in other words, Tactical Air Transport (TacAT) aircraft and battlefield helicopters (BH).

The threat to both TacAT and BH platforms can be categorised into two main areas – guided and unguided. Guided threats, be they optically via a command-to-line-of-sight (CLoS), infrared (IR)/thermal or radar, tend to be either heavy calibre cannons that are impracticable to armour against and still retain operational utility, or missiles with some form of high-explosive and fuzed warhead. While any form of ballistic protection can afford some measure of barrier to the fragments from a warhead, it is not designed explicitly to do so. Instead, most TacAT and BH platforms are concerned with the more ubiquitous threat of small arms (SA). Unlike large radar guided systems, rifles and machine guns can be hidden almost anywhere – for example the boot of a car – and quickly gathered and made ready for firing. They are impossible to trace, and, until recently with the advent of hostile fire indicators (HFIs), surprisingly difficult to detect when fired at you – unless, of course, unexpected shafts of daylight start appearing in the aircraft (usually accompanied by a ‘ting-ting’ sound), systems start failing or, ultimately, crew or passengers start getting hit.

You also can’t see tracers until the rounds have already gone past you. As an example, on the author’s last operational sortie in Afghanistan, we returned to a Forward Operating Base (FOB) one afternoon only for them to note over the radio that they were surprised to see us again – we had, apparently, been engaged by a 12.7 mm DShK (informally known as ‘Dushka’) when we had visited them earlier in the day. We were blissfully unaware – no damage to the aircraft, no sign of the tracer arcing past us. I was instantly reminded of Sir Winston Churchill’s comment in his book ‘The Story of the Malakand Field Force’, published in 1898, and describing, appropriately, actions on the North West Frontier between what we now know as Afghanistan and Pakistan: “Nothing in life is so exhilarating as to be shot at without result.”

 

Weighing the value of protection

The anecdote provides a useful segue to describing a typical BH armour fit, and some of the rationale behind it. That day in 2011, I was flying an RAF CH-47 Chinook helicopter in ‘standard’ Theatre Entry Standard (TES) for the time. We were equipped with an upgraded countermeasures system, a pair of 7.62 mm M134 Miniguns to deter attacks (but a 12.7 mm heavy machine gun outranges a 7.62 mm weapon), an optoelectronic turret to assist night flying (which was extremely difficult, especially during the ‘Red Illumination’ period of the lunar month) and a comprehensive ballistic protection (BP) kit.

I’d been the Requirements Manager that oversaw the programme to buy the BP kit, run in concert with a project that delivered a far better cargo offload system to the legacy cargo handling system. When I’d first got to the Chinook in 1997, the armour fit was rudimentary; we had steel plates bolted to the cockpit floor, sat in armoured seats, and had both ‘wing armour’ plates, that swung into position to offer some protection from fire coming in from the side, and wore chest plates in our flying equipment. While steel armour is undoubtedly effective, it has a number of issues.

First, it is really heavy; all aircraft are sensitive to weight, but helicopters, with the need to take off and land vertically, even more so. Second, large amounts of additional metal on an airframe can affect sensitive equipment, especially magnetic compasses. All helicopters vibrate, and while it would seem logical that additional plating would contain cracks, more often it merely serves to transfer the damaging frequencies to a new, and sometimes unmonitored or weaker, part of the structure. Finally, steel might be good at stopping rounds, but it also presents a ricochet hazard. This is important because at low level, aircraft and helicopters seldom fly in straight lines (to make any would be gunners’ tracking task harder) and often the platform is not engaged from directly underneath (most armour kits cover the floor only). If the aircraft is engaged from the side while manoeuvring, and hit, rounds can come through the unprotected fuselage sides and roof, hit the steel plates on the floor, and cause rounds to ricochet around the interior – think of the grisly landing craft scene in ‘Saving Private Ryan’.

The catalyst for the RAF’s moves to enhance the armour fit for its Chinooks was the ‘Battle of Majar al-Kabir’ in Iraq in June 2003, shortly after the cessation of major combat activities. The growing mistrust between locals and occupying forces burst into insurrection, leading to a small number of Royal Military Police (RMP) becoming isolated and besieged in a local police station. A Chinook was scrambled with a Quick Reaction Force (QRF) to relieve the pressure on the RMP team but flew into a storm of insurgent gunfire and was forced to retreat. The Chinook received over 100 small arms hits but was lucky enough to be missed by the multiple rocket-propelled grenades (RPGs) launched at it. Seven troops in the cabin were wounded by gunfire – some seriously.

The fact that the Chinook had not been shot down despite the multitude of hits was reassuring to the aircrew who flew it, but less so to the troops and passengers we carried, who now realised how vulnerable they were. An urgent operational requirement (UOR) was drafted for a new BP system for the aircraft, this time to protect both the cockpit and the cabin. The UK MoD selected armour provider Plasan to provide its Chinook Kit via a combined programme including new Cargo Handling Systems, managed by Permali UK.

Plasan’s approach was far more up-to-date than simply bolting steel plates to the cabin floor. The armour itself was made of a composite, layered, material. This is significantly lighter per square metre than steel, and it, to an extent, ‘breathes’ with the airframe, helping to mitigate the transference of energy and cracking. The composite material is less brittle than steel and the kit is made up of a number of closely-fitted individual panels rather than large continuous plates. These panels have access holes through them to enable the crew to still use the Chinook’s tie-down points, meaning that cargo and key role equipment, such as M134 Minigun ammunition boxes and Robertson’s extended range fuel system (ERFS), can still be fitted and used normally.

 

Importantly, the composite material absorbs energy rather than merely deflecting it, resulting in far lower chance of ricochets, and reducing the energy of those rounds and splinters that do. The reduced weight also enables the system to feature side wall protection; in the Chinook it means that the cabin sides are protected up to the level of halfway up the cabin windows, with cut-outs to permit the windows to be used normally, including as a means of emergency egress. When seated on the sidewall seats, most troops are screened from direct gunfire from the side, even more so if in a combat configuration and sat directly on the armoured floor using lap belts. Such protection does, however, come at a cost and with limitations.

Pragmatically, the most likely prevalent threat to Western helicopters are the users of former Soviet Union weapons, of which, by far the most proliferated is the AK-47 family of assault rifles. The AK-47 is chambered to the 7.62 × 39 mm round, which is available in a number of ammunition types, including the most common, Full Metal Jacket (FMJ) ball, but also armour-piercing (AP) and tracer. Given that the most likely encountered threat is the AK-47, and the most testing ammunition is AP, most BP manufacturers set that round as the baseline for their kit. A panel that can withstand a 7.62 × 39 AP round is also capable of standing up to a larger 7.62 × 51 mm or 7.62 × 54 mm ball round in most circumstances – in effect the difference between a personal weapon (AK) and a general purpose machine gun (GPMG) such as the FN MAG/M240, PKM or M60. Accepted testing standards for BP assumes a near point-blank range engagement with maximum muzzle velocity, therefore, at more representative combat ranges, there is a strong chance that baseline BP will protect against AP and AP Incendiary rounds in the GPMG calibre range.

 

This is important, because protection needs to be weighed against mass. Increasing the baseline BP kit to cover larger calibres and more penetrating bullet types will, inevitably, come with a concomitant increase in kit weight. A full CH-47 kit from Plasan (cockpit, ramp, cabin floor and side panels) weighs around 2,000 kg. That’s a fair chunk of the platform’s disposable payload (about 20%) but still leaves plenty of mission flexibility between fuel and cargo – because it’s a Chinook. It’s not so easy to manage with machines with more marginal performance, especially in ‘hot and high’ conditions.

Closing thoughts

Armouring an aircraft or helicopter is a key decision for commanders. Fitting BP will manifestly increase the chances of the aircraft returning, and of the crew and passengers being able to fight another day, but it needs to be, literally, weighed against the impact it can have on the aircraft’s mission effectiveness. The migration from steel to composite has helped, and transparent armour for cockpits, permitting pilots to use their markers on the ground during hover and dust landing evolutions, is now coming to the market from companies such as OSG.

When, as a survivability consultant, I’m asked to list the absolute minimum airframe equipment I would have on a platform, be it TacAT or BH, to take into any form of combat, it’s always the same three things: IR suppression, door guns and BP. BP is simply, in my opinion, as important as that.

 

Paul ‘Foo’ Kennard