Regrettably, advances in helicopter design have not been as impressive as for fighter aircraft. This is despite the fact that helicopters have been utilised in every conflict situation and despite the availability of technology to permit generation leaps in helicopter design. Rising costs and lowering priorities of helicopter development projects have also meant digression from lofty doctrines seeking air mobile manoeuvring groupings and autonomous helicopter forces. However, combat and tactical mobility roles of the military helicopter preoccupy land forces. The presence of military helicopters on the battlefield is essential as is their logistical applications. While the ongoing and foreseeable helicopter projects can be seen as positive steps in the direction of military helicopter development, the possibility of single platform designs tailored for specific roles appears to be remote, at least in the foreseeable future.
Discounting scarce and sporadic employment for strategic missions, the military helicopter is a tactical platform. Its roles have evolved impressively over the years. Casualty evacuation was the humble beginning, soon to be followed by increasingly aggressive and offensive roles in support of land and maritime forces. The latter confined by the limited scenarios that could involve helicopter support, have not expanded as much as those supporting land forces. For the land battle however, the advent of the military helicopter was as historically significant as that of the battle tank.
The empowerment of the land forces commander was substantially enhanced by the helicopter…
The empowerment of the land forces commander was substantially enhanced by the helicopter. Whilst the land forces fought the land battle and gained ‘ground’, the air forces fought the air battle to keep the land campaign going. It was the helicopter which, though conceptually part of ‘air’ forces, remained conjoined with land forces through an invisible umbilical connection.
There is no doubt about the advantage the versatile helicopter provides in the battlefield. Nevertheless, development in helicopter technology has not been as speedy as in the fixed-wing domain. While fixed-wing combat aircraft have entered ‘fifth generation’ and are nudging the sixth, helicopter evolution has lagged behind, cruising speed being the single major constraint. This article addresses the current thought processes and technologies for rotary wing military machines in the world, dwells upon the limitations of the helicopter as a platform and crystal gazes into the future of the military helicopter, with some prescriptive comments specific to India.
The need for higher forward speed is bemoaned both by helicopter pilots and the commanders. The downing of an MH47 Chinook in Afghanistan earlier this year with a loss of 30 US lives was quoted as an argument in favour of higher speed to reduce vulnerability to ground fire. Simply stated, speed would help military helicopters to achieve missions more efficiently, helping them to reach critical targets and destinations in shorter time while providing better immunity against enemy fire.
Development in helicopter technology has not been as speedy as in the fixed-wing domain…
Vulnerability of military helicopters has also been a subject of concern. While helicopters would operate in the battlefield generally flying below 100 feet, some would actually follow the terrain, hug contours and even use them to play hide and seek with the enemy. Nap-of-the-Earth (NoE) flying is the attribute helicopters are endowed with the agility and manoeuvrability to perform that very interesting genre of flying, involving flying not above but between obstructions such as trees or terrain features.
Thus, the operating envelope of military helicopters is largely confined to the vicinity of the ground, infested with enemy weapons, some of which are optimised for aerial targets and some others such as small arms though not designed against helicopters but are equally lethal. In addition, the probability of an additional hazard of friendly fire by trigger-happy troops on the ground, adds to the susceptibility of the helicopter to being ‘downed’ during a mission in the battlefield.
The helicopter’s vulnerability also arises from the noise its rotor system generates. As the Soviet helicopter pilots learnt in Afghanistan, even small arms fire from a perch higher than the flight path could render the helicopter unfit to continue its mission. More recently, Operation Geronimo highlighted the requirement for helicopters to be more agile, manoeuvrable, quiet and stealthy. These would render them less detectable and therefore less vulnerable to enemy action. The loss of a helicopter at Abbottabad also highlighted the fact that a helicopter is most prone to accidents when in close proximity to the ground during landing and while taking off or when undertaking winching/cargo swing operations while hovering close to the ground. That brings us to the next perceived requirement for evolving and emerging designs – survivability. Crash resistance, a feature to minimise damage to the helicopter in case of an uncontrolled or partially controlled contact with ground below, comes at a weight penalty but remains an essential criterion for military helicopter design. Peripheral requirements could include the unmanned rotary wing craft. Afghanistan provided the opportunity to prove this technology with cargo missions being executed pedantically and successfully by the US Marines there. A concept of a ‘hybrid’ design that is becoming more attractive envisages unmanned flight performed through remote piloting.
However, the pilot will be in the cockpit to perform the final stages of the mission or to take over in case of a system failure/malfunction. To summarise, the pipedream of the military helicopter pilot as he looks into the future is a fast, stealthy, survivable AirWolf type machine that will achieve all missions semi-autonomously and with safety.
The Speed Problem
Conventional helicopter design has remained predicated to the rotor system which restricts maximum speed to around 180 knots. Fixed wing aircraft can be made to travel faster by refinements in airframe design to reduce drag and by increasing engine thrust. Helicopter design is different inasmuch that the hull and engine power are not the speed determinants; the spoil sport is the rotor system which imposes inherent limitations on speed on account of its design. One solution is the tilt-rotor design wherein the plane of the rotor disc tilts through 90 degrees.
Thus, the rotor disc can be horizontal for a vertical lift off and then tilted forward to become a vertical disc providing forward thrust much like a propeller system. The V22 Osprey, produced jointly by Boeing and Bell, is one such successful Vertical Take Off and Landing (VTOL) design adopted by the US Air Force and US Marine Corps. It has a maximum speed of 275 knots at sea level and 305 knots at 15,000 feet. These speeds are considerably higher than conventional helicopters although still no match for fixed wing aircraft. A variation is the Oliver VTOL proposal for a six-engine craft called the Hexplane which, it is hoped by the developer, would reach 350 knots at 35,000 feet. Other designs aimed at increasing speed include the twin contra-rotating rotor system with a tail propeller for extra thrust in forward flight. AgustaWestland is looking at the possibility of blades that can alter shape during flight.
US Defense Advanced Research Projects Agency (DARPA) is funding the development of a Disc-Rotor Compound Helicopter. This intriguing design is a cross between a helicopter and a fixed-wing airplane, with the helicopter blades extending from a disc sitting atop the aircraft and letting it take off and land like a helicopter. However, once those blades are retracted into the disc, drag is minimised and the aircraft can fly like a fixed wing aircraft, powered by engines beneath each wing. The design is similar to the V22 Osprey inasmuch that it is a mix of a helicopter and a fixed wing design. However, the V22 Osprey experience has not been one of unadulterated success. There have been fatal accidents despite which the speed advantage it represents has retained it as an attractive military VTOL option.
The need for higher forward speed is bemoaned both by helicopter pilots and the commanders…
Indeed, the Federal Aviation Administration is yet to certify it for civil use. Some aver that the Sikorsky S92 M would do all that the V22 Osprey is expected to do, and in a more efficacious way. The Sikorsky X2 and Eurocopter X3 are designs with contra-rotating rotor systems and propellers for forward thrust. The X2 has already demonstrated a speed of 250 knots.
Despite the fact that military helicopters have been and are being built in large numbers for multi-faceted roles, new designs have been inconsequential barring the tilt rotor VTOL. Most of the current helicopters are essentially designs from 1970s and 1980s which have been reconfigured or modified to incorporate new technologies. These include sturdier airframe materials, more powerful engines, stealth features such as radar defying paints and fuselage shapes, crash resistant undercarriage and seats, more formidable rotor systems and so on. Only modest investments have gone into helicopter R&D across the world and technological innovation has largely evaded the military helicopter.
According to Walter J Boyne, a retired pilot, a former Director of the US National Air & Space Museum and the author of “How the Helicopter Changed Modern Warfare”, the helicopter is the ‘beloved stepchild’ within the family of military hardware. Investment in rotary wing design development has not been as focused as it ought to have been and so, while the currently flying designs would last until the 2030s, their replacement programmes are not reassuring. It is possible that the current designs, themselves not-too-proud variations of older designs, may continue even beyond the 2030s.
The US experience in Vietnam was an invaluable learning path in the tactical employment of helicopters. However, since then, new lessons have had to be learnt. Afghanistan has been one learning ground, the other being Iraq. The 40-Apache raid in Iraq was an unmitigated disaster. Two pilots were shot down and captured and thirty helicopters were damaged to such an extent that the mission was rendered untenable. Needless to say, thinkers and planners in the US military are looking at the future of the military helicopter with a new awareness and expectation. The US Army, which currently operates close to 4,000 helicopters in various roles, is looking at a combination of rotor and fixed wing as the possible solution.
The target date is 2030 for the new ‘vertical lift’ aircraft and a US Army led programme, the Joint Multi-Role (JMR) Demonstrator, is drawing up an ambitious wish list with inputs from the Coast Guard, Special Operations Command and NASA. The final objective appears to be a design with vastly improved avionics, electronics, range, speed, survivability, operating altitudes and payloads and a speed of 200 knots. The ‘multi-role’ part of the programme alludes to several roles ranging from attack configurations to cargo, medevac, anti-submarine warfare, search and rescue.
The US Army’s next generation helicopter could be ‘optionally manned’, that is, it could be capable of autonomous flight for a full mission or a substantial segment of a mission. The initial demonstrator models are expected to be designed starting in 2013 and the first prototype could fly in 2017. The US Army has shown a keen interest in the Common Infra-red Counter-measure (CIRCM), a state-of-the-art laser jammer that would deflect incoming missiles. CIRCM is expected to be fielded by 2018. The JMR is a part of the Pentagon’s longer-term plan known as Joint Future Vertical Lift (JFVL); JMR and FVL have thus become synonymous. The programme is intended to field by 2030, light, medium, heavy-lift and ‘ultra-class’ behemoth, the Joint Future Theatre Lift (JFTL), a sort of rotorcraft equivalent to the versatile C-130 that could hoist huge vehicles and equipment without the need for a long runway.
The probability of an additional hazard of friendly fire by trigger-happy troops on the ground, adds to the susceptibility of the helicopter…
One concrete step that has already been taken in the direction of the JMR is a fifty-fifty partnership between Pratt & Whitney and Honeywell Aerospace for developing the Advanced Affordable Turbine Engine (AATE), aimed at providing a 30 per cent increase in horsepower for helicopters while at the same time cutting fuel consumption by 25 per cent. The engine, developed under an Army plan called the Improved Turbine Engine Program (ITEP), will eventually be a drop-in replacement for the GE T700 turbo shaft engine that currently powers the AH-64 Apache and UH-60 Black Hawk. The Army will be able to achieve improved performance and fuel savings by retrofitting those aircraft with the ITEP engine in the short run.
By 2037, the CH-47 Chinook will be outdated, followed closely by the AH-64 Apache and UH-60 Black Hawk in 2040. It remains to be seen whether the US Army will be able to induct into service suitable and satisfactory replacements for these and other helicopters currently in use with it. Meanwhile, Sikorsky has proposed a new CH 53K super Stallion helicopter to be operational by 2019 and to carry 12.3 tonnes at 6,000ft at 35˚C (roughly three times the lift capacity of the CH-53E). The helicopter is also expected to carry that load over a distance of 204km.
Sikorsky is also developing the S-97 Raider helicopter for the US Army’s prospective Armed Aerial Scout programme. The coaxial-rotor, propeller-driven machine is based on the company’s revolutionary X-2 design, and is expected to undergo flight testing in 2014. Unlike a conventional helicopter, the S-97 is expected to cruise at 220 knots with external weapon loads and 235 knots if clean. It is planned to have a maximum speed of 250 knots. This project is funded entirely by private industry, three fourths of it coming from Sikorsky. Interestingly, the X-2 technology is also applicable to the US Army’s JMR/FVL initiative as the technology permits scaling up or down.