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The battle-rhythm for the unveiling of contenders for the U.S. Army’s Future Attack and Reconnaissance Aircraft (FARA) program is starting to resemble the arrival pattern for London buses: You wait seemingly forever, and then three arrive almost at once.
Only two weeks ago, Bell revealed the first renderings and details of its proposal, the Bell 360 Invictus, which I discussed in detail here. This week, coinciding with the Association of the U.S. Army (AUSA) conference in Huntsville, Ala., another ‘Big Beast’ of the helicopter industry, Sikorsky (part of the leviathan-like Lockheed Martin), has finally revealed its proposed competitor, the Sikorsky Raider X. Hot on its heels came Karem’s formal unveiling of its FARA concept, the AR-40.
This leaves just one Rumsfeldian ‘Known – Unknown’ left to be revealed, the proposal from Boeing. Industry sources speculate it may not be publicly announced until early 2020. This is, potentially, very close to the U.S. Army’s intended decision date of March 2020 when the field of five concepts will be culled to just two, both of which will be awarded a development contract to deliver a flying prototype in 2022 under a highly ambitious project timeline. The Army has publicly stated it wants the winning design in frontline service by 2028, and is open to any and every suggestion of how it can further accelerate this aggressive timeline. It’s one of the key drivers behind both Bell and now Sikorsky recycling technology from previous aircraft – acting as an accelerator and a de-risking methodology at the same time.
So, what of these two new contenders? Let’s start with the Sikorsky Raider X.
First things first. They really ought to consider changing the name.
Whilst ‘Raider X’ sounds cool, and is a deliberate namecheck on the S-97 Raider prototype that has been flying for several years (to provide confidence to the Army and budget-holders that the technology is not ‘all new’), it’s going to cause confusion. Why? Because the USAF has already christened its in-development Long Range Strike Bomber the B-21 Raider.
In fairness, if the rationale behind the name is to reference Pop Culture by comparison to the ‘Cylon Raiders’ in the re-booted ‘Battlestar Galactica’ series, then the B-21 has a far more cogent argument – it actually looks like something out of a dystopian Sci-Fi future. The B-21 is also planned to enter service in 2025, so it will be in the inventory first under current schedules. The potential for politicians and senior military staff to make a very public gaffe with two brand-new aircraft under development at the same time with very similar names is very real. Moreover, one can only imagine the confusion if a future Force Commander’s intent of ‘send 3 Raiders to pacify that area’ is misunderstood and taken out of context.
Putting the name to one side, what about the Raider X itself?
Firstly, the overall configuration should be no surprise to any observer. Sikorsky has been developing the coaxial drive system for decades. The Advancing Blade Concept demonstrator, developed in conjunction with NASA in the 1970s, proved the utility of the coaxial rotor design with additional thrust provided by fuselage mounted jet engines. The concept emerged again in the X2 demonstrator, which first flew in 2008. The X2 configuration was near identical to the proposed Raider X; a coaxial rotor system with a tail-mounted propeller offering additional thrust for increased cruise and dash speed.
In tests, the X2 achieved speeds in level flight in excess of 250kts (comfortably in excess of the FARA requirement) and proved that the rotors could be slowed down in high speed cruise. This is an important capability; primarily it decreases the drag caused by the blade tips approaching the speed of sound (Mach 1); this drag requires a significant increase in power to overcome. Higher blade speed also risks ‘Retreating Blade Stall’ where the blade flying ‘downwind’ cannot balance the lift across the disk, as it runs out of angle of attack. It can result in a dramatic, asymmetric, loss of lift across the rotor disk, and result in a violent departure from controlled flight.
Finally, and often overlooked for a Scout helicopter, a slowed rotor can offer significant noise reduction.
The X2 spawned two offspring with an identical configuration; the S-97 Raider and the much larger SB>1 Defiant, which is a joint program with Boeing seeking to win the U.S. Army’s Future Long Range Assault Aircraft (FLRAA) competition. The Raider X is a logical growth from the S-97 Raider prototype, leveraging off the configuration but increasing the aircraft size to meet the U.S. Army’s requirement set, not least the mandated use of the General Electric T901 engine, being developed under the Army’s Improved Turbine Engine Program (ITEP).
However, it’s not just the Coaxial/Thrust Compounded aspect of the Raider X that differentiates it from most current attack helicopters. Similar to the AVX/L3 proposal and the Karem AR-40, the Raider X places its Pilot and Co-Pilot Gunner (CPG) in a side-by-side, rather than tandem, seating configuration. Ever since the rapid design and introduction of the Bell AH-1 Cobra during the Vietnam War, attack helicopters have almost entirely featured a tandem configuration – only the Russian Kamov KA-52 ‘Alligator’ (or, as NATO term it, the ‘Hokum-B’) produced in comparatively limited numbers has adopted it – and even then, most likely, as it was the easiest way to add a second seat to the KA-50 ‘Black Shark’ when Russian crews reported that the workload was too much for a single pilot to cope with.
The rationale behind the tandem arrangement is quite logical. Firstly, it presents the narrowest possible frontal aspect to the potential enemy; this make the aircraft harder to acquire and track visually, reduces the Radar Cross Section and makes the aircraft a harder target to hit with ballistic weapons such as machine guns and RPGs. Secondly, it is far more aerodynamic – and improving aerodynamic efficiency not only improves speed, it also reduces the power required to attain that speed and, ergo, increases range. Finally, the tandem arrangement permits the Pilot/CPG to both sit on the centreline, or ‘boresight’ of the aircraft. This reduces any parallax issues over cockpit displays or the use of the EO/IR and other targeting and pilotage sensors.
Side by side has its advantages and adherents too. It enables better cross checking of crew drills and instruments, and enables the crew to communicate non-verbally if they are working a number of very busy radio nets. A side by side cockpit also permits larger individual displays to be used, which may well save weight rather than duplicating smaller screens in two separate cockpits. In battle conditions, it also enables a rapid assessment and treatment of an injured crew member. It must be remembered that the FARA aircraft will do both Reconnaissance and Attack. The former role, when filled by Scout helicopters (the OH-6 Cayuse and OH-58 Kiowa), used side by side arrangements. In the case of the OH-6, designed for the Army by Hughes aircraft, the 4-seat cabin and low cost were to permit a number of roles, including Observation, Scout, CasEvac and light attack. The Army will have an idea where its priorities lie today, but all of the FARA designs appear far more potent as attack platforms than the OH-58.
You’d be forgiven if you’ve never heard of Karem Aircraft. They are the true minnow in the FARA competition, but the CEO, Israeli emigre Abraham Karem, was responsible for the design of one of the most distinctive and successful designs of recent years, the MQ-1 Predator drone. After selling the MQ-1 design to General Atomics, Karem has stayed engaged in aviation and the AR-40 is his latest venture.
The AR-40 also has a side-by-side cockpit configuration, and at first glance, looks like a number of design cues from the Bell Invictus and Sikorsky Raider X have been fused together. There are, however, some unique features exploited by the AR-40. Firstly, it only has a single main rotor, not a co-axial like the Raider X. The rotor system is special, however: It uses ‘Optimum Speed’ technology designed in conjunction with the U.S. Army R&D program. This system allows the 3 blades to ‘fly’ at different pitch angles during their rotation, dependent on lift, g and drag factors. This increases efficiency and reduces the noise footprint.
The AR-40 doesn’t have a shrouded tail rotor like the Bell Invictus. Instead, it has a rotating tail rotor, somewhat reminiscent of the exhaust on the F-35B, enabling it to produce counter-torque effect at slow speeds and in the hover, whilst pivoting to increasing thrust in the cruise. It is also lift compounded, with a significant wing mounted mid-fuselage. However, unlike the compound wing on the Invictus, the AR-40 wing tilts. This is important for two reasons.
Firstly, one of the problems with a compound wing is that in the hover, the rotor downwash ‘pushes’ down on the top of the wing, leading to reduced hover performance. By tilting the wing up, the effect of downwash on the wing is significantly reduced. The second factor is that unlike the graphics of the Invictus, which show external pylons and weapons on the wing, we have to assume that a tilted wing will likely be for aerodynamic effect only and will not be ‘plumbed’ for external fuel tanks and weapons.
It remains to be seen what the assessors from the U.S. Army make of the FARA competitors, and how they will weigh their respective merits in terms of projected performance, capabilities, cost and, above all, risk. There is also the need to consider the unseen ‘dead-hand’ of pork-barrel politics. Perhaps when we see the final line up of competitors next year we’ll have a better understanding of whether the Army feel they need an aircraft closer to the high-end AH-64 Apache in capability or evoking more of the spirit of the retired OH-58.
The ball is now in Boeing’s court to complete the field. It will certainly be, for the neutral, a fascinating few months as the Army assesses the pros and cons of the configurations and settles on the last two for the showdown.