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Top to bottom: RH-90 Blueprint; RH-90 in Dynamic Green Demonstrator colour scheme; RH-90 UCMH-101 of the 32 Assault SQN bearing alpine camoflage
RH-90 Incursor Heavy Attack Helicopter
The RH-90 is a heavy attack helicopter which is most distinctive for its contra-rotating, co-axial rotor layout. The RH-90 is a helicopter designed to serve as an airborne weapons platform and as such is one of the largest purpose built attack helicopters ever created, coined specifically to carry the maximum amount of weapons and deliver them with the utmost precision. Designed to complement the smaller RH-77 and not replace it, the RH-90 prowess in the anti-armour role as well as its air-to-air capabilities makes it one of the deadliest helicopters ever to take to the skies.
Origins
The RH-77 and RH-90 were conceived and created at the same time in roughly the same time period, although neither helicopter would share any components or design work with the other and the two project teams never spoke. Unlike the RH-77 which was designed in Mikoyan-Guryevich as a light attack helicopter, the RH-90 was designed for the barren plains and wilderness of United Coronado.
The RH-90 was designed for a full scale invasion where the government of United Coronado wanted a helicopter that could wipe out enemy armour the moment it rolled over the border. Simply put, the avionic systems of the RH-90, which uses a radar similar to those employed on fighter jets, can target over fifty different targets in the air or on the ground and engage sixteen of them with radar guided missiles simultaneously. It comes as no exaggeration to say that the RH-90 is one of the few weapons in the world which can wipe out an entire battery or armoured column in mere minutes.
Avionics
Designed to be one of the most potent attack helicopters anywhere in the world, Coronadan engineers were not happy with just mediocrity for the avionics suite which would adorn their new project
A TAS or Target Acquisition System is the avionic tool which pilots will most heavily rely on when they are fighting in combat. The TAS is made up of several stabilized electro-optical sensors, a laser rangefinder and laser target designator, this allows the TAS to serve a powerful telescope to ensure that pilots can see the target, accurately determine the range to the target and then paint the target with a laser beam to serve as a point to guide missiles. The TAS assembly can rotate +/- 140 degrees in azimuth, +60/-90 degrees in elevation, giving the pilots an excellent view of the surroundings, and can even allow the pilots to see what is below the aircraft. The movements of ATAS can be slaved to the head movements of the helicopter crew to point in the direction that their head is facing. Images from the camera to be projected onto the crew helmet-mounted optical sights, overlaid upon their view of the cockpit and battle space. ATAS also contains a thermal imaging infrared camera and a full colour daylight television camera, with 1280x1040 resolution.
The DH-01 radar was designed specifically for the RH-90 and RH-77, drawing from principles from other aircraft constructed by Gemballa. The DH-01, made by Cervelo, is a Active Scan Radar which serves as a Fire Control Radar which is designed specifically to provide information (mainly target azimuth, elevation, range and velocity) to the firing system of the helicopter in order to calculate a firing solution. The DH-01 offers a track while scan capability which allows it to fire on some targets while simultaneously tracking others.
The Cervelo DH-01 Active Scan radar is designed for strike operations and features a low-observable, active-aperture, electronically-scanned array that can track multiple targets in any weather, including storms. The Cervelo DH-01 Active Scan changes electromagnetic frequencies at more than 1,000 times per second to greatly reduce the chance of being intercepted by an enemy aircraft. If the radar happens to be spotted, it can then focus its radar emissions on an enemy aircraft, to overload enemy sensors and thus jamming the enemy radar. This radar fitted to the RH-90 employs a very erratic search pattern made possible by the enourmous computing power at the disposal of the crew which naturally makes it even harder to track. The DH-01 was designed with the Low Probability of Intecept theorem as paramount with a strong emphasis on the lowest possible observability to other aircraft or other systems. Unlke many other radar systems, the DD and DH series of radar has very few moving parts and is much less likely to malfunction in the air than other radar systems employed by other aircraft.
An AESA or Active Electronically Scanned Array radar system represents the forefront of modern radar technology. These radars are deceptively hard to intercept because an AESA radar will change its frequency every pulse, at up to 1000 times per second. Since the AESA can change its frequency with every pulse, and generally does so using a pseudo-random sequence, integrating over time does not help pull the signal out of the background noise. Nor does the AESA have any sort of fixed pulse repetition frequency, which can also be varied and thus hide any periodic brightening across the entire spectrum. Traditional Radar Warning Receivers are essentially useless against AESA radars. This means that the RH-90 can look for long periods of time without being seen in the process.
Jamming is likewise much more difficult against an AESA. Traditionally, jammers have operated by determining the operating frequency of the radar and then broadcasting a signal on it to confuse the receiver as to which is the "real" pulse and which is the jammer's. This technique works as long as the radar system cannot easily change its operating frequency. When the transmitters were based on klystron tubes this was generally true, and radars, especially airborne ones, had only a few frequencies to chose among. A jammer could listen to those possible frequencies and select the one being used to jam.
Since an AESA changes its operating frequency with every pulse, and spreads the frequencies across a wide band even in a single pulse, jammers are much less effective. Although it is possible to send out broadband white noise against all the possible frequencies, this means the amount of energy being sent at any one frequency is much lower, reducing its effectiveness. Moreover, AESAs can be switched to a receive-only mode, and use the jamming signals as a powerful source to track its source, something that required a separate receiver in older platforms.
AESAs are so much more difficult to detect, and so much more useful in receiving signals from the targets, that they can broadcast continually and still have a very low chance of being detected. This allows the radar system to generate far more data than if it is being used only periodically, greatly improving overall system effectiveness.
The radar utilises a separate transmitter and receiver module for each of the antenna's radiating elements. Making up the array of the AESA radar are over 5000 15cm long individual transmit and receiver modules. Each tiny TRM weighs in at just 50 grams, yet still contains a power output of six watts apiece, a relatively high amount. To remove the high amounts of heat generated by the AESA, the array is liquid cooled and mounted in a light weight polymer for support.
This radar sits atop the rotors in the cylindrical radome. Although it may look awkward and potentially unsafe so have such an expensive piece of equipment sitting in such a prone location, having the radar mounted high on the aircraft improves it’s ability to locate and track targets at low altitudes.
This information gathered by the Radar Warning Receiver, Missile Approach Warning Receiver and the Active Scan radar itself is processed by two Indeon Common Integrated Processors (CIP). Each CIP can process 12 billion instructions per second and has one gigabyte of memory, allowing it to store a wealth of information and making the system nearly impossible to overload. Information can be gathered from the radar and other onboard and offboard systems, where it is then filtered by the CIP which will effectively 'gist' the meanings of the signals onto several cockpit displays, enabling the pilot to remain on top of complicated situations by having all the information simply presented onto the data displays in the ergonomic cockpit.
Integrated into the DH-01 is the Cervelo S5 Terrain following radar. The system works by transmitting a radar signal towards the ground area in front of the aircraft. The radar returns can then be analysed to see how the terrain ahead varies, which can then be used by the aircraft's autopilot to maintain a reasonably constant height above the earth. This technology enables flight at very low altitudes, and high speeds, avoiding detection by enemy radars and interception by anti-aircraft systems. This allows the pilot to focus on other aspects of the flight besides the extremely intensive task of low flying itself.
Adding to the powerful Avionics array is the Battlespace Network function which allows the aircraft to connect to and share information gathered from other aircraft in the area. The Battlespace Network is essentially a secure satellite connection for which data, in simplified form, is transmitted between two or more aircraft and is theoretically capable of linking the entire airforce of a nation.
This means that even though only one helicopter has a lock on a target, any other helicopters in range of the target will also be able to engage even if they do not have a radar lock.
The DH-01 can both scan and track targets as well as communicate simultaneously through the use of both processing units as well as the use of designation when it comes to antennae which make up the constellation of data sending and receiving equipment.
The sheer power and capability of the DH-01 means that it can scan and track almost any aerial or ground target no matter the size of the enemy's radar cross section. From a distance of 300km, the DH-01 can successfully detect a target which has a radar cross section of roughly five square metres and can detect a target with a cross section of less than 10 square centimetres from twenty kilometres away.
In total, the RH-90 can simultaneously track and record movements for a total of 72 different aerial or ground targets and engage up to sixteen at once using active radar homing missiles. This gives the RH-90 the ability to address any numbers deficit it may go into battle facing by effectively fighting multiple aircraft at any one time.
Cockpit and Flight Systems
The RH-90 features a sophisticated digital fly-by-wire system which is similar to that fitted on other helicopters. The computers "read" position and force inputs from the pilot's controls and aircraft sensors, along with pre-programmed mission waypoints to detect and plot exactly what the aircraft should be doing as opposed to what it is actually doing. Due to the complexity of maintaining the RH-90 in a stable state at all times, effectively using the RH-90 against enemy forces would be very difficult without the use of these computers. The fly-by-wire system is one of the few components which is granted emergency power in the event of an engine failure. The computers solve differential equations to determine the appropriate command signals that move the flight controls in order to carry out the intentions of the pilot.
The programming of the digital computers enable flight envelope protection. In this aircraft designers precisely tailor an aircraft's handling characteristics, to stay within the overall limits of what is possible given the aerodynamics and structure of the aircraft. For example, the computer in flight envelope protection mode can try to prevent the aircraft from being handled dangerously by preventing pilots from exceeding preset limits on the aircraft's flight-control envelope, such as those that prevent stalls and spins, and which limit airspeeds and g forces on the airplane. Software can also be included that stabilize the flight-control inputs in order to avoid pilot-induced oscillations.
Since the flight-control computers continuously "fly" the aircraft, pilot's workloads can be reduced to a minimum while in transit. Stalling, spinning and other undesirable performances are prevented automatically by the computers while still permitting a great deal of 'freedom' to the pilot when engaging in extreme manoeuvring.
The cockpit of the RH-90 is an entirely digital 'glass cockpit' display without any traditional analogue instruments. Data is gathered and processed by a multitude of computers, Global Positioning devices and air pressure monitors to accurately determine characteristics of the aircraft.
Rather than sitting side by side as pilots would in most helicopters, the pilot of the RH-90 sits behind his co-pilot/gunner in a line abreast formation. The aft-mounted pilots seat is approximately 0.75 metres higher than the seat in front which ensures excellent visibility at all times for both pilots.
The RH-90 uses the Symmetriad Aerospace Systems AHG-1 Helmet which not only provides pilot safety, but also allows them to use some of the most sophisticated targeting systems available anywhere in the world. .
The AHG-1 helmet also plays an important role in keeping the pilot fully up to date with his or her surroundings. Rather than projecting the information pertaining to the aircraft onto the canopy as many Heads Up Displays would, the AHG-1's Helmet Mounted Display displays biocular video and symbology information on the helmet visor, providing pilots with all information necessary to execute both day and night missions under a single integrated configuration. The system enables pilots to accurately cue onboard weapons and sensors using the helmet display. In tandem with this is the Night Vision function which can activate across the visor fully or only half, allowing the pilot to see a half-illuminated and half-dark image when flying at night.
The HMD also allows the aircraft systems to alert pilots of potential threats and hazards, significantly improving situational awareness. Advanced night imagery is provided by the helmet mounted night camera and aircraft Distributed Aperture System (DAS). The RH-90 HMDS’s accuracy and very low latency enables the RH-90 to negate the need of a HUD. The HMDS is the “virtual” HUD of the aircraft.
In addition to this, the HMD can also 'paint' targets which have been identified on radar and alert the pilot to their real time position in the air by placing a thin box around their location.
The HMD can also use optical sensors mounted in the glass display to slave the aim of the main gun to the pilot’s eye. Rather than use a complicated and inaccurate joystick to control movements of the gun, all the pilot needs to do is look directly at the target and computers will automatically align the gun to where the pilot is looking.
The HMD is a clear piece of glass, which automatically polarizes if the pilot is facing into the sun.
Armament
The RH-90 employs Active Radar Homing missiles as its primary weapon for anti-armour. Active radar homing is a missile guidance method in which a guided missile contains a radar transceiver and the electronics necessary for it to find and track its target autonomously. Active radar homing is rarely employed as the only guidance method of a missile. It is most often used during the terminal phase of the engagement, mainly because since the radar transceiver has to be small enough to fit inside a missile and has to be powered from batteries, therefore having a relatively low Effective Radiated Power, its range is limited.To overcome this, most such missiles use a combination of command guidance with an inertial navigation system in order to fly from the launch point until the target is close enough to be detected and tracked by the missile. The missile therefore requires guidance updates via a datalink from the launching platform up until this point, in case the target is maneuvering, otherwise the missile may get to the projected interception point and find that the target is not there.
The RH-90 also employs general purpose unguided or laser guided rockets, which can either be high explosive or flechette rockets, which explode in mid-flight and unleash a rain of tungsten darts upon the enemy. Either choice of rocket is capable of wiping out enemy infantry or armour, however flechettes are more suited to the former, while high explosive is designed for the latter. Laser guided rockets require the co-pilot gunner to put the cross hair on the target, unguided requires the pilot to point the helicopter in the direction of the target. Indicators on the HUD show when a target is inline with the rockets.
The Emraad MG90 Chain Gun is the Area Weapon System on the RH-90. The MG90 is mounted in the lower section of the chain gun turret. It uses a 2.8 kW electric motor to load 30 mm linkless ammunition at a rate of 725 shots per minute. The gun has a positive cook-off safety (open bolt clearing) and double ram prevention. The gun can be slaved to the eye of the pilot or co-pilot gunner to fire on the target that the crew member is looking at. This is done by motion sensors mounted on the HUD.
The RH-90 is most notable for its two storage bays mounted into the fuselage of the helicopter. These bays can be configured to hold several different kinds of ordnance, ranging from laser guided missiles to gravity bombs. Designers found that MTOW of the helicopter allowed the helicopter to carry even more ordnance than what it theoretically could carry with a 70% fuel load, therefore the bays were added to give the helicopter more space for weapons. Each bay can mount four guided missiles or seventy rockets or a 1000kg bomb. When possible, the RH-90 should carry ordnance internally as this reduces the frontal RCS and also the amount of drag on the airframe.
Ordnance that doesn’t fit within the bays can be mounted on the external wings which also have four hardpoints apiece. The two centre-most hardpoints have a capacity for 1,000kg of ordnance each, the third hardpoint from fuselage is rated at 750kg and finally, the missile rack on the outer of the wing, designed to hold two short range air-to-air missiles has a rating of 200kg. The RH-90 can fly with all of these hardpoints and bays loaded to their maximum limit, although it is unlikely to.
Defensive Systems & Protection
The RH-77 also employs a DAS. A defensive aids system (DAS) is a military aircraft system which defends it from attack by surface-to-air missiles, air-to-air missiles and guided anti-aircraft artillery. A DAS typically comprises chaff, flares, and electronic countermeasures combined with radar warning receivers to detect threats. On some modern aircraft, the entire system is integrated and computer-controlled, allowing an aircraft to autonomously detect, classify and act in an optimal manner against a potential threat to its safety. The engines have extremely intense insulation and cooling, eliminated their heat signature and hindering enemy heat seeking missiles' ability to track the helicopter.
The RH-90 also features the Cervelo SDH-5 threat detection radar encompassing a Radar Warning Receiver and a Missile Approach Warning System. This alerts pilots to when a radar lock is engaged, and also allows the pilots to track enemies with a very narrow radar wave, which can be as focused as precisely to 1° by 1° in azimuth and elevation, making the system extremely accurate and can increase the chance of a succesful evasion. The SDH-5 can also communicate to other allied fighters in the area and alert them to the possible threat if the are not already, likewise the SDH-5 can receive this information. This is not featured on civillian versions of the aircraft.
Countermeasures in the form of Chaff and flares are provided as standard. These are automatically controlled by the MAWS.
Also operated by the MAWS is the "Blinder" system. When a missile approaches the helicopter, the MAWS, through a seperate countermeasure system, will "blind" the missile with a powerful beam of infra-red light. This causes the missile to lose the track on any target due to its receiver seeing only heat surrounding it and not the pin prick from the engines that it was originally chasing.
Fuel required is stored in one of five specially designed tanks which are alligned along the centre of the fuselage and located centrally. Each fuel tank is comprised of a tri-layer protection system to reduce the risk of the fuel exploding when struck by enemy rounds. The outer layer is comprised of Ti-Al-64, a light yet very strong material with impressive resistance to compressive forces; the role of this layer of metal is to prevent small bullets from piercing into the fuel tank itself, or to suitably slow down the velocity of the bullet. The second layer is made up of anti-spall liner to help prevent the fuel from igniting. Finally, the third layer is comprised of a leather bag which a partial self-repair capability if a tear in the bag is less than 5cm in diameter.
Should a fire break out while the aircraft is flying, the automated Fire Protection system dubbed Ansul detects where the fire is and promptly smothers the interior of the section of the airframe with a thick layer of foam. Once the Ansul has been used, it must be recharged.
Thrust
The RH-90 is most distinctive for having its co-axial rotor design which sets it apart in many ways from other helicopters including the RH-77 which was later optimized to complement the heavy Incursor. At first a conventional single rotor design was considered rather than deal with the many design problems that a co-axial design proposes, however as the design phase continued, the co-axial proposition became to tantalizing to resist.
When a rotor blade spins it creates lift which is used to overcome gravity and make the helicopter go up. The rotor can be divided into two parts, the advancing blades and the retreating blades, the retreating blades being the ones that are moving in the opposite direction to the helicopter. Rotor blades are shaped like an aerofoil, an aerofoil generates lift by the differing air pressures travelling over and under it which pull it up. The faster an aerofoil travels, the more lift will be created.
Because the advancing blades are literally advancing into the relative wind, the relative airspeed over them is higher than the relative airspeed over the retreating blades, meaning that one side of the rotor is generating more lift than the other and the faster a helicopter goes the further this gap will be increased. Helicopters counter this by 'flapping' the blades, which adjust the angle of attack on both sides of the rotor to ensure that the amount of lift on the advancing side is equal to the amount on the retreating side.
If the helicopter goes too fast, the relative airflow over the retreating blades will be too less and the helicopter will lose lift on one side of the rotor and subsequently roll sharply to that side. That is called rotor stall and can result in a loss of the aircraft. As such, conventional rotored helicopters are speed limited because of their rotor design and not because of the lack of thrust or excess of drag like aircraft.
Contra-rotating helicopters do not suffer from this problem, as there are two sets of advancing blades on opposite sides of the helicopter. This means that the helicopter is no longer limited in speed from the problems of rotor stall and also makes the craft itself much more inherently stable.
As torque forces from each rotor effectively cancel each other out, contra-rotating helicopters do not need a tail rotor to keep them flying straight without yawing uncontrollably to oppose the turning force of the rotors. Not having a tail rotor removes one of the most vulnerable parts of a helicopter and greatly simplifies the tailplane construction.
The RH-90’s employs two four blade main rotors to provide both lift and forward propulsion. The four blade design was selected due to its superior lift revolution for revolution. and noise supressing ability when compared to other three bladed designs more commonly seen on co-axial designs. The RH-90’s rotor blades slice cleanly through the air instead of hammering it like helicopters of years gone by; this greatly reduces noise and boosts fuel efficiency, by allowing the rotors to turn at a slower speed.
The rotors are made from composite materials which greatly improve 'hot and high' performance. The leading edges of the rotor blades are made from Magnesium-aluminium alloy, a material which is extremely resistant to heat yet still quite light and able to have significant amounts of force placed upon. Mg-Al is primarily seen on wheels of sports cars, hence the name 'Mag wheels.'
The remainder of the rotor blade construction including the connection to the rotor hub is made entirely from composite materials, in this case carbonfibre. This carbon fibre is an epoxy not only reinforced by carbon fibres, but also by Kevlar fibres making this a very strong material.
Thrust is provided by two Kintech GZ-1100 Turboshaft engines mounted either side of the fuselage to prevent complications from mounting them too close together. Having the engines spaced rather than aligned not only creates more room for the transmission from the rotors to the turbines, but also reduces the risk of both engines failing at the same time from foreign object damage.
Gemballa-Coronado engineers decided that the best way to reduce the signature of the RH-90 was not to focus overly on the RCS, which the co-axial set up will cause a significant spike in, and instead work on suppressing IR and sound. Exhausts of the RH-90 are blended into the fuselage and are heavily insulated to prevent the exterior of the nozzles heating, and exhaust gases are mixed with outside air to reduce their exhaust temperature.
The rotor design of the RH-90 also minimizes sound emissions from angles parallel to the rotor blades, thus making the helicopter at it’s loudest only when it is directly overhead an enemy position. At a low torque hover, the RH-90 produces only 50db from 2,500 metres, meaning the battlefield will have to be virtually silent for an enemy to hear the helicopter.
Each GZ-1100 produces 2000kw of power, power is then geared through a mechanical transmission to the rotor blades, keeping them turning at 1/8th the speed of the high-speed turbine. If the gearbox wasn’t present, the rotors would break the sound barrier and would not be able to produce lift. At first a hydraulic transmission was considered, but eventually a mechanical transmission was selected for greater durability. The Kintech TR-S transmission can be drained of oil and still fly for another 200km before finally giving out.
The turbine itself and the compressor fan are made from a carbon-ceramic blend, which is enormously strong and able to resist the extremely high temperatures inside the engine. Other parts of the engine are made from Aermet 100 which is a steel blend designed to cope with high temperatures and offer a high compressive and tensile strength.
The performance figures of the RH-90 are staggering; the powerful and sleek Incursor, not troubled by rotor stall or by the issues of a low RCS airframe, can reach speeds in excess of 360km/h. The RH-90 also offers near unmatched agility, capable of performing loops and barrel rolls and performing both in quick succession. The RH-90 is one of the few helicopters capable of performing a full Immelman turn, a very quick way of turning 180 degrees.
Airframe
Despite being designated as a heavy attack helicopter, designers had no intention of letting the weight of the RH-90 balloon to enormous proportions. Every saved gram on the airframe meant one extra gram of fuel or ordnance which could be used against the enemy. With strict diet of carbonfibre and lightweight metal alloys, weight was pared from the comparatively big Incursor with relative ease. The first prototype of the Incursor was built almost entirely out of steel and aluminium, however this prototype was more to test the capability of the co-axial rotor set up. As a result of the low emphasis on lightweight materials, the prototype weighed in at a very chubby 9,500 kg when empty.
Much of the airframe was instantly replaced with carbonfibre reinforced composite materials. Composite construction is a generic term to describe any building construction involving multiple dissimilar materials, in this case carbon-fibre reinforced polymers are used. CFRPs are comprised of a polymer, in this case epoxy, which is a thermosetting polymer formed from reaction of an epoxide "resin" with polyamine "hardener", is re-inforced with fibres of carbon which give the material it's strength. CFRPs have an extremely high strength to weight ratio which makes them ideal for use on aircraft.
Carbonfibres in this particular matrix are woven into a tight grid which partially resembles chainmail. These fibre matrixes are then used to reinforce the polymer (in this case epoxy) to make it a viable alternative to other metals, the same strengths for a much lighter weight.
The downside of CFRP's is that they can be extremely expensive to replace and require much more mantinence than more typical aircraft materials such as aluminium would. Therefore, these CFRP's have been made into panel forms allowing them to be easily removed and replaced should they be damaged, as well as being covered by a layer of outer aluminium.
Al-Li or Aluminium-Lithium alloy was also used extensively as a cover for the CFRP's body. Lithium is the least dense elemental metal, much less dense than alumiunium which is in itself less dense than most other metals, therefore when the two are alloyed together, the density and weight of the resulting material is less than that of the alloy while being stiffer at the same time and more resisitant to strain. Al-Li was a perfect choice to act as a cover for the damage and mantinence-prone CFRP's which are layed under it.
Finally, titanium (Ti-Al-64) armour plating is used around the most vulnerable parts of the helicopter’s airframe, particularly around the engines and transmission as well as the undersides and surroundings of the cockpit, covering roughly 90% of the airframe. Titanium is rarely used on Gemballa aircraft due to it’s high cost, however recent superproduction of the material deep in the wilderness of the Coronadan landscape lowered the cost enough to make it a worthwhile alternative to the more commonly used Aermet 100 steel used on most Gemballa aircraft. The titanium plating accounts for over half the weight of the RH-90 despite making up a much smaller fraction of it’s composition.
In order to suppress the immense heat created by the pair of engines, the interior of the engine nozzles are lined with a carbon ceramic lining to absorb the heat created and prevent it from heating up the metal lining on the outside. As a partial turbofan effect, air is sucked in through the intake of the engine, bypassing the turbine and mixing with the exhaust gases to reduce their temperature.
The finishing touches to the airframe are made with radar-resistant material to thinly veil the exterior of the cockpit. This material gives an effect similar to iron ball paint. It contains tiny fibres coated with carbonyl iron or ferrite. Radar waves induce molecular oscillations from the alternating magnetic field in this paint, which leads to conversion of the radar energy into heat. The heat is then transferred to the aircraft and dissipated. These fibres are so small, if one were to run their hand over the exterior panelling, they would not detect a change in smoothness. Unlike the spheres, these fibres are much less susceptible to damage.
The RH-90, in contrast to the RH-77, does not adopt a low RCS airframe due to the problems with observability posed by the co-axial rotor set up. Noting that the effects created by these rotors would ruin any chance the RH-90 had of achieving radar invisibility, designers saw little reason to waste their time trying to reduce the signature of the remainder of the airframe. To this end, designers instead optimized the exterior for outright performance as well as ease of maintenance.
The frontal aspect of the RH-90 is the only part of the airframe which has been designed to partially reduce it’s radar cross signature, with a low-observability shape characterized by creased edges rather than the smooth lines which ape the rear of the aircraft. As designers assumed that the RH-90 would hover behind allied lines to engage enemy armour from a long range, there became no need to consider optimizing the rear of the aircraft to work against radar.
This considered the clean exterior of the RH-90 offers a much better aerodynamic shape than most other attack helicopters, which is partially to blame for its ability to reach much higher speeds than other co-axial designs.
The stub wings that serve as racks for ordnance mounted externally produce a lift force of 80kN each when the helicopter reaches speeds of 300km/h although these do not have control surfaces. The lift produced by these can be cancelled out if small spoilers on the rear of the wings are activated.
The canopy of the RH-90 is made of six inch thick plexiglass, comprising of three layers of laminated glass and a further three layers of transparent polycarbonate.
