General Description
The MH-64 Coushatta Heavy Cargo Helicopter is designed as a western equivalent to the Russian Mil-26 helicopter, capable of carrying nearly 30 tons in order to transport heavily armored vehicles, such as Armored Fighting Vehicles like the Bradley, Puma, and Warrior, as well as general APC's like the Stryker, in to combat. It's incredibly large size is intended specifically to carry armored vehicles, being a medium strategic lifter fulfilling a role that virtually no other VTOL aircraft can. These vehicles also serve as a force multiplier for airborne forces, allowing them to deploy in heavy IFV's with substantially more powerful weapons. The vehicles can also land further away from enemy forces, given the speed of the armored vehicles, and carry a large amount of food and water with them, as well as logistics supplies such as water filters, to make them more independent and self sufficient in the field. The vehicle chassis is based on that of the CH53 Sea King, but it is heavily up armored, allowing it to better protect the soldiers within it, using a number of high strength composites, including dyneema and ceramic to protect the soldiers within, as well a titanium pod similiar to the A-10 Warthog designed to protect the crew from the most severe of threats. The vehicle, on top of using 4 engines instead of 3, also has coaxial rotors and wings with the same wingpsan and aerodynamic lift as the A-10 warthog which is 53 feet wide, much smaller than the vehicle's rotors. This is designed to increase drag in flight, and thus fuel efficiency, making it a hybrid winged aircraft. The vehicle also makes use of an optional, secondary back tandem wing, of approximately the same size, designed to increase drag by an additional 30%. At the lower velocity of the aircraft, this helps increase efficiency and drag capabilities, allowing for an easier time maintaining flight, or a heavier payload if taking off from a short distance, as compared to vertical distance. The rotors are based on the CH53 Sea King's but are slightly stronger and larger, and the rotor is also slightly larger to accommodate the fourth engine. Like the CH53 and Mil-26, the unique main gearbox is relatively light but can absorb an enormous amount of shaft horsepower, which is accomplished using a non-planetary, split-torque design with quill shafts for torque equalization. A split-torque design is also used for the 5,670 kg (12,500 lb) gearbox on the American three-engine Sikorsky CH-53K King Stallion, of which the MH-64 is based.
The vehicle uses a large, coaxial set of rotors, which both increases stability and power of the engines, and is primarily how the massive lift capabilities of the aircraft are achieved. One of the problems with any single set of rotor blades is the torque (rotational force) exerted on the helicopter fuselage in the direction opposite to the rotor blades. This torque causes the fuselage to rotate in the direction opposite to the rotor blades. In single rotor helicopters, the antitorque rotor or tail rotor counteracts the main rotor torque and controls the fuselage rotation. Coaxial rotors solve the problem of main rotor torque by turning each set of rotors in opposite directions. The opposite torques from the rotors cancel each other out. Rotational maneuvering, yaw control, is accomplished by increasing the collective pitch of one rotor and decreasing the collective pitch on the other. This causes a controlled dissymmetry of torque. Dissymmetry of lift is an aerodynamic phenomenon caused by the rotation of a helicopter's rotors in forward flight. Rotor blades provide lift proportional to the amount of air flowing over them. When viewed from above, the rotor blades move in the direction of flight for half of the rotation (advancing half), and then move in the opposite direction for the remainder of the rotation (retreating half). A rotor blade produces more lift in the advancing half. As a blade moves toward the direction of flight, the forward motion of the aircraft increases the speed of the air flowing around the blade until it reaches a maximum when the blade is perpendicular to the relative wind. At the same time, a rotor blade in the retreating half produces less lift. As a blade moves away from the direction of flight, the speed of the airflow over the rotor blade is reduced by an amount equal to the forward speed of the aircraft, reaching its maximum effect when the rotor blade is again perpendicular to the relative wind. Coaxial rotors avoid the effects of dissymmetry of lift through the use of two rotors turning in opposite directions, causing blades to advance on either side at the same time.
Another benefit arising from a coaxial design includes increased payload for the same engine power; a tail rotor typically wastes some of the available engine power that would be fully devoted to lift and thrust with a coaxial design. Reduced noise is a second advantage of the configuration; some of the loud "slapping" noise associated with conventional helicopters arises from interaction between the airflows from the main and tail rotors, which in some designs can be severe. Also, helicopters using coaxial rotors tend to be more compact (with a smaller footprint on the ground), though at the price of increased height, and consequently have uses in areas where space is at a premium; several Kamov designs are used in naval roles, being capable of operating from confined spaces on the decks of ships, including ships other than aircraft carriers (an example being the Kara-class cruisers of the Russian navy, which carry a Ka-25 'Hormone' helicopter as part of their standard equipment). The U.S. Department of Transportation has published a “Basic Helicopter Handbook”; Ten hazards have been listed to indicate what a typical single rotor helicopter has to deal with. The unique coaxial rotor design either reduces or completely eliminates these hazards. Coaxial rotors are better at dealing with Settling with power — have reduced Retreating blade stall — Reduced Medium frequency vibrations — Reduced High frequency vibrations — None Anti torque system failure in forward flight — Eliminated Anti torque system failure while hovering — Eliminated. The reduction and elimination of these hazards are the strong points for the safety of coaxial rotor design, which makes the vehicle practical not only for it's higher lift capacity and torque, but also for it's improved safety and stability. This is a necessary feature for military helicopters which undergo extreme stresses in combat, and thus flight stability is of considerably higher importance than raw power alone, making the design practical.
Wings are also used to increase lift capacity when in flight and increase aerodynamic efficiency, but do not increase vertical lift capacity. The wings are roughly comparable to the A-10 warthog in function, and are quite small, shorter than the overall width of the vehicle's rotors, allowing it to be stored in roughly the same locations, with the wings tilted upwards or even removed for storage. The vehicle on a short runway, smaller than that of an aircraft carrier, can carry up to 120,000 pounds in part due to the wings, but when landing in rough terrain must dump the extra weight in order to be able to take off again, or have enough space to achieve short take off. This also substantially increases the vehicle's maximum height with it's payload, as well as fuel efficiency, however it is still quite low even in comparison to other helicopters. With a medium or light payload the altitude of the aircraft is 35,000 feet, however more practical payloads at altitude are between 5,000 and 15,000 feet, given the enormous strain of the heavy weights. The aircraft is commonly used in a downloaded fashion, well below it's maximum capability, both for practical reasons and to help preserve the aircraft's integrity by reducing wear and tear on the vehicle. The vehicle is much slower than many comparable winged helicopters, with the primary emphasis being on fuel efficiency and payload.
Despite only being marginally bigger than the enlarged CH53 cabin, it is substantially heavier, with the original CH53 being 33,226 lb (15,071 kg), and the newer vehicle being 28,200 kg (62,170 lb), largely due to the increase in armor. In order to effectively double as a gunship and provide increased protection for the crew, the vehicle's armor has been increased, allowing it to serve as a heavy transport vehicle, in order to take hostile fire. The vehicle can withstand up to armor piercing 14.5mm rounds over it's entire body, and can resist more powerful rounds at altitude or over certain areas such as the crew cabin, up to a 30mm round. The armor is a composite material, using spaced armor and dyneema backed ceramic armor, with the ceramic being extremely durable and resistant to repeated impacts, unlike many forms of ceramics which shatter under stress. The high hardness of the armor and it's strength allows it to stop more powerful armor piercing rounds, and the spaced armor allows it to diffuse the energy of a blast, such as from a shaped charge or squash warhead, over space thus defeating it's effect. Numerous active defense systems, designed to shoot oncoming missiles and large projectiles are utilized to increase the vehicle's protection relative to it's weight, as well as other countermeasures such as flares, infrared and UV strobes, and to a lesser extent radar resistant materials helps protect the vehicle from various forms of missiles. The vehicle also sports substantially heavier weapons, largely being equipped with two Mauser Bk-27, 27mm cannons with a a combined rate of fire up to 3400 RPM, replicating the speed of many gatling guns such as the GAU-8, while being much smaller. The barrels are more heat resistant, being made of cobalt chrome, which in large part compensates for the otherwise excessive heat build up. Four pod attachments exist to mount weapons, such as the AMG-114 hellfire missiles or Hydra missiles, and the wings and internal bomb bay can be used to carry heavier bombs, such as 500 to 2000 pound JDAM bombs, or cruise missiles which are air deployed, for precision bombing. While due to it's lack of maneuverability it is not nearly as effective a gunship, it is useful for providing defense for the aircraft, troops on the ground, or to strafe vulnerable enemy troops when it flies by. Against light threats it is particularly effective, but is primarily reserve for the cargo transport role.
ArmorThe Armor of the vehicle perhaps is the most notable change from the original CH-53, with it taking almost every other design consideration from the aircraft. The vehicle makes use of high strength, semi-perforated titanium armor, as well as other high strength composites such as carbonfiber, dyneema and nano-ceramics. The titanium has small holes in it, smaller than a bullet, which allow it to be approximately 3 times lighter weight than titanium of comparative thickness, but still stop the same rounds. The armor is only semi-perforated, for aerodynamic reasons, and to prevent small shrapnel from entering the holes. The titanium is extremely hard and high strength, possessing 1500 MPA, and offers superior performance than AR500 or ATI500 steel at only 60% of the weight, which when combined with the perforated nature of the armor, makes it much lighter and stronger than comparable steel or aluminum armors. It is also cheaper for it's thickness, and the titanium used is only approximately 30% more expensive than the comparative steel armor, making it a cost-effective option.This makes up the external element of the armor, but beneath this, spaced approximately a foot away, is the under-armor, which is a carbon fiber vehicle hull, covered in dyneema, and nano-ceramic. Except for the carbon fiber this armor is also perforated, and is capable of stopping high velocity, hardened armor piercing rounds, such as tungsten carbide penetrators, as well as providing substantial resistance to incendiary and explosive rounds. The ceramic is arranged in a hexagonal tile arrangement, similiar to Chobham armor, which allows it to take hits over the entire body and allow for easier repair, and is extremely lightweight. 3 pounds of dyneema is sufficient to stop small arms rounds, such as the 7.62mm NATO, and when combined with nearly equivalent weights of carbon fiber and ceramic, can stop far more powerful cartridges, especially after passing through the titanium SLAT armor on the outside. The armor due to it being spaced possesses inherent protection against RPG's and other shaped charge weapons, diffusing the force of the blast over space, as well as incendiary or explosive rounds and SQUASH warheads. The exact thickness of the armor varies, but it can withstand 14.5mm rounds over the entire body of the aircraft, and has substantially better protection at high altitudes when the rounds have lost most of their energy.
The Nano-ceramic used is not only extremely strong and hard, but less fragile than many previous ceramics, capable of withstanding multiple hits without shattering, and possessing greater energy absorption. The ceramic armor works as more than just hard armor and also works in a way as semi-reactive armor, reflecting the energy of the round back on itself and disintegrating oncoming projectiles. The (pulverised) ceramic strongly abrades any penetrator; Against lighter projectiles the hardness of the tiles causes a "shatter gap" effect: a higher velocity will, within a certain velocity range (the "gap"), not lead to a deeper penetration but destroy the projectile itself instead. Because the ceramic is so brittle the entrance channel of a shaped charge jet is not smooth—as it would be when penetrating a metal—but ragged, causing extreme asymmetric pressures which disturb the geometry of the jet, on which its penetrative capabilities are critically dependent as its mass is relatively low. This initiates a vicious circle as the disturbed jet causes still greater irregularities in the ceramic, until in the end it is defeated. The newer composites, though tougher, optimise this effect as tiles made with them have a layered internal structure conducive to it, causing "crack deflection". This mechanism—using the jet's own energy against it—has caused the effects of Chobham to be compared to those of reactive armour. This should not be confused with the effect used in Non-Explosive Reactive Armour: that of sandwiching an inert but soft elastic material such as rubber, between two armour plates. The ceramic tiles also have a rubber and energy absorbent backing, both dyneema and carbon fiber, which helps absorb and dissipate energy from high strength rounds, as well as a small graphite layer.
