The main prerequisite for the emergence of the RAH-66 helicopter is the 1982 report of the year, which analyzed the capabilities of existing US helicopter gunships. It stated that most of the armed vehicles could not effectively fulfill the assigned combat missions in the context of an armed conflict with the Warsaw Pact. The US armed forces needed a new car capable of overcoming the enemy’s air defenses, finding targets, and destroying them.
In the 1983 year, just a few months after the report was released, the Pentagon initiated the launch of the LHX program (Light Helicopter Experimental), the purpose of which was to create two helicopters based on a single design. One of them (known as the LHX-SCAT) was intended for reconnaissance and strikes, and the second (LHX-UTIL) was seen as a multi-purpose machine.
The new program immediately attracted the attention of aircraft manufacturers, since winning the competition implied signing several of the largest contracts for the supply of equipment. The ground forces alone, with the exception of the Air Force and the Marine Corps, planned to order up to 5 thousands of new helicopters. It was planned to buy LHX-SCAT 2900 helicopters for replacing AH-1, OH-6 and OH-58 helicopters, as well as more 2 LHX-UTIL thousand for replacing obsolete multi-purpose UH-1.
Nevertheless, the prospect of obtaining large contracts was complicated by the requirements of the military. The army wanted to get helicopters with unique characteristics, the development of which would require special efforts. It was necessary to ensure the lowest possible visibility in the radar, infrared and acoustic ranges. In addition, the maximum speed of the helicopter was to reach 400-450 km / h, which significantly exceeded the capabilities of all the existing machines at that time. The LHX-SCAT reconnaissance and attack helicopter was supposed to have a single cabin, a set of special equipment and a take-off weight of the order of 3800 kg. LHX-UTIL was designed to carry six people or 600 kg of cargo, had to be controlled by two pilots and be slightly larger than the modification SCAT.
Four leading US aircraft manufacturing companies submitted bids for the LHX competition. Bell, Boeing, Hughes and Sikorsky expressed their desire to develop a promising machine. The specialists of these organizations had their own opinions about the prospects for the development of helicopters, which led to the emergence of several projects with completely different looks. For example, the company "Sikorsky" offered a car with coaxial bearing screws and pushing tail. Such an arrangement was supposed to ensure the highest possible flight speed. It is noteworthy that the company Sikorsky continued to develop similar ideas in the future and is now engaged in a similar project S-97.
During the development of preliminary projects, it turned out that the creation of LHX helicopters with the required characteristics is quite a difficult task, which is why the participants of the competition were forced to join forces. The Boeing helicopter unit began working with Sikorsky, and Bell specialists began collaborating with colleagues from McDonnell Douglas, which included Hughes by this time. In the autumn of 1988, these two consortia received contracts for the continuation of work.
The task of this stage was to determine the possibility of fulfilling the requirements while maintaining the set values of take-off weight and cost of the machine. In addition, the layout of the helicopters was checked and the first works on the integration of electronic equipment were carried out. At this stage, it became clear that the customer would have to soften the requirements for promising technology. Providing a maximum flight speed of over 350 km / h proved to be extremely difficult from a technical point of view. In addition, studies have shown that low-altitude flight at such speeds will be available only to highly qualified pilots.
The military changed the requirements for maximum speed, and also canceled the development of a multi-purpose helicopter LHX-UTIL. Since the mid-eighties, funding for the LHX program has been steadily declining, several times it has been proposed to stop work. Nevertheless, the program continued, although reduced. Due to limited financial capabilities, the Pentagon and the participating companies were forced to apply new methods of working out technical solutions. Most of the ideas and suggestions were tested using computer simulation. Some units and assemblies were tested on flying laboratories.
By the spring of 1991, the military determined who would develop the new helicopter, and then begin its mass production. Of the two proposed projects was chosen developed by the union of Boeing-Sikorsky. The project received a new name: RAH-66 Comanche. Like some previous American helicopters, the new car was named after one of the North American Indian tribes. In this case, the letter RAH was used for the first time in American practice. The helicopter, capable of equally well performing reconnaissance and shock missions, was given the appropriate designation - Reconnaisence and Attack Helicopter.
The development contract for the RAH-66 project was signed in April 1991. The choice of the developer made it possible to concentrate all efforts and direct all available funding to just one project, which, in particular, made it possible to begin full-scale tests of various systems proposed for use on a new machine. It should be noted that this possibility was extremely important, since the project had a greater degree of novelty and required checking or refining many proposals.
Designing a new helicopter took a lot of time. The first prototype of the Comanche helicopter was removed from the assembly shop of the Sikorsky plant only at the end of May 1995. A few months were spent on ground tests. The first flight was to take place at the end of 95, but was eventually moved to 4 on January 1996. As time has shown, the tests of two prototype prototypes built by the reconnaissance and attack helicopter were delayed for eight years.
One of the main requirements for the LHX / RAH-66 helicopter was a reduction in visibility for enemy detection equipment. For this reason, the Comanche helicopter received a number of specific features that distinguish it from other equipment of its class. Thus, the outer surface of the fuselage of the machine is formed by a large number of straight-line panels, interlinked with each other at different angles. A rotor hub fairing, a steering screw in an annular channel and a retractable chassis are used. For placement of weapons proposed to use the internal cargo compartments on the sides of the fuselage. At the same time, external compartment covers were equipped with pylons for armament suspension. The nose turret with a gun was supposed to unfold on 180 ° and place the barrels in a special casing-fairing.
To reduce visibility in the infrared range, the helicopter received an original exhaust cooling system. After exiting the engines, they mixed with cold atmospheric air and were thrown out through long slit nozzles located along the sides of the tail boom. This system was used for the first time in the United States. Prior to this, the reduction of heat produced was achieved using special nozzles for exhaust nozzles.
According to reports, the whole range of measures to reduce visibility has led to quite high results. So, in comparison with the AH-64 Apache helicopter, the effective scattering surface decreased by about 600 times. Comparison of these helicopters in thermal radiation shows a fourfold advantage of Comanche.
The main structural element of the RAH-66 helicopter is a long box girder, on which all units and fuselage skin panels are fixed. Most of the power elements and panels of the helicopter's skin were made of composite materials based on metals and plastics. An interesting feature of the fuselage design was the layout of the skin. About 40% of its panels were made removable and could be removed for servicing the internal units. Damage to the cladding panels while maintaining the integrity of the power kit did not affect the strength of the entire structure.
The layout of the fuselage length 14,4 m corresponded to modern views on the placement of units. In the bow there was a double cabin with a common lantern, as well as equipment compartment and a remote-controlled installation with an automatic gun. In the middle part of the fuselage were the engines, the main gearbox, part of the equipment and the internal weapon compartments. The tail boom was given for placement of some units. To reduce the visibility of the steering screw with a diameter of 1,37 m, place it inside the annular channel, and the horizontal tail set on the top of the keel.
A retractable three-point chassis was located in the middle and rear fuselage. The main racks were retracted by turning back, tail - by turning forward. The design of the struts and shock absorbers made it possible to absorb part of the impact energy during landing with increased vertical speed. In addition, in the parking position, the racks could partially retract, reducing the parking height of the machine relative to the full 3,4 m.
Initially, the LHX helicopter was supposed to have one turboshaft engine, but later it was decided to use a more reliable twin-engine powerplant. In the mid-eighties, a competition was launched for the development of a promising helicopter engine, in which the development of LHTEC won. In the middle part of the fuselage of the RAH-66 helicopter, under the rotor, were installed two T800-LXT-801 engines with an 1560 horsepower X. Auxiliary power unit WTS124 is provided, located between the main engines and used as a starter and means of ensuring the operation of some systems.
In the middle part of the fuselage there was a rotor hub, equipped with a fairing. The rotor with a diameter of 11,9 m had five blades, completely made of composites. In terms of the blades had a rectangular shape, as well as equipped with arrow-shaped ending. It was argued that the main rotor maintains performance even when large-caliber small rifles hit weapons.
In the forward part of the fuselage was a double crew cabin with a tandem arrangement of pilots. An interesting fact is that the pilot was in the front cockpit, and the weapon operator was located in the rear. This non-standard location of the pilots was used to ensure the best possible view from the commander's cabin.
Both cabins had the same instrumentation. Both pilots had a set of flight instruments and a complete set of controls. The main element of the dashboards of both cabins were two LCD displays with dimensions 200х150 mm. The left monochrome screen was designed to output the video signal from surveillance systems, the right color screen to display navigation, flight and tactical information. In addition, there were several smaller monochrome displays in the booths. At the bottom of the dashboard installed keyboard to enter the necessary information.
An important element of the onboard equipment of the RAH-66 helicopter became pilot helmets with a helmet-mounted indication system. The helmet system, depending on the mode of operation, could display information about flight parameters, a three-dimensional map, an image from surveillance systems, etc. Thus, using the helmet-mounted shield, the commander could receive the information necessary for piloting, and the operator could use the armament without being distracted by the dashboard.
The cockpit had a set of protection. Pilot seats were covered with light bulletproof armor. To protect against chemical, biological or nuclear weapons, a small overpressure was maintained in the cabin. The system of pressurization also protected the compartments of electronic equipment.
The avionics of the Boeing-Sikorsky RAH-66 Comanche helicopter was located in one nose compartment, located under the operator’s cabin, and two tailguns. In the avionics of the helicopter used only digital equipment. The basis of radio-electronic equipment were two digital computers that ensured the interaction of other equipment and the processing of all necessary information. To simplify production, the BREO complex on the 70% was compatible with the equipment of the Lockheed Martin F-22A Raptor fighter.
In view of the reconnaissance mission, the helicopter received a set of means of detection, communication and data transmission. To determine its own coordinates and locations of detected objects, RAH-66 received a combined (satellite and inertial) navigation system. The helicopter was supposed to carry a radar station, which is a development of the Longbow system used on the latest modifications of AH-64 helicopters. Provided infrared and television viewing systems of the front hemisphere, as well as a laser for highlighting targets. Optical-electronic systems made it possible to observe a sector with a width of 52 ° in azimuth and 35 ° in elevation.
An interesting feature of the Comanche avionics has become the algorithms for working in the search mode and target attack. It is assumed that to increase the survivability of the helicopter should not leave the shelter for a long time. In this case, the crew must climb to the required height, conduct a scan of the terrain and again hide in the folds of the terrain. The equipment “remembers” the collected information, thanks to which the operator can find the target and without any risk prepare for an attack. In the memory of the onboard systems there were signatures of the main targets, objects and equipment of both the enemy and the NATO countries. It was assumed that the automatic recognition of the type of object will reduce the likelihood of fire on their own.
The RAH-66 helicopter was capable of both independently attacking targets and transmitting information about them to other units. Information was transmitted over a noise-free radio channel.
To control the helicopter, it was proposed to use a two-channel digital radio-tracking system with triple redundancy. Used EDSU could be used in three modes. In the first, she did not automatically take into account the flight parameters, completely transferring control of the machine to the pilot. In the second mode, the automatics, based on data from various sensors, helped the pilot to maintain a given speed and altitude, and also controlled the power plant and parameters of the propellers. The third mode is a full-fledged autopilot, interacting with the weapon control system. In this case, the automatics could independently withdraw the helicopter to the combat course and carry out the attack of the indicated target. To control the engines used a separate digital system.
The RAH-66 helicopter's built-in armament consisted of one XM301 automatic cannon with a rotating block of barrels. The gun had three barrel caliber 20 mm. Ammunition guns - 320 or 500 shells. The gun was mounted on a turning turret, which allows shelling targets in the forward hemisphere. When firing at air targets, the XM301 can make up to 1500 shots per minute. To defeat ground targets was used half the pace.
An interesting feature of the turret was the used transport position. To reduce the visibility of the helicopter, if necessary, the gun barrel was turned back along the flight and placed in a special casing. Due to limited volumes inside the nose of the helicopter, the project authors had to use an interesting ammunition system. The drum shop on 500 shells is located under the operator’s cabin, at a sufficiently large distance from the cannon. Supply of ammunition was carried out using a special conveyor.
Missile armament was proposed to be transported in the airborne cargo compartments. The dimensions of these compartments were determined by the dimensions of the AGM-114 Hellfire air-to-surface missiles and the AIM-92 Stinger air-to-air. In addition, the helicopter could use unguided Hydra 70 missiles. The development of new weapons specifically for the RAH-66 helicopter was not planned. For the suspension of weapons it was proposed to use the holders on the side flaps-hatches of cargo compartments. Before using the weapon, the sash should have been raised to a horizontal position. Each of them had three suspension assemblies.
To increase firepower, the RAH-66 Comanche helicopter could use the EFAMS suspension system. It consisted of two wings mounted on the sides of a helicopter. The suspension assemblies on these wings increased the total ammunition of rocket armament, making it possible to solve more complex shock tasks. In this case, however, the installation of the wings to some extent reduced the maximum speed of flight.
The initial technical task of the LHX project involved the creation of a helicopter with a take-off weight of about 3800 kg. Ready "Comanche" turned out much more difficult. The mass of the empty helicopter exceeded 4200 kg, normal takeoff - 5800 kg. The maximum take-off weight reached 7900 kg, which is more than twice the initial requirements. However, the technical task has changed several times in accordance with the results of new research and calculations.
The tests, which started at the very beginning of 1996, allowed the flight data of the new helicopter to be established. The maximum speed reached 324 km / h. After installing the fairing of the supra-sleeve radar, which had the shape of a truncated cone, the maximum speed dropped to 317 km / h. The suspension of the additional wings of the EFAMS also reduced the flight speed by about 20 km / h. Cruising speed without a headset antenna reached 296 km / h. With antenna - 275 km / h. The practical ceiling of the helicopter is 5 km, the static one is 3,5 km. Due to economical engines and volumetric internal fuel tanks, the helicopter's practical range was brought to 900 km. Ferry range - 2335 km.
The project RAH-66 was one of those developments, the fate of which was affected by the collapse of the ATS and the USSR, as well as other geopolitical changes of the late eighties and early nineties. Reducing the cost of promising projects has affected the development of a new helicopter. So, by the mid-nineties, plans for the purchase of Comanches had been reduced from 5000 to 1300 units. In the future, the issue of new reductions in planned purchases was repeatedly raised. In addition, the changing views of the military. Since the start of the design work, the customer has repeatedly changed the requirements for a promising machine. Several times in the assignment there was a bias towards reconnaissance or strike capabilities.
Testing, refinement and refinement of various systems promising helicopter continued until the end of 2003 year. By this time, discussions on the feasibility of the project began again in the US ruling circles. Supporters of the RAH-66 helicopter appealed to its high performance and versatility. Opponents, in turn, pressed on the financial side of work. By this time, about 7 billions of dollars had been spent on the development and testing of the Comanche helicopter. Taking into account further work and construction of serial equipment, the total cost of the project could pass for 40 billions.
Numerous discussions have mentioned other arguments against the new helicopter. It was noted that the development of the machine was delayed for more than two decades, and the repeated refinements of the technical specifications can not provide the required relevance of the project. In addition, critics reminded of the military use of helicopters in Afghanistan and Iraq, believing that the characteristics of the new RAH-66 are insufficient or redundant to solve certain tasks. It was also noted that reconnaissance operations can be conducted by unmanned aerial vehicles and do not require the creation of specialized helicopters.
The fate of the project RAH-66 Comanche was decided 24 February 2004, when the leadership of the American Ministry of Defense decided to stop all work. The closure of the project hit the Pentagon’s budget. In order to compensate for the premature termination of the development, the military department was forced to pay compensation to Boeing and Sikorsky companies in the amount of about 1 billion dollars.
By the time the project was closed, two prototype helicopters were built. Machines with dismantled equipment a few years later were transferred to Aviation US Army Museum (Fort Rucker, Alabama). The developments on the RAH-66 project did not disappear. Ideas and solutions created during the development of the new helicopter are now used in new projects of helicopter technology. Some items of equipment were later offered for use on new versions of the AH-64 Apache attack helicopter. In addition, in the future it is planned to develop a new helicopter, which will replace the existing equipment. Perhaps this machine will become a direct development of the Comanche, which ten years ago did not suit the military and politicians.
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