In order to adapt to the battlefield environment of 2 1 century, RAH-66 Comanche was designed as the first stealth helicopter in the world. The stealth of RAH-66 is no less than that of B-2 and F- 1 17 aircraft. In addition to the stealth technology of these two aircraft, new technologies specially developed for this aircraft are also adopted. The stealth technology used by helicopters is slightly different from that of fixed-wing aircraft because it is difficult for radar to detect helicopters blocked by hills. If the helicopter flies close to the ground, the chaotic echo on the ground will also cover the helicopter, making the radar ineffective; This is the advantage of helicopter stealth.
Because the radar wave propagates outward in a conical shape, the echo also propagates outward in a conical shape, and the power density of the echo increases rapidly with the shortening of the distance, so the radar can detect the target with a small radar cross-sectional area at close range. The fact is the same. Many radars can detect his F- 1 17 aircraft 8 kilometers away, but it is not a threat to it because of its high speed. On the other hand, the helicopter flies very slowly, so the radar has enough time to give an alarm. This is the shortcoming of helicopter stealth.
L, stealth for radar detection
The radar cross-sectional area of RAH-66 helicopter is smaller than that of any helicopter at present, only 1% of them. Such good stealth performance is mainly due to its stealth shape and the extensive use of composite materials and radar jamming equipment.
The turret of RAH-66 photoelectric sensor is an angular plane prism, which has the function of dissipating radar reflected waves. The side of the fuselage is composed of two halves of the corner, which avoids the shortcomings of strong omnidirectional scattering of radar waves by cylindrical and hemispherical fuselage. There are "brackets" on both sides of the tail beam, which can deflect and reflect radar waves so that they cannot return to the detection radar. The culvert at the tail is inclined to the left, and the vertical tail at the tail is inclined to the right, and a horizontal stabilizer is installed on it. This structure will not form an angular reflector with an included angle of 90 degrees between metal surfaces, and can strongly reflect radar signals. On the front of an ordinary helicopter, the air inlet is a strong radar reflector like a corner reflector, while the two engines of RAH-66 helicopter are encapsulated in the fuselage, and the air inlet is suspended and buried above the two sides of the fuselage, and the air inlet is prismatic, which will not form a strong reflection on radar waves. The rotor hub and blade root are equipped with fairings to form a smooth transition fusion body, which can also reduce the reflection of radar waves. The shape of the paddle is carefully selected, so it is not easy to be found by radar.
Another shape design measure of RAH-66 to reduce the cross-sectional area of radar is to use built-in missiles and retractable super-drop frames. RAH-66 can carry 14 missiles at most, six of which are hung on the closable hatch with integral lifting beam, and are usually closed and opened when launching. The built-in missile cabin was first used for helicopters. The 20mm "gatling" gatling gun can form a larger radar cross-sectional area, so it is designed to rotate 180 degrees in the horizontal plane and be stored backwards in the turret fairing. The short wing used for hanging weapons or auxiliary fuel tanks can be removed, and the short wing can be removed when carrying a small amount of weapons and stealth requirements are high. The rear three-point landing gear can be retracted. After retraction, the hatch of the super-descending frame is closed for shielding, which can reduce the radar reflection cross-sectional area.
In order to reduce the radar cross-sectional area, RAH-66 also widely uses composite materials, which account for 5 1% of the total weight of the helicopter structure. The composite materials used by the US military helicopter UH-60 Black Hawk only account for 9%. RAH-66 is a practical helicopter with the most composite materials in the world. The composite materials used in the fuselage structure include skin, hatch, stringer, partition frame, central keel box beam structure, turret fairing, ducted tail rotor shield, vertical tail wing and horizontal stabilizer. The composite materials used in the rotor system include flexible beams, blades, torsion tubes, torsion arms, rotating inclined plates, sleeve shafts and rotor fairings. The transmission system is made of composite materials, including transmission shaft and main gearbox. The composite materials used are toughened epoxy resin, bismaleimide resin, graphite fiber, glass fiber and Kevlar fiber.
The RAH-66 helicopter can also be equipped with a radar jammer, which can jam the detection radar. Its working principle is that the incident radar wave can be turned into a pulse signal, and at the same time, the reflection data of the helicopter under this condition can be measured, and a false echo can be sent out, thus achieving the purpose of disabling the detection radar.
The radar reflection characteristic signal of RAH-66 is low, so low-power jammer can be used, which reduces the weight and cost of jammer. Unlike AH-64, it needs a higher power jammer. It is not difficult to see that stealth technology is a technology that makes the radar system ineffective and makes it impossible to detect aircraft. In fact, stealth technology has four aspects, except radar detection, infrared detection, acoustic detection and visual stealth.
2. Infrared detection stealth
It can be said that RAH-66 is the coldest helicopter and the first helicopter to fully apply infrared suppression technology to the fuselage.
The infrared suppressor is installed in the tail beam, and its unique long exhaust port is designed with enough bending length to make the hot gas and cooling air exhausted by the engine completely and effectively mix. The cooling air is sucked in through the second air inlet above the tail beam, mixed with the hot exhaust of the engine, then discharged through the downward gaps on both sides of the tail beam, and then blown away by the downwash airflow of the rotor, so that the exhaust temperature is obviously reduced, thus protecting the helicopter from the attack of heat-seeking missiles.
3. invisible to the naked eye
RAH-66 adopts a two-seat tandem cockpit, with slender fuselage, concealed weapons and retractable overhead pylon, which not only reduces the radar reflection area for helicopters, but also makes it difficult for naked eyes to find it if the distance is not close enough. The cockpit adopts flat glass, which can effectively reduce the diffuse reflection of sunlight. The surface of the whole aircraft is dark and not reflective paint, which reduces the reflective intensity of the helicopter. These are also beneficial to visual invisibility. RAH-66 uses a five-blade rotor, but it is related to reducing visual detection. Because the apparent brightness when the rotor rotates is related to the flicker frequency, that is, to the passing rate of the rotor blades. If the stable light source is blocked for half the time, when the flicker frequency is 9.5 Hz, the actual display brightness is twice that of the stable light source. 9.5 Hz is about the flicker frequency of two blades. The higher the frequency, the lower the brightness. The flicker frequency of each blade is 36 Hz, and the brightness will be reduced by 50%. When the rotor is five blades, the possibility of visual detection can be reduced by about 85% compared with a helicopter with two blades. This phenomenon is called Brooke effect, which is also confirmed by experiments.
4. Secret detection of sound
Before seeing the helicopter with naked eyes, we can also detect and identify the helicopter through its sound. Therefore, RAH-66 has taken the following effective measures to reduce the sound. The rotor tip swept back can reduce the noise sound pressure by 2 to 3 decibels, so it is difficult to distinguish the noise of five blades from that of two blades. The ducted tail rotor can also reduce noise, because it eliminates the interaction between rotor and tail rotor wake. The narrow slit exhaust ports on both sides of RAH-66 tail beam can not only reduce the infrared radiation mark of engine exhaust, but also eliminate the noise of engine exhaust. Another method of noise reduction of RAH-66 is that the blade profile and curvature from the blade root to the blade tip are the same, which can make the outer section of the forward blade reach high speed and the backward blade will not stall, so that the helicopter can reduce the rotor speed at low speed (167 km/h), thus reducing the rotor noise.
Usage feature
The advanced bearingless rotor has good maneuverability, which makes the pilot have a clear feeling of manipulating the fighter. The 8-blade ducted tail rotor can make RAH-66 turn sharply, making it turn 90 degrees and 180 degrees at the forward speed within 3 to 4.5 seconds. This is far superior to ordinary helicopters, and it is easy to catch fighters in air combat. When the tail rotor blade rotates in the culvert, it will not encounter the turning obstacle caused by the aerodynamic sound of the sound seam of the tail rotor, such as branches, and it is not easy to hit the staff when driving on the ground. The high-level stabilizer can be folded down, which is beneficial for the transport plane to airlift the whole helicopter.
The fuselage is made of composite material with basin keel beam in the middle, which is the main load-bearing structure. More than half of the skin can be opened without loading the skin, which is convenient for maintenance. When the weapon door is opened, it can be used as a maintenance platform. The nose mask is hinged and can be opened to the left, which is convenient for accessing the sensor and ammunition compartment to work. The airframe structure can withstand an overload of 3.5G and the shooting of bullets or shells with diameters of 762mm, 12.7mm and 23mm.
The landing gear is a rear three-point retractable energy-absorbing landing gear. There is only one wheel on each landing gear. The main landing gear can "bend your knees" to squat, reducing the height of the helicopter and facilitating the air transport of the transport aircraft. The RAH-66 can land at a sinking speed of 1 1.6m/s, and the pilot will not be injured.
Two T800 turboshaft engines are installed on the curved shoulders of the fuselage with digital engine control devices. The power of a single unit is 895 kilowatts. The amount of oil in the fuel tank is 10 18 liters. The fuel system is crash-resistant, and there is an inert gas generation system to prevent the fuel from catching fire after the helicopter crashes.
RAH-66 adopts a tandem stepped cockpit, with the shooter in the back seat and the pilot in the front seat, which is different from other armed helicopters. The pilot is in the front seat, which greatly expands the field of vision and is very beneficial to the terrain following flight.
In fact, both the front and rear driver's seats can be manipulated. The two cockpits have the same LCD flat panel display, which not only simplifies the control switch, but also makes all tactical actions less than.
In a three-page menu program, most tactical actions can be performed by pressing a button.
The cockpit adopts double filtration overpressure system, which has the ability to prevent atomic, biological and chemical weapons. Pilots can go to war without wearing protective clothing.
weapon system
The weapon bay of RAH-66 can hold six 2-meter-long missiles. Under all flight conditions, the opening time of the hatch is less than 5 seconds, and the opening action will not cause harmful effects on the weapon. The closed weapon cabin not only has stealth function, but also can reduce flight resistance. The weapon cabin has a fire detection system, which can quickly abandon the weapons in the cockpit when necessary.
The short wing of RAH-66 can carry 864kg weapon load in different combinations. If the short wing is attached to the external fuel tank, the RAH-66 can fly 2355 kilometers across the Atlantic Ocean. The short wing can carry 32 70mm Hydra rockets, or 8 Helfa missiles, or similar missiles. The internal pylon of RAH-66 can carry 14 Helfa missiles or similar missiles.
The rotating turret is equipped with 20 mm caliber double-barrel guns, and the firing rate is 1500 rounds/min when dealing with air targets and 750 rounds/min when dealing with ground targets. The azimuth angle of the turntable is 240 degrees and the pitch angle is 60 degrees. The ammunition box contained 500 rounds of ammunition. It takes less than three people to refuel RAH-66 and load its turret and weapon bay 13 minutes. RAH-66 is equipped with advanced avionics, and it has reconnaissance and combat capability under bad weather conditions day and night. If you can find the target first in a battle, you can strike first and fire before the target fires. The advanced navigation and target aiming system can provide high-definition infrared images of the battlefield at night, which makes the helicopter have excellent combat capability. Compared with Apache helicopter, RAH-66 Comanche helicopter can increase the distance to find the target by 40% and shorten the response time by 95%. It is not easy to find this picture. If it's okay, give a point.