United States Defense Department continues to develop and acquire systems which provide the required capabilities to the war-fighters. B-2 stealth bomber has unique wing configuration and stealth technology. The structure of B-2 is similar to B-35 which was developed in 1940 ‘s by Northrop. The first B-2 was displayed publicly on November 22, 1988. Its flight was on July 17, 1989. This aircraft got its full operational capability in Dec., 2003. The main contractor which is responsible for its system integration and design is Northrop Grumman Integrated Systems. Development of B-2 was started in 1981. Air-Force was given approval for the procurement of 132 operational B-2 aircrafts in 1987, chiefly for strategic bombing missions. The purpose of development of B-2 was changed to regular operations after the demise of the Soviet Union. So, the order was reduced to 20 operational aircrafts and one test aircraft.
General specifications of the United States Airforce B-2 spirit are shown in below figure:
CONCEPT DEVELOPMENT STAGE
Military Aircraft designers wanted to design the aircrafts which can avoid the interceptors and missiles. They learned the new method which is known as stealth. This new method was used to build an aircraft which can absorb or deflect radar signals and finally lead to reflect very little back to the radar unit. This aircraft was the first type of weapon system to be researched for benefits of stealth. This new technology progressed in 1970’s and they looked forward to make the long range stealth bomber. United States president knew about these developments and it appeared to be the main reason for the cancellation of B-1. During 1970’s, there was a need to replace the old Boeing B-52 Stratofortress. Aircrafts like SR-71 Blackbird used some components of stealth technology but it was not good enough to deflect most of the radar signals. In 1979, stealth technology had come to the point where they could build the true stealth bomber.
In mid 1970’s, Defense Advanced Research Projects Agency began the Experimental Survivability Testbed project. Contracts were given to the Northrop and Lockheed for the first testing. Northrop developed the stealth technology and then it is incorporated in the operational aircraft designs such as B-2 stealth bomber. Northrop’s Advanced technology program design got selected over the Lockheed design on October 20, 1981. They redesigned the bomber in mid 1980’s because the profile of mission was changed to low-altitude from high altitude. The redsign postponed the program by two years and it added around 1 billion US
dollars to the program. Around 23 billion US dollars spent on reseacrch & development of B-2 by 1989 secretly. The B-2 became one of the most expensive aircraft in the world which priced more than 1 billion US dollars per plane. Below figure shows the various components and their respective manufacturers.
Concept Exploration of B-2 program initiated officially when the Advanced Strategic Penetrating Aircraft (AFSPA) studies were conducted. The concept exploration phase included the definition of needs by Strategic Air Command and also the derivation of system requirements for Full Scale Engineering Development program. Concept of Stealth Technology attracted the aircraft engineers after the invention of the radars. Studies of radar absorbing materials yielded to a concept called iron paint. This technique is used to embed iron particles in a quarter inch thick flexible rubberized film. Northrop finally developed the radar cross section prediction code which is known as GEMSCAT. Northrop encouraged by the DARPA and air force to continue its stealth technology efforts. Therefore, Northrop continued its research on different techniques to reduce radar cross section. They developed an aircraft which incorpaorated a new concept given by Hughes known as Low Probability of Intercept. The entire program resulted in an aircraft called Tacit Blue aircraft. The first flight of Tacit Blue was on February 1982. The most significant thing is that this aircraft validated the design approach for the B-2 because it became the main role for the maturation of stealth technology, engine inlet integration, the tailoring of radar cross section pattern and all the other factors which were important for the development of the B-2. One of the reasons to deflect radar signals in B-2 is its reflection angles which is shown in the below figure:
In mid 1980’s, Air force observed the progress by both contractors that they instructed aeronautical system division to prepare the request for proposal for the full scale engineering development of advanced technology bomber. Both contractors used their designs to prepare the better response to radar signals. Each contractor conducted a lot of trade offs between low observables and classical air performance characteristics. Northrop developed a design which is high altitude cruise design, aerodynamically efficient and has low observable levels. Both the contractors looked other companies to help them in the program. Northrop selected Vought and Boeing whereas Locheed selected Rockwell. Finally, Northrop won the contractor award and the contract was signed on December 4, 1981. Government evaluators evaluates the contractor’s design. If the evaluator was not convinced by the contractor’s design or he had some better approach to it then he was allowed to directly talk to the contractor engineer. After their discussion, the government evaluator made the proposed specification language and present this proposal to the specification board so that these specifications should be included in government’s performance based specifications. If these specifications were successfully defended before the board then these specifications got incorporated in the official document of specifications. All specifications which were part of contract between government and Northrop except the radar cross-section specification. Both government and contractor agreed the data on configuration was not good enough and that the radar cross section model required further testing. Then they also agreed on conducting more penetrability analysis with the revised data before the table could be completed with confidence required for the design basis. In the mean time, B-2 force on force campaign was developed. This model tested the B-2’s force capability on annual basis as the design matured and nature of threat improved. This annual testing helped the decision makers regarding the cost benefit of the B-2 force. The process to reach the final set of requirements and approved by both government and contractor was time consuming and put both of them at risk from contract award to signing but the benefit was that the clearly understood set of requirements among all parties and all reached to the mutual agreement. The three company airframe structure team was given the task to look for other ways to reduce the risk factors and weight of the base structure. These three companies came with the new wing structure. The new wing structure has additional part of planform change as shown in the right figure in the below picture:
Due to the efforts of the industry and the government during 1979-1980 that the requirements for B-2 were derived. There are a lot of factors due to which the B-2 is much expensive and it is qouted by Air Force in 1998 as 1.157 billion US Dollars. The most significant reason for this huge price is the considerable measures taken to assure the stealth characteristics of the bomber. Workers always took special care while assembling its components otherwise they can increase the radar cross section and damage the contours of the plane. It is also equipped with very expensive electronic components and exterior coating which helps the aircraft to become invisible for the detection. The engine in the B-2 was made by General Electric Aviation Department and it is known as F118-GE-100. The predecessor of F188 engine is F101 engine. F101 engine was used in the B-1 bomber. Using the same design two new engines were created i.e. F110 and F118. These new engines have the better performance than the F101 engine and it is shown below:
Above picture is from : http://www.dmitryshulgin.com/b-2-spirit/
The above powerful engine produce 19000 lbs of thrust and has no afterburner which also helps in reducing the detection of the aircraft. Flight testing of the given engine was started in 1989.
The B-2 has the complex design and also the entire design was made keeping one thing in mind i.e. it should be very hard to detect. The airframe was built with the concept of stealth. The windows of B-2 has fine wire mesh which was designed to sctter the radar signals. Its shape has few leading edges which makes it harder to detect by radar. The unique shape of the B-2 makes it unstable while flying so it relies on a computer to stabilize it. B-2’s landing gear doors has hexagonal shape whih breaks up its radar profile. B-2’s bomb rack assembley can hold eighty 500 lbs bombs. Its rotary launch assembly can deploy weapons in quick succession. The maximum speed of B-2 is 604 mph and maximum altitude is 50,000 feet. 21 B-2’s were delivered at the base station in Missouri. The rate of reliability is 90 percent ithe first three years of its operation. The rear wings of the B-2 were in w-shaped while the front wings were at 33 degrees angle. The cockpit of the B-2 aircraft can accommodate two members. This cockpit has electronic flight instrumentation system which is used to display the sensor data status of
weapons, avionics systems etc. B-2 stealth bomber is fuel efficient and is highly aerodynamic. B-2 stealth bomber is very much automated that even a single crew member can fly while the other crew member can sleep.
The main technologies which made it less detected by radar are leading edges which can deflect the radar and coatings which improved its radar deflecting capabilities to much higher strength. The combination is so good that even it has the large wingspan, B-2 bomber’s radar signature is astonishing 0.1 sq. metres.
B-2 stealth bomber was made for the conventional and nuclear weapons. B-2’s in the traditional role from Whiteman, diego garcia & guam can cover whole world with only one re-fueling. Below is the picture depicting the same and also the payloads:
ENGINEERING DEVELOPMENT STAGE
The Engineering Development Stage means the transition from the conceptual stage to the practical engineering stage of the system. This stage allows the complete system to perform all the desired functions. There are different organizations which participated in this stage such as avionics system engineering group, weapons sytems engineering organization, logistics organization of Northrop, boeing systems organization etc.
Weapon Systems Engineering organization role was to evaluate the weapon system effectiveness, vulnerability and survivability. Also, it is responsible for the stealth technology development and its evaluations. This organization has many groups such as low observables materials laboratory, low observables process development, survivability analysis, grey butte test range etc. and all of these groups have their own specific roles in the engineering development stage. Logistics system engineering group’s main role was to support the requirements for the future weapon system. The new thing added to this organization was reliablity & maintainability engineering. There was another feature which impacts largely on the development and design of aircraft weapon system which is known as primary system reliability. Avionics systems engineering organization was responsible to monitor all the subsystems and gather the requirements regarding the avionics. Boeing systems engineering organization performs various functions such as co-ordination with Northrop, systems engineering integration, technical integration etc. Air Force discovered various cracks on the back section of stealth bomber. Air Force confirmed that these cracks were not dangerous but maintenance team is required to check these cracks whether these were growing.
the upgraded version has smart bomb rack assembly and the advanced data & voice communication by programmable communication terminal.
It has AN/APQ 181 radar system which is also known as world’s stealthiest radar. This radar system is designed specifically for B-2 stealth bomber. It has 21 different modes for navigation updates, destination search, delivery of weapons etc. it has two antennas i.e. low probability intercept & sophisticate software mode. These two antennas equals the stealth properties of the bomber. The APQ-181 has two radar sets for operational redundancy & to meet the specifications of reliability.
B-2 apirit stealth bomber has defensive management sub-system. This system gives the protection against the threats. Components of this system are provided by various organizations like honeywell, raytheon, lockheeed martin but the main component is made by the lockheed martin. The ZSR-63 or APR-50 is made to identify, classify & search any malicious
system which radiates radio frequencies. The input of this system is the antenna over the airframe and then system does the signal processing and provides the updates to crew of the aircraft. Flight control actuation system for B-2 bomber was moog. It is made of sensors, actuator controls, servo-motors, redundancy mangement etc and is shown in the below figure:
Flight Control Actuation System
The B-2 navigation system was designed basically for the autonomous navigation. Bomber aircrafts requires the accurate navigation systems which are durable for long periods. Previous aircrafts like B-1b required the periodic updation by radar position & velocity. In B-2 navigation
subsystem included the star tracker due to which it improved its un-aided navigation accuracy. The star tracker reduced the requirement of periodically updation by radar position and velocity in B-2 stealth bomber. B-2’s navigation subsystem consists of inertial measurement unit(IMU), avionics control unit(ACU), AIU power supply unit(PSU), airborne time transfer unit(ATTU). The block diagram of navigation subsystem is given below:
B-2 has extremely-high frequency(EHF) satellite communication(SATCOM). The testing of EHF SATCOM increment one flight started in se., 2010. It is designed to give capability to three different increments. Increment one upgraded the flight management
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