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  • Published on: 7th September 2019
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BACKGROUND

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

NEED ANALYSIS:

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

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 processing capabilities of B-2. This upgradation laid the foundation for the increments two and three. Increment one replaced the current version of management computer with two data drive units to maximize the data storage capability and also the two integrated processing units. Increment two will

replace the MILSTAR AN/ASC-36 Ultra-High Frequency(UHF)/Air Force Satellite Communications (AFSATCOM) System with advanced line of sight terminal to assist the extremely high frequency communications connectivity. Increment three will give the full integration of software for the B-2 EHF satellite communications and also for the global info grid connectivity.

Another important thing in the engineering development stage is the material for the wings. Three major companies Boeing, Vought and Northrop designed the main proposal for the B-2 with notable quantity for the composite material. These three companies proposed different materials such as Vought mainly proposed the titanium structure, Northrop primarily proposed the radar absorbing structure and Boeing proposed for outboard and aft center wing structures. Below composite structures were started developing during 1980’s:

Above composites were used in different weapon system but the database of engineering was

limited. B-2 development team faced few difficulties im using these composite materials because B-2 requires other characteristics such as low observable, landing gear door, weapon bay door etc. So all these characteristics requires very much complex composite structure. If

only the traditional materials like steel aluminium were used in making of B-2 then it would had been so heavy for an aircraft. Ultimately the use composite materials is required in making the B-2. The development team also initiated the wing development with the traditional aluminium material as the backup if in case the composite material fails to satisfy all the requirements for the B-2. After experimant and analysis the team declared that composite material can be used in making the aircraft structure. Preliminary design review has two main things and both includes changes to the configuration of the baseline. Avionics system engineering studied on different defensive alternatives. Then they made changes to the aircraft and finally the approved suite was included in the new avionics baseline program. Also it was included in the avionics specifications. The other change was to incorporate the third crew member. But after conducting a lot of studies on it they thought that the two member crew was enough to do the specified missions. However, airforce team said that the complex missions in the future will increase the workload and then third member would be required. Then again the extensive study was conducted which leads to the preliminary design review and they decided to make provisions for another crew member.  To do this few things needs to be moved here and there such as weapons launchers moved back little bit and also the avionics which was there in the crew station, now moved to another new location which is in the aft of aircraft. Northrop

computer aided lofting tool was developed. This tool was very helpful to integrate different

companies and also their members. This tool played the major role in the process of system engineering. Also, there was preliminary deign review-2 and its main focus is to reduce the risk areas. Risk reduction plans were made for different areas and one specific team was given the responsibility to reduce risk areas. One manager from Northrop introduced the concept of risk closure. Preliminary design review-2 is shown in below figure:

The risk closure program was appreciated by everyone and therefore used during the full development of B-2 aircraft. This program was domainant for atleast two years during the full

scale engineering development program. This program was then joined with other organizations such as program operation & control. Risk reduction plans were the main focus in the whole program to reduce the different kind of risks and after some time individual risk reduction plans were also combined with this program.

POST DEVELOPMENT STAGE

The validation and testing events for the B-2 A stealth bomber were conducted by various organizations.. Its structural testing was done by Northrop Grumman. Northrop Grumman did the fatigue testing by making two aircrafts. On one of the aircrafts Northrop’s team attached computer controlled hydraulic plates. They attached these plates on the airframe to simulate the flying conditions. They observed that the wing can handle the stress over 160 percent before it cracks. Also, they observed that the structure reached 150 percent design specifications. B-2 bombers also went through the substantial environmental testing. The B-2 spirit team is upgrading its seats especially in form of ejection seats. The main aim for this enhance ment is the safe escape for the pilots. Also, they are reducing the time and cost for installation & maintenance of seats. After the development of the B-2 bomber, the team is continuously working on the improvement of its communication technology. They are improving the comunication technology so tha B-2 bomber has larger connectivity during the nuclear explosion. The nuclear explosion event is also known as electro magnetic pulse environment. They will also add the new receiver to the current structure of B-2. This new receiver will have ultra high frequency satellite connection. The new upgrades are also working on the defensive mangement system. In 2008, computing architecture of B-2 was greatly redesigned. Now it includes the new IPU(Integrated Processing Unit) which can communicate with the sytem using the new installed network of fiber optics. They also updated the two radars and to do this updation Northrop Grumman got the contract from air force. Northrop

Grumman needed to change the frequency of the radars because United States department sold the previous radio spectrum to someone else. Finally in 2009, B-2 passes the the United States Air Force audit. Also, they replaced part of wing edge with the new material because the current material degraded swiftly. Following graph shows the budget of B-2A by the united States department of defense.

Also, after the development of B-2, they observed that the cost of B-2 stealth bomber is very much as compared to previous aircrafts. Also, the maintenance cost increased very much. Cost became one of the primary reason to reduce the number of orders of B-2 aircraft. Below is the figure showing the cost camparison of b-2 with the previous aircrafts:

United States Airforce was accepting the B-2’s in three blocks i.e. block-10, block-20 & block-30. As the technology advanced with time, B-2’s computer systems also needed to be replaced by the advanced processors to increase its performance and maintenability. In the beginning it accepted the 6 aircrafts then it accepted 10 aircrafts in block-10, 3 in block-20 & 2 in block-30. B-2’s in the block-10 configuration were used mainly for the training and were placed at Whiteman air-force base station. In this configuration, aircrafts were unable to support the traditional weapons. In block-20 configuration, aircrafts had the cpability to lauch the

traditional & nuclear weapons. In the last configuration i.e. block-30 , the aircrafts satisfied all the capabilites required by the air-force. Block-30 has twice radar modes than block-20 configuration aircrafts. Below is the figure showing the upgrades of B-1, B-2 and B-52 aircrafts over the years:

After more than 10 years of development of B-2 stealth aircraft and more than 5 years of its flight testing, United States air-force has still not displayed the B-2’s met his mission requirements. Executing the test plan was slower than expected. The plan o complete its testing was till July, 1997 but aircraft took much time and was not completed by the mentioned

date. In the original fleet of B-2, twenty one aircrafts were built. In more than 22 years of its operation, only one incident happened due to which air-force lost its one B-2 stealth bomber. This incident happened while taking off from air-force base staion in Guam. 19 aircrafts are still at Whiteman base station and one aircraft is used for testing at California.

CHALLENGES

One of the most challenging tasks is to build an effect and efficient aircraft which could not be detectable by any radar signals. It requires specialized knowledge in the stealth technology. As explained earlier, aircrafts like SR-71 blackbird used some components of stealth technology but those are not good enough so B-2 came up with better stealth technology in it. But there are other challenges which B-2 faced like its radar could not tell the rain cloud from mountainside which costed around 2 billion US Dollars each. According to the report of General Accounting Office, the skin of plane could not handle heat, rain or damp. This skin was made of composites and thermoplastics which is transparent to radar. So, it was supposed to give the aircarft its radar escaping stealth qualities. If this skin is removed then this bomber would loose its uniqueness of stealth technology. Therefore, it was one of the major challenge B-2 has faced. Also, it has two huge vents which creates drag. Team is working on this challenge and the new version they are trying to incorporate four smaller vents. One other challenge faced while making of B-2 was the engine location because engines were placed in the structure where they could influenced its surroundings such as loading of the materials and the temperature control. It created the demand for the thermo-dynamists to choose materials so that they can handle the huge temperatures. Also, acoustic engineers were also required at this time to handle the acoustic thermal temperature. Finally they determined the configuration after many test and analysis. Another challenge they faced during the first flight was the heat blanket on the air wing went out of the way and burnt huge part of the wing. It is now believed that it was the biggest repair of composite ever done and after that it was tested succesfully. Other challenge

is the cost of the B-2 bomber and one reason of this huge cost is that it has two weapon bays. Team is trying to reduce the cost in the new version by making single weapon bay which can carry nuclear weapons and large missiles. One of the other challenge it faced is its attacking capabilities. According to experts B-2 aircrafts are less efficient than other attacking aircrafts because of the compromises & maintenance needed by stealth structure. Also critics pointed out the extravagant money spending on the stealth technology.   

SUMMARY AND LESSONS LEARNED

The whole process of B-2 from need analysis to challenges is filled with lot of learnings because it is a very complex aeronautical system. Every department contributed a lot in the whole process like logistics department, weapon control department, navigation system department etc. when requirement caused the risk in design that could have affect on performance, cost, time then team constructed alternative approaches after having discussion with the user. Perseverance showed by the teams especially the design team ensured that life cycle standardization was merged directly into design process. Standardization consistency is required to achieve the highest payoff. Standardization consistency by the design teams along with the process standardization is required for the efficient performance of the aircrafts.

The main reason for the B-2’s success was the sharing of information among all the departments, employess & staff to facilitate standardization. Personnels at Air-force base in Missouri knows the best ragrding the fleet of stealth bomber. In reality, they are the experts on long range strike bombers. Recently, the United States government passed the budget of more than than 5 billion dollars for the development of new long range strike aircrafts. So the United States next stealth aircraft is already in development stage and will be fully developed near to 2025. But B-2 stealth bombers are expected to remain in service till 2058.

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