F 35C Joint Strike Fighter Additive Manufacturing Tailhook Redesign 4/24/16 Submitted to Lockheed Martin Representative Team EDSGN 100, Section: 23 Group 4: Kiran Judd, James Harris, Madeline Woody, and Zach Ceneviva Abstract: The objective for the project was to design, prototype, and manufacture an effective redesign of the Lockheed Martin F 35C tailhook, utilizing additive manufacturing. The F 35C tailhook, like many other subtractive manufactured parts, suffers from a waste of excess material and limitations when creating advanced designs. The main question relating to the current process is how does one eliminate the total amount of material used, while still retaining the original strength? For this reason, when designing the prototype material reduction, affordability, accessibility in the field, effectiveness, and durability were treated with the utmost importance with respect to design criteria. After the printing of the prototype, it was necessary to test the design criteria in order to see if the efficiency and reliability met the desired goals for the tailhook. The tailhook prototype did not pass all of the set criteria for its design, but performed especially well when compared to the set criteria for the durability. Although the initial prototype performed well during the durability test, it did not perform as well as hoped within the material reduction, affordability, and effectiveness categories. These areas proved to be lacking, leading to corrections which would later lead to the improved second prototype, created by the team. Following the improvements implemented within the second prototype, an effective, durable tailhook was created utilizing additive manufacturing processes.
Table of Contents Introduction Pg. 2 4 Methods Pg. 5 6 Results and Discussion I Pg. 7 9 Results and Discussion II Pg. 10 13 Conclusion Pg. 14 References Pg. 15 Appendix Pg. 16 17 1
Introduction: The Goal of this project was to redesign the F 35C Joint Strike Fighter tailhook while improving the capabilities of the legacy design, through reduced weight, reduced part count, faster assembly, and improved performance. The subsequent design process aimed to solve the current deficiencies found within the F 35C tailhook subtractive manufacturing process. For this reason, the design produced intended to solve Lockheed Martin s problem, while providing the United States Navy and Marine Corps an ability to manufacture tailhooks aboard aircraft carriers. The F 35 Lightning II is a 5th Generation fighter, combining advanced stealth with fighter speed and agility, fully fused sensor information, network enabled operations and advanced sustainment [1]. There are three variants of the F 35 that will replace the current legacy fighters for the U.S. Air Force, the U.S. Navy, the U.S. Marine Corps. The Joint Strike Fighter developmental program was signed into action on November 16, 1996, selecting Lockheed Martin and Boeing as competing companies for the JSF concept demonstration phase [2]. On October 26, 2001, the Lockheed Martin X 35 design beat out the Boeing X 32, wining the Joint Strike Fighter contract. Although both aircraft designs were found to meet or exceed the given requirements, it was decided that the X 35 would have less risk and more growth potential over the X 32 [2]. The United States plans to acquire around 2,500 aircraft, intending to provide the bulk of the manned tactical airpower for U.S. Air Force, Navy and the Marine Corps over the coming decades. Deliveries of the F 35 Joint Strike Fighter for the U.S. military are scheduled to be completed in 2037, having a projected service life of about 50 years [2]. The first production F 35 rolled off of the assembly line in Fort Worth, Texas, in February of 2006, proceeding to make its first flight in December of the same year. Over the next few years, flight and ground test articles of all three variants rolled off the production line and began collecting test points. In 2012, the F 35 program ramped up with 30 aircraft deliveries and an increase in testing operations across the United States [2]. It was during this time that the program reached several milestones in weapons separation testing, angle of attack testing, aerial refueling training, and surpassed more than 5,000 flight hours with more than 2,100 recorded flights in that year [2]. Figure 1: The chart shows the three variants for the F 35. The standard F 35A, vertical take off STOVL F 35B, and carrier based F 35C are depicted with their respective service branches. [3] 2
As testing continued on the F 35, problems began to arise within the carrier based, or C variant of the fighter. The F 35C variant has larger wings and more robust landing gear than the other variants, making it suitable for catapult launches and fly in arrestments aboard naval aircraft carriers [4]. Its wingtips also fold to allow for more room on the carrier s deck while deployed. Landing testing had began to show that the design of the tailhook, the device meant to capture the arresting wire on the deck of an aircraft carrier, had various shortcomings. It was later found that the placement on the aircraft s fuselage was causing the tailhook to bounce and thereby miss the arresting wire while landing. After two years of redesigning, Lockheed Martin produced a new, improved version of the original tailhook, aiming to improve upon the inabilities of catching the arresting wire seen on the early model [4]. Although Lockheed Martin designed an improved variant of the tailhook, critics still argue that it does not operate to complete standards. The manufacturing process used to create the tailhooks is also described as being a complicated, wasteful process due to the usage of subtractive manufacturing methods [4]. For this reason, the design team chose to redesign the tailhook utilizing additive manufacturing in order to reduce material used, reduce weight, and improve the manufacturing process. Before the design and prototype phase, it was necessary to select a set of design principles and criteria in order to properly follow the 8 step design process. After careful consideration for the needs of the Lockheed Martin, the mission of the F 35C tailhook, and the producibility of the tailhook, a set of criteria was created. The five main criterion for the tailhook redesign are presented in Table 1. Table 1 : Design Criteria and Set Requirements Design Criteria Material Reduction Affordability Specifications For Requirements Must use at least 10% less material Must be 15% cheaper when mass produced (2,500 planes) Accessibility in the Field Effectiveness Durability Ability to be 3 D printed aboard US aircraft carriers Must consistently hook onto arresting wire Must withstand 250N force 3
These design criteria were created using a brainstorming process, that allowed each group member to contribute ideas that would be most effective when solving the problem. The material reduction requirement was created to facilitate a design that Lockheed Martin and the United States Military could use to reduce the amount of material required. Affordability was the least important criteria due to the fact that the costs for production of the tailhook would be minimal compared to the current cost of $159 million per plane. Accessibility in the field was an important criteria, because the ability to 3 D print a tailhook while being deployed aboard an aircraft carrier would provide major advantages in repair time and logistical support. Effectiveness and durability criteria were created in order to address the shortcomings of previous tailhook models, while increasing the strength of the arresting gear. The durability of 250N was scaled down from 20,000N based off of the size of the prototype, the material of the prototype, the print method of the prototype, and the size of the prototype. All of these factors differ greatly from how the actual part would be printed. 4
Methods: After the creation of design criteria that were described in the introduction, multiple solutions were considered for the tailhook prototype. It was later narrowed down to four main designs. The four designs consisted of a solid steel, solid titanium, lattice structure steel, and lattice structure titanium redesign all utilizing additive manufacturing. Each of these design concepts had specialized strong suits in differing areas, which allowed for a large variety of design options to choose from. The design concepts and their specialties are displayed within Table 2. Table 2 : Prototype Design Concepts and Design Specialties Prototype Concept Solid Titanium Solid Steel Lattice Structure Titanium Lattice Structure Steel Design Specialty/Benefits Extremely strong, lightweight Relatively cheap, strong Extremely strong, lightweight, less material Relatively cheap, strong, less material After the the solution requirements were defined, they had to be weighted in order of importance, allowing them to be applied to the prototype concepts, thus quantifying their effectiveness. The criteria were then weighted as decimals on a scale from 0 to 1, with the most important criteria taking the majority of the weight. Material reduction was weighted the highest, due to the fact that Lockheed Martin wants to improve the manufacturing process through additive manufacturing. There would be no level of improvement if more material was utilized, because it would increase both costs and weight. Effectiveness and durability were both the second most highly weighted, because it was extremely important to make the tailhook catch on the arresting wire properly. This allows for a confidence in the design s ability to withstand the forces while landing and its ability to catch properly. Accessible in the field was given the second to lowest weight, since this is not an imperative goal for Lockheed Martin. Affordability was given a smaller weighting than the rest of the criteria because it is not as explicitly important to the overall mission of improvement. The F 35C currently costs around $159 million, thus the cost of the tailhook will be relatively insignificant in comparison to the costs of the entire airplane. The weight for each criteria and the subsequent score for each prototype concept can be seen in Table 3. 5
Table 3 : Data table shows criteria weighting and performance of each prototype concept Solid Titanium Solid Steel Lattice Titanium Lattice Steel Criteria Weight Rating Score Rating Score Rating Score Rating Score Material Reduction 0.40 1 0.4 1 0.4 1 0.4 1 0.4 Affordability 0.05 1 0.05 0 0 0 0 1 0.05 Accessible in the Field 0.15 1 0.15 1 0.15 1 0.15 1 0.15 Effectiveness 0.2 0 0 0 0 0 0 0 0 Durability 0.2 1 0.2 0 0 1 0.2 0 0 Total 1.0 0.7 0.55.75.60 Following the weighting of the criteria, a set of tests were produced to evaluate the effectiveness of each prototype within its criteria. These tests are represented within Table 4 below: Table 4 : Data table shows criteria and how they are tested on the prototypes Design Criteria Material Reduction Method of Testing Calculate amount of material used Affordability Calculate the cost of the prototype (2500 units) Accessibility in the Field Effectiveness Durability Research plausibility Pull tailhook, hooking it on fixed fishing wire which acts as the arresting wire Hang weights from fixed hook to calculate force exerted on tailhook 6
Results and Discussion I: After completing the selection matrix, it was obvious which design best fit the criteria for the tailhook redesign. The lattice structure titanium tailhook earned a total score of.75 (Table3), placing it high above the other three design options. The next step in the design process required for the modeling of a prototype for the best chosen solution. After completing a CAD model within Solidworks, a proper prototype was ready to be printed out of polylactic acid filament, utilizing the maker commons Makerbot 3 D printers. Various calculations were made in order to miniaturize the size of the prototype to a proper scale in order to fit the printing base plate. A approximate 1:12 scale was set to enable a realistic conversion between the prototype size and actual size of the tailhook. The initial prototype was created with a length of 6 in and varying width depending on location of the tailhook. Figures 3 & 4: These pictures show the first physical prototype created during the design process utilizing Makerbot 3 D printing After the prototype was complete, testing began for each criteria. This was done by devising experiments that tested whether the tailhook passed or failed. The first prototype test, material reduction, was used to see if the tailhook would reduce material usage by at least 10% as the goal projected to accomplish. Calculations were devised and the prototype measurements were converted into real life sizes. Utilizing material analysis within Solidworks, it was found that the volume of material was 34523.16 cubic millimeters. After comparing this volume of material to an object of same design that utilizes subtractive manufacturing, it was found that it used 43.2% less material. Thus, the initial prototype passes the material reduction test. The second prototype test was used to test the affordability of the redesigned tailhook. The actual F 35C tailhook would be manufactured utilizing titanium, a highly corrosion resistant, lightweight, and strong metal costing $200 per 1 kg [5]. When converting into real life 7
dimensions, it was determined that the cost of the tailhook would be $26,000. Thus, the initial prototype fails the affordability test. In order to test the accessibility within the field, research was conducted to discover if it was possible for a 3 D printer to be used aboard an aircraft carrier. After careful research, it was found that the USS Harry S. Truman currently utilizes small 3 D printers, to aid with the production of spare parts [6]. This lead to the conclusion that current aircraft carriers would hold the ability to operate powder bed 3 D printers in order to reproduce factory model F 35C tailhooks. Thus, the initial prototype passes the accessibility within the field. Figure 5: Sailor aboard the USS Harry S. Truman operates 3 D printer used to create spare parts when needed. [6] The next experiment tested the effectiveness of the tailhook when it tried to hook onto an arresting wire. The main goal of the test was to have the tailhook consistently attach to the arresting wire without issue. This was done by attaching fishing wire in a horizontal orientation to two table legs just above the ground. Fishing wire was then attached to the end of the tailhook and tied to the end of a tape measure. The tape measure was extended outwards over the fishing line and was then retracted to pull the tailhook backwards. As the tailhook was pulled back, it was forced into contact with the fishing wire acting as an arresting wire, thus testing its catching abilities. After conducting numerous trials, it was found that the tailhook constantly caught the arresting wire, thus passing the test. Figure 6: Picture displays the setup of the fishing line that acted as the arresting wire. The tailhook catches the arresting gear as it is pulled backwards by the tape measure. 8
The final test conducted on the tailhook prototype was the durability evaluation. The tailhook needed to be designed to withstand massive amounts of forces, due to the stress that would be placed on the tailhook as it caught the arresting wire. This was tested by fixing the tailhook to an IV pole in a hanging, vertical position. Hanging masses were then added in small increments to the tailhook until failure was reached. The tailhook prototype withstood 267 N of force before it finally failed, proving to withstand a larger force than the design requirements. Thus, the initial prototype passes the durability test. The total amount of force withstood was greatly impaired by the material used to create the prototype. PLA filament is not a strong material and did not display performance that is comparable to that of the actual model. When printing the final model, titanium would be used, greatly increasing the strength and effectiveness of the design. Figure 8: The picture displays the setup of the durability test where weights are slowly added to increase the amount of force acting on the tailhook. This is done until the design fails. The initial prototype performed well overall, but was held back by limitations in the additive manufacturing process used and shortcomings in design. The Makerbot additive manufacturing process is useful, but does not produce prototypes on a level that the actual model would be. This is due to limitations found with the materials and 3 D printing methods used. These limitation can be overcome when actually printing the model utilizing a powder bed 3 D printer with titanium. This change would provide a much stronger performance/quality of product, while also eliminating the usage of major supports/rafting. After completing the tests, it was found that almost every area of the design can be improved upon in the second prototype to better meet the design goals and performance levels. An example of this is that the lattice structure model was unable to be implemented into the initial prototype, but will be added when the second prototype is created. 9
Results and Discussion II: Based on the results gathered during the evaluation of the first prototype, modifications were required to better improve the design. The initial prototype failed to implement the lattice structure, thus it was implemented as one of the added features to the second prototype. The length of the tailhook was also increased to 9 in, while adding extra supports to the locations of failure found by the durability test. Figure 10 & 11: These pictures show the improved second physical prototype created during the design process utilizing Makerbot 3 D printing. After the second prototype was completed, testing once again began for each of the design criteria. This was done utilizing the same experiments that were carried out on the initial prototype, allowing for the design team to determine if the second tailhook passed or failed. The results for the testing of the second prototype are displayed within table 5. 10
Table 5 : Data table shows criteria, how they are tested on the prototypes, and the results of the testing on the second prototype model. Design Criteria Method of Testing Results Material Reduction Affordability Calculate amount of material used Calculate the cost of the prototype (2500 units) Uses 82.7% material than subtractive manufacturing Cheaper than first prototype, but still 10% more expensive than subtractive manufacturing Accessibility in the Field Research plausibility Yes, same research used for prototype 1 Effectiveness Durability Pull tailhook, hooking it on fixed fishing wire which acts as the arresting wire Hang weights from fixed hook to calculate force exerted on tailhook Hooked ⅘times on the arresting wire Withstood 70lbs = 311N After completing testing, it was clear that the second prototype was a large improvement over the initial model, building upon the failures found during the initial tests. The second prototype met almost all of the design criteria and accomplished this by adding support to stressed areas for improved performance, cutting down on material used through the lattice structure, improving the part quality, and providing a design that can be printed within the field aboard a US aircraft carrier. The only area that the second prototype failed, was its ability to decrease the overall cost of the manufacturing process. Even after improving the design of the prototype, it was still found to be 10% more expensive than subtractive manufacturing. This is because the operating costs of a powder bed fusion 3 D printer, coupled with the costs of titanium powder are very expensive. Although the prototype failed the affordability criteria, the design team did not view this as a flaw that takes away from the usefulness of the design/process. The F 35 already costs $159 million, making a 10% increase in the tailhook cost insignificant. The benefits of the lattice structure, material reduction, the ability to print within theatre greatly outweigh the 10% increase in the overall cost of the tailhook production. Following the prototype testing, a 3 D scan was conducted in order to test the accuracy of the build. This was done utilizing the software program 123D Catch, where a 3 D image is created by series of photographs taken at various angles using photogrammetry. After completing the 3 D scan, seen in figure 12, it was concluded that the printed build was accurate in accordance to the design. This was concluded after comparing the image of the 3 D scan to both the solidworks model and printed model of the prototype. When doing this, it was 11
concluded that the 3 D scan matches the appearance of the solidworks and physical models, thus proving the accuracy behind the build. Figure 12, 13, & 14: These pictures show the second prototype 3 D scan, the solidworks model, and the physical build of the final prototype, respectively. These images were compared to the 3 D scan in order to determine the accuracy of the print. The second prototype offers numerous advantages over previous subtractive manufacturing processes used to create the F 35C tailhook. The most significant of these advantages is the ability to easily implement lattice structures into the design of the tailhook. This is very challenging to accomplish while using subtractive manufacturing methods and can sometimes be impossible to do. 3 D printing allows for a relatively fast build time that contains advanced features that subtractive manufacturing cannot accomplish. Another benefit is that the additive manufacturing of the tailhook requires much less material than the same part that is created using subtractive manufacturing. This allows for a huge savings in material usage, but at an increase to cost of the production. The prototypes produced may have been built out of PLA plastic, but this will not be the same for the full size models implemented within the F 35C. For this reason, it is recommended that Lockheed Martin produces the tailhooks out of titanium, utilizing powder bed fusion 3 D printing. This allows for a the tailhook to be printed out of a strong, but lightweight metal that can be formed into complex shapes. One of the most revolutionary features to the design is that it can also be manufactured in the field. This means that a powder bed 3 D printing located aboard an aircraft carrier can be used to produce a new 12
tailhook, rather than having to fly or ship a new piece over. This provides a huge advantage over previous manufacturing processes, allowing for a greater range of operations, without a reliance on delivery of replacement parts/supplies. Although the second prototype performed extremely well during testing, it was found that it would be more expensive than the current subtractive manufacturing process. The total cost came out to be $20,020 per unit, making it 10% more expensive than subtractive manufacturing. This does not come as a surprise due to the high operating costs of a titanium powder and powder bed fusion 3 D printers. The second prototype had a total build time of 2 hours and 10 minutes when printed with the Makerbot 3 D printers. After converting the model to its full size and taking the 3 D printing method into consideration, it was estimated that the final tailhook model would take 15 18 hours to complete. This is a relatively short build time when compared to the time it would take for the same piece to be subtractively manufactured or for the navy to ship a new part to a carrier. The downside to this printing method and build time is that only one unit can be printed at a single time. 13
Conclusion: The F 35C Joint Strike Fighter program is dealing with a major issue caused by the failure of the tailhook effectiveness and manufacturing process. The F 35C tailhook, like many other subtractive manufactured parts, suffers from a waste of excess material and limitations when creating advanced designs. For this reason, the purpose of the project was to design a suitable replacement for the F 35C tailhook that improved its capabilities and manufacturing process. The design created was made with the use of brainstorming techniques and applications of specific criteria, material reduction, affordability, accessibility in the field, effectiveness, and durability. The techniques and specifications were utilized in order to produce the most effective tailhook design possible for the problem. After this was done, a design was produced that met all the above criteria, while also adding improvements to the process of manufacturing, by implementing additive manufacturing. Some of the most positive features include the lattice structure design, accessibility within the field, and lightweight strength. For these reasons, it is recommended that Lockheed Martin use a powder bed 3 D printer to produce tailhooks out of titanium. This material and additive manufacturing process allows for a lightweight, strong design to be produced. The entire design process for this project taught lessons of teamwork, ingenuity, recovery from failure, and a goal to strive for constant improvement. These lessons were learned throughout many phases of the design process, and allowed the group to improve ideas and designs with the help of others. The final design of the tailhook proved to pass all the criteria set before it with the exclusion of affordability and will move on to be an effective additive manufacturing platform once it enters full production. 14
References: [1] F 35." Lockheed Martin. N.p., n.d. Web. 5 May 2016. <https://www.f35.com/>. [2] "F 35 Lightning II." Military. N.p., n.d. Web. 5 May 2016. <http://www.military.com/equipment/ f 35a lightning ii>. [3] JSF Family of Aircraft." Air Force Public Affairs. N.p., n.d. Web. 23 Apr. 2016. <http://cdn.ientry.com/sites/webpronews/article_pics/jsf family variants.jpg>. [4] "F 35 Tailhook." F 16 Net. N.p., n.d. Web. 23 Apr. 2016. <http://www.f 16.net/forum/download/ file.php?id=15350&t=1>. [5] "Reducing metal alloy powder costs for use in powder bed fusion additive manufacturing: Improving the economics for production." Digital Commons. N.p., n.d. Web. 5 May 2016. <http://digitalcommons.utep.edu/dissertations/aai3611283/>. [6] "Aircraft Carrier USS Harry S. Truman and Kearsarge Print Spare Parts at Sea with 3D Printers." 3ders. N.p., n.d. Web. 23 Apr. 2016. <http://www.3ders.org/articles/20151228 aircraft carrier uss harry s truman and kearsarge print spare parts at sea with 3d printers. html>. [7] "F 35 Tailhook." Blog Spot. N.p., n.d. Web. 23 Apr. 2016. <http://2.bp.blogspot.com/ S9FQLUZ3pm8/ UFrPm4jaKqI/AAAAAAAAcyc/nfFviqfN7C8/s1600/F 35C_Tailhook.jpg>. 15
Appendix: Figure 15: Final design for the tailhook prototype, complete with lattice structure and added support. Table 6 : Results of Second Prototype Testing Design Criteria Material Reduction (Goal: Use 10% less material) Affordability (Goal: Must be 15% cheaper) Accessibility in the Field (Goal: Must be able to be printed aboard a US carrier) Effectiveness (Goal: Must consistently hook arresting wire) Durability (Goal: Must withstand 250N) Results Solidworks Analysis Used: 82.7% less material Pass Cost Analysis for Powdered Titanium: Cheaper than first prototype, but still 10% more expensive than subtractive manufacturing Fail Researched Plausibility: 3 D printers already used aboard US carriers Pass Physical Test Described in Results: Hooked ⅘times on the arresting wire Pass Force Calculation: 70lbs = 31.7515 kg 31.7515kg*9.8m/s 2 = 311N Pass 16
Part Orientation: When the design team printed the first two prototypes, it utilized a Makerbot 3 D printer to do so. This required the prototypes to be printed on their backs with supports/rafting added to the bottom of the tailhook. This was done in order to always have material to build off of when printing the piece. Since the final model will be printed using powder bed fusion 3 D printing, rafting/supports are not necessary, because the powder itself will act as supports for the model. For this reason the tailhook should be oriented so that it is printed on its side. This will help to create a stronger build, because of the orientation of the material s layering. Lockheed Martin workers and US Navy flight support crews do not have to worry able any changes in the installation process of the tailhook, because it will still be installed the same as previous models. The installation should follow the orientation seen in Figure 16. Figure 16: Tailhook orientation assembled within the F 35C [7] 17