EM 121 Winter Project: Landing Gear Design

Transcription

1 EM 121 Winter Project: Landing Gear Design Summary Your objective is to design a lightweight and safe link for a landing gear mechanism (see Figure 1) that will allow the landing gear to safely retract to a specified angle. For a successful design, the strut will begin in the vertical position, your link will assemble to the device, and the link will not break or stretch more than 10% of its original length as the strut is slowly lifted to and held at an angle of 10 below the horizontal. Designs consisting of small link masses are considered better designs. Link Figure 1. A typical landing gear mechanism. (1 hydraulic ram, 2 hinge mechanism, 3 strut, 4 wheel boss, 5 wheel, 6 fuselage/wing; source: Details Figure 2 shows a schematic of the prototype landing gear mechanism we will use in this project.

2 Driven arm: short link Driven arm: long link Shoulder screws Your link Pin Shackle 7 possible hole locations on strut Wheel Strut Figure 2. Prototype landing gear mechanism. You will design the 2-D profile of the link that initially holds the wheel and strut in the vertical position to within ±5 and allows the wheel to be slowly lifted up into and held in the retracted position at 10 below the horizontal without breaking or permanently stretching more than 10% of its original length. One end of the link is joined to the shackle by a shoulder screw, and the shackle is pinned at one of 7 possible hole locations on the strut. You will get to choose which hole you will use. The other end of the link is joined (again by a shoulder screw) to the long link on the driven arm of the landing gear mechanism. The diameter of the shoulder screws is nominally inches. Drawings that describe the geometry of the landing gear mechanism are provided in this handout, but the source CAD files will not be distributed. The actual mechanism will be available in the Rotz Lab for inspection during business hours. The mechanism will be on display in the back of the Rotz Lab, in the Engine Control Lab. If the door to the Engine Control Lab is locked, please see one of the ME technicians to be let in: Mike Fulk in the ME Machine Shop (EL 202), Ron Hofmann in DL 205A, or Jerry Leturgez in CL 204. You are encouraged to view the mechanism and take whatever measurements you need for your analysis and, if you wish, to create a solid model of the device in SolidWorks. Do

3 not disassemble the mechanism or attempt to experimentally determine your design this project is about analysis, not experiment. Your link will be laser-cut from a Nylon 6/6 sheet (a rigid plastic). We supply the material, and the thicknesses available to you are inches, inches, and inches. Part of your design choice is which sheet thickness to use. The published yield stress of the Nylon and tensile test results for specimens fabricated from Nylon sheets purchased over the last few years are included in this handout. Think carefully about which set of tensile test data to use for your design. You will work in teams on this project; the teams will be assigned by your instructor. You must fairly and evenly distribute the tasks, make sure everyone understands the analysis and decisions, and coordinate your deliverables. If teammates are behaving unprofessionally, talk to me. I will adjust individual student scores based on how they behave as a teammate. Deliverables 1. By 11:30 pm on Sunday, January 29, an to your instructor with the following information: Subject line: EM 121 link design for Team #, where # is your team number. A CAD file in.dxf format defining the outline of your link. The name of the CAD file must be given as Team#_thickness.dxf (for example, Team107_062.dxf for Team 107, using inch plastic). Once your link is cut, you will have the opportunity to inspect the link. If there are manufacturing flaws that would adversely affect your link s performance, you will be able to have another link cut. 2. By 5 pm on Monday, February 13, a printed, typed memo that summarizes your team s design, analysis, and contest performance, with attachments providing documentation of your analysis and design process. A memo template and the rubric that will be used for grading are provided in this handout. For your convenience, a Word document of the memo template will be available on the website.

4 Week Mon Tues Wed Thur Fri 8 Link.dxf due Sunday 11:30 pm 9 Contest day Exam 3 Project work day 10 Memo due by 5 pm Testing your link (contest day) There will be a contest on Wednesday, February 8 in the Rotz Lab to determine whether or not your link meets the design requirements without failing, as well as to determine the performance portion of your grade. Testing will occur according to the following schedule: Section Instructor Testing period 1 (5th hour) Kawano 1st hour 2 (6th hour) Kawano 2nd hour 3 (5th hour) Adams 4th hour 4 (6th hour) Adams 5th hour 5 (5th hour) Moseley 7th hour 6 (6th hour) Moseley 8th hour 7 (5th hour) Buckley 3rd hour 8 (6th hour) Purdy 6th hour If your team cannot have at least two team members present during the assigned section time, we can move your team to compete with a different section. However, this must be arranged in advance. The testing procedure is as follows: 1. The length and weight of the link are measured by the instructor. (This will probably be done before the day of the contest.) 2. The team carefully assembles their link to the landing gear mechanism.

5 3. The instructor will check that the strut is within ±5 of the vertical. 4. The motor is started and the landing gear will rise slowly until it is at 10 from the horizontal. 5. The team removes their link and the instructor measures the new length to check for permanent deformation. Grading Your project grade will be based on two components with the following percentages: Memo and analysis Performance 70 pts (see memo rubric) 30 pts (see below) 100 pts Memo and analysis grade: The memo template and grading rubric are included in this handout. The memo is likely different from what you are used to and it cannot be successfully completed at the last minute. Please read all instructions carefully. Performance grade: The performance portion of your grade is based on whether or not your team s link passes the test and how your (successful) design compares to other designs in your section based on the criterion that a lighter link is more desirable: Fails because your link does not assemble to the device 15 pts fractures at any time during the test exceeds the permanent deformation limit after testing holds the strut in a mostly vertical position before testing but not within ±5 of the vertical (at the discretion of your instructor); performs successfully otherwise 17 pts 17 pts 20 pts Passes the test Your score is based on the mass of your link compared to all surviving links: xx = (your link s mass) (mass of lightest link) (mass of heaviest link) (mass of lightest link) 0.66 < xx 1 (heavier third) 24 pts

6 0.33 < xx 0.66 (middle third) 0 < xx 0.33 (lighter third) xx = 0 (lightest link) 26 pts 28 pts 30 pts

7 Device geometry and hole locations These drawings were created in a goodfaith attempt at modeling the actual landing gear mechanism, and they contain some (but not all) measurements for the device. If you need additional dimensions, take measurements on the actual device. It is also a good idea to verify the given measurements. All provided measurements are in units of inches.

8 The combined wheel-strut assembly weighs approximately 42 lb. The center of mass lies along the dashed line, about 30 inches from the very top of the strut.

9 Experimental material properties The material used for the links has been tested in the past, with the following test results. You will need to perform some calculations to convert the dimensions and peak pull forces into stresses. Nylon 6/6 Published yield strength per ASTM D638 10,000 psi 2007 sample test results Actual pull speed = 2.3 inches/minute Sheet thickness (in) Specimen width (in) Peak pull 1 (lb) Peak pull 2 (lb) sample test results Actual pull speed = 2.0 inches/minute Sheet thickness (in) Specimen width (in) Peak pull 1 (lb)

10 Laser cutter and.dxf file FAQ What is the tolerance on the laser cutter? ±0.005 inches. What is the minimum size for the links (that is, the smallest width we can manufacture)? The minimum should be inches. What is the size of the laser beam? The laser beam is inches in diameter and cuts at the center of the line. If two lines are drawn inches apart, then the cut part will be inches wide. Does the laser cutter make perfectly straight lines? No. Very small waviness is seen for some cuts, particularly for very thin or small features. How do you create a.dxf file from an existing model in SolidWorks? 1. Make sure the solid model is scaled correctly so the resulting link is the correct size. If your link should be 3 inches long, make sure the model is also 3 inches long. 2. Right-click on the surface that is to be the profile of the link and select Export to dxf. 3. Under Options, change the version to R12, then click OK. 4. Select a folder and filename. 5. On the left-side toolbar, there is a green check mark click that. 6. A preview should show up on a black background. Make sure the 2-D profile shows up with no dimensions at all (a coordinate system is okay). 7. Save the file. This is the.dxf file to attach to your . I am afraid I created the.dxf incorrectly. How can I check it?

11 1. Open the.dxf file in SolidWorks. 2. Use a drawing template with inch units. 3. The import dialog will open with lots of options. Just click Finish. 4. Use Smart Dimension to verify that all sizes (including the mounting holes!) are correct. 5. When you are satisfied the geometry is correct, close the drawing file without saving it. Your original.dxf file should still be there you are just throwing away the temporary drawing you created.