P15462Manufacturing Processv1

Foam Cutting: Wings, Tail, and Fuselage

  1. Generating .dat Files
  2. If you have a series of (x,y) points in Excel (as we often did) make sure that all the points are 5 characters long (negative signs count as a character) (see below). Save as a space delimited text file with 5 spaces between the columns. These data points should be on an ‘airfoil scaling’ from 0-1. Then the scale will be increased (or decreased) when importing the data points into Foam Works. It will work just fine to scale your (x,y) points before bringing the .dat file that contains them into Foam Works, but to minimize the number of files you are generating (the same airfoil of varying scales), it is best to do the scaling in Foam Works.

  1. To properly format your .txt file (before converting it to a .dat), use the following format (as described in the image above).
  2. The first column should be moved in by 5 spaces
  3. The x value should be formatted: X.XXXXX
  4. There should be 5 spaces between the x and y values. If the y value is negative, than the negative sign counts as the 5th space
  5. The y value should be formatted: X.XXXXX
  6. Change your folder settings so that file extensions are not hidden and change the file extension from .txt to .dat
  1. Converting .dat file to .dxf to G-code (.tap)
  2. Open up Foam Works and generate a .dxf file from your .dat file.
  3. Generate G-code (.tap)by uploading your .dxf files. For a taper you will upload two different files, otherwise you will upload the same file twice.
  4. NOTE: We did not use the taper calculator functionality in Foam Works when generating G-code. Regardless of the type of taper (leading edge taper, or trailing edge taper) we specified in foam works, the .tap file that we ran would ALWAYS cut a leading edge taper. This is NOT what we wanted, so we had to stagger the towers manually at the start of the cut to get the proper taper on the trailing edge (this will be discussed in more detail below).
  5. Finally, saving your G-code will save two files: a .dxf file and a .tap file. The .tap file is the one used while running the foam cutter.
  6. Practice Cuts (A Good Debugging Tool)
  7. Practice cuts expose unanticipated errors in your data points or dimensions. The following details specific adjustments we have had to make in our processes (see Cut Wings/Tail/Fuselage for specifics on how).
  8. If ever in doubt about the potential results of a cut setup and to ensure the airfoil profile is correctly scaled, run from zero and stop at leading edge (when y1 and y2 are equal to zero) with a cold wire and without any foam in place. Measure x-distance travelled by each tower from the straight line marked on the table. Using the front platform edge will yield inaccurate results as it does not align perpendicularly with the towers.
  9. Cutting the Wings
  10. The wing is broken into three sections. Root, Middle, and Tip.
  11. Root: The root has no taper and is3.5 inches in width. This part is made so that the glued plane (of the geometric and not the flying variety) isn’t also the shear plane at the edge of the fuselage structure. The root cord length is 10 inches. However, after making multiple practice cuts of various wing sections we noticed that the physical scaling of the airfoil is not a true reflection of the scaling applied in Foam Works.For example, a physical chord length of 9.5 inches was measured for a Foam Works airfoil scaling of 10 inches. In order to achieve a physical chord length of 10 inches, a scaling of 10.5 inches was applied in Foam Works. This same ½ inch increase in chord length was applied for the mid airfoil (8.5” in FW, and 8” physically) and the tip airfoil (6.5” in FW, and 6” physically). (IMAGE OF FOAM CUTTER SHOWING SCALING PROBLEMS)The amperage used to cut EPP is around 2.7 amps and the feed rate was 6.
  12. To begin the cut the wire is zeroed half an inch forward of (along the platform which is in the positive X direction) the reference wire mark.
  13. Note: for all purposes the reference origin for each cut is the right edge of the cutting platform and the front wire burn mark on the platform (need image).
  14. Make this point your X zero. Raise each wire mount to be 4.375 inches from the red base of the tower. This is the Y zero.
  15. Back the wire out horizontally to place your foam piece, heat the wire, and load your G-code.
  16. Once the wire is heated, click go-to-zero and the wire will cut into half an inch of the foam.
  17. Run the G-code. Note your airfoil will be cut upside down.
  18. Middle: The middle section of the wing is the first section from the root with a taper. The cutting process will be much like that of the root but with a tapered starting point, or zero point (this means that the towers will need to be staggered in the x direction prior to beginning the cut) (IMAGE OF TOWER STAGGER). This is due to the fact that the foam cutter starts at the trailing edge and our plane has a tapered trailing edge and a non-tapered leading edge. The width of this section is 12.25 inches.
  19. The new zero has the right tower only half an inch past the line drawn onto the platform (referred to as the burn mark) but the left tower (x2) must be 3.42 inches deep from the burn mark.
  20. Back out the wire once it has been re- zeroed and prep your station much like you did for the root cut.
  21. For this cut we used 2.7 amps and we increased the feed rate as the cut was finishing near the trailing edge to 8.5, this is to avoid burning through the very thin trailing edge of the wing.
  22. Tip: The tip of the plane concludes the taper and follows all the instructions that the Middle section does. For the tip section, the left tower (x2) needs to be 3.94 inches deep. The width of this section is also 12.25 inches.
  23. For the Right Wing, backwards airfoils need to be used, meaning an airfoil that has its trailing edge at the origin. Don’t worry so much about what this means (only that it was a bitch to work out), all of the .tap files required for both the Left and Right wings are generated and ready to use. During the cut, the wire will also run towards the user rather than away. Follow the previous steps but zero the wire at least 11 inches from the black line on the platform (this will ensures that the wing with a 10” chord is cut entirely within the foam block)
  24. Cutting the SparHole: Mark the center of thehole location on both ends of the wing with a sharpie. Cut slits in two 0.25” ID washers, just wide enough for a wire to fit through, with a Dremel tool. Secure the washers in place with pins around the outside of the washer, never passing over the center diameter (IMAGE HERE of manual hole cutting setup). Use the manual foam cutter in the aero club room, or another if one wide enough is available. With one person holding the wing in place and two othersguiding each end of the foam cutter, move the wire in unison through the slit in the washers. Hold at the center of the hole for between one and two seconds. Then move towards the leading edge until hitting the washer, and move down and around the washer in a three-quarter circle until reaching the slit in the washers. Move up together through the slit and out of the wing, retracing the path you entered by.

  1. Cutting the Horizontal Tail
  2. The horizontal tail cut is much simpler than the wing section because it is not tapered. However, since the tail is 26 inches long and the foam cutter cannot cut anything longer than 18”x18” the cut will be in two parts. Follow the initial zeroing process like the root cut of the wing. After the tail has been cut and glued together, cut a notch in the center for the boom to meet the tail spar.
  3. To cut the horizontal tail, load the horizontal_tail_with_hole.tap file from the Foam Cutter Files folder.

  1. Cutting the Vertical Tail
  2. To cut out the vertical tail, load the vertical_tail_with_center_cut.tapfile from the Foam Cutter Files folder.
  3. Cutting the Control Surfaces
  4. The control surfaces will be cut out of blue EPO foam. The reason for this is that the blue EPO foam maintained a thicker and more consistent trailing edge geometry during the practice cutting phase than we were able to achieve with EPP foam. So in order to cut the control surfaces out of EPO, all 4 tapered wing sections will need to cut out of EPO.
  5. Cut control surfaces with a Dremel. Trace the profile beforehand. Note, for our plane the control surfaces were cut perpendicular to the taper because the taper is on the trailing edge. Set the Dremel to the lowest possible speed setting (this gave the best result in terms of minimizing cut width and damage to the part being cut out).
  6. Secure trailing edge prior to cutting, as vibrations can create roughness in the cut. For best results, when cutting along the span hold the Dremel such that it is over the rest of the wing, not the control surface.
  7. Tail control surfaces can be cut with foam cutter, just leave them in their respective blocks of foam to ensure straight cuts.
  8. NOTE: Cardboard control surfaces have been used in place of fiberglassed EPO foam control surfaces
  9. The team was unsuccessful in fiberglassing our EPO control surfaces. This was due to the following reasons:
  10. We believe that the thinness of the parts contributed to difficulty in fiberglassing them.
  11. The ratio of hardener to resin was never properly understood
  12. Ultimately, this led to fiberglassed EPO control surfaces that were not rigid enough to meet our requirements
  13. In place of fiberglassed EPO, we chose to use corrugated cardboard as it is both lightweight and rigid, and is very easy to replace should one or more of the control surfaces be damaged.
  14. In the future, we’d recommend 3D printing the control surfaces.
  15. Cutting the Fuselage
  16. It was discovered that the foam cutting software cuts circles towards the user rather than away, like airfoils. As a result the zero point had to be much further into working plane. A similar half inch zero into the foam was used. The foam is provided in sheets of 2 inch thick foam. Since the fuselage is 4 inches in diameter the foam is made from gluing two sections together and letting it cure before the cut.
  17. Note: Because the zero point is in the foam, after the cut the user must manually back out the wire from the material.
  18. The rounded end caps were generated by cutting a semicircle and rotating the part every 45 degrees to make a total of four cuts. The material between the cuts is sanded down to make a flusher surface.
  19. The fuselage is cut into three sections, nose, mid, and tail which have the lengths 5 inches, 6 inches, and 5 inches respectively. The middle section will be hollowed out by cutting a smaller circle inside. This will be the housing for the electronics.
  20. Cut a section of foam out in the nose to house the battery, this is to add weight to the nose and keep the center of gravity near the aerodynamic center.
  21. Drill a hole in the rear segment for the tail boom.
  22. After all the fuselage cuts are made, glue the three sections of the fuselage back together.

  1. Cut Servo Slots
  2. Use a drill press with an end mill to cut slots for the servos to sit in. It is best to trace locations for the servos prior to ensure accuracy in size and shape. The end mill should be selected such that it is a small enough diameter to accurately trace the shape of your servo.
  3. After plunging the bit to proper depth, move the wing around accordingly until enough space has been hollowed out. If necessary, square off edges and corners using an exacto knife.
  1. Sewing Snuggie

Manufacture Electronic Chassis:

  1. Solder purple wire extension to motor. The stock wires off the motor are quite short. Ours were 18 awgwires and Dr. Gomes had stock wire to extend another foot.
  2. Solder male battery connection to the speed controller. Buying parts separately is cheaper however it makes the connections on the parts nonexistent to be more universal. We purchased the male version of the connector the battery required and soldered it in place. That being said the speed controller had female banana plugs for the motor mount.
  3. Solder male banana plugs to end of wire extensions of the motor. Be careful when sizing the banana plugs, a label on the speed controller led us to purchase the wrong sized motor, we suggest measuring the inner diameter of the female connector directly.
  4. Thread motor shaft for prop components. The gentlemen in the machine shop are more likely than not to be better skilled for this job. The trick is holding the motor in proper place to tap the shaft. Since we pulled the propeller from the bought plane we wanted the tread pitch and diameter to match that motor.
  5. Attach prop components. All the prop components were pulled from the purchased plane and so assembly was easy. However our motor was oriented differently than the old motor and as a result we had to use two nuts to pinch the prop in place (if left un-pinched the prop would be tightened against the fixed surface of the motor and would not rotate).
  6. The servos are shipped pre wired. See photo for proper wiring connections.
  7. Check to see all of your electronics communicate properly with the controller. Each time the controller is turned on and the battery is plugged in to the electronics the speed controller must be “armed”. This is done by adjusting the throttle in a specific order so that the throttle control has the same range and the speed controller. The speed controller should come with an instruction manual to guide the arming process. However, the purchased plane did not come with such instructions and only after we searched the internet forums for the part number were we able to properly arm the system.

Drill and Cut Frame:

  1. Cut carbon fiber tubes to model length using a Dremel tool
  2. Drill a hole through the rod near the tips for end clips.
  3. Fuse the wing spars by gluing a drill bit blank halfway into one of the wing spars. After cure, glue the surface of the exposed blank and place that into the other spar. This has effectively extended the length of the wing spar.

Make Control Surfaces and Push Rods:

  1. Cut piano wire into desired lengths.
  2. Straighten wire:
  3. Drill a hole slightly larger than the diameter of the piano wire into a wooden block that can be held in one hand.
  4. Put one end of the piano wire into a drill chuck. Stick the rest of the wire through the hole in the wooden block until the drill is touching the wood.
  5. Pull the trigger and as the wire spins draw the wire through the hole at an angle of about 30-45 degrees. Make the angle more exaggerated the father the drill is from the block of wood. Move quickly to get better results.
  6. Fix the push rods to the servo motors and control surface horns.