*Edits to make:
- Add vacuum bagging pics
- Update materials list and preface
- Add more detail to procedure
Purpose
The purpose of this procedure is to provide a step-by-step guide for members to construct a fin can, which consists of a phenolic tube with four fins attached, covered in either fiberglass (for a test fin can) or carbon fiber (for a flight fin can). Below is a list of risks, required materials, and a step-by-step procedure including the expected length of time that each step should take.
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- Gloves
- Dust masks
- Safety glasses
- Respirators
TEST FIN CAN PROCEDURE
Cut and Sand Fins (2 hours)
1) Cut plywood fins to shape on the laser cutter
2) Put on safety glasses and a dust mask
3) Sand the face of each fin using 120 grit sandpaper
4) Bevel edges of fins using a Dremel and sanding bit
Cut and Sand Tube (1 hour)
5) Wearing safety glasses, cut phenolic tube to size on a bandsaw
6) Put on safety glasses and a dust mask
7) Sand tube until it fits over the motor case (start with 60 grit, work up to 220)
8) Score the tube (using 60-180 grit sandpaper)
Prepare Tip-to-Tip Cutouts (4 hours)
9) Prepare paper cutouts for tip-to-tip layup
10) Stick wax to fiberglass using spray glue
11) Cut fiberglass shapes with scissors
12) Record mass of fiberglass (will use later to calculate wetness ratio)
13) Mark centerline of each piece with sharpie
Attach Fins to Tube (Root Bond) (1 day)
14) Score fins
15) Put tube in fin can jig
16) Put on gloves
17) Mix epoxy
18) Put 5-minute on root chord of each fin
19) Slide fins into slots in the jig
20) Finish assembling jig by putting the top layer of the jig on and securing the nuts
21) Attach stabilizing feature
22) Let cure
Root Fillet (1 day)
23) Remove the fin can from the jig
24) Put on gloves and respirator, ensuring the respirator fits well with a positive/negative pressure test
25) Mix laminating epoxy with colloidal silica
26) Use fillet tool to add fillets
27) Let cure (24 hours)
28) Sand the root fillets
29) Mark centerlines on the tube
Tip-to-tip Layup (1 day)
30) Put on your respirator and gloves
31) Mix epoxy
32) Record mass of epoxy used
33) Wet the glass sheets with laminating epoxy using squeegees
34) Remove the sheets from the wax paper and apply to the tube (layup)
35) Implement "Vacuum Procedure"
Post-processing (3 hours)
36) Sand fin can
FLIGHT FIN CAN PROCEDURE
Cut and Sand Fins (1 day)
1) Cut fins out of 1/8” G10 sheet on the waterjet
2) Cut phenolic leading edge on waterjet
3) Use a mill to cut slot into the phenolic
4) Use a mill to cut tabs in the G10
5) Attach the phenolic leading edge to the G10 fin core with epoxy and let cure
6) Score the fins
Cut and Sand Tube (3 hours)
7) Cut phenolic tube to length
8) Make sure it fits over motor case
9) If not, sand using 60 grit sandpaper, working up to 220 grit
10) Score the tube
11) Check to see that the tube fits in the fin can jig
Tube Layup Preparation (2 hours)
12) Prepare paper cutouts for carbon fiber tube layup
13) Spray the wax paper with spray glue
14) Apply the carbon fiber
15) Cut the carbon fiber/wax paper on the laser cutter (this is safe because the carbon fiber has not been wetted yet)
16) Record mass of each piece (to calculate wetness ratio later)
Tube Layup (1 day)
17) Put on respirator and gloves
18) Wet the carbon fiber pieces with epoxy
19) Record mass to use for wetness ratio calculation
20) Carefully separate the carbon fiber from the wax paper and apply it to the tube (layup), using more epoxy when necessary
21) Let cure for 24 hours
Root Bond (1 day)
22) Put tube in fin can jig
23) Put on gloves
24) Mix epoxy
25) Put 5-minute on root chord of each fin
26) Slide fins into slots in the jig
27) Finish assembling jig (put top layer on, push gently until the slots contact the leading edge, tighten the nuts)
28) Attach stabilizing feature
29) Let cure
Tip-to-Tip Preparation (4 hours)
30) Make paper cutouts for tip-to-tip layup
31) Spray wax paper with spray glue
32) Stick CF to wax paper
33) Use paper cutout to cut shapes
34) Record mass of shapes (for wetness ratio)
Root Fillet (2 days)
35) Put on respirator and gloves
36) Mix colloidal silica and epoxy
37) Apply inner fillets
38) Let cure for 24 hours
39) Sand inner fillets
40) Wearing gloves, apply outer fillets (Proline)
41) Let cure for 24 hours
42) Sand outer fillets
43) Mark centerlines
Tip-to-Tip Layup (1 day)
44) Mix epoxy
45) Wet the carbon fiber pieces
46) Record mass (for wetness ratio)
47) Separate the carbon fiber from the wax paper and apply to tube (layup)
48) Follow “Vacuum Bagging” procedure
Post-Processing
49) Follow “Oven Cure” procedure to cure fin can in Autoclave
Preparation (Tube)
Sanded inside of PML phenolic fiberglass-overwrapped tube (FGPT-6.0, 6.007” ID) on one end with 60-grit sandpaper, periodically testing to see if it fit over our motor case (don’t push too hard or it’ll get stuck)
Marked 22” length and cut tube on horizontal bandsaw (Gelb)
Sanded inside of tube with 60-grit sandpaper from other end
Sanded the outside of the tube with 60-grit (this is to increase surface area so that the fins and the fiber will bond better)
Preparation (Fins)
Laser-cut plywood fins
Sanded either face with 60-grit, and edges with Dremel sanding bit
Scored fins (on either face and on root) with scalpel
We later did not use the plywood fins because they did not fit into the fin can jig.
Waterjet G10 fins
Epoxied leading edge using superglue, paper and clamp (paper so that the clamp didn’t get stuck to the glue) because the G10 delaminated on the waterjet (in the future, use “Brittle Material”, “Low Pressure” to avoid delam
Sanded either face and the root with 60-grit sandpaper
Root Bond/Fillets
Set up layup jig
Use a level to ensure that each layer of the jig is level
Remove top layer
Check that tube fits snugly by sliding it into the jig
Check that the fins fit snugly into the slots
Tighten the nuts
Slide the tube in
Root Bond
Wearing gloves, mix 5-minute epoxy thoroughly
Apply using small popsicle stick along root of fin
Carefully slide fin into slot in jig, press against the tube
Repeat for other 3 fins
Put top layer on and push gently against leading edge of fins to ensure a snug fit
Let cure for 15-20 minutes
Root Fillets (1 day per set of fillets using slow hardener, 2 fillets - 1 in the morning, 1 in the evening, using fast hardener)
Carefully remove the fin can from the jig (the fins are NOT bonded very securely because we used 5-minute, so handle with care!!)
Support tube horizontally on either end (make sure fins aren’t touching anything
Turn tube such that the area between two fins is level with the ground (the fillets will be applied to the inside of each fin so we want them to be horizontal)
Mark desired radius on either end of each fin (both on the fin and on the tube) using Sharpie
Tape along the fin and the tube, leaving an exposed area where the fillet will go. Tape also around the tube (where the epoxy would go if it dripped past the leading edges)
Put on respirator and, using a large paper cup (not the shallow blue epoxy boats or the silica will get everywhere), mix three pumps resin + 3 pumps slow hardener.
Stir well with popsicle stick, then mix in colloidal silica until consistency is in between ketchup and mayonnaise (should drip slowly but evenly off popsicle stick)
Apply mixture to exposed area, leaving ~0.5 inch on either side so that epoxy doesn’t drip. Use fillet tool to smooth out/remove excess epoxy
Remove the painter’s tape (do it before the epoxy cures so it doesn’t get stuck)
Let cure (24-36 hours for slow hardener, ~6 hours for fast hardener)
Repeat for remaining 3 sets of fillets
Wearing a dust mask, sand the fillets, wipe with wet shop towel to remove debris
Rotate the tube such that one fin is vertical
Repeat steps 5-7, and apply epoxy to the remaining exposed ~0.5 inches
Let cure, and rotate tube to do next fillet ends
Repeat step 15 until all fillet ends completed, and, wearing a dust mask, sand the fillets
Layup Preparation (Cut-outs)
Because we used fiberglass for the test fin can, we made a cut-out template on cardboard instead of using the laser-cutter.
On a large piece of cardboard, make a cutout template by measuring the distance between the fins and the height of the fin collar (tube), and tracing the outline of a fin on either side. Add a tab on one side
We need to make 3 different cutout sizes so that when the plies are added (small → large), there is a slight slope/transition. Trace another outline on the same template with a 1.5” offset. Repeat again for a 3” offset.
Using large sheets of parchment paper (wax paper works as well), place over the template and trace the large outline in Sharpie
Cut along the mark, making a parchment paper cutout.
Using spray glue, lightly spray the cutout. If you use too much glue (by spraying too closely), the fiberglass will be more difficult to remove from the cutout, and the fibers will deform/edges will fray.
Placed cut-out face-down on fiberglass and cut it out carefully. Made 4 cut-outs per size (one for each tip-to-tip, so 4 cut-outs x 3 sizes x 2 sides of the fin = 24, divided by 4 fins = 6 plies per fin) but in the future we want 12 plies per fin
Removed the fiberglass from the cutout then marked the centerline
Repeat for the other two sizes (medium and small)
Mark centerline on tube
Record the mass of one of each size
Layup
Talk about starting with small cutouts and go to big
Lay Mylar over the table
Record the mass of an empty mixing boat and tare the scale
Wearing gloves, mix 1 pump slow hardener + 1 pump resin in a mixing boat. Record the mass of the epoxy (scale should be tared, so boat mass neglected)
Pour epoxy along the small cut-out and smooth using a Squeegee until the fiberglass is just permeated. Don’t add too much! Note the size of the cut-out (small) and how many boats of epoxy were required, and record for later calculating of wetness ratio
Use a paint roller to remove excess epoxy
Position the fin can horizontally
Gently remove the fiberglass from the parchment/wax paper, and apply to the fin can, starting by aligning the centerlines and smoothing out toward the tip on either side. Make sure there are no bubbles, or that the fiberglass isn’t pulled away from the fillet
Rotate the fin can carefully and add the next ply
Once all the small plies are added, repeat steps 4-8 (except for the measurement step, which only needs to be done once for the first small ply)
Vacuum Bagging Preparation
Set up layup jig
Cut out peel ply, bleeder fabric, release film, and vacuum bagging
Make inner cylinder out of vacuum bagging
Slide cylinder on jig, slide fin can over
Add peel ply
Add release film
Add bleeder fabric
Attach vacuum bagging to vacuum tape (4 pieces)
Add vacuum bag
Vacuum
Insert tube
Turn on vacuum, monitor
Leave overnight
50) Wearing a dust mask and respirator, sand the fin can