Overview
The
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objective of this fin can is to introduce the new members to the layup process, refresh old members to the layup process, and ensure that we acquire all the necessary materials to be efficient in future layups. This fin can is mostly a replica of Hermes II. It lacks leading edges, and the fins used were the wrong size.
This fin can is the first in the series of 3 fin cans for Hermes III (Rusty, Dusty, and Crusty.) This is the story of Rusty.
The format for this page is based on Hermes II Flight Candidate Fin Can #2
CHANGES FOR CHANGES FOR NEXT TIME:
- Do plies by 1, 1, 1, 1, 2, 2, 2, 2,.... instead of 1A,2A,3A...1B,...
- Log how much epoxy per side of the fin can
- Update sizes of vacuum bag, bleeder, peel ply, etc.
- "A pain to get in the bag and I don't think it will distribute the pressure from vacuum evenly"
- Correct shape and size
Summary of changes from Hermes II Fin Can:
- Weigh the tube, then weigh the fin can after cured with bag removed
- Calculate the volumes of materials
- Sand the area of the fin can where the fin will attach to ensure proper contact during root bond
- Root bond with Systems 3000, not 5 minute
Summary of changes from Hermes II Fin Can:
- No leading edges (intentional)
- Incorrect fin size (unintentional)
- Mix up of one of the "6" plies (unintentional)
- Lack of surface prep (intentional)
Ply Mass Log: (includes wax paper & some painters tape!!!)
| Index | Meas. 1 | Meas. 2 | Meas. 3 | Mass (g) | Index | Meas. 1 | Meas. 2 | Meas. 3 | Mass (g) |
|---|---|---|---|---|---|---|---|---|---|
| 1A | 33.5 | 33.2 | 33.4 | 33.37 | 1C | 33.1 | 33.2 | 32.8 | 33.07 |
| 2A | 33.4 | 33.8 | 33.7 | 33.63 | 2C | 33.6 | 34.0 | 33.7 | 33.77 |
| 3A | 31.9 | 32.3 | 32.2 | 32.13 | 3C | 33.7 | 33.9 | 33.4 | 33.66 |
4A | 34.2 | 34.3 | 34.6 | 34.37 | 4C | 33.3 | 33.6 | 33.8 | 33.57 |
| 5A | 39.0 | 38.9 | 39.1 | 39.00 | 5C | 39.9 | 39.9 | 40.2 | 40.00 |
| 6A | 42.0 | 41.9 | 41.8 | 41.90 | 6C | 42.1 | 42.0 | 42.6 | 41.23 |
| 1B | 33.4 | 33.1 | 33.2 | 33.23 | 1D | 33.2 | 33.5 | 33.3 | 33.36 |
| 2B | 33.5 | 33.4 | 33.6 | 33.50 | 2D | 34.2 | 34.6 | 34.4 | 34.40 |
| 3B | 31.9 | 31.6 | 32.3 | 31.93 | 3D | 34.0 | 33.9 | 33.9 | 33.97 |
| 4B | 33.9 | 34.1 | 34.1 | 34.03 | 4D | 34.2 | 34.5 | 34.3 | 34.33 |
| 5B | 41.2 | 40.7 | 40.9 | 40.97 | 5D | 32.2 | 32.0 | 31.9 | 32.03 |
| 6B | 41.7 | 41.8 | 42.0 | 41.83 | 6D | N/A | N/A | N/A | N/A |
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Hermes III Test Fin Can CF-Epoxy Ratio Estimates.xlsxProcedure Overview (copied from ref. page)
Carbon fiber mass fraction: 0.408
Epoxy mass fraction: 0.592
This information is so close to being useful but isn't quite there because we can't use rule of mixtures to actually calculate what our elastic modulus.
Procedure Overview
Below is the detailed procedure for how the second flight candidate fin can Rusty was manufactured. insert more detail
For each step, there is an overview of the process, followed by required materials for this step and then numbered substeps. Some safety notes:
- A respirator is required for all steps involving sanding fine particles like carbon fiber and phenolic.
- A respirator is required when using colloidal silica carbosil before it is completely mixed into the epoxy. The respirator can be taken off once the silica carbosil is completely mixed UNLESS the epoxy you are mixing it into also requires a respirator.
- A respirator is not required when only using West Systems 3000 epoxy.
- Gloves are required when sanding carbon fiber to prevent small splintersWhen using the Dremel, use safety goggles that completely cover your eyes to protect from stray projectiles
- Use safety goggles that completely cover your eyes when sanding so that fine particles do not irritate them
SUMMARY OF FIN CAN MANUFACTURING
| Design fin can | Approx. Time Required | # People Required | Notes | |||
|---|---|---|---|---|---|---|
| Fin Design & Manufacturing | 36 hours | The more the merrier. | Manufacturing procedure and detailed breakdown described in "Hermes 2 Fin Design & Manufacturing" | |||
| Design/make jigs | ||||||
| Root bond jig | 3 | 2 | Allow for tolerance so fins fit, but don't make slots too loose. Make sure you have a top plate. Too small:
| |||
| Fillet jig | used H2's | N/A | Fillet jig | 3 | Two wooden pieces with a U-shaped slot on which the fin can rests horizontally. Need a larger fillet tool so that the fillets for Hermes 3 are larger | |
| Fillet tools | 2 | 1 | ||||
| Tube preparation | ||||||
| Sand tube | 2 | Sand inside with flapper wheel so that it fits over the motor case. This is WAY faster than doing it by hand. Make sure to wear a dust mask or, even better, a respirator | ||||
| Tube layup | 6 | 2-4 | Rough up the outside of the tube before layup. You should have at least 3 layers of carbon fiber. Talk to Drela about tube layup techniques (make sure there aren't any bubbles!) | |||
| Root bond | 1 | 5-minute is ok, but if you have time, use a stronger epoxy. Do not use 5-minute, it's not strong enough!! Make sure the root of the fin is roughed up to improve the bond. | ||||
| Root fillets | Need 4 sets of fillets but it takes 8 rounds cause you gotta do the ends of each side separately (read below for more detail). You'll have to backtrack from when you want to do the layup to when each fillet has to be done by (can speed up using heat gun) Use System 3000 epoxy and make sure there are NO bubbles (degas the epoxy)! Also consider proline fillet + epoxy fillet to add strength. Make sure the area of the fins where the root fillet is applied is roughed up with sandpaper so the bond with epoxy is stronger! | |||||
| Layup preparation | ||||||
| Laser-cut CF cutouts | Be careful not to laser-cut over the taped edges of the carbon fiber squares that you use for the cutouts (the tape will be difficult to remove and fray the fibers). Also, don't spray glue wax paper until after laser cutting because the wax paper might catch fire or start smoldering in the laser cutter. | |||||
| Spray-glue to wax paper | ||||||
| Sand fillets | If you do the fillets right, you should barely have to sand them. Make sure to wear a respirator whenever sanding fiberglass. | |||||
| Prep vacuum materials | The shape of each vacuum bagging material (peel ply, breather, bleeder, vacuum bag) should be a square, and you need four squares of each material since there are four fins. The width of the cutouts should be around 4 inches longer than the tip-to-tip distance (not too long or too short). The length of the cutouts should be around 4 inches longer than the fin collar (see images to get an idea of the size). | |||||
| Layup | ||||||
| Wet plies/weight | ||||||
| Layup | ||||||
| Put on vacuum bagging | ||||||
| Vacuuming | Watch the gauge on the vacuum pump to make sure it drops to at least ________ Did this overnight | |||||
| Oven Cure | ||||||
| Set up oven/vacuum materials | ||||||
| Follow epoxy cure cycle | 12 hours | Make your life a lot easier by assigning shifts (i.e. have 3-4 people helping so you don't have to sit in front of the oven the whole time). Even better, find access to an Autoclave so you don't have to adjust the temperature manually. | ||||
| Remove vacuum materials | This takes a while, but it can be done with patience. Make sure you don't lose track of any of the vacuuming supplies (like the vacuum pump attachment) when you throw out the bagging materials. | |||||
| Clean up edges | Did this using a Dremel right after the fin can was taken out of the vacuuming materials so that people don't get hurt on the sharp edges. | |||||
| Static load test | ||||||
| Design/build jig | Make sure jig is rigid enough (we used 80/20, which bent when the fin can was tested in the Instron) | |||||
| Determine testing loads | ||||||
| Static load test | ||||||
| Analyze data | ||||||
| Post-processing | ||||||
| Sand fillets/outside | Don't sand the fillets too much! Instead, smooth by adding Bondo or epoxy to add material instead of taking it away. (see row directly below for more details) | |||||
| Outer fillets on low spots | ||||||
| Paint | ||||||
| Total manufacturing time |
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| Tube layup | 6 | 2-4 | Rough up the outside of the tube before layup. |
| Root bond | 2 | Used 5 minute epoxy because this is a practice fin can. Noticed gaps between the fins and the collar. | |
| Root fillets | 6 | Did two fillets a day for a total of 8 fillets over 4 days. Degassed Systems 3000 epoxy in the vacuum chamber before applying epoxy to fin. Need to sand the fin better. | |
| Layup preparation | |||
| Laser-cut CF cutouts | 4 | 2 | Be careful not to laser-cut over the taped edges of the carbon fiber squares that you use for the cutouts (the tape will be difficult to remove and fray the fibers). Also, don't spray glue wax paper until after laser cutting because the wax paper might catch fire or start smoldering in the laser cutter. |
| Spray-glue to wax paper | 1 | 2 | |
| Sand fillets | 0 | If you do the fillets right, you should barely have to sand them. Make sure to wear a respirator whenever sanding fiberglass. | |
| Prep vacuum materials | 3 | 4 | The shape of each vacuum bagging material (peel ply, breather, bleeder, vacuum bag) should be a square, and you need four squares of each material since there are four fins. The width of the cutouts should be around 4 inches longer than the tip-to-tip distance (not too long or too short). The length of the cutouts should be around 4 inches longer than the fin collar (see images to get an idea of the size). The sizes for Rusty were not correct. Dusty will have the correct sizes listed. |
| Layup | |||
| Wet plies/weight | |||
| Layup | 8 | ||
| Put on vacuum bagging | 2 | ||
| Vacuuming | 24 | Watch the gauge on the vacuum pump to make sure it drops to at least -26 mm Hg | |
| Oven Cure | |||
| Set up oven/vacuum materials | |||
| Follow epoxy cure cycle | 12 hours | See oven shift google doc. | |
| Remove vacuum materials | This takes a while, but it can be done with patience. Make sure you don't lose track of any of the vacuuming supplies (like the vacuum pump attachment) when you throw out the bagging materials. | ||
| Clean up edges | We didn't clean up any edges because this was a practice fin can. | ||
| Static load test | This section has yet to happen because Shannon and Charlie are working on a fin can test jig. Will update later. | ||
| Design/build jig | |||
| Determine testing loads | |||
| Static load test | |||
| Analyze data | |||
| Post-processing | |||
| Sand fillets/outside | |||
| Outer fillets on low spots | |||
| Paint | |||
| Total manufacturing time |
1. Tube Preparation
The fin can is supposed to fit over the motor case. It never does. If this were a flight fin can, we would sand the inside of it with a flapper wheel until it did, but Rusty is simply Rusty, not Dusty nor Crusty.
Rusty starts at a phenolic tube which is overwrapped with 3 plies of carbon fiber. The phenolic tube acts as insulation from the motor case because we do not know the temperature on the outside of the motor case. The carbon fiber overwrap bears the structural loads. During the overwrap layup, the phenolic tube was placed on
The fin can fits over the motor case (at least, it's supposed to...). Since it didn't quite fit, we sanded the phenolic tube using a flapper wheel, and then overwrapped it with 3 plies of carbon fiber. The phenolic tube acts as insulation from the heat of the motor case and is not structural, so carbon fiber needed to be added to bear the structural loads. During the tube layup, the phenolic tube was held by a pole over the layup jig (much like a pig on a spit). Have at least three people helping with the tube layup.
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