Rajan Wilcox
Kevlar fuel tanks are often used in aircraft models to prevent fuel leakage and potential fires in the event of a crash. The process of making a Kevlar fuel tank involves creating a foam mould, laying up the Kevlar, and then cutting the mould in half to clean out the foam. A well-sharpened pizza cutter or special scissors can be used to cut the Kevlar. After cleaning out the foam residue, the two halves of the tank are joined using a Kevlar strip or glass and epoxy. Some builders may also incorporate an inspection panel for future maintenance and repairs.
How to Make a Kevlar Fuel Tank
| Characteristics | Values |
|---|---|
| Mould | Foam or Plaster of Paris |
| Mould Liner | Saran Wrap |
| Cutting Kevlar | Special scissors or glass-cutting scissors sharpened close to a 90-degree cut |
| Cleaning the Mould | Acetone, screw driver, sandpaper, lacquer thinner, or pizza cutter |
| Joining Halves | Kevlar strip |
| Sealant | JB Weld |
| Alternative Materials | Glass and good-quality Epoxy, or carbon |
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What You'll Learn
Cutting Kevlar
Kevlar is a tough fabric that is widely used in the composite industry. It is known for its strength and ability to absorb energy, making it challenging to cut. However, with the right tools and techniques, it can be done effectively and safely. Here are some detailed instructions for cutting Kevlar:
Choosing the Right Tools:
- Scissors: When using scissors, opt for sharp scissors with serrated edges, such as ceramic scissors or Kevlar-specific cutting scissors. These scissors have small teeth that "bite" into the fibres, preventing slippage during cutting. Electric scissors with serrated edges are also an option.
- Knives: If using a knife, a razor knife is recommended. Choose one with a snap-off blade to provide a fresh cutting edge, as Kevlar can quickly dull blades. Always use a straight edge and apply hand pressure to keep the fibres down when making straight cuts.
- Other Tools: For thicker Kevlar, a pizza cutter or wire cutters can also be used. A waterjet machine can be effective, but it may not be readily available.
Safety Precautions:
- Personal Protective Equipment: When cutting Kevlar, always wear proper personal protective equipment (PPE). This includes cut-resistant gloves, safety glasses, earplugs, and a mask or respirator to prevent inhalation of composite dust.
- Work Surface: Use a hard, non-wood surface as your cutting board to provide a stable base and prevent damage to your tools.
- Dust Mitigation: Use a shop vac with a vacuum hose placed near or under the trimming area to minimise dust created during the cutting process.
Techniques for Cutting:
- Mitigating Fibre Movement: Kevlar fibres can be challenging to cut due to their individual movement. To mitigate this, use masking tape over the fibres to hold them in place during cutting.
- Multiple Passes: For thicker Kevlar fabrics, you may need to make multiple passes with your cutting tool to achieve a clean cut.
- Clean Straight Edges: If you desire clean straight edges, a razor knife is your best option.
Remember, cutting Kevlar can be a tricky process, and it may take some practice to master it. Always take your time, prioritise safety, and use the appropriate tools to achieve the best results.
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Cleaning the tank
Cleaning a Kevlar fuel tank thoroughly requires careful consideration during the build process. It is important to plan for future access to the tank's interior for cleaning and maintenance.
One method to achieve this is to create an inspection panel, similar to those found on full-size aircraft fuel bags. This access point will allow for the periodic inspection, cleaning, and repair of the tank. Alternatively, consider adding removable access points to the tank, such as under the wing, to facilitate future cleaning and maintenance.
If you choose to create a mould for your Kevlar fuel tank, you should consider the type of mould material and the process of removing it after the Kevlar has set. Foam is a commonly used material for creating moulds. However, removing the foam from the inside of the tank after curing the Kevlar can be challenging. Simply pouring in solvents or fuel will not effectively remove all the foam residue. A more effective approach is to cut the tank in half after the Kevlar has set, carefully dig out the majority of the foam, and then sand or scrape the remaining foam residue. You can use a screwdriver to dig out most of the foam, and then sandpaper or a similar abrasive to remove the remaining bits. Finally, flush the tank with a suitable solvent to dissolve any remaining foam molecules. Note that using acetone as a solvent will melt the foam but leave behind a difficult-to-remove blue goo. Therefore, it is recommended to use an alternative solvent, such as lacquer thinner, to fully clean the tank's interior.
Once the tank is clean and free of any mould residue, you can join the two halves back together using a Kevlar strip at the joint. Ensure that the tank is properly sealed to prevent leaks.
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Sealing the tank
First, it is important to create a mould that will form the shape of your fuel tank. This can be done by using a material like foam, which can be carved or shaped to your desired size and shape. Once you have your foam mould, you will need to lay up the Kevlar on top of it. Make sure you have the necessary tools to cut the Kevlar, as it requires special scissors or glass-cutting scissors sharpened to a 90-degree angle.
After laying the Kevlar over the mould, you will need to cut the tank structure in half. This step is important as it allows you to remove the moulding material, such as foam, from the inside of the tank. Use a sharp tool, like a screwdriver, to dig out as much of the foam as possible. You can also use a technique mentioned by a user, involving the use of acetone to melt the foam; however, this may leave behind a residue that can be difficult to remove. Therefore, it is generally recommended to physically separate the halves and clean out the foam.
Once the halves are cleaned out, you can seal the tank back together. Use a Kevlar strip at the joint to join the two halves. Ensure that the seal is perfect by using a suitable adhesive or epoxy. You can also consider adding brass tubing to the tank before sealing, which can be welded in place for added functionality. Finally, glass the two halves together, and your Kevlar fuel tank is now sealed and ready for use.
It is worth noting that some users suggest adding an inspection panel to the tank, similar to those found in full-size aircraft fuel bags. This allows for future inspections, repairs, and cleaning of the tank. Additionally, consider adding removable access points to check or change fuel plumbing or seals if needed. These access points can be strategically placed under the wing, for example, to provide easy access for maintenance.
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Using foam moulds
Making a Kevlar fuel tank using foam moulds can be done in several ways. One method, suggested by a hobbyist, involves using a 3D printer to make the moulds of the tank. The first step is to find drawings of the tank and convert them into a 3D format. Once you have your 3D model, you can print the moulds for the tank.
Another method, referred to as the "lost foam" method, involves creating a foam plug by carving it from blue, grey, or pink foam. This foam plug is then covered with a low-temperature covering, such as ultracote, and waxed several times before moulding. After the moulding process, a hole is cut for the stopper, and the foam is melted out with acetone. The ultracote can then be removed.
It is important to note that Kevlar is challenging to cut and trim, and using acetone to melt the foam will leave behind a blue goo that is difficult to clean. To address this, it is recommended to split or seam the tank or create an inspection panel for easier access to the interior of the tank for cleaning and maintenance.
When creating the mould, it is essential to ensure that all the fabric adheres well to the walls to avoid bubbles. Alternatively, you can use a vacuum device to press the fabric against the mould. After catalysing for 12 to 24 hours, depending on the ambient temperature, the pieces can be removed from the mould.
The final step is to trim and join the two shells of the tank with epoxy glue. For added safety, a small strip of Kevlar can be glued over the joint.
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Reattaching the tank halves
First, it is important to understand why the tank halves need to be separated in the first place. One of the key reasons is to allow for the removal of the foam used during the moulding process. While acetone can be used to melt the foam, it tends to leave behind a blue residue that is challenging to clean. Therefore, physical separation of the tank halves provides better access for thorough cleaning.
When it comes to reattaching the tank halves, there are a few methods that can be considered. One approach is to use a Kevlar strip at the joint, as suggested by a builder who shared their process online. This method involves cleaning out the inside of the tank halves and then securing them together with the Kevlar strip. This technique ensures a strong and durable joint between the halves.
Another method for reattaching the halves involves glassing them together. This process, as described by one builder, includes drilling holes for brass tubing, JB Welding the tubing in place to ensure a perfect seal, and then glassing the two halves back together. This approach provides a strong and secure bond between the tank halves, creating a reliable fuel tank.
Additionally, it is worth noting that some builders choose to incorporate removable access points or inspection panels in their designs. These access points can be located under the wing, for example, and serve multiple purposes. They provide the ability to inspect, clean, and repair the tank periodically, ensuring its long-term reliability. These access points also allow for adjustments to fuel plumbing or seals, making maintenance and potential upgrades more feasible.
In conclusion, reattaching the tank halves of a Kevlar fuel tank requires careful consideration and the selection of an appropriate method. Whether it involves using Kevlar strips, glassing, or incorporating removable access points, the goal is to achieve a secure joint that ensures the tank's functionality and safety.
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Frequently asked questions
Kevlar is a strong material that can help contain fuel and prevent fires in the event of a crash.
A sharpened pizza cutter or special scissors can cut through Kevlar.
After creating a foam mold and laying up the Kevlar, cut the tank in half to clean out the foam. You can use a screwdriver to dig out most of the foam, and then sand or use a solvent to remove the remaining residue.
Use a Kevlar strip at the joint to join the two halves of the tank, and glass the halves together.
