Rajan Wilcox
The Sling 4 is a light aircraft with impressive fuel capacity and endurance. The fuel tanks are located in the wings of the plane, and the process of installing and testing them is complex and time-consuming. Builders of the Sling 4 aircraft pay close attention to the fuel tank installation process, which includes tasks such as leak testing, mounting, and sealing the tanks. The standard 52-gallon tanks offer 5.5 hours of endurance, with the option of adding 12 gallons to extend endurance to 7 hours. The fuel lines are another important aspect, with builders sharing experiences and tips on using materials like aluminum tubing and firesleeves to ensure safe and efficient fuel delivery.
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What You'll Learn
Fuel tank leak testing
Preparation:
Before beginning the leak testing, it is essential to prepare the fuel tanks and necessary equipment. Allow the fuel tanks to dry completely, following the manufacturer's recommendations. In the case of the Sling 4, the manual suggests a drying time of 3 days, but using a Class B-4 sealant may require a longer drying time, as mentioned in a builder's log. Ensure you have the appropriate tools for the testing procedure, such as hoses, fittings, and a pressure gauge or tester.
Testing Procedure:
The soapy water test is a widely recognised method for its simplicity, low cost, and effectiveness. Here are the steps to perform this test:
- Place the fuel tank on a flat surface, ensuring easy access for viewing and testing.
- Seal all openings around the tank, except for the inlet.
- Pump compressed air into the tank through the inlet, maintaining a recommended pressure of no more than 5 PSI.
- Use a sponge or sprayer to cover the tank with a solution of one part standard detergent or soap and three parts water.
- Observe the tank for any signs of leaks, such as bubbles forming on the surface.
- If leaks are detected, document them properly and proceed with repairs before shipping or installing the tank.
Alternative Methods:
While the soapy water test is widely used, there are alternative methods available, such as the manometer test, as mentioned in a Sling 4 builder's log. This test involves measuring pressure changes over time to detect leaks. Additionally, there are custom leak testing devices, such as the Proportion-Air leak test device, which can fill and maintain pressure in the fuel tank while measuring flow to detect leaks.
Safety and Maintenance:
In summary, fuel tank leak testing for the Sling 4 involves a combination of preparation, testing procedures, and safety considerations. By following the steps outlined above, you can effectively detect and address any leaks in the fuel tanks, ensuring the safety and optimal performance of your aircraft.
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Fuel tank sealant
The Sling 4 is a light aircraft that can be built at home. Builders have to ensure that the fuel tanks are properly sealed to prevent leaks. One builder has noted that they used Class B-4 sealant on their left fuel tank, which took a week to dry. They also used sealant on the rivets of the fuel tank and used soapy water to check for leaks.
Another builder has opted for CS3204 sealant for their standard-sized fuel tanks. They ordered 4 x Kit 2: 6 oz cartridge (Fill: 3.5 oz. sealant) and 1 x Kit 3: 6 oz can (Fill: 16 oz. sealant). The cartridges are for the inside seams of the fuel tanks, while the can is for the outside ribs and other bits that are hard to access.
A third builder has shared their experience with sealant on their fuel tank, noting that they were afraid to work with the sealant, which slowed their progress. They also used sealant on the rivets of the fuel tank and used a syringe to apply it neatly and evenly.
It is important to note that the fuel tanks in the Sling 4 are located on the wings of the aircraft. The standard 52-gallon tanks give 5.5 hours of endurance before dipping into reserves.
Some builders have also shared their experiences with the fuel lines, which connect to the fuel tanks. One builder used a high-temperature RTV epoxy to seal the joints of the firesleeves, which protect the fiberglass strands from becoming soaked with oil or debris. Another builder shared that they initially planned to use aluminum tubing for the fuel lines but learned that it is not typically used forward of the firewall due to heat exposure.
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Fuel tank installation
The fuel tank installation process for a Sling 4 involves several steps and considerations. Firstly, it is important to determine the location of the fuel tanks and plan the routing of the fuel lines. In the case of the Sling 4, the fuel tanks are typically mounted on the wings. This requires careful measurement and alignment to ensure the tanks are securely attached to the wings.
The installation process begins with preparing the fuel tanks and ensuring they are sealed properly. This includes using appropriate sealants, such as Class B-4 sealant, and allowing adequate time for the sealant to dry, which may take longer than the recommended time in the manual. It is crucial to follow the manufacturer's instructions and industry standards for safety.
The next step involves leak testing the fuel tanks to identify any potential issues. This can be done using a manometer or by following the methods described in the Sling 4 manual. It is important to let the tanks dry on the wing for an extended period before performing the leak test. During the testing process, connections are made using hoses and fittings, such as the -4AN hose tester kit.
Once the fuel tanks have passed the leak test, the fuel lines can be installed. This process can be challenging, as it involves making precise bends in the tubing to connect various components, such as the bulkhead connectors, gascolator, and fuel pump. It is important to use the correct type of tubing, as materials like aluminum tubing may not be suitable for prolonged heat exposure in certain areas.
To secure the fuel lines in place, brackets and clamps can be used, especially when navigating around sharp corners or tight spaces. It is important to consider the accessibility and potential for leaks when installing fuel filters. The cabin, for example, may not be the ideal location for fuel filters due to these concerns.
Finally, additional considerations should be made to protect the fuel lines from potential damage or flammability. For example, applying a high-temperature RTV epoxy to seal joints and prevent fiberglass strands from becoming soaked with oil or debris. This ensures the safety and integrity of the fuel system.
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Fuel tank capacity
The fuel tanks in a Sling 4 are located on the wings of the plane. A user on the Sling Pilots forum has documented the process of building their Sling 4, including the installation of the fuel tanks. They mention bending the fuel vent tubes and performing a leak test on the left fuel tank.
The fuel tank capacity of the Sling 4 appears to vary depending on the model and configuration. Some users mention having a 46-gallon main tank capacity, while others mention different figures.
One user mentions that the standard tank capacity for the Sling TSi low-wing model is 53.2 gallons, with the option to add long-range tanks that increase the total capacity to 65.4 gallons. Another user mentions that the standard tank capacity for the Sling TSi is 52 gallons, with the option to add 12 gallons for a total of 64 gallons.
A third user mentions that the old main tanks have a capacity of 88L / 23.2 GAL for the main tank and 40L / 10.6 GAL for the long-range tank, while the new main tanks have a capacity of 99L / 26.2 GAL for the main tank and 26L / 6.9 GAL for the long-range tank.
It's important to note that the fuel tank capacity may vary depending on the specific configuration and options chosen for the Sling 4. The figures mentioned above may not be applicable to all models and configurations of the Sling 4.
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Fuel lines
One builder shared their experience with installing fuel lines in their Sling 4, noting that it took longer than expected. They initially planned to use aluminum tubing, similar to what they had used in the fuselage. However, they encountered challenges in making the necessary bends in the tubing to connect the bulkhead connectors, gascolator, and fuel pump. Some of these bends were compound and beyond the capability of their bending tool, requiring manual adjustments. Additionally, they found it difficult to install the firesleeve over the aluminum fittings, especially the elbows. After consulting with other builders, they learned that aluminum tubing is not typically used forward of the firewall due to its inability to withstand prolonged heat exposure. As a result, they had to improvise and make adjustments to their initial plan.
Another builder opted for hard lines for both fuel and brake lines, deviating from the kit's design of using rubber tubing. They chose to use 3003 Aluminum Versa-tube in 3/8" OD size for the supply and return fuel lines, which can be bent by hand or with a tube bending tool for 90-degree bends. They shared photos illustrating how they shaped the fuel lines to fit behind the closeout panel and secured them with custom brackets and cushion clamps to keep the tubes in place. They also decided to place the fuel filters in a rubber hose segment between the fuselage and wing, rather than inside the cabin as per the kit manual, to avoid potential fuel leaks in the cockpit.
To prevent leaks, one builder shared their experience with sealing the firesleeve ends using Permatex epoxy, a method also employed by the Sling Build Assist Center. They also wrapped the ends of the firesleeve with safety wire, confident that their hose connections were secure and leak-proof.
Additionally, builders have weighed the options of using aluminum or Teflon fuel lines, with some opting for aluminum due to its longevity and standard use in RV aircraft. However, concerns about fuel spilling during filter replacements in the wing root have been raised, prompting reconsideration of filter placement.
Overall, the installation of fuel lines in the Sling 4 can be a complex process, involving careful planning, bending of tubing, securing connections, and leak prevention measures. Builders have shared their experiences and learnings to provide insights and guidance for others undertaking similar projects.
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Frequently asked questions
The fuel tanks are located in the wings.
The standard tank capacity is 52 gallons, which gives 5.5 hours of endurance. The new main tank capacity is 99L / 26.2 GAL.
The installation process involves leak testing, sealing, and riveting the fuel tanks to the wings.
