Katerina Swanson
Radio-controlled (RC) vehicles, airplanes, and accessories are popular among hobbyists and enthusiasts. RC fuel tanks are an essential component of these models, and understanding how they work is crucial for optimal performance and safety. The setup and installation of an RC fuel tank involve several key considerations, such as tank positioning, pressure management, and the use of appropriate materials to ensure a secure and functional fuel system. In this discussion, we will delve into the intricacies of RC fuel tanks, exploring their design, assembly, and maintenance to provide a comprehensive guide for enthusiasts seeking to enhance their RC endeavours.
| Characteristics | Values |
|---|---|
| Installation | Relatively simple, but requires basic plumbing skills |
| Location | Instructions for the plane indicate the best position; usually, the centreline is aligned with the engine's centreline |
| Considerations | Effect on CG (centre of gravity); tank location should not alter the handling of the plane |
| Tank Material | Polyethylene plastic; impervious to RC fuels and tougher than the plane |
| Tank Design | Octagonal shape for easy installation; no internal fuel tubing to harden and leak air |
| Assembly | Requires a careful and thorough procedure to ensure a leak-free tank |
| Connections | Flexible fuel tubing connects the clunk to the brass tube of the feed line |
| Clunk | Weighted end on the pickup line to keep it in fuel during rolls and flying inverted |
| Fuel Flow | Fuel is drawn through the pickup and holes in the main shaft; vent line prevents a vacuum state that shuts off fuel flow |
| Maintenance | RotoFlow Fuel Systems require no internal maintenance |
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What You'll Learn
Installation
Installing an RC fuel tank is a relatively simple process, but it is important to be careful and methodical to ensure engine safety. The first step is to locate the fuel tank in the plane. The instructions for the plane will usually indicate the best position, with the aim being to prevent having to suck the fuel uphill and to minimise the impact on the centre of gravity. The tank should be mounted on a layer of foam rubber to prevent it from rubbing against the airframe and developing a hole. Double-sided tape can be used to secure the foam to the airframe and the tank to the foam. Straps made from hook and loop material can also be used to hold the tank firmly in place while allowing for removal.
The next step is to connect the fuel system. All fuel systems must have a line to the carburetor and a vent line. The vent line is usually connected to a fitting on the engine's muffler, while the feed line is connected to the engine's carburetor. The RotoFlow Fuel System is a popular option for RC fuel tanks and is known for its reliability and ease of installation. The system features a rotating pickup assembly that draws fuel through several holes in the main shaft under the swinging pickup assembly. The RotoFlow tanks are octagon-shaped, which can make them easier to install in certain planes.
When assembling the fuel system, it is important to ensure that the weighted pickup line is not too long, so that the weighted end does not rub against the opposite end of the tank. The fuel line should be sized so that the clunk is near the back of the tank but does not get stuck in any position. Flexible fuel tubing can be used to connect the clunk to the brass tube of the feed line. It is also important to note that some fuel lines expand when initially exposed to fuel, so it may be necessary to make the pickup line slightly shorter than the length of the tank.
To assemble a leak-free tank, the following steps can be taken:
- Remove the center screw and disassemble the stopper assembly.
- Input a 30-degree bend in the last 3/8" of the brass tube for the vent line using a tubing bender.
- Cut a notch in the end of a short piece of flexible fuel tubing (1/2"-3/4" long).
- Slide the rear plastic segment of the stopper assembly over the brass tubing on the vent and feed lines, followed by the front plastic segment.
- Insert the screw into the stopper assembly and turn it just enough to engage the rear plastic piece.
- Reconnect the flexible fuel tubing to the brass tubing of the vent and feed lines.
- Push the stopper assembly onto the neck of the fuel tank and tighten the screw carefully, being sure not to over-tighten.
- Perform a pull test on the stopper assembly to ensure that it is securely attached to the tank.
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Location
Locating the fuel tank in an RC plane is simple. Usually, the instructions for the plane indicate the best position for the tank in that airframe. The centreline of the tank should be on the same level as the centreline of the engine. This alignment prevents the fuel from having to be sucked uphill. While this "perfect alignment" is not always possible, it is important to get as close as possible.
Another consideration is the effect of the tank on the plane's centre of gravity (CG). The tank should be as close as possible to the CG point so that when full, it does not push the nose down excessively. Equally important is when the fuel is burned off and that weight is lost, the CG won’t shift to the rear, a condition that can alter the handling of some planes dramatically.
To reduce the chance of a tank rubbing against the airframe and developing a hole, tanks are usually mounted on a layer of foam rubber. This foam rubber is typically 1/2”-thick and held in place with double-sided tape between it and the airframe. A strip of double-sided tape is also placed between the tank bottom and the foam to further keep everything in place. Double straps made from hook and loop material hold the tank firmly but allow it to be removed if necessary.
The RotoFlow Fuel System is a popular choice for RC fuel tanks. Its octagon shape makes it easier to install, as it can be run around the top surface of the tank and taped down. A layer of foam can also be taped to the top of the tank to provide isolation from airframe vibrations.
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Assembly
Assembling an RC fuel tank is a relatively simple process, but it is important to be careful and thorough to ensure the tank functions correctly and does not cause issues with the engine or airplane.
Firstly, the fuel tank should be located in the plane according to the instructions for that airframe. The tank's centreline should be aligned with the centreline of the engine to prevent fuel having to be sucked uphill. The tank should also be located close to the CG (centre of gravity) point so that the weight distribution does not change dramatically as fuel is burned off. To prevent the tank from rubbing against the airframe and developing a hole, it should be mounted on a layer of foam rubber, secured with double-sided tape and double straps made from hook and loop material.
The next step is to connect the fuel tank to the carburetor and a vent line. The vent line prevents the tank from going into a vacuum state that could shut off the fuel flow to the carburetor. The RotoFlow Fuel System is a popular choice for RC fuel tanks, as it does not have internal fuel tubing that can harden and leak air, and it is compatible with gas or glow fuels without modification. The mechanism within the tank consists of a brass tube running from front to back, sealed at one end by a machined aluminium cap with twin O-rings. The other end of the brass tube should have a 30-degree bend in the last 3/8" for the vent line, which can be created using a Du-Bro Tubing Bender.
To assemble the fuel line, flexible fuel tubing should be used to connect the clunk to the brass tube of the feed line. The clunk should be weighted to keep the pickup line in the fuel during rolls and flying inverted, and the fuel line should be sized so that the clunk does not rub against the opposite end of the tank. A notch should be cut into the end of a short piece of flexible fuel tubing (1/2"-3/4" long). The rear plastic segment of the stopper assembly should be slid over the brass tubing on the vent and feed lines, followed by the front plastic segment. The screw should be inserted and turned just enough to engage the rear plastic piece. The flexible fuel tubing can then be reconnected to the brass tubing of the vent and feed lines, and the stopper assembly pushed onto the neck of the fuel tank and tightened carefully. A pull test should be performed to ensure the stopper assembly is secure.
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Pressure
Another important factor is maintaining the correct pressure inside the tank. As fuel is drawn out, it must be replaced with air at normal atmospheric pressure through a separate vent line. This vent line is crucial to prevent a vacuum from forming inside the tank, which could shut off the fuel flow to the carburetor. The vent line is typically connected to a fitting on the engine's muffler, while the feed line is connected directly to the carburetor.
The design of the fuel tank itself also plays a role in maintaining pressure and ensuring uninterrupted fuel flow. Traditional RC fuel tanks used internal fuel tubing, which could harden and leak air over time. Modern designs, such as the RotoFlow Fuel System, have eliminated internal tubing by incorporating a brass tube that runs the length of the tank. This tube is sealed at one end and fitted with a machined aluminium cap with twin O-rings at the other, ensuring a solid seal and maintaining pressure.
Additionally, the RotoFlow Fuel System addresses concerns about potential air leaks at the rotating pickup assembly. This system utilises high-tech flourosilicone aerospace seals, doubled up at both ends of the rotary pickup and backed by stainless retainers. These seals, developed by NASA, are expected to last 25 to 30 years, far exceeding the system's three-year guarantee. The unique octagonal shape of the RotoFlow tanks also makes them easier to install and provides more efficient use of space within the fuselage.
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Maintenance
Installation
While installing a fuel tank may seem straightforward, it is crucial to follow the basics correctly. Take the time to assemble and install the tank properly, ensuring it is securely mounted in the optimal position. This includes considerations such as aligning the tank's centerline with the engine's centerline to prevent fuel flow issues and maintaining the center of gravity.
Tank Protection
To protect the tank from damage and prevent leaks, it is recommended to mount the tank on a layer of foam rubber with double-sided tape. This setup helps to secure the tank in place and reduce the chance of it rubbing against the airframe and developing holes. Additionally, double straps made from hook and loop material can be used to hold the tank firmly while allowing for easy removal if needed.
Ventilation
Proper ventilation is essential for the fuel tank to function correctly. Ensure that there is a vent line connected to the tank, allowing air to enter and maintain normal atmospheric pressure. This vent line prevents the tank from going into a vacuum state, which could shut off the fuel flow to the carburetor.
Fuel Line Considerations
The fuel line should be configured correctly to ensure smooth fuel delivery. The line should be the appropriate length to reach the fuel without becoming stuck or restricted. It is also important to consider the use of a weighted end on the pickup line to keep it in the fuel during manoeuvres.
RotoFlow Fuel Systems
If using RotoFlow Fuel Systems tanks, which feature a unique design and construction, there is no maintenance required inside the tanks once installed. These tanks are made from durable polyethylene plastic, compatible with various fuels, and feature a reliable sealing mechanism. The rotating pickup assembly, while initially raising concerns about potential air leaks, has been designed with high-tech flourosilicone aerospace seals for long-lasting performance.
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Frequently asked questions
Installing an RC fuel tank is a simple process. First, locate the fuel tank in a position that prevents having to suck the fuel uphill. Second, ensure the tank is mounted securely, usually on a layer of foam rubber, to reduce the chance of it rubbing against the airframe and developing a hole. Finally, connect the fuel tank to the carburetor and a vent line.
The vent line prevents the tank from going into a vacuum state that could shut off the fuel flow to the carburetor. It allows air to enter the tank and maintain normal atmospheric pressure as fuel is drawn out.
The weighted end, known as a "clunk," ensures that the pickup line remains in the fuel during rolls and inverted flying. This design allows the aircraft to perform attitude changes without starving the engine of fuel.
To assemble a leak-free RC fuel tank, follow these steps: remove the center screw and disassemble the stopper assembly, bend the brass tube for the vent line, cut a notch in flexible fuel tubing, connect the clunk to the brass tube using the fuel tubing, and secure the stopper assembly to the tank.
Tank pressure, also known as "muffler pressure" or "crankcase pressure," is a method of pressurizing the fuel tank to ensure that high-G maneuvers do not result in fuel starvation to the engine. Pressurizing the tank forces fuel upwards, even during tight loops or high-G conditions.
