Rc airplane fuel system setup

In our case this cavitation phenomenon is mostly made of air bubbles, not gaseous kerosene bubbles so strictly speaking the term "cavitation" should be replaced by "air bubbles release under vacuum conditions" but this obviously not very convenient. On our RC jets systems, the fuel pump is perfectly capable of creating the depression required to make the fuel cavitate.

As a general rule, any pump voltage in excess of 3,0V could create this type of vacuum if there is enough restriction in the system upstream the pump.

A restriction in the fuel lines will generate fluid drag in the stream that will lead to a slight overpressure upstream the obstacle and a slight underpressure downstream of it. If the restriction is high enough, the pressure drop will make the fuel cavitate or foam. That restriction might be caused by a valve, a junction, or a pinched line. You will see bubbles appearing at this location as if there was an air leak….

Another interesting phenomenon is the air trap cavitation. Soft Nalgene air traps have a tendency to collapse in case of a restriction and big pump demand. The walls of the air trap could touch the sides of the air trap bag, thus reducing the filtering area. Additionally if some air bubbles are trapped upstream of this bag, they will cover it. This will increase the flow drag and the vacuum downstream the filter.

At some point the filter will cavitate and it will look exactly as if the bubbles were making their way through the air trap bag! As a general rule, cavitation can be generated in a fuel system for engines of N thrust or more. It can be avoided by carefully choosing the fuel system components and planning for proper fuel lines routing to avoid tight bends. I will come back to this later. This static electricity discharge appears under certain atmospheric conditions: on dry and dusty days.

The electricity is captured by the engine parts while the air charged particles are travelling through it. When a certain potential difference is reached, the electricity will travel backward through the fuel lines into the pump and ECU and shut it down. This phenomenon is exponential with the quantity of air displaced by the engine. Bonding is the fact of using that static electricity dispenser additives and metalizing the different components of the engine to fuel interface.

The engine metalizing wiring: a thin yellow wire is used at the bottom of this picture to connect the stainless steel pipe to the PSX engine bracket, to the fuel pump and to the fuel tank. Large quantities of fuel pumped into the plane with a significant electrical potential difference can also create a problem. Metalizing the plane as described above shall give you a good defense against all these phenomenon.

A good fuel system needs to use good tanks. They must be leak free and the tank arrangement shall be such that the flow drag is reasonable. As a general rule, try to avoid having two tanks in series. Parallel them if you can.

If this cannot be done, then use large bore tank internals and interconnecting lines. When ever legal or possible, we highly recommend the use of bladder systems for your jet or piston engines.

The reason for this is that these systems are air free. This allows to feed the engine with no risk of air bubble ingestion at any point of the flight, in any position and supply a continuous positive flow of fuel atmospheric pressure pushes on the bladder at all times. This is turn allows the removal of air traps,with saves a lot of complexity, risk of failure and about 1 to 3 lbs of dead weight.

The latest professional units we sell are super fuel resistant and very strong. For rigid tanks, as a good practice, I recommend reinforcing the walls seams with a Kevlar tape. The tank leaks can be detected by moderately inflating them with air in and putting them in a water bucket do not use a powerful compressor to inflate them!

Mark the leaks usually pin holes with a water proof marker. Then apply EHP epoxy resin to the marked areas with a piece of plastic bag and push on, to fill the pin holes. For a bladder system, a tank leak can be sealed by welding. Another area to watch is the tank cap or fuel stopper.

A lot of ARTFs use rubber caps expanding into the bare fiber. This will introduce leaks on the long run. I strongly recommend using aluminium tank stopper rings glued with Hysol on the tank end like the one used on our UHF fuel stopper.

For all tank plumbings, it is essential to use Viton material. The reason is that Viton tubes are designed to stay immersed permanently in fuel and stay flexible. This is essential to keep the clunk mobile and moving towards the fuel. Also, Tygon chemical composition got changed a couple years back and the tubing sweats chemical after a few years. Wee found out that this sweating could obstruct the capilliary injection needles of the jet engine.

This method is used to avoid reverse bending the line that could get stuck at the front of the tank. Measure the length of your tank from the stopper to the end wall. Cut two sections of 3 " o four ultra flexible Viton tubing. They will be used to connect the stopper tube to the long brass tube, to the clunk. Cut a section of brass tube in the measured length minus 2". Insert the Viton lines on both ends of the tube by 1".

Spray the tube with Zip Kicker before inserting. This will ensure that the line is lubed along the tube and slides properly. Zip Kicker has no silicon and does not contaminate kerosene higher risks of fuel stick clogging.

Insert the fuel clunk on the line. The clunk has an aggressive barb and will require more pushing than the tube. Safety wire all connections as per chapter 1. Example of wrong technique: in the picture below, the Tygon line will harden relatively fast. This setup will send a lot more air into the air trap.

Note that for semi-rigid setup, the clunk will never be at the front of the tank. This means that on long dives, the pickup line will suck air.

This is acceptable if you put your engine to idle in your dives. However hardcore aerobatics pilots should not use this setup as it will put most air traps to their limits.

Here is the seating of the clunk in the tank in the horizontal position:. Otherwise there would be a risk of sucking the clunk flat against the wall and immediately starve the engine. In this position, the clunk will feed air to the air trap. At this point the air trap will play its role and provide buffer fuel to the engine. If you like to keep your engine running full power in the dive, then we'd recommend that you use the next setup.

This method was not recommended previously as there were no proper heavy clunks and flexible enough lines to avoid reverse bending the pickup.

It would eventually get stuck at the front of the tank, resulting in a fixed pickup point flameout at the end of the flight guaranteed. Additionally most plastic lines including Tygons would harden with time and render this scenario more likely.

However our new specific UHF clunk is heavy weight while compatible with regular fuel stopper diameters and allows for a super flexible Viton line to never get stuck in a reverse bend scenario.

It is also optimally designed to avoid pinching the thin wall Viton line. Additionally the super high quality Viton tubes that we use are completely unaffected by immersion in kerosene or diesel and will never harden. A long section of ultra flexible Viton tubing is used to connect the stopper tube to the clunk.

When you are done with the plumbing, dry test the tank. Just turn it in all positions. S afety wiring is essential here as the clunk is constantly falling and pulling on the Viton line Note that with large tanks of 8" diameter or more, the fuel clunk line can reverse itself into the tanks, which is acceptable. Just make sure that the tank does not have any blobs of glue that could block the clunk in position.

Also note that in this case, a cross slotted clunk is necessary to avoid having it sucked flat against a wall and completely blocking the system. This would not happen on the previous semi rigid scenario if setup as described. Here is an example of plumbing on a box type bladder :. Air traps are not necessary for bladder systems , provided you refuel with an air purging pump unit. It can also weaken any glued joints and potentially damage parts of the radio gear.

Also, consider fuel barbs on the ends of the inlet and vent lines. Barbs are a quick and affordable way to prevent fuel hoses from sliding off. Most RC fuel lines for nitro engines are the flexible silicone variety. The most common issue RC pilots have is with lines that slip off.

Barbs or simple zip ties are the way to secure these lines from the tank to the carburetor and muffler. Another thing worth knowing is the fuel tank clunk.

The clunk refers to a short piece of tubing inside the tank with a heavy weight at the end to keep the tube in line with gravity. Why is this so vital? Well, model RC planes fly at all angles, experience G-force, and do fancy acrobatics in the air. All these maneuvers move the fuel around, and the less there is, the more space it has to swoosh.

The clunk arrangement is a simple yet effective way to keep the fuel tube submerged in nitro fuel. The two RC airplane filters are fuel and air. The job of a fuel filter is to prevent dirt clogging up the carburetor. The air filter stops dirt from reaching the engine. RC fuel filters are inexpensive and vital for the optimal functioning of any nitro-powered aircraft. RC air filters are harder to come by, so you may have to improvise.

Filters are not optional if you want full protection for your model plane. Always filter the fuel from the jug to your fuel tank. Ask at community forums if you need help with creative air filter ideas. RC nitro-powered planes typically use two kinds of pumps.

These are simple fueling pumps. The other pump takes fuel from the tank and delivers it to the engine. They are the engine fuel pumps. Some pilots prefer manual pumps to get fuel from the can to the tank.

These simple devices use a type of squeeze bulb and are ideal for filling smaller models. Electric pumps are better for larger tanks. You now have a basic understanding of the RC airplane fuel system. This next section looks at nitro fuels in more details and the things you need to know to get the right blend for your aircraft.

Not all RC airplane fuels are equal, so a little knowledge helps to get things right. RC model aircraft fuel is a special blend of three main ingredients and minor additives. There are several blends of nitro fuel available. Each one is suited to different types of engine and performance requirements. The 3 primary ingredients used in RC nitro fuel include:. Submit your video here. Profile Data.

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Lost your password? Please enter your email address. You will receive mail with link to set new password. Subscribe Button Subscribe. Model Airplane News. The removable fuel tank tray can also secure your battery packs. This system works extremely well, especially with large airplanes.

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