Clean fuel is imperative for the safe operation of a WSC aircraft. Of the accidents attributed to powerplant failure from fuel contamination, most have been traced to:
- Failure to remove contamination from the fuel system during preflight.
- Servicing aircraft with improperly filtered fuel from small tanks or drums.
- Storing aircraft with partially filled fuel tanks.
- Lack of proper maintenance.
Rust is common in metal fuel containers and is a common fuel contaminant. Metal fuel tanks should be filled after each flight, or at least after the last flight of the day to prevent moisture condensation within the tank.
Another way to prevent fuel contamination is to avoid refueling from cans and drums. Use a water filtering funnel or a funnel with a chamois skin when refueling from cans or drums. However, the use of a chamois will not always ensure decontaminated fuel. Worn out chamois will not filter water; neither will a new, clean chamois that is already water-wet or damp. Most imitation chamois skins will not filter water.
Letting fuel sit for weeks without using it will cause it to go bad. Even if gas does not go bad, it will often lose octane with time. For premixed gasoline and two-stroke oil, there is another set of problems. Fuel and oil are normally mixed at a 50:1 ratio. If premixed gas sits in a plastic container for a while, the gas will evaporate leaving a richer oil mixture in the container. In any case, fresh gas should be used when possible.
Never mix oil and fuel in an enclosed area. Not only are the fumes irritating, but with the right fuel/air mixture can cause an explosion. Do all oil and gas mixing outside. Refueling from fuel cans should also be done outside. Never smoke while refueling. Be careful when refueling an aircraft that has just landed. There is danger of spilling fuel on a hot engine component, particularly an exhaust system component. Refueling should be done using only safety-approved fuel containers marked with the type of fuel stored in them. Confusing premixed fuel and fuel that has no oil in it can be disastrous.
Metal Versus Plastic Fuel Containers
There are advantages to using both metal and plastic containers. Metal cans will not allow the sun’s ultraviolet rays in to harm the fuel. It also will not develop static charges that a plastic container develops. However, a metal can is more prone to sweating when going from cool to warm temperatures on humid days. Metal cans and gas tanks are best kept either empty or full of fuel to leave no room for moist air.
Plastic fuel containers are easy to handle, inexpensive, available at discount stores, and do not scratch the finish on airframes. Plastic cans also do not sweat, and do not need to be stored topped off. However, fuel does deteriorate a little faster in plastic. Also, plastic containers can get charged with static electricity while sliding around in the bed of a pickup truck, especially if the truck has a plastic bed liner. [Figure 4-19]
Many states now have laws prohibiting people from filling plastic containers unless first placed on the ground. Static electricity can also be formed by the friction of air passing over the surfaces of a WSC aircraft in flight and by the flow of fuel through the hose and nozzle during refueling, if fueling at a pump. Nylon, Dacron, and wool clothing are especially prone to accumulate and discharge static electricity from the person to the funnel or nozzle. To guard against the possibility of static electricity igniting fuel fumes, a ground wire should be attached to the aircraft before the fuel cap is removed from the tank. The refueling nozzle should then be grounded to the aircraft before refueling is begun and should remain grounded throughout the refueling process. The passage of fuel through a chamois increases the charge of static electricity and the danger of sparks.
The aircraft must be properly grounded and the nozzle, chamois filter, and funnel bonded to the aircraft. If a can is used, it should be connected to either the grounding post or the funnel. Cell phones should not be used while refueling due to possible fire risks.
Mixing Two-Stroke Oil and Fuel
Two-stroke engines require special two-stroke oil to be mixed into the fuel before entering the engine to provide lubrication. In some engines, an oil injection pump is used to deliver the exact amount of oil into the intake of the engine depending on the throttle setting. An advantage of an oil injection system is that pilots do not need to premix any oil into the fuel. However, an important preflight check is to ensure the two-stroke oil reservoir is properly filled.
If a two-stroke engine does not have an oil injection system, it is critical to mix the oil with the fuel before it is put into the tank. Just pouring oil into the fuel tank does not allow the oil to mix with the gas, and makes it difficult to measure the proper amount of oil for mixing.
To mix two-stroke oil:
- Find a clean, approved container. Pour some gas into it to help pre-dilute the two-stroke oil.
- Pour in a known amount of two-stroke oil into the container. Oil should be approved for air-cooled engines at 50:1 mixing ratio (check the engine manufacturer for proper fuel to oil ratio for the WSC aircraft). Use a measuring cup if necessary. Shake the oil-gas mixture to dilute the oil with gasoline.
- Add gasoline until the 50:1 ratio is reached. If using a water separating funnel, ensure the funnel is grounded or at least in contact with the fuel container.
- Put the cap on the fuel can and shake the gasoline and oil mixture thoroughly.