reasonable compromise when the proper auto gas octane is not available. 

Manufacturers of two-stroke engines and four-stroke engines used on WSC aircraft typically recommend the use of 89 octane minimum auto fuel for their engines. Additives are put into auto gas primarily to reduce harmful emissions rather than boost performance. The additives are supposed to be listed at the pump, but the accuracy of this posting should be questioned. 

Methanol alcohol has corrosive properties and can damage engines. Engine manufacturers do not recommend more than five percent methanol in fuel. Consult the POH for specifi cs on an engine. 

Ethanol alcohol is less corrosive than methanol. However, it attracts water and is not as economical as gasoline. Ethanol does not get very good fuel economy. Avoid fuels with any more than 10 percent of ethanol. 

Consult the POH for specifics on an engine. Manufacturers provide specific recommendations for the percentage of alcohol in fuel. The posting on the pump may not be accurate and alcohol content can vary greatly between fuel brands and stations. Additionally, higher percentages of alcohol will be added to auto gas in the future. 

A simple test can be conducted to measure the fuel’s alcohol content to ensure the fuel used stays within the manufacturer’s recommendations. Use a general aviation sump collector which includes graduation marks. Add water to a specific mark. Then add fuel to fill the collector up to the line for gas. Cover the top and shake it vigorously. After it settles, the water and alcohol will combine and it will look like there is now more water in the sump collector. The difference between the initial amount of water fi rst put into the collector and the new level of combined water and alcohol equals the amount of alcohol in the fuel. Compare this amount of alcohol and the amount of fuel to determine the percentage of alcohol content in the fuel. 

Methyl tertiary–butyl ether (MTBE) does not have the corrosive or water attractive properties of the previously mentioned additives and is added to fuel to improve air quality. It has been banned in several states because it is carcinogenic and has been found in ground water. It does not attract water, but it is expensive, and found only in some of the better grade fuels. 

## Fuel Contamination 

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 prefl ight. 

• 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 fi ltering 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 fi lter water; neither will a new, clean chamois that is already water-wet or damp. Most imitation chamois skins will not fi lter water. 

## Bad Gasoline 

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. 

## Refueling Procedures 

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. 

