Fuel Systems

Regardless of the type of engine it uses, every powered airplane requires a fuel system, which includes fuel tanks, fuel lines, and either a carburetor or fuel injection system to deliver fuel to the engine.Airplanes with high wings, like the Cessna Skylane, often use a gravity feed system to get fuel from the tanks to the engine. Airplanes with low wings use electric or mechanical pumps to deliver fuel under pressure to the engine through a tank selector.

Fuel systems usually include two or more tanks. Some use rubber bladders, while others use "wet wings" where the wing structure itself forms the fuel container. Sealant keeps the fuel from leaking around rivets.

Water Problems

Because water is heavier than gasoline, it flows to low points in the tanks and fuel system plumbing. Drains are installed at these low points so you can remove water that was pumped in with the fuel or that collected on the tank walls.

Types of Fuel

Most airplanes use either kerosene or aviation gas, commonly referred to as avgas. Turbine-powered airplanes, whether turbojet, turbofan or turboprop, use kerosene. Piston-powered airplanes use avgas.

Both kerosene and avgas come in multiple grades. Turbine fuel, referred to as jet petroleum, or JP, comes with various additives. Avgas comes in various octanes. The engine manufacturer specifies the grade of fuel for each engine. The most common general aviation fuel, 100LL (low lead, although it has a significant lead content), is dyed blue for easy identification. Fuel rated at 80/87 octane is dyed red. Kerosene, regardless of grade, is clear or straw colored.

In an emergency, fuel of a higher grade than specified can be used; if your airplane's manual calls for 80/87 and only 100LL is available, you can use it. The converse is not true. An engine that requires 100LL will quickly destroy itself if fed 80/87. Any piston engine will be destroyed if you attempt to run it on jet fuel. Moral: Always supervise the fueling of your airplane.

TIP: You can make managing the fuel system and operating the engines in Flight Simulator more challenging by changing options on the Fuel tab of the Aircraft Settings dialog box. For more information, see the topic "Setting Fuel Options" in the Using Flight Simulator section of Pilot's Help.

Fuel Management

Fuel mismanagement—running out of fuel or mismanaging the fuel supply—remains one of the most common causes of aviation accidents. This simple, pilot-related mistake, is completely avoidable.

Airplane fuel capacity is measured in gallons or pounds. Most performance charts for light general aviation airplanes state fuel consumption for a given power setting in gallons per hour. Turbine-powered airplane fuel consumption rates are normally given in pounds per hour (PPH).

It's important to watch the clock as closely as the fuel gauges when flying. The CARs require you to arrive at your destination with at least 30 minutes of fuel on board during the day under VFR. You need 45 minutes of reserve fuel at night. The rules for IFR operations are even more strict.

Managing the Fuel

Managing the fuel supply involves two basic tasks.

1. Drawing fuel from the appropriate fuel tanks by using the fuel tank selector. It's best to alternate between fuel tanks, keeping track of the time used out of each tank. Running one tank dry and then switching to the other can lead to embarrassing—and dangerous—engine failures.
2. In an aircraft with a piston engine, adjusting the mixture control to make sure the air/fuel mixture entering the engine is appropriate as the aircraft changes altitude. Turbine-powered aircraft have automatic fuel control systems that manage fuel flow.

TIP: You can make managing the fuel system and operating the engines in Flight Simulator more challenging by changing options on the Fuel tab of the Aircraft Settings dialog box. For more information, see the topic "Setting Fuel Options" in the Using Flight Simulator section of Pilot's Help.

Electrical Systems

Most modern airplanes are equipped with an electrical system, which usually includes a generator or an alternator, circuit breakers or fuses, a battery, and wiring. Either a load meter or an ammeter keeps the pilot informed about the health of the system. Electrical power is distributed over a bus to the various devices that use it.

Starting Power

The original application of electricity in airplanes was to power a starter, which eliminated the need to hand prop a plane. Today, electricity is now used for everything from avionics to CD players and for heating food in the galleys of large airplanes.

Large airplanes often have auxiliary power units (APUs) to provide power on the ground. These small jet engines provide ground power and turn generators that create the massive amounts of power required to start turbofan engines.

Batteries

Small airplanes such as the Cessna Skylane RG and Extra 300S use lead-acid batteries much like those in cars. However, airplane batteries are designed specifically for use with aircraft engines.

Master Switch

Aircraft like the Cessna Skylane RG have a master switch that turns on the electrical system and starts drawing power from the battery. It's important to turn the master switch off after shutting down the engine—leaving it on drains the battery.

Generators and Alternators

Batteries provide the initial burst of electrical power to start an airplane engine, but the demand caused by lights, avionics, and other devices would quickly drain even a powerful battery. To provide power to the electrical system and keep the battery charged for the next start, aircraft are equipped with generators or alternators.

Most modern light aircraft use alternators, which provide a better, more consistent supply of electrical energy through the range of engine speeds, especially when the engine is idling.

Powering Up

In an airplane equipped with an electrical system, power from the battery turns an electric starter. The starter rotates the engine until the combustion begins; then the generator or alternator comes on line.