Understanding the Fuel System in Aircraft

In aircraft, two things are mixed together to create combustion: fuel and air. Let’s talk about how the fuel system works and why it is so important. The fuel system’s job is to move fuel from the fuel tanks to the engine. In small airplanes, there are two main types of fuel systems: gravity-fed systems and fuel pump systems.

Gravity-Fed Fuel Systems

High-wing airplanes, like the Cessna 172, often use gravity-fed fuel systems. In these airplanes, the fuel tanks are inside the wings, which are located above the engine. Because of gravity, the fuel naturally flows from the tanks down to the engine. Even though a fuel pump isn’t always needed for normal operation, many high-wing airplanes still have a pump as a backup. This pump might be powered by the engine, by electricity, or by both. The backup pump is especially helpful during emergencies.

Fuel Pump Systems

In low-wing airplanes, like the Piper Arrow, a fuel pump system is necessary. This is because the fuel tanks are located below the engine. Gravity alone cannot push the fuel upwards to the engine. To solve this problem, low-wing airplanes have two fuel pumps:

1. The engine-driven fuel pump, which is used during normal operations.
2. The electric fuel pump, which acts as a backup in case the main pump fails.

Fuel Priming

Some airplanes have a tool called a fuel primer. The primer sends fuel directly into the engine cylinder before starting the engine. This is especially useful in cold weather. For airplanes without a fuel primer, like the Cessna 172, the electric fuel pump can be used to “prime” the engine instead.

Fuel Tanks

Airplane fuel is stored in fuel tanks, which are usually inside the wings. These tanks are filled from the top. On the top of the tank, there is a fuel cap that can be opened to add fuel. These caps are usually designed to let outside air into the tank. This is called venting and is very important because it prevents a vacuum from forming inside the tank.

If the tank were not vented, fuel would stop flowing as the tank empties because air would not replace the fuel. Some airplanes also have fuel vents that stick out from the wings. When the airplane moves through the air, these vents let air into the tank to help maintain proper pressure.

Fuel Sensors and Gauges

Inside the fuel tanks, there are fuel sensors that send information to the fuel gauge in the cockpit. This gauge tells the pilot how much fuel is in the tank. However, pilots should always visually check the fuel level because fuel gauges are only required to be accurate when the tank is empty. Never trust the fuel gauges completely!

Checking for Contaminants

Before flying, pilots must check that the fuel is clean and free of contaminants, like water. Airplanes have fuel sumpsor drains that allow the pilot to take a small fuel sample using a special tool called a fuel sump cup. The pilot looks at the fuel to make sure it is clean and the correct color.

Most small airplanes use a fuel called 100 Low-Lead (100LL), which is blue. Pilots must check both for impurities and to confirm that the fuel’s color is correct.

Fuel Selector

Airplanes have a fuel selector to control which tank the fuel comes from. The selector usually has four positions:

1. Left – Fuel comes only from the left tank.
2. Right – Fuel comes only from the right tank.
3. Both – Fuel comes from both tanks at the same time (this is used during normal operations).
4. Off – Fuel flow to the engine is completely stopped. This position is usually used in emergencies, such as during an engine fire.

In the Cessna 172, the fuel selector has only three positions: left, right, and both. To completely stop the fuel flow, a separate fuel shutoff valve is used. This valve is located near the fuel selector and is activated by pulling a knob.

Why Understanding the Fuel System Is Important

Knowing how the fuel system works is crucial for pilots. It helps ensure the airplane runs safely and efficiently. Before every flight, pilots check the fuel levels, inspect for contaminants, and confirm the fuel selector is in the correct position. By understanding these systems, pilots can avoid dangerous situations and keep their flights safe!

Test your knowledge

Understanding The Fuel System In Aircraft
Submitted by Michael Egertonin Basic Aeronautical Knowledge2 weeks ago6 responses


    

		    

    

    

		        
        
    

	
    

         Your response contain errors which are highlighted in red. Please correct them and try again.    
    

        

			                Cancel
			
			                
					Previous                
			
            
                 Continue            
            
                 Finish            

			                
					Start Quiz                
			        
    

    
    
    
    
    
    
	


    
    
This question is required.
    
 Please wait..
    
Years,Months,Weeks,Days,Hours,Minutes,Seconds
    
Year,Month,Week,Day,Hour,Minute,Second
    
Please select minimum {0} answer(s).
    
Please select maximum {0} answer(s).
	
    

    

        
            
            Toggle Editor        
    

Learn More - the Basic Aeronautical Knowledge Certificate Programme, is an effective way to demonstrate your knowledge and passion for aviation.

https://aviationenglish.com/bak-certificate-programme/basic-aeronautical-knowledge-certificate-programme.html

#aviationenglishasia #aviationenglish  #BAK #basicaeronauticalknowledge #aviationtheory  #flighttraining #pilottraining #hkaviation #vhhh #aviation #icaoenglish #pilot #atco #flying #piloting #studentpilot #Pilot #見習機師 #CadetPilot  #機師英語要求 #ICAO英語 #ICAOtest #cadetpilotprogramme #icaoenglishtest #studentpilot #futurepilots #generalaviation