Aircraft fuel nozzles are essential components that play a crucial role in the fueling process of aircraft. These aircraft fuel nozzles are engineered with precision and excellence, using durable materials and expert quality. Jet fuel nozzles undergo rigorous testing and adhere to strict industry standards to ensure safe and reliable operation, even in harsh conditions.

With their advanced technology and intricate design, these nozzles meet the highest level of professionalism, fulfilling the demanding requirements of the aviation industry and contributing to the smooth and reliable operation of aircraft worldwide.

This article will discuss the distinctions between the two types of fuel nozzles, their benefits, and their drawbacks.

Underwing Fuel Nozzles

Underwing fuel nozzles play a crucial role in the aviation industry by facilitating efficient fuel transfer and ensuring safe operations. The precision and reliability of these nozzles are emphasized, as they are constructed with durable materials and advanced techniques to meet strict industry standards. As a result, they are highly dependable and long-lasting.

Additionally, underwing fuel nozzles undergo rigorous testing and quality control procedures to ensure they meet the highest safety standards and can withstand various environmental conditions. Aviation professionals rely on these nozzles for their exceptional engineering and performance, ultimately contributing to the overall efficiency and safety of aircraft operations.

Underwing Fuel Nozzles

In the underwing supply system, fuel is delivered through the couplings under the wings or to the side of the fuselage. The fuel is then directed to fill the different tanks inside the aircraft through internal ducts and special valves.

Underwing Supply System

The A320 aircraft’s fuel system schedule shows the fuel tanks, which consist of tank or booster pumps that the pilot can control. In most cases, each tank has two pumps powered by the aircraft’s primary electrical system. These pumps are responsible for pumping fuel from the tanks to the main engine-driven fuel pump, delivering fuel to the engine.

In aircraft capable of flying at high altitudes, tank pumps are necessary because the reduced pressure at higher altitudes can cause fuel to boil, leading to vapor locks that prevent fuel from entering the engine-driven pump.

Once the tank pumps pump the fuel, it is directed to the low-pressure (LP) fuel valve, also known as the spar valve. From there, the fuel passes through the engine-driven pumps. Some aircraft have low-pressure and high-pressure pumps driven by the engine’s high-pressure compressor.

Low Pressure Fuel Valve for Aircraft Overwing Refueling

In normal operations, the left-wing tank supplies fuel to the left engine, and the right-wing tank supplies fuel to the right engine. In an engine flameout, the remaining engine can be supplied with fuel from the other side using a crossfeed valve. For example, if the right engine fails, fuel from the left-wing tank can be directed to the right engine by opening the crossfeed valve.

In most larger aircraft, the refueling points are located under the wings, although they are on the side of the fuselage in some aircraft. This point is called the refuel coupling, where the fuel bowser hose is connected. This type of fueling is known as pressure fueling, as the fuel is delivered to the tanks at a high pressure.

A control panel is available to manage the refueling. In this panel, the operator can set the required amount of fuel. Once the hose is connected, the refueling valves open, and the fueling process begins automatically. During refueling, the outer tanks are filled first, and once they are complete, the fuel overflows into the inner and center tanks. When the fuel level reaches the desired value, the refueling valves are closed, and the fueling process stops.

LP Fuel Valve

Advantages of Underwing Fuel Nozzles

  • Efficient Fuel Delivery: Underwing fuel nozzles allow for faster fuel delivery due to high pressure and flow rates.
  • Safety: Underwing fuel nozzles have features like flow control valves and pressure relief mechanisms. These measures ensure that the fuel is delivered at the correct pressure and prevent overfilling or spillage.
  • Rain Supply: Underwing fuel nozzles allow for a fuel supply even in the rain.
  • Compatibility. Underwing fuel nozzles are primarily compatible, making them versatile for fueling operations.

Disadvantages of Underwing Fuel Nozzles

  • Design Complexity: Underwing fuel nozzles have a complex design, making them a more expensive option than overwing nozzles.
  • Increased Maintenance Requirements: Underwing fuel nozzles require regular maintenance to ensure proper operation. The complex design of these nozzles can lead to more frequent breakdowns or repairs.
  • Difficulty Operating: Underwing supply nozzles are heavier and larger than overwing, making it challenging to operate, especially overwing fuel nozzles.

Overwing Fuel Nozzles

Over-wing fuel nozzles are crucial in efficient and safe aircraft refueling. Designed with precision engineering and adhering to strict safety standards, these nozzles are essential components in the aviation industry.

Safe Refueling with Overwing Fuel Nozzles

In light aircraft, the fuel tanks are typically situated inside the wings and can be filled through a filler cap on top of the wing. To ensure proper fuel balance and remove any moisture, drains are located at the bottom, and vents allow for internal pressure equalization. The fuel quantity is measured by a sensing unit in each tank and displayed on the cockpit’s fuel quantity gauges.

Aircraft Fuel Nozzles

High-wing aircraft rely on gravity to feed fuel to the carburetor. On the other hand, low-wing planes and those with fuel-injected engines require an engine-driven pump to supply fuel. An electrically powered pump is also essential for engine start and backup purposes.

A fuel pressure gauge is used to monitor the pump’s performance. The pilot can select which tank feeds fuel to the engine using the fuel selector valve. Some systems may require alternating between tanks, while others offer the option to use both tanks simultaneously. Additionally, the selector valve has an “Off” position.

Overwing Fuel Nozzles

For aircraft with carbureted engines, a manual primer adds extra fuel for starting, while fuel-injected engines use an electric fuel pump. Before reaching the engine, the fuel passes through a strainer to remove contaminants and water. The fuel filter’s sump is located below the engine, and a fuel sample is taken from it during preflight.

Advantages of Overwing Fuel Nozzles

  • Easy Accessibility: Accessing fuel tanks is easier with over-wing fuel nozzles above the wing, making rapid refueling more convenient, especially for smaller aircraft.
  • Simplicity: Over-wing fuel nozzles have a more straightforward design than underwing ones. This simplifies maintenance and reduces the likelihood of breakdowns or repairs.

Disadvantages of Overwing Fuel Nozzles

  • Slower refueling process: Fuel delivery through the wing can be slower than underlying fuel nozzles. The fuel must travel a longer distance, which can take longer.
  • Fuel Spillage: Over-wing fuel nozzles have an increased risk of fuel spillage, primarily due to the requirement for manual handling and the likelihood of operator error.

Wrapping Up

The choice between underwing and overwing aircraft fuel nozzles depends on several factors, including aircraft type and specific operational requirements. Underwing fuel nozzles provide efficient fuel delivery and enhanced safety features but can pose challenges in accessibility and maintenance. Over-wing fuel nozzles offer easier access and simplicity but can result in a slower refueling process and an increased risk of fuel spillage.

Ultimately, it is crucial to consider the specific needs of the aircraft and refueling operation to choose the most suitable type of fuel nozzle. By understanding the advantages and disadvantages of fuel nozzles under and above the wings, aircraft operators can make informed decisions that optimize efficiency, safety, and reliability.


2 thoughts on “Underwing Vs Overwing Aircraft Fuel Nozzles (Compared)

  1. Keith Reay says:

    Enjoyed the article, a useful training tool I think.
    I was surprised you didn’t include the overwing nozzle types, ie duckbill.

    1. Hi Keith, follow our blog posts and learn more about the overwing. Since you are also following our quiz/answers, you may have noted a great dive on this already-discussed topic through our LinkedIn page. Thanks for your valuable request; I hope our answer meets your expectations.

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