Power shifts between an APU and a GPU on an aircraft.

When it comes to aircraft propulsion, the importance of suitable equipment cannot be overestimated. Aircraft propulsion relies on two main sources: external power and onboard power. External power is sourced from a Ground Power Unit (GPU), which is commonly used in hangars to power various components such as the aircraft’s lighting and avionics. Onboard power, on the other hand, is generated by the Auxiliary Power Unit (APU), a device installed in the aircraft that does not have the mobility characteristics of the Ground Power Unit.

In this article, we aim to look into the power transfer mechanisms within an aircraft, specifically focusing on the transition from an internal power source, such as the Auxiliary Power Unit (APU), to an external power source typically represented by a Ground Power Unit (GPU). Our objective is to provide a comprehensive understanding of the circumstances and underlying reasons that necessitate this transfer of power.

First of all… What is an APU?

An Auxiliary Power Unit (APU) gives an aircraft the ability to operate independently so that it is no longer dependent on auxiliary equipment such as a ground power unit. The APU is a compact jet engine and is often located in the tail of the aircraft, although in certain cases it can also be located in an engine nacelle or in the wheel well. The APU is activated solely by the aircraft battery and once operational, it supplies power to various aircraft systems and also provides bleed air for air conditioning and engine starting.

In cases where the APU is approved for in-flight use, it serves as an additional power source in the event of an engine generator failure. Moreover, it proves valuable for providing bleed air during an in-flight engine restart, for supporting engine start, or for operating the air conditioning systems when operating conditions or company policy require takeoff with engine bleed air disabled.

Main Characteristics:

• • The APU is an on-board power source designed specifically for aircraft;
  • It provides power for onboard systems, such as lighting, air conditioning, and avionics when the main engines are off;
  • APUs are typically powered by jet fuel, making them ideal for aviation applications;
  • It is always on board, an easily available power;
  • Enhances passenger comfort;
  • Supports maintenance operations;

Where to Use:

• • APUs are indispensable for aircraft when they’re on the ground, whether at the gate, maintenance hangar, or remote locations;
  • They ensure the comfort and safety of passengers and crew during boarding, maintenance, and in emergencies;

GPU: The Ground-Based Power Solution.

A Ground Power Unit (GPU) is used to supply aircraft with power while they are on the ground. When an aircraft is on the ground, it needs power to operate various systems, including lighting, avionics, and air conditioning. This power can either come from the on-board Auxiliary Power Unit (APU) or the GPU. The GPU supplies the electrical energy required to operate the onboard systems via a cable connection to the aircraft. As a rule, GPUs supply 115 volts of alternating current (AC) at 400 Hz, while smaller aircraft rely on 28 volts of direct current (DC).

The use of Ground Power Units (GPUs) allows the Auxiliary Power Unit (APU) to be deactivated. Deactivating the APU not only reduces noise and emissions from the airport, but also helps to reduce fuel consumption and wear on the auxiliary power unit. 

There are mainly two distinct technologies used in the aviation industry to provide external power to aircraft on the ground- Diesel GPUs (Ground Power Units) and solid-state GPUs. Development in Battery technology has opened a market for the battery GPUS. By leveraging advanced lithium-ion battery technologies, new models of battery GPUS have been coming to market (check more news soon on Sinepower Battery GPU).

Diesel GPUs, powered by diesel engines, offer robust and reliable power sources. They are known for their versatility and ability to generate significant electrical power, making them suitable for various aircraft types. On the other hand, solid-state GPUs employ advanced electronic components to deliver power more efficiently. Solid-state units are often favored for their reduced environmental impact, lower maintenance requirements, and quieter operation. Both types of GPUs play crucial roles in supporting aircraft operations during ground activities, ensuring a seamless power transfer for essential functions such as pre-flight checks and maintenance procedures. Choosing between diesel and solid-state GPUs often depends on specific operational needs and environmental considerations.

Main Characteristics:

• • The GPU is a ground-based power source used to provide electricity to aircraft when they are on the ground;
  • It connects to the aircraft via special cables and adapters, ensuring a reliable source of power;

Where to Use:

• • GPUs are used at airports, hangars, and seaports to provide power to aircraft and vessels.
  • They are ideal for pre-flight preparations, maintenance, and emergencies when aircraft are on the ground.

So, what about the shift in power between these two devices? What steps are involved in this process?

APU On, GPU Off:

• • Before departure or after landing, the APU is often started to provide power to the aircraft’s systems while on the ground.
  • The ground crew connects the GPU to the aircraft, but the power from the GPU may not be used immediately.
    

Transition from APU to GPU:

• • When the GPU is connected and ready, the flight crew or ground crew can initiate the transfer of power from the APU to the GPU.
  • This transition is frequently controlled through the aircraft’s electrical system panel or cockpit controls.
    

GPU On, APU Off:

• • Once the power transfer is complete, the APU can be shut down to conserve fuel and reduce engine wear.
  • The aircraft is now powered by the external GPU, which continues to supply electricity for the aircraft’s systems.
    

The specific procedures for power transitions can vary depending on the aircraft model. Aircraft manufacturer’s manuals and airline operating procedures contain instructions for operating and switching power sources for a specific aircraft. The goal is to optimize power consumption, reduce fuel burn, and ensure a smooth transition between power sources during ground operations.

Making the Right Choice: Why Choose Us?

Now that you understand the key characteristics of both APU and GPU, you may be wondering where you can find reliable equipment. At Sinepower, we specialize in the supply of high-quality ground power units, static frequency converters, and industrial power equipment for the aviation and marine industries.

Here’s why you should choose us:

• Expertise: With over 40 years of experience, we know the unique power supply requirements of the aviation and shipping industries.
• Customized Solutions: We offer a range of power units that can be tailored to meet your specific needs.
• Reliability: Our products are known for their durability and performance, ensuring smooth operation.
• Eco-Friendly: Our GPUs are environmentally friendly and help you reduce your carbon footprint.
• Customer Support: We provide exceptional customer support to ensure you get the right solution and assistance when you require it.

The choice between APU and GPU depends on your specific needs and where you require power. Contact us today and let us drive your success!