Ground power units supplied to African clients

6th February 2009 By: Darren Parker

Aerospace equipment supplier Aztec Electronics has supplied a number of 28-V dc 400-Hz combination converters, which supply power to aircraft as they dock on the ground, to a series of African military clients.

Aztec Electronics is the sole sub-Saharan African distributor of American aerospace equipment manufacturer JBT AeroTech’s range of 28-V dc 400-Hz ground power units (GPUs) and preconditioned air (PCA) units. JBT AeroTech is also responsible for the manufacturing of the new passenger boarding bridges used at OR Tambo International Airport, in Johannesburg.

Aztec’s vehicle-mounted Circonian GPU was upgraded in 2008 to include a JBT AeroTech static frequency converter in place of the Circonian’s rotary converter. The GPU has been deployed on peacekeeping opera- tions over the past 12 months, where it is used on military aircraft, and is reportedly performing well.

Aztec’s latest product is the combination converter air conditioner, which is a diesel- powered 28-V dc 400-Hz combination converter and PCA trailer unit.
PCA units are used for modern trainer and fighter jets, which require cold, high- pressure cooling air to be pumped through the aircraft’s electronics when ground power is applied, so as to prevent the high-tech electronics from overheating.

While the PCA is essential for the ground operation of the aircraft, the cold air supplement is not required while flying, as its own on-board cooling system serves to cool the electronic components sufficiently in-flight.

Speaking of a number of new fighter jets having been released in Europe and in the US, Aztec Electronics sales engineer Dean Marcus explains how new GPU/PCA combination unit designs are being developed to accommodate some of the new jets, such as the relatively new fourth-generation Gripen fighter jet.

In passenger aircraft such as Boeing 747s and A380s, the air conditioning component is not such a necessity, as the electronic components are not in danger of overheating while being active on the ground. Instead, the cooling unit serves to provide comfort to those remaining inside the cabin of the aircraft as it docks on the ground.

Marcus says that at South African airports, few such air conditioning units are available for passenger planes. He says that one might notice, upon arriving or departing from the Johannesburg airport, that while the plane is docked, the on-board air conditioning is seldom operated, and in a sealed cabin on a hot day, the effects can be extremely uncomfortable.

He says that the mere comfort of the passen- gers or staff aboard a grounded aircraft has not yet proved to be adequate reason for airport management companies and airlines to invest in the equipment.

Further, the difficult times faced by airlines over the past year have caused subsidiary industries to be affected too, says Marcus. “To convey to airlines the need for conditioned air is sometimes difficult, based on the capital cost. However, when one compares the cost of running air conditioning from a ground-based unit, rather than the aircraft auxilliary power unit (APU), then it makes a lot of sense,” he says.

“It’s not an essential item though, and that makes it a hard sell sometimes for the commer- cial customers.”

However, GPUs are readily accepted as a necessity, because to power the aeroplane’s electronics without the use of a GPU would require the employ of the APU, which is a turbine engine that makes significant noise and uses a significant amount of jet fuel. It also requires regular maintenance, which is expensive and complex, when compared to the simple maintenance required on a GPU’s diesel generator.

The GPU’s are diesel powered, and while some noise is inevitable, it is much quieter to run than the APU, which increases safety and efficiency factors for those working around the aircraft, as they are able to hear better. It also uses much less fuel than an APU.

Older GPU technology included a rotary converter, to convert the 50 Hz from the gene- rator into the 400 Hz required by the aeroplane. Such was the GPU Aztec supplied to power Air Force One on former US President George W Bush’s visit to South Africa in 2003.

However, Marcus explains that new electro- nic conversion technology has now replaced rotary conversion, which includes enhanced safety features.

At some airports, particularly in more remote locations, fixed GPUs are not always available, and so portable PCA/GPUs are used. These can either come in the form of a fully fitted truck, complete with a diesel generator, converter, and pressurised air conditioning unit installed. Otherwise, the units may come in the form of a trailer, which can be towed behind any vehicle.

Aztec also manufactures its field-proven range of Kwik Start battery-powered GPUs. The latest addition to the Kwik Start range is the 6NSB400R, which is a trans- former/rectifier-based portable GPU that uses six North Star NSB170FT pure lead/tin VRLA AGM batteries to provide 28-V dc power at up to 1700 A, for turbine engine starting.

Currently, Aztec is engaged in preliminary talks with an African airline regarding the supply and maintenance of mobile, diesel-powered GPU/PCA combination units for its fleet of large commercial passenger aircraft, including Boeing 737s, Boeing 747s, as well as a number of Airbus variants.

Aztec has been supplying GPUs and aircraft batteries, mainly to the military, for 30 years. It is the South African agent for Enersys’ Hawker brand and Concorde aircraft batteries, which are suitable for all aircraft, from single-engine Cessnas, to fighter jets, to mili- tary transports, to large passenger planes.