Evergreen Aviation to convert four Boeing 747-200F aircraft for operation during peak fire danger season in USA
Evergreen Aviation plans to have the first of up to four converted 747-200F 'Supertanker' aircraft available for the peak fire season in the USA in around three months following a further round of flight tests on an enlarged tank system.
"Around July we will go through a series of drop tests again, this time with a 75,800 litre (20,000USgal) capacity tank system," says director of flight operations for the Boeing Supertanker Penn Stohr. The final tests will be used to clear a supplemental type certificate (STC) that will be the basis for a further three conversions to be completed at Evergreen Air Center in Marana, Arizona.
The larger tanks are being fabricated in Texas and are made from lighter aluminium, unlike the prototype steel 37,900 litre tanks used in the initial tests. These were conducted from 21 March to 24 April and included around 82 live drops and some 100 'dry' runs. Just over 2 million litres were dropped over the test phase, which was conducted over some 50 flights in and around Marana airspace. The modification involves fitting the tanks, two large air tanks for pressurisation, pumps and dump valves in the forward section of the aft cargo hold immediately aft of the unpressurised main body gear undercarriage bay. The air tanks are capable of applying up to 12bar (175lb/in2) of pressure to the water container tanks, and keep them regulated at around 4.1bar during normal operations. Water or retardent is dumped through four valves arranged fore and aft in the belly immediately aft of the undercarriage bay centreline.
Having begun with high-altitude test drops at 10,000ft (3,050m), Stohr says further drops were made at 400ft and 140kt 260km/h). "There is no centre of gravity shift, no pitch change and no unusual turbulence." Tests were also conducted with gels and foams, and included low-level water drop tests.
GUY NORRIS / LOS ANGELES
Source: Flight International
