Recently completed tests on the leased 747-400 -8 technology demonstrator have "dramatically increased confidence that we'll be able to meet our targets on range," says 747 chief project engineer Corky Townsend. "Its still too early to say whether we'll beat it by a lot, but It is really looking positive."
The leased -400 was flown to help establish the exact baseline performance of the model and to collect more precise data against which to predict the true improvements expected from the all-new 747-8 wing. "We did some testing a few years ago on the -400 [for the proposed trailing edge wedge modification] and the wing seemed to wash out or untwist more than we thought it would," she says.
The latest tests verified wing wash-out much more precisely using a set of inertial reference position indicators at the centre of the fuselage as well as outboard of the outboard engines and at the wingtips. "From these tests we have found out the -400 wing wasn't untwisting as much as we had been showing in our modelling," explains Townsend. The result therefore means the performance of the baseline -400 wing is not as good as originally thought, meaning by default that the predicted performance of the -8's supercritical, aft-loaded wing will be better than expected. "The result is worth about a half a point of lift/drag ratio, which is a significant improvement at this stage and will allow us to meet the range requirements."
Townsend says this is still aimed at 14,800km (8,000nm), which is slightly less than the desired range of some longer-range operators such as Emirates, which have pressed Boeing to sacrifice size for range. However, she indicates that further range can be gained from the 5.6m (18.3ft) stretched version. "We still have a lot of items to work through, including weight reduction," she says. A fuller idea of the predicted weight will be available by mid-2007 when design loads data will be compiled. "At this point if we look at the aircraft from a top down starting point, its weight is heavier than traditionally it would have been...which structurally gives us some opportunities to get weight out."
Source: Flight International
