While the Boeing sales team strives to sign a launch customer for the passenger version of the  747-8, design engineers are busy working towards a firm configuration of both passenger and freight models in October.

“These are quite exciting times, and we’re right on track for hitting that firm configuration target,” says 747-8 chief engineer of product development Roy Eggink. The focus is perfecting the aerodynamic lines, loadings and laws of the designs in a series of four major windtunnel test campaigns running in parallel at Boeing sites in the USA and at Qinetiq in the UK.

Retaining the familiar baseline appearance of today’s 747, albeit with a stretched fuselage for both the passenger and freight versions, the two -8s are 90% common, but have a “significantly enhanced” 68.5m (244ft)-span supercritical-section wing, new engines, systems and landing gear and an upgraded flightdeck. With an overall length of 74.3m, the -8 Intercontinental is a 3.5m stretch over the current -400, while the 76.3m-long -8F will be a 5.6m stretch. The freighter is to enter service first in around September 2009, while the passenger model is targeted for February 2010.

New features likely to be adopted as a result of windtunnel tests include a partial fly-by-wire flight-control system directing electrically signalled spoilers for manoeuvre load alleviation, as well as drooped ailerons for approach and landing. “Drooped ailerons are still in the mix,” says Eggink, who says the proposed flaperon mooted early on has been dropped. “We‘re sticking with two ailerons, one inboard and one outboard.”

Work at the Boeing Transonic Wind Tunnel (BTWT) in Seattle is tasked with testing the final high-speed design, and is scheduled to run until mid-March. “Then we’ll perform high Reynolds number tests at NASA  Ames in May, and will be there throughout the second quarter of 2006,” says Eggink. After this, the model will return for more tests in the BTWT in the run-up to the final configuration freeze.

Tests at the UK’s Qinetiq tunnel in Farnborough are aimed at evaluating the noise characteristics of the -8 in low-speed runs. “A key design criteria for the -8 is community noise and we need to understand the baseline with the new flap configuration,” says Eggink. The -8 design replaces the 1960s-era triple-slotted inboard and outboard trailing-edge flap design of the 747 with a 777-style double-slotted inboard and single-slotted outboard flap arrangement.

The Qinetiq work takes a break in mid-February when the model returns to Seattle for tests at the low-speed acoustic facility at Boeing Field. The US-based tests are aimed at “fine tuning” the precise noise characteristics of the fully integrated airframe before wider-scale tests resume in the UK later in the second quarter.

Initial noise results are so encouraging, says Eggink, that “QC1 on approach for the passenger version still looks do-able, and we’re definitely on target for QC2 approach and landing. We think we could also get the -8F to QC1, and that’s looking pretty good,“ he adds. The challenge with getting the -8F to meet London Heathrow’s stringent “QC” noise quota rules is the aircraft‘s 40,860kg (90,000lb) heavier weight on approach. “That drives up the thrust, so to get QC1 for the freighter would be a good thing.”

Nozzle tests related to the General Electric GEnx-2B67 engine are also under way at Boeing Field. These are aimed at defining the new nacelle, which will incorporate chevron noise-reduction features on the trailing edge of both the primary and secondary exhaust/bypass nozzles. The first cycle of testing on the nacelle is due to wrap up in February, with continuous tests set for the remainder of the development period, which sees firm configuration set for the engine around June and first engine to test in the third quarter of 2007.

Tests at the low-speed acoustic site, which will also include the model recently in the UK, are set to continue through the year examining every feature that could lead to possible noise reductions. In addition to the large features, such as the new wing,  engines and simpler flaps, Eggink says the tests will evaluate noise-related effects of undercarriage alignment, fairings and structures. “The devil is definitely in the details,” he adds


Source: Flight International