FLUG REVUE December 2003: Boeing 777-300ER in flight test

777-300ER FLIGHT TESTS ADVANCE

By Sebastian Steinke

A picturesque, fiery red sunrise in the treeless prairie around Glasgow, Montana. Across the gently curving fields one has an unhindered view to the horizon in every direction. No houses, no cars, no people. From miles away one can see the white, floodlit tail fin of the parked 777-300ER, known internally as WD502, registration code N5016R, across the extensive apron, as it is being prepared for flight testing at Glasgow Industrial Airport in the middle of September.

Boeing 777-300ER

Having once been a B-52 bomber base in the 1960s and since then abandoned for many years, this remote airfield was awoken from its Cinderella-like sleep by Boeing, turned into a purely private test airport in the north of the USA and is currently being used as an important stage on the certification journey of the latest Boeing model, the 777-300ER. Today's flight programme features “community noise testing”, i.e. official measurements of the noise emitted by the two GE-90-115B turbofans, the most powerful civil engines in the world.

In the solitude of Montana, one can complete these precision noise measurements much more quickly than normal, without any outside interference. For this reason, the facilities have been hired not just for new Boeing models from the C-17 through to the 747-400ER, but Embraer and Bombardier are also carrying out flight tests and taxiing trials here on their new regional jets. Over a dozen engineers, mechanics and factory fire service personnel are being flown in from Seattle for the measurement programmes.

“Our overflight goal is the microphone field in the extended approach centre line, shortly before the touchdown zone,” explains flight test director Jeffrey Scott, who himself will be sitting in the cockpit between the two pilots and co-ordinating the work of up to 14 colleagues at computer terminals in the cabin, in an interview FLUG REVUE. “For example, I tell the pilots from downwind that we are still 15,000 feet away, and after a short countdown we turn onto the final approach. This will entail taking up a precisely specified flight attitude, speed and rate of descent. Recording will begin after a ground signal. Later on we will check whether we have kept precisely to all the requirements.”

With different combinations of predefined flap settings and engine output. or what are known as powerlines, the aircraft will then fly precision circuits for an hour or so. Even though the undercarriage is extended, the aircraft will hardly touch down, as the pure takeoff runway noise tests on the ground have already been completed. As the flight continues, the fuel payload goes down and the same powerlines are repeated with the now lighter aircraft. Only after the lunchbreak does the twin-jet come in to land, when the wind starts to gust.

“We need absolutely calm air and, if possible, no low-lying clouds, as these actually alter the sound propagation,” explains flight test director Scott. For this reason, the meteorologists in Glasgow play an important role in the proceedings. Shortly before the 777-300ER takes off for the test flight, a single-engined Boeing sensor aircraft takes off, and then spirals its way to altitude over the measurement field, measures the temperature and dewpoint at various altitudes and transmits this data to a ground station on the measurement field.

There, not far from the three “master microphones”, Chris Hunting is sitting in his laboratory container packed full of computers, the “Mobile Acoustics Center”, whose radio callsign appropriately is “Big Mac”. As “flyover noise engineer”, the noise expert is treated with great respect by the entire test team, since at the end of the day his measurements will determine whether an aircraft has complied with the ever more stringent noise limits that today can decide the fate of a model.

The officially prescribed noise measurements using the master microphones and all kinds of additional equipment for filtering out noise caused by windshear and low-level wind are virtually mandatory for the noise experts, but that is not all: a second microphone field nearby at the end of the runway, comprising no fewer than 156 recording positions arranged in a grid, also registers every individual noise source on an aircraft flying overhead. The computers then work all night long crunching their way through the mountain of figures, until the next day they spew out a kind of detailed noise footprint of the aircraft, which may contain some real surprises. Chris Hunting: “For example, on one occasion we found out at this point that the rectangular openings for anti-icing air on an aircraft were causing unnecessary noise due to air vortices. After we rounded off the openings, the noise was eliminated. I regard this test airfield with its ideal conditions and especially on account of the microphone grid as among our crown jewels,” he says.

Naturally the test series is also attended by representatives of the aviation authorities. The American FAA has even sent its own test pilot along, who is allowed to control the measurement flights from the left-hand seat alongside Boeing's responsible 777 test pilot, Suzanna Darcy-Hennemann. The European JAA has also sent two representatives.

“In our experience, there are surprises on around half of the measurements taken of aircraft noise emissions,” explains JAA representatives Willem Franken from the Netherlands. “Every individual part that has air circulating around it can generate unwanted noise, not just the engines. And just because the thrust is declining, that doesn't mean that the overall profile is necessarily quieter. But on the 777-300ER we are not expecting any surprises, as the aircraft is already pretty familiar. Nevertheless, it's always a good idea to attend the start of a test series oneself so that one can understand the data better. But we don't have to fly along, we prefer to sit below in the flight test centre, where all the threads come together.

Besides, on the approach we are measuring what is probably the loudest configuration,” Franken continues. “That means flaps, leading edge slats and landing lights extended, landing gear lowered, and an unfavourable trim condition.” On the other hand, the regulations regarding departures are less stringent, he explains. Here the test pilots are allowed to venture a spectacular “parade departure”, with extreme initial angle of attack and ensuing cutback, such as are unlikely to be experienced later on in real operation. “But what is normality?” asks the Dutchman philosophically.

“So I don't pay much attention to the apparently more lenient regulations on departure,” says test pilot Suzanna Darcy-Hennemann with a smile. “The state regulations may be more lax, but my engineer colleagues from the company make up for it with extra requests. In any case, the tests are going well for us,” the test pilot from California is relieved to report, and then she gives her impressions of the general flying characteristics of the aircraft. With medium takeoff weight, the 777-300ER is virtually no different from a normal -200 or -300. When it is very heavily laden, on the other hand, it is more like a 747-400, and in direct mode without computer support it resembles a 767.

Following the successful conclusion of the measurements in Montana, the two 777-300ER test aircraft WD501 (24 flights) and WD502 (16 flights) will have to fly several times over the Pacific to get their ETOPS certification for extended flights over water. Amongst other things, this will entail deliberately flying eight segments 330 minutes long with only one engine, so as to simulate a diversion landing. The longest flight that WD502 is scheduled to make, from Sydney to Recife, will last 19 hours.

At the beginning of October, after 893 test hours in the air and 925 on the ground, 777 programme manager Lars Andersen was proud to report that the 777-300ER consumes one percent less kerosene, needs less runway to take off and can therefore carry a good tonne more payload than was expected. Boeing is cutting back the scope of the tests from 1,600 to 1,500 flying hours and from 1,000 to 925 hours on the ground. After the type certification, which it is hoped to achieve in December, and certification of the cabin interior in the first quarter of 2004, launch customer ILFC will take delivery of the first 777-300ER in April for Air France. After removing the test equipment and extensive component replacement, WD502, “our” test aircraft from Montana, will then be the second aircraft to be delivered to a customer.

From page 6 of FLUG REVUE 12/2003

Last updated 10 November 2003

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