What Does a Plane Go Through Before It Can Fly?
Anyone who's sat in a window seat and watched an airplane's wing shake through turbulence like a leaf on a tree has surely wondered: Just what does a new airplane have to go through before it can be certified safe to carry passengers?
All airline industry eyes have been on Boeing as of late, as the Chicago-based aircraft manufacturer tests its new airplane design, the 787 Dreamliner -- a super-efficient aircraft made from composite materials that Boeing says will bring big-jet ranges to mid-size airplanes. (The plane will carry 210 to 250 passengers on trips up to 8,200 nautical miles.)
But long before that airplane will be shipped off to the clients who have already placed their orders, among them United Airlines and Royal Jordanian, there's an incredibly long list of tests to be done.
According to an FAA statement, the federal agency "sets the standards for the certification and continued safety of all aviation products. For an airplane, the agency outlines the requirements the manufacturers have to meet for the structure, materials, and all components in the airplane. The manufacturer must demonstrate through testing or with data that the product meets the government's standards."
On top of what the government requires, manufacturers add their own testing to new-design airplanes like the Dreamliner, according to Todd Sigler, Assistant Vice President of Civil Aviation for the Aerospace Industries Association, which represents the nation's leading manufacturers of commercial, military and other aircraft. "The individual manufacturers have gone above and beyond those [FAA] rules and in many cases, that's based simply on their experience or knowledge of how the airplane will be used," says Sigler. "The FAA's requirements aren't a low standard by any means, but they're set to have applicability to a broad number of products."
And today's airplanes, says Sigler, get wrung out from "nose to tail and wing tip to wing tip" during testing to ensure they can encounter all types of situations during service and remain undamaged.
"They [airplanes] have to be able to show their tolerance to levels of in-flight icing encounters, cold weather testing, hot weather testing," he says. "The things they test for certainly aren't way out in left field, like this will never happen, but they [manufacturers] take it to another level of severity."
Frank Santoni, chief pilot of commercial planes for Boeing Test & Evaluation -- which evaluates all of the company's products -- is one such individual testing the limits of his manufacturer's planes, including the new 787 Dreamliner.
For Santoni and his staff of around 50 test pilots, takeoffs that lead to the plane's tail striking the runway, stalling mid-air and flying through icy conditions without the de-icers switched on is all in a day's work. On any given day, Santoni and his team of about 50 test pilots at Boeing might find themselves in the cockpit of a 747, 777 or the Dreamliner performing maneuvers the rest of us would deem insane.
"As a passenger, it's a pretty benign environment [aboard a commercial flight]," says Santoni. "You fly from point A to B, staying within a normal flight envelope.
"We have to test out beyond that, where the airplane may experience that once or twice in a lifetime event," he says. "We have to make sure it's okay out there."
And the process of testing, says Santoni, is a highly choreographed dance. "We have in the order of thousands of test conditions that we do to certify airplanes," he says, adding that the test program is usually talked about in terms of how many hours the newly designed plane has flown during tests.
To date, the five 787 Dreamliner airplanes currently in the testing phase have flown over 1,300 flight hours. And while there is no standard amount of test hours for new planes, according to experts, past aircrafts have averaged anywhere between . 1,800 and 3,300 hours before getting certified.
Santoni takes us through some of the most interesting and exciting tests a new plane endures before it meets manufacturer standards and gets FAA certification:
One of the first ways a newly designed plane is put to test in-flight comes via flutter testing. To understand the concept of flutter and how it affects a plane's structure, says Santoni, imagine an opera singer singing at a very high pitch with the ability to shatter crystal. When an airplane surface vibrates very rapidly [like the crystal glass] it can lead to damages, and flutter has been named as a cause in a number of past airplane accidents. "Most of the times [when flutter is seen], this is an at altitude cruising event," says Santoni. "If you have a loose surface, like a door, it could start vibrating and actually damage that surface.
"We have to be sure that airplanes don't have that tendency, because that's not a good thing to happen," says Santoni, who added that test
"When flutter happens, [the test pilot] can definitely feel it," says Santoni. "But we have instrumentation on the airplane that hopefully detects it before." The 787 Dreamliner passed its flutter testing with flying colors. "There was nothing predicted and there was nothing there," said Santoni.
Any passenger who's ever taken off in an airplane and wondered how the tail manages to avoid skidding on the ground as the plane's nose lifts can rest assured -- there's a flight test to address that concern. Minimum unstick speed testing, one of the most interesting in-flight tests, is a way to show "what the minimum speed is that an airplane can take off at," says Santoni. It's also one of the most exciting assignments a test pilot can get, he says, since planes only get to do it once in their lifetimes.
"What we want to find out is that minimum speed to get enough wind over the wing so that the airplane will actually get into the air," says Santoni, explaining that a woodblock tail skid is put on the back of the airplane where it touches the surface of the runway. "When you get close to the speed, you actually pull the nose up and the pilot can feel the tail touch the surface and it vibrates the airplane some, you can actually feel it, and you wait for the airplane to take off."
Once the minimum speed for takeoff has been determined, it is put into the airplane's manual so that pilots will know to take off at higher speeds to avoid the tail striking the runway. And while the idea might sound terrifying to most of us, test pilots "look forward to doing it because it's so unusual," says Santoni. "We practice in simulators before we go; it's a very regimented build up."
Airplanes rotate service throughout their lifetimes and can end up anywhere in the world. To prepare for any possible weather conditions, new designs are tested in extreme heat and extreme cold on the ground and in-flight to ensure avionics continue to function and the plane operates as expected.
The 787 Dreamliner has already undergone cold weather testing and is currently being tested in extreme heat conditions in the southern parts of the US, says Santoni. "We're taking it to very extreme examples of heat down at Edwards Air Force Base or in Arizona and other places where we'll test all the components out in extremely hot weather," says Santoni. "There are lots of places where you have delicate equipment and you want to be sure the cooling is adequate in that area. That's probably the most critical part --component cooling and making sure we don't cook some critical instrument some place on the airplane."
Along with extreme heat (temperatures can get up to 120 degrees), the new designs are tested in extreme cold conditions, too, during flight test in places like Fairbanks and Anchorage, AK. "We'll fly in de-icing, we'll take the airplane and deliberately put it into an icing environment where we'll ice up the wings and the engines and be sure that it can fly in that kind of weather," says Santoni, adding that the Seattle area is one of the best places to test for icing.
"We try to put it in as many critical environments as we can, so we know it will be good anywhere, because the airplane could wind up anywhere," he says.
Imagine an airliner fully loaded with passengers, cargo and enough fuel to get it across the Pacific. It's screaming down the runway for takeoff -- when suddenly it's forced to stop. The test to ensure the airplane's brakes can handle sudden braking at high speeds when loaded with maximum weight is called maximum brake energy testing, and Santoni counts it among the most exciting tests to perform as a pilot.
"We load the airplane up to its heaviest weight with fuel and weights that we put in the cargo bay -- up to its maximum weight," he explains. "And you get to a point at the end of the runway, at full power -- a very high speed that you calculate is the maximum speed the brakes can take -- then the pilot applies full brakes and holds them until the airplane stops." Speeds during this test normally reach about 200 miles per hour before the brakes are applied. "By the time the airplane stops, the brakes are glowing red," says Santoni, "There's thousands of degrees of heat in the brakes, and you get to see that it works."
This test on the amount of load the airplane's frame can support without breaking is one of the more interesting, ground-based tests that new designs endure. When the Dreamliner was recently put to the test which all newly designed planes undergo, the goal was to demonstrate that the airplane's all-composite wings could support 150 percent -- or one a half times -- the maximum load they would ever be expected to encounter during an entire lifetime of flying.
During the test, an infrastructure framed around the plane holds it in place and provides a counterbalance system; the fuselage is pressurized to 150 percent its normal operating pressure. Next, hydraulic actuators incrementally apply a series of loads, bending the wing upwards while simultaneously pulling down on the fuselage to counteract the upbending of the wing.
Watching the process is like watching an enormous machine perform some kind of mechanical yoga. After 120 percent of the test load is reached, the data is assessed before pushing the airplane to 150 percent to ensure it meets the design objective. When the 787 Dreamliner passed this crucial test in early April, applause broke out in the control room.
It's vital for aircraft manufacturers to know the speeds at which an airplane will stall so that pilots flying the aircraft in commercial service will never get there, says Santoni. Stall speed testing is another in-flight test the 787 Dreamliner and other new aircraft undergo. For a newly designed airplane, hundreds of stall tests are carried out at different speeds and with different weights to make sure the airplane characteristics are good, says Santoni.
"You actually slow the airplane down in flight, so slow that the wing stops flying and that's called a stall -- where you don't have enough air on the wing to produce lift and then the airplane will cease flying," he explains.
If you do this with the wing "clean," [with the flaps up and in cruise position], says Santoni, "you get a lot of natural buffet on the wings so the airplane shakes pretty dramatically -- and that lets the pilot know yeah, you're stalling and shouldn't be there."
Sounds exciting, doesn't it? These tests and many more are part of a day's work for the pilots who work hard to ensure that their airplanes are as safe as possible before the first passenger boards.
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