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Flight loads survey is often compared to a roller coaster ride because of the extreme up and down maneuvers that result in moments of weightlessness inside the cabin. The Boeing 747-8 Freighter recently completed its flight loads survey testing, which is designed to validate the airframe's structural capability.

Boeing 747-8F goes on roller coaster flight (Video)

If you want to ride a roller coaster for five hours with few breaks in between, then conducting flight loads survey testing is the job for you.



During flight loads survey, Boeing test pilots will pull the nose of the airplane way up before pitching it down to put additional force or stress on the airframe. The image above is from an animation created with actual flight data from the 747-8 Freighter's flight loads survey.

"You really get to go on a roller coaster ride because we go up in the air, come down, and pull up again," explains Boeing engineer Arlene Saiz.

Saiz was part of the team that completed flight loads survey testing of the new Boeing 747-8 Freighter. The flights, designed to validate the airplane's structural capability, created moments of weightlessness as the airplane went from zero gravity to more than two and a half times gravity in a matter of seconds.

"It's a challenge to keep yourselves strapped in, your computer, your notes, and make sure you're watching the right things, while keeping your lunch down," explains flight test engineer Jeff Kaiser.

"It is as much as you want to push an airplane." Captain Craig Bomben, Boeing test pilot

It may sound like fun but it is grueling work for the people onboard and the airplane itself. Boeing test pilots performed extreme aerial maneuvers such as repeatedly pitching the airplane down and then pulling up, conditions that imposed tremendous force on the fuselage, the wing and other flight control surfaces.



Flight loads survey maneuvers put tremendous stress on the wing. Above, the image on the left shows Boeing 747-8 Freighter's wing during normal flight operation. The image on the right, taken during an extreme flight loads survey maneuver just seconds before, shows how much the wing is bent upwards.

"It is as much as you want to push an airplane," says Captain Craig Bomben, one of the Boeing test pilots who flew the 747-8 during flight loads surveys. "I mean some of the test points are up to two and a half Gs. In service, that's very close to the over-stress limit of the airplane."

Going over two times the force of gravity greatly increased the load on the 747-8 Freighter, which flew many of the flights at its maximum takeoff weight of nearly one million pounds.

"What we're trying to do is take it to the outer corners of the design envelope and demonstrate that the airframe can withstand the flight maneuvers at the gross weights we designed it to," says Andy Hammer, the 747-8 Flight Test manager who is overseeing an exhaustive certification program for the new cargo airplane.

"A lot of time you don't have time to think about what's going on in terms of motion, you just have to concentrate on what you're looking at." Richard Figueroa, Boeing Flight Test engineer

The 747-8 Freighter is 5.6 m (18.3 ft) longer than its predecessor, the 747-400, and has a maximum structural payload capability of 140 metric tonnes (154 tons). The airplane will have nearly equivalent trip costs and 16 percent lower ton-mile costs than the 747-400, plus 16 percent more revenue cargo volume.



Some of the extreme flight loads survey maneuvers result in a temporary condition of zero gravity inside the airplane. The orange object in the upper right corner of the image is a jacket that was left untied to show the effect of weightlessness.

In the cabin, even before the airplane takes off, the flight test engineers and structural analysts prepared by taping or tying down their carry-on items, from their lunch to their laptop.

"If you don't tie things down, it will literally go straight up to the ceiling," says Kaiser. "It can come down and hit you on the head."

During the aerial acrobatics, the team tried their best to stay in their seat while monitoring the airplane's performance.

"A lot of time you don't have time to think about what's going on in terms of motion, you just have to concentrate on what you're looking at," explains flight test engineer Richard Figueroa.

The team member say the effort is well worth it because it ensures the 747-8 Freighter will be able to handle forces far beyond what it will experience once in service.

"The airplane handled great," says Capt. Bomben. "Easy to fly, well behaved and just did a great job."