Boeing is in the midst of several months of flights with its ecoDemonstrator 757 in a first-round effort to evaluate new technologies in 2015 that are expected to reduce environmental effects on natural laminar flow as a way to improve aerodynamic efficiency while reducing noise and carbon emissions.
On the ecoDemonstratror 757, the left wing has been modified to test Boeing-proprietary technologies in support of future wing designs, including advances related to natural laminar flow. Specifically, a variable-camber Krueger shield is being tested to see how well it can block insects from accumulating on the wing leading edge.
A Krueger shield is a flap that comes down over the leading edge of the wing to provide added lift for the plane. During the testing, an IR camera attached to the top of the fuselage will monitor the air flow over the wing. Boeing will be flying through different environmental conditions to study the potential effects that the conditions have on the wing flow.
Boeing is also under contract with NASA's Environmentally Responsible Aviation (ERA) Project to test two technologies on the ecoDemonstrator 757. On the right wing, in a series of flight tests near Shreveport, LA, NASA will test bug-phobic coatings to reduce the residue left by bug strikes on the leading edges of aircraft wings; the goal is to enable more drag-reducing laminar flow over the remainder of the wing. Studies have shown that keeping the flow smooth over a wing can reduce fuel consumption as much as 6%.
NASA supplied leading edge panels for the right wing that incorporate nanotechnology surface coatings. The testing will determine whether the coatings are effective in resisting insect contamination that can result in more drag and greater fuel use for future wing design. While the issue of bug residue might seem small, any disruption in the smooth flow of air over the surface of a wing increases drag.
"Increased drag means increased fuel consumption, which results in more pollutants in the atmosphere. The goal of our project is to develop aircraft concepts and technologies to reduce the impact of aviation on the environment over the next 30 years," said Fay Collier, Manager for the NASA Aeronautics Research Mission Directorate's ERA Project.
Engineers at NASA's Langley Research Center developed and tested a number of non-stick coatings in a small wind tunnel and on the wing of a NASA Langley jet. They selected the best candidates to test on the right wing of the ecoDemonstrator.
During 15 planned flights researchers will install sections of coatings onto the leading edge slats of the ecoDemonstrator 757. First they will establish a baseline using uncoated surfaces, to capture insect accumulation rates. Then they will remove those sections and install samples of the five treated panels. One of the things engineers want to test is how durable the coatings are. Treated surfaces will only be effective as drag reducers if they can withstand the harsh flying environment.
"Solutions to reduce fuel use by one or two percent may not sound like much," said Collier. "But shaving aircraft fuel consumption even a few percentage points can save millions of dollars and help protect the environment from harmful emissions."
On the vertical tail, NASA and Boeing are testing active flow control (AFC) to improve airflow over the rudder and maximize its aerodynamic efficiency. The team installed 31 tiny jets called sweeping jet actuators that can manipulate, on demand, the air that flows over the ecoDemonstrator 757's vertical tail and rudder surfaces. An aircraft’s vertical tail is primarily used to add stability and directional control during takeoff and landing, especially in the event of an engine failure. But when the aircraft is cruising at altitude the same large, a heavy tail is not necessary.
Ground studies by a team of NASA, Boeing, University of Arizona, and Caltech researchers on a full-scale 757 vertical tail in a wind tunnel at NASA's Ames Research Center showed the AFC jets could increase side force by 20 to 30%. Researchers expect the flight tests to confirm those results. A 20% increase in side force could allow designers to scale-down the vertical tail by about 17% and reduce fuel usage by as much as 0.5%.
Engineers theorized they could reduce the size of the vertical tail by using the sweeping jets to generate the same side force during takeoff and landing that a larger tail does. That would reduce the weight and drag of the airplane and decrease its fuel consumption.
"Our researchers have been working hard to develop technologies to reduce airplane fuel consumption, noise, and emissions. Being able to prove those concepts in flight tests gives them a better shot of getting into the commercial fleet," said Collier.
Instruments onboard the ecoDemonstrator 757 flight test airplane will measure the performance of the AFC enhanced vertical tail in nine flights. During those tests, the plane will fly various maneuvers to evaluate the increase in vertical tail and rudder side force caused by the jets. The maneuvers will include simulated engine failures and variations in jet arrangements and flow rates.
ecoDemonstrator program engineers are reviewing some options for additional tests. This particular set of tests will go well into June, possibly July, and Boeing will announce any additional tests with the ecoDemonstrator 757, which was leased for testing purposes, before then. After the flights are complete, Boeing will work with the Aircraft Fleet Recycling Association and the lessor, Stifel's aircraft finance division, to recycle the 757 using environmental best practices.
Since it was launched in 2011, the ecoDemonstrator Program has tested more than 40 technologies with a Next-Generation 737 and a 787 Dreamliner. The program strives to test technologies over a spectrum from near- to long-term application. All the technologies are at different stages of readiness.
Several technologies tested on the ecoDemonstrator 737 in 2012 have moved to the next phase of development or have been adjusted based on the testing. That program tested 15 technologies including aspects of the Advanced Technology Winglet that is expected to improve fuel efficiency by 1.8% on the new 737 MAX.
Technologies tested on the 787 are still being evaluated for future use. That program included the first flight tests using green diesel in a 15% blend with conventional petroleum jet fuel. The tests will be used to support industry efforts to approve the use of green diesel in commercial aviation.
With the exception of Boeing proprietary technology, NASA knowledge gained in collaboration with Boeing from ecoDemonstrator research will be publicly available to benefit industry.