Reducing the Load: The Weight Trimming of Commercial Aircraft

Commercial aerospace is an industry that operates in extreme margins. Though you may feel like you're paying an arm and a leg for your next flight, remember that airlines are paying too; each flight is associated with a variety of costs, from landing fees to personnel. One of the largest costs associated with commercial aviation is fuel. From the beginning of the jet age, fuel costs have been a constant driver for innovation in commercial aircraft as designers and operators sought new ways to cut down on its consumption. The fuel-guzzling turbojets of the 1950-60s that released billows of black smoke during takeoff, have been replaced by the ultra-high-bypass turbofans of today, which provide fuel-efficiency and significantly lower emissions. Aircraft wings have been improved from the bulky straight wing seen on the prop-liners of yesteryear to the sleek, supercritical designs of today, also in the name of fuel efficiency.

While aerodynamics and engine performance are obvious contributors to aircraft fuel efficiency (or lack thereof); one of the most important factors to fuel consumption, for which even small changes can have enormous financial implications, is weight. The most basic principle of flight is that an aircraft is able to overcome its weight, acted on by the force of gravity, to become airborne. In order to do so, power must be applied by the engines. And just like an automobile for which gas consumption surges with weight; increased weight on an aircraft means additional acceleration time and an escalation in the fuel consumption required to takeoff, climb and cruise. All of which equates to higher operating costs for the airline. Slight variations in weight can have enormous financial effects when considering the volume of flights completed by a given airline over the course of a year. So, strap on your sweatbands and let's examine some of the weight-trimming methods employed by aircraft manufacturers and airlines in the quest for peak efficiency.

As noted earlier, engines are critical to aircraft economy. Engines impact the overall weight of an aircraft through both the actual weight of the engine (design and materials) and the engine's fuel efficiency (technology), which affects the fuel load required for a given flight. Civil aircraft engines have come a long way since Charles Taylor worked with Wilber and Orville Wright to develop a gas fueled, 12 horsepower, four-cylinder engine with non-interchangeable parts and a 12 hour TBO to launch the Wright Flyer. From v-type piston engines like the Liberty L-12 (whose firsts include crossing the Atlantic, the U.S., and circling the globe), to radial and rotary piston engines such as the Le Rhone 9C9 that powered WWI fighters, and finally the gas turbine engines that power most modern aircraft today. Improvements in gas turbine engines over the past few decades have been remarkable. Staggering advancements in engine design, materials and technology have led to significant reductions in aircraft weight, while providing OEMs with exciting options for their projects. When selecting the engine for the ARJ21 in 2002, COMAC was focused on fuel efficiency and reduced emissions. Ultimately, GE's CF34-10A was selected to power China's first commercial aircraft. At the time of the engine's release, GE noted: "the CF34-10A represents a considerable increase over the other CF34 engine models, it incorporates the same basic development philosophy and operational features that have earned exceptional market success for the CF34-3 and -8 Series engines: low-risk, proven technology, low operating costs through high reliability, ease of maintenance, excellent fuel economy and outstanding environmental characteristics."

Seven years later, under the joint venture CFM, GE & Safran released their latest single aisle aircraft technology with the LEAP engine. According to Safran, with a bypass ratio of 11:1 the LEAP engine "…offers operators exceptional technical, economic and environmental performance, with a 15% reduction in fuel consumption and CO2 emissions versus current engines, and up to 50% margin on NOx emissions versus CAEP/6, and in compliance with the most stringent noise standards." Furthermore, CFM notes that the 3-D resin transfer molding carbon fiber composites used for the fan blades and fan case help reduce engine weight by 500 lbs per engine. As a result, the LEAP (1-C) was selected to power COMAC's C919 single aisle aircraft, as well as the latest single aisle aircraft from Airbus (1-A) and Boeing (1-B). And, from a purely superficial standpoint, it sure is pretty!

Another way manufacturers are cutting aircraft weight is by exploiting the latest materials. Enter composites. A composite is a material made from two or more different materials, often with greatly varying properties, that when combined are stronger than any one of the individual materials. Manufacturers are using stronger, lighter carbon fiber composites for aircraft wings, fuselage and tails in place of aluminum to cut weight and improve durability. According to Quora, carbon fiber is about 40% lighter and about ten times stronger per unit volume than aluminum. Boeing designed their 787 Dreamliner to be roughly 20% lighter by building an air-frame that is almost half carbon fiber reinforced plastic and other composites. COMAC also plans to reap the benefits of using composite materials to cut weight and increase efficiency in the development of their latest project, the CR929 wide-body aircraft (a joint venture with the UAC). In an exciting step forward for the project, COMAC successfully completed manufacturing tests of full-scale 15 x 6-meter composite fuselage panels!

While the airframe and engine come to mind first when considering ways to cut weight, the aircraft's interior and furnishings have a tremendous impact on the overall load. Everything from the restrooms to the inflight magazine registers on the scales, which means the entirety of the plane's interior is scrutinized for potential reduction. Beginning with the seats, significant weight savings can be found by making seats thinner, more narrow (much to the chagrin of passengers), or by using lighter composite and metal hybrid materials. Southwest Airlines rolled out a new line of seats created by B/E Aerospace for their latest fleet. These new seats are made of a leather fiber composite called eLeather that affords passengers a wider seat, while offering the airline weight savings in the form of lighter materials. Meanwhile, Genghis Khan Airlines opted for the slimmer, lighter weight seats with USB ports for their new ARJ21 fleet to reduce the load and increase fuel efficiency. The slim seats save both space and weight, while the USB ports enable the BYOD (bring your own device) option versus heavy seat-back entertainment systems.

As aircraft manufacturers and airlines seek ways to cut weight and increase customer comfort, the aircraft seating industry is expanding to provide options. Expliseat, a relative newcomer to the industry (established in 2011) is looking to disrupt the world of airplane seats with cutting edge products. The France-based company developed titanium seats weighing in at just 4kg per passenger. The company claims that their seats will save airlines between 3 to 5 percent in fuel consumption through a 50 percent weight reduction when compared to standard seats.

Now that you're settled into a comfy streamlined seat, you may want to turn on the light and read a book, connect to Wi-Fi and use your device, or see what movies are showing on the seat-back monitors. All of these activities require wiring to work, which requires bundling to keep the wires and cables organized, which requires bracketing to keep the bundles secure. And, now we've added a pound or two to the aircraft. Apex, a non-profit trade organization focused on the airline passenger experience notes that wiring is essentially an aircraft's nervous system. "Connecting everything from the fly-by-wire flight control systems to the coffeemaker in the galley requires miles of wires, thousands of connectors and tens of thousands of support brackets". They note that narrow-body airliners have up to 40 miles of wiring, wide-body airliners have up to 150 miles of wiring, and double-decker aircraft can have a staggering 320 miles of cables! That means, if you were to drive from Pittsburgh, PA to Philadelphia, PA in order to watch a great football team, you could stretch the cables for a double-decker airliner along the entire five-hour route and still have cable to spare…sheesh! As a result, manufacturers are developing new techniques and using new materials to lighten the load of aircraft wiring. Apex noted that Airbus was able to realize a 25 percent weight savings on wiring by using Draka Fileca's Star Quad KL24 high-transmission rate data cable for the A350, and Boeing was able to reduce the wiring on the B787 Dreamliner (replacing the B767) by 20 miles. So as technology (and our dependence on it) advances, so too will the means by which we stay connected.

Thus far, we've looked at some of the big items that can be updated to trim weight, but what about the small stuff? These are the things that seem minor, but can have a large cumulative effect over the course of a year. Let's start with the folks in the cockpit. Pilots need technical manuals, charts and other documents on-hand at all times during a flight. As a result, airlines would stock the cockpits with binders containing the requisite documents. This method was not only heavy, but it consumed large amounts of critical space and required that updates be completed by hand. So, to solve the problem of weight, space and time, airlines began furnishing pilots and crew with tablets containing all necessary information. This paper to digital swap results in a weight savings of 40 - 80 pounds (depending on the aircraft & airline) per flight, saves hundreds of thousands of gallons of fuel per year, enables quick on the spot updates to materials, and frees up space in the cockpit. Not a bad return on that investment.

Beyond the cockpit door, airlines have cut weight by switching beverage service from bottles to cans, selecting thinner glassware and meal trays for premium cabins, cutting the number of lemons and limes on board by slicing wedges thinner, decreasing the number of pillows and blankets stocked on board, and reducing the size and/or thickness of the paper used for the inflight magazine. In fact, CBS news reported that United Airlines realized a savings of about $300,000 a year after reducing the paper stock of their in-flight magazine by just one ounce per copy. So on your next flight, take a close look at the little green wedge perched on your beverage, its slimmed down profile makes the aircraft greener and saves the airline money through fuel efficiency, which could in turn make your wallet greener through lower ticket prices. Here's to hoping anyway!