Boeing’s Gift to Chapped Fliers explains one of the more unusual benefits of the upcoming 7E7′s composite fuselage:
Airline executives and engineers have been lauding the 7E7 for state-of-the-art materials engineering: The fuselage will be made mostly from fiber-reinforced resin composites. Those materials, and the use of large component sections, will allow Boeing to complete each 7E7′s final assembly in as little as three days, compared with the 13 to 25 days it typically takes for current Boeing planes, according to program manager Mike Bair. And the jetliner will sip fuel, helping lower costs for beleaguered airlines.But passengers likely will place one benefit above all others: increased humidity. The 7E7 could end the stuffy noses, irritated eyes and scratchy throats that now make long flights an endurance test for passengers.
Cabin air in all current jetliners is very dry — from 5 percent to 15 percent relative humidity, depending on where one sits, how long the flight lasts and how full the cabin is, said Boeing cabin environment expert Dave Space.
Outside air at 35,000 feet averages 68 degrees below zero, Space said — far too cold to hold moisture, so relative humidity runs less than 1 percent. When that air is drawn into the cabin, it is heated by air conditioning packs in the plane’s belly to become breathable. But cabin humidity remains low, humidified mostly by evaporation from food and beverage service and from passengers’ exhalation. In first class, where there are fewer bodies, cabin humidity is 5 percent to 10 percent; in a crowded coach section, it’s 10 percent to 15 percent. (By comparison, humidity in a relatively dry climate, like Southern California’s, is about 30 percent.)
Cabin air is kept dry because moisture condenses on the inside of the fuselage skin, corroding the metal structure. The corrosion is a maintenance nightmare for airlines, and could shorten an airplane’s useful life. The 7E7′s composite fuselage will be practically immune to that corrosion, so Boeing can make the cabin much more humid.
It’s too bad we have to wait until 2008.