The U.S. Air Force has discovered that vertically mounted wiper blades on the KC-135 Stratotanker reduce aircraft drag by about 1% during cruise conditions, potentially saving the service $7 million annually in fuel costs.First, I find this intensely amusing, and second, why did it take until 75 years into the jet age to discover this?
The wiper blades on the Boeing KC-135 traditionally are positioned horizontally on the windshield as part of the original 1950s-era design. As aviation aerodynamics research later indicated, placing wipers vertically when not in use could improve aerodynamic efficiency.
The team used a KC-135 from Rickenbacker Air National Guard Base in Ohio for comprehensive airframe ground testing. A computational fluid dynamics model revealed a reduction in drag of 0.8% for repositioning the blade vertically and 0.2% for a slimmer wiper design. After collecting sufficient data, the team is ready to begin airworthiness testing and certify the updated design with the FAA.
23 April 2020
I would not have thought that a minor change to KC-135 wiper blades can improve fuel efficiency by over 1%: