Formation flying — when one aircraft flies behind another — reduces drag and results in improved fuel consumption in the trailing vehicle; however, no sensor currently exists that directly measures drag. Instead, pilots rely on fuel flow measurements or induced aircraft moments — roll, pitch, and yaw — to estimate the best location within a leading vehicle's wave vortex. Fuel flow alone is a lagging drag estimate, which leads to inaccurate estimates. Aircraft moments alone also do not sufficiently indicate the best location for the trailing aircraft.
NASA researchers have conceptualized a way to more accurately estimate the best location for a trailing aircraft in a formation in order to optimize fuel efficiency. The wake vortex of a leading aircraft creates an updraft that minimizes drag on a trailing aircraft, resulting in reduced fuel consumption. This method estimates the location for optimal fuel savings. Operators can save 5 to 10 percent in fuel costs per hour through optimal aircraft placement. Given that a loaded aircraft uses thousands of gallons of fuel per hour, even minor improvements in fuel efficiency can add up to significant savings.
This patented drag performance function software combines fuel flow measurements (“slow” but direct measures of performance) and aircraft moments (“fast” but indirect measures of performance) to guide an aircraft in formation flight to a relative position that reduces drag. The technique uses a predetermined assortment of weighted measurements and feeds them into a peak-seeking control system. As new fuel flow measurements are available, the control system updates the optimal weightings.
The system uses readily available aircraft measures to quickly and more accurately estimate the optimal location for drag reduction.