Pinpointing Consumption "Sweet Spot" Makes Formation Flight More Fuel Efficient

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. This patented software technology offers a solution. How It Works NASA's 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. Why It Is Better The system uses readily available aircraft measures to quickly and more accurately estimate the optimal location for drag reduction. Even relatively small reductions in drag can add up to significant fuel conservation and cost savings.