sentences:  Prior to her arrival at the AVA, Prandtl had been unsuccessfully working on solving a differential equation for his lifting-line theory for the spanwise lift distribution of an airplane wing.Lotz was able to overcome his difficulties and solve the equation, and additionally developed a relatively simple method for practical use.She published what is now known as the "Lotz method" in 1931 for calculating the lift on a three-dimensional wing, and it became a standard technique used internationally.