The lift varies since the aircraft flies fast through regions where the air has different velocity.<p>Think about a column of ascending air, and the plane flying quickly through that. All else being equal, the plane will accelerate vertically until it is traveling vertically at the same speed as the air column (if the column is large enough).<p>That&#x27;s why flying low and fast is extremely bumpy and taxing for aircraft. Lots of air speed variations.