the mcdonnell douglas yc-15 had four engines, while the boeing version had two. the yc-15 used large double-slotted flaps that extended over 75 percent of the wingspan to enhance stol capabilities. to save costs, it used a modified dc-8 nosewheel unit and the dc-10 cockpit, adapted for a two-person crew, with two lower windows for visibility during short-field landings.