Hydrogen propulsion using low-temperature proton exchange membrane fuel cells (LT-PEMFC) offers a promising alternative to conventional combustion engines by reducing component complexity, lowering operating temperatures, and potentially decreasing operating costs. This study presents a comprehensive system-level analysis of hydrogen-powered LT-PEMFC propulsion systems for aircraft. Custom-developed models integrate fuel cells with auxiliary subsystems, including thermal management, compression, and power electronics, to size the propulsion system and fuel capacity according to a defined mission profile.