Complex sentence: Pilcher set his sights upon powered flight: he developed a triplane that was to be powered by a 4 hp (3 kW) engine; however, construction of the triplane put him heavily into debt, and Pilcher needed sponsorship to complete his work.
Split into simpler sentences: Pilcher set his sights upon powered flight: he developed a triplane, which was to be powered by a 4 hp (3 kW) engine. However construction of the triplane put him heavily into debt, and Pilcher needed sponsorship to complete his work.