Complex sentence: The Seabee was the brainchild of Percival "Spence" Spencer, a former Republic P-47 test pilot who had convinced the Republic board of the need for a light sport plane to meet a demand for private aircraft from pilots returning from WWII.
Split into simpler sentences: The Seabee was the brainchild of Percival "Spence" Spencer, a former Republic P-47 test pilot. He convinced the Republic board of the need for a light sport plane to meet a demand for private aircraft from pilots returning from WWII.