Clayton was in serious condition and King was in fair condition Friday in the burn unit at Wishard Memorial Hospital in Indianapolis, according to a hospital spokesman.
Clayton had built the two-seat Glastar GS-1 plane from a kit sold by Glasair Aviation of Arlington, Wash.
Friend Tom Vickers told WISH-TV in Indianapolis the two men spoke about the plane several times and that Clayton had planned Thursday's flight to test whether repairs had fixed some mechanical problems.
"Jerry was going to fly it before he put it up for sale," Vickers said.
Vickers said Clayton had problems with the plane in 2011 and had to find an Federal Aviation Administration-certified mechanic to repair it. He said Clayton wanted to get the test flight in before his certification expired at the end of the month.
"Gerald was very meticulous toward the plane and the procedures, and with everything he did," Vickers said.
FAA investigators have interviewed at least 10 witnesses but had not spoken with Clayton or King as of Friday morning, Columbus Police Lt. Matt Myers told The Republic.
The crash occurred about a mile from the Columbus airport and near Clayton's home, which is a third of a mile from the site.
Larry Ruble, who lives across from the scene, praised Clayton for limiting the damage. Only one house had significant damage.
"I think it's awesome that Gerald somehow only hit the corner of that house, because if you look at this neighborhood he could have plowed into several people," Ruble said.