It is difficult to find information on people after the 1930 census. Maybe someone related to him will see your message. I found a couple of things about him.
Social Security Death Index Name: Robert H. McDonald SSN: 308-20-0208 Last Residence: 39572Pearlington, Hancock, Mississippi, United States of America Born: 16 Nov 1921 Died: 10 Oct 1998 State (Year) SSN issued: Indiana (Before 1951 )
U.S. World War II Army Enlistment Records, 1938-1946 Name: Robert H McDonald Birth Year: 1921 Race: White, citizen (White) Nativity State or Country: Indiana State: Indiana County or City: Floyd
Enlistment Date: 14 Sep 1942 Enlistment State: Kentucky Enlistment City: Louisville Branch: Branch Immaterial - Warrant Officers, USA Branch Code: Branch Immaterial - Warrant Officers, USA Grade: Private Grade Code: Private Term of Enlistment: Enlistment for the duration of the War or other emergency, plus six months, subject to the discretion of the President or otherwise according to law Component: Selectees (Enlisted Men) Source: Civil Life
Education: 3 years of high school Civil Occupation: Automobile Serviceman Marital Status: Single, without dependents Height: 67 Weight: 116 You might write or call this cemetery and see what information they have. Or you might write for his military information. U.S. Veterans Gravesites, ca.1775-2006 Name: Robert H McDonald Service Info.: CPL US ARMY AIR CORPS WORLD WAR II Birth Date: 16 Nov 1921 Death Date: 10 Oct 1998 Cemetery: McDonald Chapel Cemetery Cemetery Address: English, IN 47118