It depends a little bit on what you're considering rc and how you define "largest." Are we going by scale, wingspan, or gross weight? Do you count an aircraft that flies autonomously? How about one that is flown via a wired remote?
Back in WWII the US had Operations Anvil and Aprhodite. The following is taken from the wikipedia page.
"The plan called for B-17E/Fs that had been taken out of operational service (various nicknames existed such as "robot", "baby", "drone" or "weary Willy"
[3]) to be loaded to capacity with
explosives, and flown by radio control into bomb-resistant fortifications such as German
U-boat pens and
V-weapon sites." "The drone was loaded with explosives weighing more than twice that of a B-17's normal bomb payload."
The B-17 had a max takeoff weight of 65,500 pounds and a wingspan of 103 feet 9 inches.
There is also the Bally Bomber, a 1/3 scale B-17 which is not rc, but was built from a set of plans for a 1/9 scale rc B-17. I'm including it here only for the novelty of the thing.
http://theballybomber.com/