But can we get much bigger?

Collapsar is a stock+DLC+KJR spaceplane SSTO that, in fact, comes in three variants. Each of them is about 230 meters long, consists of ~1.4k parts and weights about 9600 tons if fully loaded.
243 R.A.P.I.E.R. engines, 4 Mammoth engines and 4 Goliath engines consume about 20.5 tons of fuel each second on takeoff. Total atmospheric thrust peaks at about 130 000 kN.
Two of three versions are capable of delivering at least 2000 tons of payload to orbit. However, craft's fuel tanks need to be partially empty for most optimal takeoff from the KSC runway: payload capability increases if the tanks are full, but you need to take off from one of Kerbin's polar caps for it to fly in this case.

From what I could find, this is the largest and heaviestlifting stock SSTO spaceplane that anyone has ever published in the KSP community. Its only contender is A Reasonably Sized Spaceplane by Bradley Whistance, which does not use any airbreathing engines and does not carry any payload except fuel despite being two times heavier than Collapsar.

It was very painful to make this video and I apologize for several visual bugs that can be seen in it.

MUSIC:
Call of the North by Niklas Johansson

LINKS:
A nice little screenshot gallery: https://imgur.com/a/4LbBc0g
Full 2195t run video:    • Collapsar SSTO: full 2195,5 tons to o...  
Reddit:   / skyaboveend  


CRAFT DOWNLOAD:
Basic version (KJR strictly recommended): https://kerbalx.com/vanlaukaus/Gclas...
Collapsar HV (KJR practically required): https://kerbalx.com/vanlaukaus/Gclas...
Collapsar LR (KJR practically required): Soon™
.
.
.
.
.
.
.
.
.
.
.
.
.
‪@MattLowne‬ ‪@Stratzenblitz75‬ ‪@vaos3712‬ please see this