Hey! you really inspired me with this idea . I've been doing a plane only mode for the last week now and its awesome, really nice challenge and a good bit of ropeplay story for my kerbals. I became a little stuck at the same point, trying to unlock the nodes for turbojet. i ended up only taking the science and aero routes so my kerbals had a great idea... To help design a plane that works in space we needed to study planes in zero-gravity! So Jeb and Bill ran around KSC collecting all the things they would need to build tiny planes and asteroids and then we designed and built a zero-G plane, complete with a play roo...i mean a zero-g serious tiny plane testing bay. After diving from 14000m to get zero-g while 'analysing' how the timy planes behaved they were able to get a lot of data. 3 zero-g test flights later and after about a year and a half of analysis I just managed to get to my first SSTO plane and now trying to build to launch a satellite payload to get science from the mun and minimus SOI. (sure i know strapping the MPL to a plane and diving about isn't neccessarily useful, but it made sense for my game and meant i had a viable reason to spend a year an a half warp for the science wall) let me know how its going for you! really interested to see how you're tackling it!