I bought some parts at the R&D center but they do not appear available at the Spaceplane hangar :
http://s15.postimg.org/baixp1b0b/tech.png
So I expected to see the Whiplash engine somewhere: http://s24.postimg.org/gzw3gtl5x/000.png
Am I assuming something wrong? Do I miss a pre-requirement somewhere to use those parts?
Thanks!