I would not risk it. Most airlines want to see a visa or residence card. This is not only Ryanair but also Brussels Airlines. So maybe no immigration officers but the airlines can cause you trouble. If I were you, I postpone the trip. This applies for air travel. Bus travel is worse: on a bus trip in Germany we were stopped two times for passport checks. This was with a flying brigade, so not at the border itself. They also did this in France (although there it was more for drugs).