Does your suitcase have the mesh part? Can your cape fit there?
Other suggestions, don't roll up your cape... put everything you need down first then sit on it, put your cape over that and zip the suitcase up. Sometimes rolling up items doesn't save you space. There is also carrying a duffle bag or a backpack as your carry on or wear your cape thru airport security and drap it over your bag. (Say your using it to keep you warm like a blanket?)
I once fit 5 cosplays, 4 trench coats, 4 pairs of shoes, and a dozen other things in one suitcase before so anything is possible xD.
(Sidenote: Almost didn't make it turn the airport with it though because it was 48.5lbs and weight limit was 50...)
Kawaii Kon 15 cosplays: Klaiver - Ace Attorney, Mink - DMMD
Events: Kawaii Kon 15, Hoku kon 15