yeah fixed wing. KC-135R to be exact(CFM 56 engines). I've actually used some "IEMs" by a company called AirBuds that worked somewhat well in the jet, however I haven't found any fullsize headphones that would do a decent job of protecting my hearing from the outside engine noise
Well at least it's not a C-130!
Given the low frequency vibes coming at you, I would probably suggest looking into an active noise cancelling headphone. Pure acoustic damping is never going to get you past the "somewhat" phase.