You don't "NEED" an instructor but it is the best way.
Basically what you you WILL need is either an instructor or a large trash bag. In most likelyhood you will crash and destroy your plane if you try to fy on your own. You may be one of the fortunate few who gets by w/o an instructor but the odds are way against you. As a full scale pilot with @2000 hrs I can tell you that other than aerodynamic theory there is little that transfers to RC.
Please use an instructor and enjoy this hobby.