There are significant differences between these two words, and savvy writers should know them.
The word historic refers to something that is historically significant. A building might be historic (Monticello). An event might be historic (signing of the Declaration of Independence). But any research about the two is historical research.
So historical means “of or relating to or occurring in history.”
Note: When you use the indefinite article before historic or historical (or history or historian), you should choose a, not an. When you accent the first syllable of a word beginning with h, use a. If the accent falls on a later syllable, use an. Thus:
A historical event (accent on his). An habitual offender (accent on bit).