Am I being taken advantage of by working on a committee member's research with no payoff?
Yes, you should discuss the issue of authorship. From this description, we can't tell you whether or not you are being taken advantage of. In general, whether authorship is appropriate depends on the intellectual content of your contribution. 

To discuss the issue, start by saying "I'd like to discuss the issue of authorship on this project." If you'd like to be direct, you could then say, "I have committed a lot of time to this project. I am under the impression that my work is substantial enough that I might qualify as an author on papers arising out of this project. Under what circumstances would you consider including me as an author?" 

If you'd like to be less direct, you could instead ask several questions about your committee members' philosophy on authorship. "What sort of contributions do you believe qualify for authorship on a project like the one we are working on together?" 

If you don't like the answer (the person refuses to make you an author), then you need to set some boundaries in a professional manner. "I'd like to continue to contribute to this project. However, since there is not a possibility of authorship here, I am sure that you understand I need to prioritize my other work. Going forward, I can commit to X. If you need more help than this, I think we should revisit ways I could be compensated or qualify as an author."