Yes, in theory, you could pay the angel back upon note maturity (which would probably be principal + interest).

However, most angels may not be too happy if that was your plan all along. They're putting money in on the hopes that your success will somehow multiply their money. If you're just planning to pay them back their interest, they might as well have put that same money into a bank.

Again, it really depends on your angel -- my strong advice to you is to be forthcoming about your goals. It's better to have everyone on the same page up front... especially if you plan on having a long term relationship.