Is this a kit or a flying airplane? regardless, you will need to register the aircraft in your name with the FAA and State where it is hangared/kept and pay the applicable sales or use tax when you register for that state. typically within 30 days and Budget 5-7%. Some states audit these sales too. I received a letter from California to validate a sale I made to a fella there three years prior, asking to confirm the sale price to validate their sales tax collected. Thankfully in this case it all checked out, I could see what the buyer had indicated for a sale price.