Then, you'll have other, different questions the next time. Perhaps you will call your Uncle Ed and ask if you can talk with him for an hour about family history. Tell him that you have some questions, but tell him you'd also like to hear anything he'd like to share. Older people tire more quickly than younger ones. Watch for signs of this and offer to come back another time.
Tape recorders are great, but they make some people very self-conscious.
Be sure you have permission to tape an interview. If there's any reluctance, back off. The presence of an unwanted tape recorder may backfire in your face and you won't get anywhere near the amount of information you might have without one. Camcorders are similar to audio tape recorders, but they tend to make the subject extremely nervous. They are very distracting.