If a private pilot owns 3 planes can he use 1 logbook for all 3 or does he need to use 3 logbooks? Would the answer change if he also owns a helicopter?
Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
For pilot logbooks, the requirements of "what" needs to be logged to meet training time and aeronautical experience is specified in FAR 61.51. As long as you record all of the information required by FAR 61.51 (e.g., date, total time, day/night etc.) "where" you place the information is up to you. A single conventional logbook works fine, or you can use a spreadsheet, digital device, or any type of similar recording method you choose. Separate logbooks for each airplane is not required.
Keep in mind that you must present your logbook (in what ever form that you use to record your flight time) for inspection (upon a reasonable request from persons specified in FAR 61.51 (i)) and, if you are a student pilot on a solo cross country flight, you must carry your logbook with you (proof that you have the required instructor endorsements, etc.).
So, it's a good idea to record your flight time in a method that is easy for you to access. For this, a conventional logbook works well.
Assuming that you are talking about the pilot logbook and not maintenance logs, he can use one logbook for all three aircraft. There is a column for aircraft type and registration number, so clearly the intent is to allow a pilot to document time flown in more than one specific aircraft.
If you are asking about airframe/engine/prop records, you should keep separate logs but strictly speaking you may not have to. It would be foolish to combine the records since in the event of a sale of one of the aircraft the records must be passed a long, a complex task if they are all lines in the same log book.
The FAA governs log keeping for aircraft under §91.417 Maintenance records. which tells us what we need to log but does not really tell us how we need to log it in depth. They cover acceptable methods for logging in AC 43-9C - Maintenance Records which interestingly states
Section 91.417(a)(1). Requires a record of maintenance for each aircraft (including the airframe) and each engine, propeller, rotor, and appliance of an aircraft. This does not require separate or individual records for each of these items. It does require the information specified in § 91.417(a)(1) through 91.417(a)(2)(vi) to be kept for each item as appropriate. As a practical matter, many owners and operators find it advantageous to keep separate or individual records since it facilitates transfer of the record with the item when ownership changes. Section 91.417(a)(1) has no counterpart in § 43.9 or § 43.11.
this chunk largely applies to keeping separate airframe/prop/engine log books (which most owners do) but technically does not prevent nor explicitly rule out keeping multiple aircraft records in one book.