The real distinction is equity, not size
People assume the difference is headcount. It is not. The difference is whether members own the aircraft.
In a partnership, each partner owns a defined share of the asset. They benefit if it appreciates, they lose if it is destroyed uninsured, and they can sell their share.
In a flying club, the club owns the aircraft. Members buy the right to use it, usually through a joining fee and monthly dues. When they leave, they may get some or all of a refundable deposit back, but they are not selling an asset.
A six-person group where everyone owns a sixth is a partnership. A twelve-person group where the entity owns the aeroplane is a club. The number is incidental.
What each is good at
Partnerships suit small groups who want control and are comfortable with commitment. Decisions are fast because there are few people. Costs are predictable. Everyone has capital at risk, which — usefully — makes everyone careful. The downside is illiquidity: your money is in the aeroplane until someone buys your share.
Clubs suit larger groups, mixed commitment levels and turnover. Joining and leaving are easy, which means a member whose circumstances change can go without anyone having to find a buyer. Costs per member are lower because they are spread wider. The downside is governance: you now have officers, elections, a constitution, meetings, and the specific problem that nobody personally owns the aeroplane, so nobody personally worries about it.
The scheduling maths
The practical constraint on any shared aircraft is availability, and it degrades faster than people expect.
A single aircraft flown 400 hours a year is in use maybe 8% of available daylight hours, which sounds like plenty. But demand is not uniform: everyone wants Saturday morning in good weather. Two partners rarely conflict. Four partners conflict occasionally. Eight members on one aeroplane conflict constantly, and the aircraft has to be booked well in advance, which removes much of the spontaneity people bought in for.
Rough guidance from groups that work: two to four partners per aircraft for a partnership where people expect to fly on a whim; up to eight to ten members per aircraft in a club where booking ahead is the norm. Beyond that you need a second aeroplane, and a second aeroplane is what turns a club into an organisation.
Administrative weight
A partnership can be run on an agreement, a bank account and a monthly statement. That is genuinely the whole of it.
A club needs a legal entity, usually non-profit or an LLC; a constitution and bylaws; elected officers with defined terms; membership records; a joining and leaving process; insurance that contemplates many pilots of varying experience; a checkout and currency policy; and meetings that people have to be persuaded to attend.
None of this is hard. All of it is work, and it falls on volunteers. The most common cause of club failure is not money — it is the treasurer or secretary burning out and nobody willing to replace them.
Insurance differs more than you expect
Insuring four named pilots you know is straightforward and relatively cheap. Insuring an open membership of varying experience is a different product, usually with an open-pilot warranty specifying minimum hours, time in type and currency requirements — and premiums that rise sharply if you want low-time members covered.
Get a quote before deciding the structure. For some groups the insurance difference alone settles the question.
Which are you actually building?
Ask what happens when a member leaves.
If the answer is "we find someone to buy their share, and the price depends on what the aeroplane is worth," you are building a partnership, and you need share valuation and right-of-first-refusal clauses.
If the answer is "they stop paying dues, get their deposit back, and we advertise for a new member," you are building a club, and you need governance and a membership process.
Groups get into trouble by being ambiguous — collecting money like a club but implying ownership like a partnership. That ambiguity is fine for years and then becomes a serious dispute the first time a long-standing member leaves and expects a share of the aircraft's value.
The billing is the same problem either way
Whichever you form, the monthly job is identical: turn meter readings into member invoices, credit fuel that members bought, move money into the reserve, split fixed costs, chase what is outstanding, and show everyone where the engine fund stands. Clubs just have more members to do it for.