Rules/limitations/gotchas on the re-sale of a homebuilt?

I still don’t see why you would need a company to deal with a homebuild. If you can’t do it yourself, you need someone qualified to supervise/ inspect and sign off on it (and potentially perform flight testing). That should be it.

That is certainly a possibility. There are no guarantees. Question is, where is the problem.

Both in the UK and the US the aircraft must be genuinely amateur built to qualify for airworthiness approval and the 51% rule is interpreted as 51% of the types of manufacturing tasks that the builder performs. For the RVs you have to build the empennage kit from parts but can use the quick-build wings and fuselages as you have done sufficient of the drilling/dimpling/deburring/rivetting in the empennage to meet the requirements.

The owner-maintenance rules in the UK aren’t largely different to those for certified aircraft, there is a slightly expanded list of items that the owner can sign off themselves, but most require an authorised inspector to sign them out. But it’s more the culture amongst permit owners to do their own maintenance work.

In the US, an owner-builder can do almost anything in the way of maintenance and repairs and sign off their own annual. A non-builder owner can do the same except they need an A&P to sign off the annual. Major mods that change handling or performance still require FSDO approval and often a period of phase 1 restricted testing – I had to have that for a propeller change recently.

Selling isn’t considered a particular liability issue unless you were negligent say in concealing a significant defect. The assurance of airworthiness is essentially the responsibility of the new owner/operator. The annual sign off states that the aircraft was found to be in a condition for safe operation and deliberately avoids reference to ‘airworthiness’.

LAA aircraft generally aren’t ‘experimental’ in the American sense. They’re built strictly to plans and random deviation – e.g. the placing of the fuel selector in John Denver’s LongEZ – isn’t allowed. Relatively few types are approved, and getting approval isn’t a walk in the park, by all accounts. I understand the LAA have corrected design faults prior to approval, which have gone on to cause accidents in other countries.

It’s a mixed blessing – not as fun for tinkerers – but despite my mixed impression of LAA inspectors I’d be slightly more confident about buying a British homebuilt than an American one.

That is an interesting bit.

It means the previous owner can continue to sign off your aircraft, presumably for a fee, but he has you somewhat over a barrel unless you have a route to becoming a new “builder” without him being able to block you doing that.

What is involved in becoming a new “builder” typically? It seems a practical requirement otherwise certain maintenance cannot be done anymore without using a company.

That is not very clear. Certain things are obvious like total restoration, replace wings or other major parts, and engine. But there is no need for a company getting involved, this is not EASA regime.

You are talking about a turbine here. Would you really fiddle much with that piece of machinery with no (semi)formal education/courses from the factory or without any experience? You would also need lots of special tool and test instruments. Unless you have access to the things you need, you are probably better off letting someone else do it for you in any case. Turbine is no problem though. There are several experimental turbine helicopters flying in Norway, but no TP as I am aware of.

Are there any homebuilts which are not American designs and which are worth having for e.g. good performance (rather than just low cost)?

I can immediately think of this one, but there must be several more.
Depending on how one values one’s own labour, homebuilts are NOT low-cost. At the least, such projects tend to take several years to complete, which means a lot of interest on dead capital.

[[edit: the Mignet Pou du Ciel and its derivatives are certainly low-cost, but they are not exactly high-performance. Must be a lot of fun, though.]]

Well, the Falco is a home built of Italian design, although an American bought the rights and sold the design as plans.
The LAA website has a full list of approved types. If you buy one of those second hand in the states and import it you will need to have it inspected by an LAA inspector before it will get a permit to fly. There are some differences in approach though so you have to do your research. For example, the home builder in the states can specify his own MTOW, but in the UK the design carries the limit, not the builder.
If you want to import a type not already on the approved list then you will have an awful lot of work to do to get it put on the list.

Nevertheless, am I right in that when a US Experimental type is imported into the UK, or built from plans in the UK, it goes onto the LAA system?

The LAA have a concession to approve permit issue within limits, nominally 4 seats and 250HP IIRC and can occasionally go beyond that.

Homebuilts outside of those limits are in a similar position to Warbirds etc in that they are surveyed by the CAA.

If you want to import something that hasn’t been previously surveyed and accepted by the LAA it can be quite a protracted exercise and they are resource limited in the amount of that type of work they can process. If the LAA has issued a ‘Type acceptance data sheet (TADS)’ for the type previously, it should just be a matter of showing compliance in a similar way to importing a certified type according to its TCDS.

If you can otherwise show compliance with a design code such as Part 23, then the process should be somewhat easier, but few amateur built designs will have demonstrated that compliance.

The Yanks don’t have quite a monopoly on good performing and efficient kits, but do hold most of the cards probably as a result of their more liberal system and size of their GA population. Falco, Europa, Pioneer, Dyn-Aero etc have all made their marks.

I’d be slightly more confident about buying a British homebuilt than an American one.

What I mean is… an aircraft built under LAA supervision to an approved plan; not necessarily a British one.

I’m sure the bulk of new designs are American but that’s inevitable given that’s where the airports and pilots are. I think it probably is a fair comment that there are fewer new British homebuilt designs than there seem to be French ones, and given that both countries are fairly similar in size and both relatively aviation-minded, one wonders whether the LAA approach stifles innovation.