I know of a couple of folks in the model airplane world that had very big companies (Lockheed and Cessna) come after them for "copyright" issues. In one case, the company (two guys, cottage industry) was convinced to sign a licensing agreement (paying thousands of dollars IIRC) with no reciprocity, and discontinued their models of Lockheed WW2 airplanes as a result. Now, these were balsa sheet profile RC model kits, not exactly "exact" scale planes. Another guy got hassled by Cessna for a model of the C-140.
Was this legal? Maybe. Was it morally right? Absolutely, positively not. Did it harm the individuals who only wanted to honor these historical aircraft with a product that required people to perform a large amount of skilled assembly (ie, wasn't an "off-the-shelf replica")? Yes. Did these companies severely damage their reputation in the eyes of everyone who heard about it? Very much so. Did it have any effect whatsoever on them as a result, and did their management care one bit about this? Not at all.
There's a guy (goes by "Uncle") selling pirated model airplane plans on eBay for designs which are largely NOT "orphaned". I once looked at his feedback and prices and calculated that the guy made $20,000 per year, selling his clearly pirated plans. He's such a scumbag that according to him, he even "improves" the plans... meaning, he just edits out the copyright notices and puts his own "I own this, copy it and I'll sue you" message in it's place!
Sad fact is, that even if most folks understand the work it takes to produce something as complex as an aircraft design, there's a bunch of folks out there in Internet-land who think nothing of buying a cheap pirated copy of it, and when it doesn't go well because they have incomplete info, they will still blame the designer for their problems. A designer cannot sue everyone who tries to abuse their intellectual property (well, I guess the major aircraft companies can...) I used to work for a homebuilt aircraft company, one with a much less strict tech-support policy than some (any owner of our aircraft was welcome to call and ask questions), and yet, another company decided to enter into direct competition with us on fuselage kits. I suppose that had questions about licensing or design rights come up, they apparently counted on being protected by the expense of the legal process. Nearly all builders still chose to come directly to us for the components they were offering, and when they asked us about the other company, we just said (completely truthfully) "That company has got nothing to do with us, we know nothing about them, and they didn't ask us about it. So if you have problems with their products, we won't be able to help you sort it out, you'll have to deal with them on it." The sad part is that had they approached us and asked about collaborating, we very well might have been very interested in working out a deal with them to have them make the same product, have our official support, and cross-market (this was in a tiny, specialist niche within homebuilding, so those kinds of things are a big deal). As it was, they basically just slammed the door shut on all that, and I even heard rumors (never had confirmation that I knew of) that their product was based on an old set of plans that had been changed somewhat for all current builders. I no longer work at the company but I strongly suspect that the copycats might never make their investment back since the word seemed to get out that it wasn't an "approved" product and several builders told us they felt the whole thing seemed to them to have been done in a somewhat "subversive" manner of sorts. Was the product OK? Very possibly. If it worked as well as they claimed, it could have even been a "great" product. But the fact we didn't know that, and had no knowledge of the company beyond seeing them start advertising our own products for sale, well, many in our customer/fan base didn't seem to see their methods as a positive sign as far as I could tell. It was less of a legal issue than a moral and practical one, really.
I'm not a lawyer or anything but I think that counting entirely on the law to settle these questions is just plain crazy. So is counting on people to do the right thing... in both cases, the craziness comes from expecting either aspect to produce absolute results, which it seems that many folks nowadays do in fact expect. You must understand that at best, MOST folks will recognize the hard work it takes to produce something worthwhile... and unless you're completely unreasonable in your conditions, these folks will probably be fairly supportive of your efforts. Sadly, there will always be a few jerks who will inevitably take advantage of your work for quick personal gain at your expense... and there will always be a few less scrupulous (or downright cheap) people who will buy into them as well. How to best handle it is a very personal decision and I dunno that there's ever going to be a single good answer to it. Common answers range from "sue everyone who speaks the airplane's name without paying a licensing fee" to "make it free or nearly so, and there's no point in someone else re-selling it" to "just stay uninsured and keep the company tiny so there is no incentive for the survivors to sue", and everything in between. In the end, though, the only absolute is that ONLY the lawyers ever really come out ahead financially in such disputes if they get to the point of legal action... and they always win something... regardless of which side they're on!