The Virtual Aircraft Museum and All the World's Rotorcraft — hosted together at aviastar.org — are attractive references for people writing articles about aircraft for Wikipedia, especially when it comes to lesser-known machines. These references are often among the top hits in search engine results, and their entries are written in a confident, clear, and authoritative style.
Unfortunately, these are not suitable references for Wikipedia articles, as the text of the entries has been copied verbatim from published reference works. For example:
Wikipedia's external links policy prohibits us from linking to a site that is so rife with apparent copyright infringements. Not only could such links make Wikipedia a party to contributory copyright infringement, but the site's apparent disregard for the intellectual property of the writers and publishers whose work appears there is unethical.
If you find useful information on a page at aviastar, consider using the site's bibliography to locate the original work from which it was taken and use this work instead. If you cannot find the original work or do not have access to it, see if you can cite the same information to a different source.
(Note that the above also covers avia.russian.ee, an alternate name for aviastar.org.)