The main part of this site has nearly 250 pages. There are a number of ways to navigate the site, you can use the buttons down the side, the text hyperlinks at the bottom of the screen or there is a site navigation page that acts like a contents page for a book. There is also a set of links just under the banner that enable a user to back out of the page to the level above. Sometimes a set of related pages are linked togeter with a forward/backward/up set of arrows.
I would hope this is enough linking to find what you want on the main site. Some of the linking is missing on other parts of the site, particularly the Library. Although the layout is relatively simple, someone may choose to use an aerofoil designed for another part of the plane or modify one for another use. Human Powered Flying, http://www.humanpoweredflying.propdesigner.co.uk/ is mostly hyperlinked although it has a contents page.
Although there is no index, Google and Yahoo! (Other seach engines are available) effectively supply an index as this is a way many users find the site.
As always if you have any comments please let me know.