You can do a keyword search but the front page gets you started off right for browsing with pointers to all kinds of categories including trucks, planes, science fiction, ships, tanks, and even humans. I chose the “WWI Airplanes” category. That got me a list of subcategories breaking the planes down by country (the countries with the most planes were England, France, and Germany.) Choosing “WWI USA” brought a list of 14 airplanes, with details including dimensions of the blueprints, what viewers are available (front, top, rear, side) the size, and the date it was added. There was also an icon for source, which for some blueprints was a company and some was a person. Click on the model number for the actual blueprint.
If you’re not registered/logged in, your view of the blueprints will be limited to a 500 x 500 size. Actually I found there were many blueprints I couldn’t see, limited or not, when I wasn’t registered. Once you register (it’s free) you’ll be able to see the blueprints in the original size — and many of the ones I looked at were very large, 4009×5288 for example.
In addition to the blueprints, the site also has vector drawings, but these a) seem to be limited to cars and b) cost money to download (you buy credits, and then you download using the credits.)
Plenty to see and the blueprints would make excellent starting points for kids who like to draw cars, Star Wars vehicles, tanks, etc. I don’t think that’s the target audience but it’s the first thing I thought of when I saw the Sopwith blueprints.