h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Do the math.
They designed their own engine,
built a wind tunnel,
reinvented the kite,
and managed to tweak the flyer until it actually flew.
They had to throw out decades of tables and postulates from
people who supposedly were 'experts'.
Never mind the fact that they never quite got it to take off properly or never really caught on to the fact that flaps might be useful...

Two bicycle-building high school drop-outs,
with a little help from their sister.

I think one characteristic of a polymath is the ability to tell the scientific or artistic establishment to take a flying leap.

Benjamin Banneker comes to mind, too.

All of that sounds like engineering to me. I mean, bully for them for being able to do engineering without finishing high school, but that doesn't make them polymaths. Show me their work in biology or litereary criticism or philosophy or music and I'll reverse my position.

Actually, according to the letters I've seen in published form, they were very well read, spoke at least a couple of languages besides English and even had some insights into metallurgy and physics.

Through their mother, they were basically home-schooled.

"If a man is in too big a hurry to give up an error he is liable to give up some truth with it, and in accepting the arguments of the other man he is sure to get some error with it. Honest argument is merely a process of mutually picking the beams and motes out of each other's eyes so both can see clearly. Men become wise just as they become rich, more by what they save than by what they receive. After I get hold of a truth I hate to lose it again, and I like to sift all the truth out before I give up an error."

Wilbur Wright to George A. Spratt
April 27, 1903

And without stretching the point too far, I'd say Wilbur had a handle on Philosophy, too.