The initial CAD design for the Mark IV

The welding process

This was our first flight attempt.  If you read the 'History - long' you know it didn't go well.

The aftermath of flight test #2 - batteries were thrown everywhere and the mounting system proved to be inadequate

Damage from flight test #2 - the propeller tips were sheared off

Flight test #2 caused significant damage to several propellers.  You can see just how much propeller is missing in this photo.

Further damage from the initial tests.  It gives you an appreciation for the forces you're dealing with.

When we moved our flight testing to grass we soon learned that it really digs in and we needed bigger feet

Our first successful and stable flight!

Soon the Mark 4.5 was complete!

By summer we had upgraded the Mark IV to the Mark 4.5 by adding more propellers to improve both thrust and (surprisingly) efficiency
 

This was the payload bay where we could easily attach (aka duct tape) weights to the frame to see how it flies with different loads