Hey T.B.! That is a great question and I have an equally great answer.
In the '60s & '70s I built microfilm indoor planes. They were 1/64" sq balsa frames covered with a homemade microfilm concoction made in the tub over a metal clothes hangar frame. If you were very lucky, 1 out of every 3 tries succeeded. Then 1 out of 3 tries to get the film on the wings from the frame succeeded. Then you had to make a form fitting box to carry it to the place where you were flying it and hope that you didn't shake the box too hard on the way. Finally, you had to hope that they remembered to close ALL the windows in the armory or 1 tiny draft would make the plane crumble into a mess.
To top it off, I walked 2 blocks to the bus stop, took the bus for 1-1/2 miles, took the market street elevated for 4-1/2 miles and finally the broad street subway for a couple of miles. Some fun huh?
I learned about them from a guy I met while flying U-control planes and R/Cplanes. He competed in the Nationals quite a few times in all types of model plane flying. I learned a lot from him.
Jim
Stay Safe.