Those windows are so old that it's likely lighter than you'd think.
I used a hinge from the bottom of the window to the 2x3. Hinges so it swings down and lays flat on the exterior when the window is closed.
Actually didn't consider it swinging up as I was trying to figure a way to have...
So I played with this today, good free solution for this 8 ft long window panel in gusty winds today. I hinged a scrap piece of 2x3 onto the window bottom. Then cut a "U" out of a piece of 2x4. Then broke one arm of the U off installing it lol. Predrill needed!
Drilled holes, used a spare bolt...
That will work for some of my windows that are under my eaves. I think so anyway, I'll need a few feet of chain to reach but that's ok. Love your color scheme by the way!
I'm concerned about wind tearing mine off as well. I've seen my patio table lift up, flip, and drop back down here. So they'll need support both ways. I keep thinking I can just make something.
Same boat. I'll have about 6 of these to figure out, plus some vents. There are things called window stays.
https://www.srshardware.com/product/storm-window-stays/
But in quantity not real affordable.