29 open car windshield stay open?

[Al]

When I attempt to "open" my windshield at anything over say 20 mph the wind quickly closes the windshield. I've resorted to using something to hold the window open at speed. So after doing that for years, I'll finally ask.....is this typical of a '29 open car or perhaps I'm missing something that will allow me to hold the windshield open?

I've tightened the wing nuts as much as possible but to no benefit.

Thanks
Al