That is a really cool picture of your grandpa.
I have a few, very few, of my grandfather in Germany in the 1920s.
Riding around in very cold looking open-topped buses. I'm sure he was
glad to escape the horrible economic climate of post-WWI Europe.
I'm going to say the bike is European. Looks like 28" tires, and a
rod brake on the front wheel. What a cool brake! Friction type lever
on the outside of the tire! Awesome...
I'm thinking that picture may have more info to give. Try scanning the
area of just the bicycle at something high, like 400+ DPI. Blow that up
and lets see if any more detail comes out. You never know, sometimes
those B/W shots have very fine detail in them.
Anyway, other stuff to see there, 3-pc crank, skiptooth sprocket that
appears to have those 3-sided cutouts like a Phantom pattern. Most
likely Schwinn's designers were emulating classic designs like this one.
I cant see enough of the rear hub to be sure, but it looks like I see a coaster
brake strap on the chain stay.
The rims, if it's this old, must be wood, or steel clad wood at least.
There appears to be a peaked rear fender on it, but no front. Shame we can't
see if there's a rear rack.
And what does that light burn? It looks like it must be a gas light! That would
be right for the era.
Great picture, thanks for sharing!
--Rob