I never saw my dad's erect, but did see it many times flaccid. .. He wasn't at all bashful about openly peeing, getting dressed, undressed, or walking from his shower through the house naked openly. ... From all the observations...his, my older brother's, and mine all look practically identical in looks and dimensions flaccid. By this, I always presumed that the three of us all had identical erections, too.
I know I've seen Dad when he's had an erection, but it was buried inside my mother at those times I caught him, so I couldn't see it.

I always thought it would be cool for him to be more free, and feel comfortable enough to expose his erection. Would really like to know for sure what it looked like.
My sons and I, have been a little more open about this topic. We know each other's sizes... And have even exchanged text pictures... And discussed sexual topics.
I think openness between Fathers and Sons about such things is a good thing and awesome.