Common Gallinule (Moorhen) comes to mind - it has some white in the wing, more like a white border on a black wing than vice versa, but could maybe give an impression of more extensive white in fast flight? Though they don't fly often so might be unlikely on four separate occasions?
Another possibility might be American Oystercatcher? Though a quick look at Wikipedia suggests it's more restricted to coastal areas than its European counterpart... and I would have thought you'd have noticed the big, bright red bill! Or a last long-shot possibility, maybe a male Ring-necked Duck?!?