Why a surfaced U-boat usually loses to aircraft

Did U-boats ever successfully damage or destroy Allied aircraft with anti-aircraft guns?

Yes, but it was rare; a submarine caught fighting on the surface was usually already in a very dangerous position.

Flak U-boats and other boats sometimes scored hits on attacking aircraft. A surfaced submarine was nevertheless in a dangerous position. Pressure-hull damage that prevented diving amounted to a mission kill, leaving the boat exposed to further attacks. A serviceable submarine would normally crash-dive, while a boat forced to fight on the surface was often already damaged or unable to submerge.