How many fuel vents (Tank Air Outlet) are there in DA40NG airplanes? I wonder how many there are under each wing surface. I know that the hole on the round cover we see in the first photo is "Fuel Vent". But is it true that the part covered with a triangle in the second photo is also "Fuel Vent"? In this case, are there 2 fuel vents under one wing and 4 fuel vents in total?
You are correct. The DA-40NG fuel system has four (4) vents. The main tank contains two (2) vents and the auxiliary tank has two (2) vents as well. These vent hoses terminate on the underside of the wing approx 2 m (7 ft) from the tip. See the DA-40 NG AFM, pp 7-32.
As to your question about the location of the outer fuel vent opening, yes, the vents are on the aft side of that triangular fairing. They are pointed out in the preflight walk-around below at 12:00 and 20:05.