Cessna 172 question

[tataki]

Do you guys know why, if any reason, the fuel vent in the Cessna 172 is cut a certain way (facing the front of the airplane.
I was also told the Seminole that fuel vents are cut one way and the drains another way, and i think there are reasons for it.
Help would be appreciated.
Thank you

 

[FL420]

Do you guys know why, if any reason, the fuel vent in the Cessna 172 is cut a certain way (facing the front of the airplane.
I was also told the Seminole that fuel vents are cut one way and the drains another way, and i think there are reasons for it.
Help would be appreciated.
Thank you

Fuel vents are an opening into a fuel line leading to a tank. If they are cut at a 90° angle or a 45° angle facing to the rear of the direction of flight, air flowing past the end of the tube creates a low pressure area at the opening which can siphon fuel out of the tank.

A fuel vent consisting of just tubing should be cut at a 45° angle facing forward so as to create high pressure at the opening to force air into the tank to replace fuel being used. A plugged tube that doesn't allow any air to pass can create ever lowering pressure approaching a vacuum inside the tank as fuel is used, causing an interruption to fuel flow to the engine.

I don't know that it is critical that fuel drains designed to be used only on the ground be cut at an angle or facing a particular direction. If the drain is leaking it will siphon out faster if cut at an angle which is facing to the rear.

In the old days when fighters had relief tubes, disgruntled mechanics would sometimes spin the angled drain tube around facing forward for positive back pressure instead of to the rear for negative pressure. You really wanted to preflight that for a long mission or a weak bladder.

 

[tataki]

thank you for the answer