REFLECTOR: FUEL FEED & Vents

[Scott Baker]

Hello Keith,

Regarding your question:
>..." I have never been able to identify a situation in which the sump
> vent would do anything good for you (once the sump tank is filled the 
> first
> time).  Anyone got a scenario to the contrary?"

I have wondered about a low fuel, prolonged descent with the nose pitched 
down situation where the mains could become "unported".  If this were to 
happen, and if the sump tank were not vented, then air from the displaced 
fuel would be trapped inside the sump tank.  A vented sump tank could easily 
purge itself and refill with fuel when the aircraft reassumed a level flight 
attitude.

The likelihood of unporting the fuel supply is not as rare as we might 
think.  My older model C210 for instance, was placarded to warn the pilot to 
land with at least one-quarter (1/4) tank of fuel to avoid fuel starvation. 
Cessna designers installed two small "saddle tanks" under the floor of the 
C210A the following model year.

You pose a good question.  It's good to get a lot of clear thinking heads to 
help brainstorm ideas like this before deciding upon a design change - 
especially to something as important as the fuel system.  I donno.  One 
thing I've learned about aviation is - whatever the imagined unlikely 
event - it's probably going to happen!  Spins in a Grumman with the wrong 
fuel tank selected = flameout.  Point my 1960 C210 downhill with low fuel = 
flameout.  Many twins call for the selection of the "mains" for takeoff and 
landing to avoid the possibility of fuel starvation.

Just thinking out loud.
SB