REFLECTOR: FUEL FEED & Vents

[Jim Sower]

<><... prolonged descent with the nose pitched down ... mains could 
become "unported" ... If if the sump tank were not vented, then air ... 
would be trapped inside the sump tank. A vented sump tank could easily 
purge itself and refill with fuel when the aircraft resumed a level 
flight attitude. ...>

True enough.  It hasn't happened to me, and I regularly land with 5 - 10 
gal in the strakes.  What I envision in the scenario above if it 
happened to me is:
I start a prolonged descent and unport the strakes.  Eventually my Low 
Fuel light comes on (I'm a half gallon into the sump fuel).  I level off 
and kick the rudder toward the heaviest wing.  The fuel in the tank with 
most fuel piles up against the fuselage side and the fuel in the "light" 
wing piles up against the outboard bulkhead of the strake and unports 
the sump on that side.  Fuel flows into the sump and fills it up.
OR, I just let it go since I'm a few minutes from my destination, I have 
a half hour of fuel in the sump, and when I level off the strakes will 
again feed the sump and maintain it at whatever level it was when I 
leveled off.

I then uncap the vent and let the sump refill when I'm on the ground.

If I've NEVER has assymmetric transfer, I might vent the sump.  
Otherwise I wouldn't ... Jim S.


KeithHallsten wrote:

>Scott,
>
>That's a pretty good answer to my request for a scenario!  I'll have to
>think on it!
>
>Keith
>
>
>----- Original Message ----- 
>From: "Scott Baker" <sbakr at comcast.net>
>To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
>Sent: Wednesday, February 16, 2005 10:26 PM
>Subject: Re: REFLECTOR: FUEL FEED & Vents
>
>
>  
>
>>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
>>    
>>
>  
>