REFLECTOR: FUEL FEED [heur]

[Chuck Jensen]

Jim,

In response to your post, I would like to note that fuel vapors won't asphyxiate you but they will give you gas.  My wings also heat up as I go transonic but I'm burning fuel so fast that the pressurization from the heated wings can't expand the fuel as fast as I'm sucking it, so no fuel is pushed out of the sump, even though I'm venting, as I often do.

In all seriousness, this uneven feed thing is an old thread, but still seems to have legs because of the observed conditions.  I had the uneven feed problem but putting fuel grease on the caps and shimming out the rudder to get the ball centered knocked the differential down to a couple gallons--tolerable.

It just seems so intuitive that with sealed caps, level wings and the top of both tanks vented to a common point, that its nigh impossible for any level discrepancy between the two tanks to exist, yet.....

Chuck

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-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of Jim Sower
Sent: Wednesday, February 16, 2005 12:17 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: FUEL FEED [heur]


<... there is the potential of fuel vapors coming through the vent ...>
Someplace I thought I heard that fuel vapors (not to be confused with 
raw fuel) would asphyxiate you long before there was a combustible 
mixture.  With raw fuel OTOH there would be a combustible mixture at the 
surface of the puddle.  That said, an overpressure in the sump (from 
heating the wings or some other very unusual condition) can push fuel 
out of the sump vent if it is open. 
Again, NEVER vent the sump tank in flight ... Jim S.

Scott Derrick wrote:

> Yeah, I thought about the ice free environment thing after thinking 
> about it.
>
> But the potential for igniting the fuel system scares the crap out of 
> me.  Even without being upside down, there is the potential of fuel 
> vapors coming through the vent!
>
> Scott
>
> Alex Balic wrote:
>
>> Not that I condone that design change in any way, because I agree 
>> that it is
>> a bad idea- especially if the aircraft ends up on it's back from some
>> accident (fuel pouring into the hot engine compartment and all) but I 
>> could
>> see where some might think that it was a good idea to place the vent 
>> in a
>> high pressure area where it would not be exposed to ice or water 
>> ingestion.
>>
>> -----Original Message-----
>> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
>> Behalf Of Scott Derrick
>> Sent: Wednesday, February 16, 2005 10:14 AM
>> To: Velocity Aircraft Owners and Builders list
>> Subject: Re: REFLECTOR: FUEL FEED [heur]
>>
>>
>>
>> I think it is extremly dangerous to vent the fuel system into the engine
>> compartment!
>>
>> Why would anybody do that???
>>
>> Scott
>>
>> Ron Brown wrote:
>>
>>  
>>
>>> Tom,
>>>
>>> I don't think it is a good idea to vent the fuel system into the
>>> engine compartment, especially if you happen to flip upside down
>>> during a crash landing.  You will have lots of fuel draining out the
>>> vent system into the hot engine compartment.
>>>
>>> With the factory designed fuel vent line routed up to the top of the
>>> firewall then back down to exit the bottom of the fuselage, fuel will
>>> not leak out of the vent system when the airplane is upside down.
>>>
>>> One other thought on uneven fuel flow, even if the vents are tied
>>> together and the plane is flying level/ball centered: there is a
>>> possibility that an air bubble trapped in the vent line with fuel on
>>> either side of the bubble can cause an uneven venting of the tanks.
>>> This wouldn't happen if the vent lines always slope upward to the
>>> manifold.  I think this may be the scenario that Jim Sower is seeing
>>> from time to time.  I have had it happen a couple of times on long
>>> trips after filling the tanks nearly full.  After landing and parking
>>> in my hanger, the fuel tanks were 5 or so gallons different and
>>> remained that way until I opened the fuel caps.  STRANGE!  Wings are
>>> level when parked in the hanger.  Another experiment - I placed a 2 x
>>> 6 under one main tire, simulating a wings down.  Guess what - the fuel
>>> level difference was MUCH LESS than I have seen in the air.
>>>
>>> But again, it could be fuel caps that are not always sealing perfectly
>>> for every flight.
>>>
>>> Ronnie
>>>
>>> ----- Original Message ----- From: "Tom Martino"
>>> <tmartino at troubleshooter.com>
>>> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
>>> Sent: Tuesday, February 15, 2005 12:23 PM
>>> Subject: RE: REFLECTOR: FUEL FEED [heur]
>>>
>>>
>>> My plane flies perfectly.  Not my opinion, it is the assessment of my
>>> test pilot.  The ball is in the center and the plane flies "hands off"
>>> straight and level.
>>>
>>> I will keep looking.
>>>
>>> -----Original Message-----
>>> From: Scott Derrick [mailto:scott at tnstaafl.net]
>>> Sent: Tuesday, February 15, 2005 9:18 AM
>>> To: Velocity Aircraft Owners and Builders list
>>> Subject: Re: REFLECTOR: FUEL FEED [heur]
>>>
>>> A leaking gas cap can cause uneven fuel flow but is not the prime
>>> culprit. A bit of fuel valve lube applied to the O ring once a year 
>>> will
>>>
>>> insure this doesn't happen.
>>>
>>> A miss-rigged airplane is most likely the cause. Shim your rudders so
>>> the ball is right in the middle and you will get perfect fuel flow.
>>>
>>> To test, be sure your turn and bank is installed correctly first,
>>> garbage in garbage out. Then fly, this is the fun part.. Once you 
>>> see an
>>>
>>> uneven condition, press on the rudder that will put the ball in the
>>> middle. If you want to even up the tanks fast, press on the correct
>>> rudder so the ball is on the other side for a couple minutes, you'll 
>>> see
>>>
>>> the fuel even up and even go into the opposite imbalance if you keep 
>>> the
>>>
>>> rudder depressed. Then hold the rudder so the ball is centered, fuel
>>> will flow as it was designed to.
>>>
>>> Scott
>>>
>>> Tom Martino wrote:
>>>
>>>   
>>>
>>>> Well, now that I'm in my test flying mode ... I will really be asking
>>>> a lot of questions.
>>>>
>>>> Here are some of them, as they relate to my fuel system:
>>>>
>>>> 1. What makes the fuel tanks feed unevenly to the header tank/engine?
>>>> (My right tank is feeding twice as fast as my right tank.)
>>>>
>>>> 2. Will that cause a problem when the fast-feeding tank runs out?
>>>>
>>>> 3. I used the larger vent lines for my tanks and tied them al together
>>>>     
>>>
>>>   
>>>
>>>> with a manifold, then vented the entire system out through the top of
>>>> my firewall in the engine compartment (about four inches below my naca
>>>>     
>>>
>>>   
>>>
>>>> duct). Do you think the system gets enough venting there?
>>>>
>>>> 4. Is there a need for a "whistle" hole in any of the tank vents ...
>>>> for additional venting (like we do with the crankcase breather?
>>>>
>>>> Any help is appreciated from my more experienced Velocitologists J
>>>>
>>>> Tom
>>>>
>>>> N173EX
>>>>
>>>> (A mere 6 hours)
>>>>
>>>> ----------------------------------------------------------------------- 
>>>>
>>>>     
>>>
>>> -
>>>
>>>   
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>>
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