REFLECTOR: FUEL FEED [heur]

Scott Derrick scott at tnstaafl.net
Wed Feb 16 11:09:24 CST 2005


I disagree Jim.

The sump should "ALWAYS" be vented, per the drawings....

Scott

Jim Sower wrote:

> You're not venting into the engine compartment (at least I'm not).  I 
> have a vent from my sump tank that goes to the top of the firewall and 
> is capped off there.  On those rare occasions that the sump gets 
> emptied (like for maintenance or heaven forbid I get into my last 5 
> gals of fuel) I have to open the vent long enough for the sump to fill 
> up.  If I left the sump vented, there is the distinct possibility that 
> the strakes wouldn't gravity feed fast enough to keep up with the 
> engine (like a leaky fuel cap) and with the vent open the fuel pump 
> couldn't "draw" fuel out of a strake that wasn't pressurizing.
>
> In flight, sump tank should NEVER be vented ... Jim S.
>
> Scott Derrick wrote:
>
>>
>> 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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> http://www.tvbf.org/mailman/listinfo/reflector
>
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>
>


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