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Unequal fuel flow

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jacques.voynaud(at)cegepa
Guest

Posted: Wed Jun 13, 2007 6:56 am Post subject: Unequal fuel flow

I think this subject has been adressed before but not sure of results E 

 I have a 4 with 912 and 2 - 13 gals wing tanks E When I fill both up to cap, go flying for an hour or so, check fuel level right after landing, right tank is down to half and left tank is still full to cap E After parked on the ground for few hours, both tanks equilibrate by cross-flowing E I'm wondering if the engine would run out of gas if the right tank goes empty with the left stiill full? Any way to correct this situation? 

 The right tank is equipped with a tygon vent tube to the header tank E

  

 Jack V E Kitfox 4-1200

   [quote][b]

torgemor(at)online.no
Guest

Posted: Wed Jun 13, 2007 9:18 am Post subject: Unequal fuel flow

Hi Jack,



I'll think this is caused by a pressure differences between both main  

tanks, this can occur if there is difference between the cap's "pitot  

tubes" as height or position differences.  A very limited flow through the  

left system either the vent or the fuel line, -or sometimes a leaky cap  

gasket.



At some level in the right tank the fuel should start flowing from the  

left system as well.



As your system level out on ground after some "hours", there must be some  

kind of restriction in your left main line (?).  I'll think they should  

level out in around one hour or so, not in a couple of hours (if the A/C  

is in level). Must say that I've never made any calculation or test in  

this matter, so this assumption is kind of subjective.



A simple flow test from each side might discover a difference between the  

two.



The cap gasket is an important issue in our kind of system, make sure they  

seal properly -there should be no kind of air leakage.



Good luck.



Torgeir



 	  Quote: 	
		   On Wed, 13 Jun 2007 16:55:37 +0200, Jacques Voynaud  

 <jacques.voynaud(at)cegepat.qc.ca> wrote:


	


 	  Quote: 	
		   I think this subject has been adressed before but not sure of results.

 I have a 4 with 912 and 2 - 13 gals wing tanks. When I fill both up to  

 cap, go flying for an hour or so, check fuel level right after landing,  

 right tank is down to half and left tank is still full to cap. After  

 parked on the ground for few hours, both tanks equilibrate by  

 cross-flowing. I'm wondering if the engine would run out of gas if the  

 right tank goes empty with the left stiill full? Any way to correct this  

 situation?

 The right tank is equipped with a tygon vent tube to the header tank.



 Jack V. Kitfox 4-1200


	


--

Torgeir



Kitfox Model II, 1993

Engine: Rotax 532 with B gearbox

Propeller: IVO UL 366Q



Tromsoe

NORWAY.



Weather in Tromso right now:

http://met.no/troms/index.html



City map of Tromso:



http://www.avinor.no/English/Airports/Tromso_Airport/?module=Articles;action=ArticleFolder.publicOpenFolder;ID=1453



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andynfultz(at)bellsouth.n
Guest

Posted: Wed Jun 13, 2007 9:40 am Post subject: Unequal fuel flow

Unequal flow can be caused by unequal lengths of fuel line from the main  tanks to the header tank, unequal pitot pressures on the tank vents and/or fuel  cap gaskets not sealing properly.  If all those items check out you might  need to start checking for a restriction in the fuel line.  Once you have  your header tank full, venting it back to the main tank is not  necessary.  You can put a valve in that vent line and make it part of yout  preflight to "check header tank full" then operate off your main tank  vents.

  

 Andy  

 [quote]   --

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Wed Jun 13, 2007 3:31 pm Post subject: Unequal fuel flow

you're right, it has been  discussed before... I think the consensus was that you may be flying with  the left wing a bit low.  It would only have to be an inch or two low to  cause the drop as you have described.

  

 My mod 111-A does the same  thing and quite often after landing I'll find the right tank empty and the left  around half full...( 30- 45 min of flying time remaining).

  

  

[img]cid:660122323(at)13062007-2CC1[/img]  

 Noel Loveys, RPP, AME intern

 Campbellton, Newfoundland, 

 Canada

 Kitfox Mod III-A, 582, B box, Ivo IFA

 Aerocet 1100s

 noelloveys(at)yahoo.ca (noelloveys(at)yahoo.ca)

 

 

 Do not archive

 



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Noel Loveys
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Malcolmbru(at)aol.com
Guest

Posted: Wed Jun 13, 2007 6:44 pm Post subject: Unequal fuel flow

I also have un even fuel flow and wore about it I have a 582 with E box and  my left tank drains first my vent tub is on the right side and after my left  tank is dry and the right side gets low I can see the vent tub diping air down  tword the header tank.  running out with fuel on board sure would suck. I  sometimes wonder if I worries to much        mal  



See what's free at AOL.com. 

  [quote][b]

john(at)leptron.com
Guest

Posted: Wed Jun 13, 2007 7:02 pm Post subject: Unequal fuel flow

I have to jump in here you guys, many of you were not in the group in the beginning. Ok, many years ago, but we did loose several planes in the group, that went down due to fuel starvation and then burned because there was a full tank. You can cause one of the tanks to “port” and not draw, thus causing fuel starvation. The vent line needs to be eliminated or valved so the engine is forced to draw from the tanks. A control valve on both sides is a plus if you make sure not to allow the fuel line to wow uphill as it is turning toward the tank.   

   

I hate loosing friends, be careful  

   

John Oakley  

         

  

From: owner-kitfox-list-server(at)matronics.com [mailto:owner-kitfox-list-server(at)matronics.com] On Behalf Of Malcolmbru(at)aol.com

 Sent: Wednesday, June 13, 2007 8:44 PM

 To: kitfox-list(at)matronics.com

 Subject: Re: Unequal fuel flow  

  

     

I also have un even fuel flow and wore about it I have a 582 with E box and my left tank drains first my vent tub is on the right side and after my left tank is dry and the right side gets low I can see the vent tub diping air down tword the header tank.  running out with fuel on board sure would suck. I sometimes wonder if I worries to much       mal    

  



 

         

  

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Malcolmbru(at)AOL.COM
Guest

Posted: Wed Jun 13, 2007 7:15 pm Post subject: Unequal fuel flow

In a message dated 6/13/2007 11:03:58 P.M. Eastern Daylight Time,  

john(at)leptron.com writes:



“port”  and not draw, thus causing fuel starvation

please elaborate on this a little moor   my vent line comes from  the header 

tank behind the seat and is just a little higher than the wing  tank's  my 

vented factory gas caps are not equal in venting capacity . that  is when I blow 

threw them moor air comes threw one then the other? switching  them makes no 

difference

   malcolm KF2   582 



************************************** See what's free at http://www.aol.com

john(at)leptron.com
Guest

Posted: Wed Jun 13, 2007 9:02 pm Post subject: Unequal fuel flow

Malcolm,  

I will try not to confuse, there is two problems, one the vent line and two the tanks draining differently.  

   

The vent line is only to get the gas (air) out of the header tank. If the vent is left open, there is a possibility that the header tanks could empty and the engine will suck air through the vent line.  

   

Now, let me explain that, each of the fuel tanks has a line that has a loose 90 degree turn to get to the tank (just behind your head), this turn is usually left fairly loose or large so the wing can fold with out tearing the line out. This half loop can if left too loose, can get a bubble in it during a turn. This bubble can cause a “vapor lock” and the tank will stop feeding. If it stops feeding the header tank empties and sucks air from the vent line.  

 If the vent line is closed (valved) the engine is forced to suck from one tank or the other.  

My vent line is run down under the aircraft and ties to a normal fuel drain like under the wing. I vent or drain this every time I check fuel quality.  

   

But…. If you have a vapor lock, you can use the fuel in one tank and still run out of gas with one tank still full.   

   

Another problem, is, if you fuel both tanks and then sit on a side hill or slope of a normal parking lot, the fuel will transfer to the lower wing and run out across the wing, staining it.  

   

Answer, add valves to the two wing tanks.   

   

Also a 12 volt booster pump, just like the big guys…….i have one under the seat..  

   

John Oakley  

   

   

   

   

         

  

From: owner-kitfox-list-server(at)matronics.com [mailto:owner-kitfox-list-server(at)matronics.com] On Behalf Of Malcolmbru(at)aol.com

 Sent: Wednesday, June 13, 2007 9:15 PM

 To: kitfox-list(at)matronics.com

 Subject: Re: Unequal fuel flow  

  

       

In a message dated 6/13/2007 11:03:58 P.M. Eastern Daylight Time, john(at)leptron.com writes:  

   	  Quote: 	
		    

“port” and not draw, thus causing fuel starvation  	
  

    

please elaborate on this a little moor   my vent line comes from the header tank behind the seat and is just a little higher than the wing tank's  my vented factory gas caps are not equal in venting capacity . that is when I blow threw them moor air comes threw one then the other? switching them makes no difference  

    

   malcolm KF2   582   

  



 

         

  

See what's free at AOL.com.   

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n85ae

Joined: 14 Mar 2007
Posts: 403

Posted: Thu Jun 14, 2007 5:49 am Post subject: Re: Unequal fuel flow

This is absolutely simple, it is a very common problem, and it is caused 

by the use of a single header vent line. If the Kitfox design had vents to

both tanks the problem wouldn't be there. It is common to many other

high wing designs with similar fuel systems.



The best thing to do, is simply fly the plane and ignore it. You will still

feed all the fuel from both tanks (less unusable) to the header before 

you fall out of the sky.



Jeff Hays

Series 5, IO240B

wingsdown(at)verizon.net
Guest

Posted: Thu Jun 14, 2007 6:11 am Post subject: Unequal fuel flow

Jeff you are right. Of more concern should be steep decent with less

than 6 or 7 gals fuel onboard. Provided you have dual tanks. There are

post on this issue though.



Rick



--

mikeperkins

Joined: 22 May 2007
Posts: 123

Posted: Fri Jun 15, 2007 6:48 am Post subject: Re: Unequal fuel flow

The problem of fuel tank differential might be as simple as Jeff suggests..... I never experimented to see if I could prove that theory or not. 



HOWEVER, not taking fuel flow measurements on the ground in all three extreme flight attitudes is asking for trouble. I know of too many cases where fuel starvation was caused by poor fuel line routing and/or the loss of the fuel pump. If your system, with the pump stopped, does not supply enough fuel-rate to the carbs measured AT THE CARBS for climb power, there's likely a statisic in your future. But also, descents must be considered. 



Just think about coming back from a long cross-country with four gallons aboard and making a long, steep decent. It's likely you're main tank drains are unported at that point and you're running off the reserve in the header tank. At that point the head-pressure is so low that if you lost your fuel pump, you'd lose all fuel flow. Also, I have seen high-wing aircraft where, in climb attitude, the fuel passes through a level HIGHER than the fuel level in the aircraft. This is fine as long as there's no vapor in the line, but the moment a drain unports (low fuel combined with fuel sloshing), there's vapor in the line. With enough vapor in the line, "suction" is lost. 



Also, Skystar/Denny recommended putting the fuel valves down low, not up hight near the tanks. This is because with the valves up high, the head pressure at the valves is sometimes too low to overcome the pressure-loss (resistance) in valve itself. And fuel-flow is actually blocked by the open valve under some conditions. 



A fuel system is not house plumbing. The pressures are so vastly different that small pressure losses in fuel plumbing have to be considered. Along with other issues, these small pressures are responsible for air-locks. A friend of mine and I have made a study of fuel systems, especially badly-installed fuel systems, and the accident statistics correlate. 



It is better to push fuel than to try to pull it. Fuel starvation can come from air-locks when you try to pull fuel. Therefore, fuel pumps belong near the fuel tank, not in the engine compartment. After doing your fuel-flow tests, you might decide that putting in a second fuel pump, perhaps an electrical one, might be a good idea. If the pump is near the tanks, say at the bottom of the header tank behind the seat, you're pushing fuel "up" the floorboard in a nose-high attitude, which is what you want to do.

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