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SkySteve

Joined: 16 Dec 2007
Posts: 94
Location: Huntsville, UT

Posted: Thu Oct 16, 2008 4:04 pm Post subject: Header Tank Venting

My header tank (located behind the seat) is vented back to both wing tanks via two vent lines (one to each wing tank).  I was advised to install a shut off valve in each vent line and to open those vent lines when filling the fuel tanks, then close the vent valves for flight.  



It was mentioned that in the past, there were several crashes due to fuel starvation when the wing tanks were full of fuel.  Apparently air had mixed with the fuel in the vent lines and vapor lock stopped the fuel flow from the wing tanks to the header tank.  The result was when the header tank ran out of fuel the engine stopped due to fuel starvation. 



Is this true?  Should I install shut off valves in each of my two vent lines and close those valves for flight?

_________________
Steve Wilson
Huntsville, UT
Kitfox Model 1- 85DD
912A / 3 Blade Warp Drive
Convertible Nosewheel & Tailwheel

tc9008(at)aol.com
Guest

Posted: Thu Oct 16, 2008 5:05 pm Post subject: Header Tank Venting

I have flown a Kitfox IV  582 since 2004 and have had a problem.

 Travis

 

 

 --

tc9008(at)aol.com
Guest

Posted: Thu Oct 16, 2008 5:05 pm Post subject: Header Tank Venting

I have flown a Kitfox IV  582 since 2004 and have had a problem.

 Travis

 

 

 --

henrysfork1(at)msn.com
Guest

Posted: Thu Oct 16, 2008 5:16 pm Post subject: Header Tank Venting

<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->  Steve on my model II I have one vent line that runs from the header tank. I  run it up and ported it out thru a butt rib using a check valve. It allows air  in but will not let fuel run out. It works very well and have no problems. If  you go thru the archives you will find a number of discussions on fuel tanks,  venting and porting etc. 

  

 Dee Young

 Model II

 N345DY

 KFM 112

  

 Do not archive

 [quote]   ---

paul(at)eucleides.com
Guest

Posted: Thu Oct 16, 2008 8:40 pm Post subject: Header Tank Venting

On Thu, October 16, 2008 5:04 pm, SkySteve wrote:

 	  Quote: 	
		   



 My header tank (located behind the seat) is vented back to both wing tanks via two

 vent lines (one to each wing tank).  I was advised to install a shut off valve in each

 vent line and to open those vent lines when filling the fuel tanks, then shut the vent

 valves for flight.



 It was mentioned that in the past, there were several crashes due to fuel starvation

 when the wing tanks were full of fuel.  Apparently air had mixed with the fuel in the

 vent lines and vapor lock stopped the fuel flow from the wing tanks to the header

 tank.  The result was when the header tank ran out of fuel the engine stopped due to

 fuel starvation.



 Is this true?  Should I install shut off valves in each of my two vent lines and close

 those valves for flight?


	


I'd have to see a drawing but that doesn't make sense as I understand the

configuration. What will block the vent line is low points or multiple low points such

that they act as a trap with fuel in it and air on both sides. It can't siphon and

causes hydraulic blockage. As long as the vent line goes up continuously and

terminates in an air gap, you should never get a condition where there is hydraulic

blockage.



-- 

Paul A. Franz, P.E.

PAF Consulting Engineers

Office 425.440.9505

Cell 425.241.1618

lcfitt(at)sbcglobal.net
Guest

Posted: Thu Oct 16, 2008 9:18 pm Post subject: Header Tank Venting

Steve,



I don't understand the thinking on the double vent unless it was done to 

prevent the often seen uneven draining of the wing tanks.  This phenomenon 

has been discussed very often on the list and in one instance in the wilds 

of Idaho it resulted in a panic stop to check for an obstruction in the fuel 

lines.  After carefully measuring fuel flow from each tank, we were finally 

able to convince the troubled pilot that the fuel flow was fine and wasn't 

going to have to put it down over the Sawtooth Mountains  because of the 

uneven fuel use from his wing tanks.  Your double vents are a one off design 

change from the factory configuration.



I don't think you will find any instances of full tank fuel starvation 

proper fuel line routing and with the vents in place and putting valves in 

the vent lines and closing them in flight is contrary to the current design. 

Putting valves in the vent lines would conceivably serve to  make fuel 

system maintenance easier, but it is a lot of hardware to simply  avoid 

clamping the lines if maintenence is necessary.  Keep in mind, the following 

service letter should clear up the factory's view on the instances you refer 

to. 

http://www.kitfoxaircraft.com/support/service_letters/sl22.htmhttp://www.kitfoxaircraft.com/support/service_letters/sl22.htm 

The referenced Service Bulletin will continue the factory comments: 

http://www.kitfoxaircraft.com/support/service_bulletins/sb29.htmKeep



It is a fact that lots of us have seen what we believe to be design 

weaknesses in the factory scheme and have modified according to our own 

perception of safe, but many of the modifications fly in the face of a fine 

history of reliability.  I had 900 hours on my Model IV when I put it on the 

ground because of an oil pressure drop due to a blockage of the oil line to 

the pump - foreign object, and I have three friends who I flew with 

regularly that each had nearly 1000 hours on Model IVs.  All with one vent 

line to the right wing tank, and all with no hint of fuel flow issues with 

the factory configuration.  Keep in mind that in a fairly steep descent with 

the aft ported wing tanks, it is possible to unport the tanks if the fuel 

level is below a certain amount.  I found that to be true during the 30 

minute descent from 12,000 ft over the Sierras, to my field elevation of 

1300 ft.  With the factory design, the header tank immediately resumed 

filling from the wing tanks after reducing the descent for a time.  And that 

was with four gallons remaining in each tank measured on the ground.  I was 

descending at 400 fpm at just below redline on the ASI.



My thought is to not close the valves in flight.  I am curious about the 

source of the advice.



Lowell



---

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Thu Oct 16, 2008 10:03 pm Post subject: Header Tank Venting

At 05:04 PM 10/16/2008, you wrote:

 	  Quote: 	
		  It was mentioned that in the past, there were several crashes due to 

fuel starvation when the wing tanks were full of fuel.  Apparently 

air had mixed with the fuel in the vent lines and vapor lock stopped 

the fuel flow from the wing tanks to the header tank.  The result 

was when the header tank ran out of fuel the engine stopped due to 

fuel starvation.



Is this true?  Should I install shut off valves in each of my two 

vent lines and close those valves for flight?


	


Steve,

         Thanks for asking this question. I have finally convinced 

myself that this is possible. It's not vapor lock, but if your wing 

tank fuel feed line were to rise above the wing tank fuel level 

before travelling to the header tank, and the header was vented to 

atmosphere, the wing tank would stop feeding. (There would be no way 

to siphon from the wing tank because the header tank was vented to 

atmosphere.) Therefore you'd have to block the vent to force fuel to 

siphon from the wing tank. My system without the vent valve works 

because my wing tank feed lines run down-hill to the header tank; no 

siphon is necessary. (I could have a problem on an extremely long, 

extremely steep descent, because my fuel lines run aft from the wing 

tanks.) So I guess the answer becomes: either your wing tank fuel 

lines run down-hill, or you install the valves.

Guy Buchanan

San Diego, CA

K-IV 1200 / 582-C / Warp / 100% done, thanks mostly to Bob Ducar.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

SkySteve

Joined: 16 Dec 2007
Posts: 94
Location: Huntsville, UT

Posted: Fri Oct 17, 2008 5:29 am Post subject: Re: Header Tank Venting

Obviously there are differing thoughts on this issue.  What I am getting so far is that it MAY not be necessary to close the venting, but closing the venting will not harm anything and MAY actually HELP in some instances.  Would that be a accurate summary?

_________________
Steve Wilson
Huntsville, UT
Kitfox Model 1- 85DD
912A / 3 Blade Warp Drive
Convertible Nosewheel & Tailwheel

lcfitt(at)sbcglobal.net
Guest

Posted: Fri Oct 17, 2008 6:52 am Post subject: Header Tank Venting

Steve, in a word, No.



Lowell



---

kerrjohna(at)comcast.net
Guest

Posted: Fri Oct 17, 2008 8:29 am Post subject: Header Tank Venting

If as you suggest the header tank vent was OFF then in Lowell's example or other similar scenario the automatic refilling of the header tank would be prevented and air/fuel blockages of the two feed lines from the wing tanks WOULD likely slow or prevent flow to the header tank and encourage fuel starvation with adequate fuel remaining in the wings.

  

 Add my name to the many with asymetrical fuel flow from the tanks but no evidence of the header tank being deprived.  I don't have a low fuel warning but there are many out there to monitor the possiblity of starvation.  Were there any warnings that were triggered as a result of the asymetrical draw.  What are the specifics of the "many crashes due to fuel starvation"?  Sounds like urban myth to me.

  

 John Kerr

 Classic IV, 912ul, 780 hours.

 Logan UT

  

  ======  UOTE>< /body>  [quote][b]

n85ae

Joined: 14 Mar 2007
Posts: 403

Posted: Fri Oct 17, 2008 9:03 am Post subject: Re: Header Tank Venting

Header vents to both tanks, is usefull for equalizing pressure in the fuel

tanks. This is the culprit for  the uneven fuel flow problems in kitfoxes.

All it take is a slight pressure differential, and you'll see a lot more fuel 

flow from one tank than the other.



Jeff.

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Fri Oct 17, 2008 9:56 am Post subject: Header Tank Venting

I had uneven flow on ONE day....I was within 8 minutes of the  

airport, and the low-fuel light came on, indicating 15 minutes of  

fuel left. I noticed there was plenty of fuel in the left tank, so I  

banked a bit to the right, sending that fuel into my header tank, and  

I watched as the vent line filled up, the low-fuel light went off,  

and I flew without incident into the airport to get 22 gallons into  

my 26 (27 with header ) gallon (total) tanks. I may regret saying  

this, but each pilot should know how his/her fuel system works, and  

what can be done in a pinch to remedy a problem...either that or get  

fuel more often.



Lynn Matteson

Kitfox IV Speedster

Jabiru 2200, 572hrs

Sensenich 62x46

flying again after rebuild, and new Electroair direct-fire ignition  

system



On Oct 17, 2008, at 1:03 PM, n85ae wrote:



 	  Quote: 	
		   



 Header vents to both tanks, is usefull for equalizing pressure in  

 the fuel

 tanks. This is the culprit for  the uneven fuel flow problems in  

 kitfoxes.

 All it take is a slight pressure differential, and you'll see a lot  

 more fuel

 flow from one tank than the other.



 Jeff.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p 9194#209194

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

msm_9949(at)yahoo.com
Guest

Posted: Fri Oct 17, 2008 10:45 am Post subject: Header Tank Venting

Dee, 

  

 What kind of check valve did you use? I have the same set-up, originally with an Andair check valve but it did not prevent fuel from flowing out along with air. Eventually I installed a shut-off valve in the line which I open during fueling and close before flight.

  

 On the original question: If the header vents back into the tanks, I see no purpose for a shut off valve in the vent line.

  

 Marco Menezes N99KX

 Model 2 582-90 C-Box 3:1



--- On Thu, 10/16/08, Dee Young <henrysfork1(at)msn.com> wrote:



 [quote]From: Dee Young <henrysfork1(at)msn.com>

Subject: Re: Header Tank Venting

To: kitfox-list(at)matronics.com

Date: Thursday, October 16, 2008, 9:15 PM



     Steve on my model II I have one vent line that runs from the header tank. I run it up and ported it out thru a butt rib using a check valve. It allows air in but will not let fuel run out. It works very well and have no problems. If you go thru the archives you will find a number of discussions on fuel tanks, venting and porting etc. 

  

 Dee Young

 Model II

 N345DY

 KFM 112

  

 Do not archive

 [quote] ---

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Fri Oct 17, 2008 11:46 am Post subject: Header Tank Venting

At 06:29 AM 10/17/2008, you wrote:

 	  Quote: 	
		  Obviously there are differing thoughts on this issue.  What I am 

getting so far is that it MAY not be necessary to close the venting, 

but closing the venting will not harm anything and MAY actually HELP 

in some instances.  Would that be a accurate summary?


	


         I think so, as long as you assure the header tank is 

reasonably full. With the vents closed any vapor in the header tank 

will have to / try to migrate up the fuel tank feed lines. I'm not 

sure but that this buoyancy might be able to work against the fuel 

tank head pressure and prevent its feeding. Again, I've never heard 

of it, and I used 3/8" line from my wing fuel tanks to the header 

tank to make sure vapor and fuel could exchange freely.

Guy Buchanan

San Diego, CA

K-IV 1200 / 582-C / Warp / 100% done, thanks mostly to Bob Ducar.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

henrysfork1(at)msn.com
Guest

Posted: Fri Oct 17, 2008 11:53 am Post subject: Header Tank Venting

<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->  Marco I used a check valve that was designed for use in a vacuum system on  a Holley carb. The check valve is about the size of a nickel and about as thick  as two nickels together. I choose a check valve because I didn't want fuel  to spill out but do want the header tank to breath. You ask the  question about the shut offs, someone with a greater mind than mine designed the  tank. If the tank is shut off it will no breath as designed or at least that’s  my view. I have no problems with fuel slobbering out of the vent and have no  problems with fuel flow. It works for me.

  

 Dee Young

 Model II

  

 Do not archive

 [quote]   ---

Float Flyr

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

Posted: Fri Oct 17, 2008 2:22 pm Post subject: Header Tank Venting

Lynn:



What you did was one of the things my flight instructor made me practice as

part of a forced approach.  Even the certified spam cans have issues with

fuel delivery form the wing tanks on occasion.



My plane only has a vent to the right wing tank..  The left tank is only

half the size of the right and yes I do have unequal fuel flow.  I also have

a clear section in the vent line so I can see when fuel in the header starts

to run out long before it does.  When I install the 912 I was thinking about

relocating the header behind the seat.  In that location I will no longer be

able to see the vent line.



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Fri Oct 17, 2008 2:54 pm Post subject: Header Tank Venting

Noel-

I also have a clear vent line running up to my right tank, which is  

equal in size to the left tank. However, I can see my vent line even  

with the header tank behind the right side of the seat. My fuel line  

and the vent line run parallel to the diagonal braces behind the  

seat, and all I need to do is glance over my right shoulder  

occasionally to check for fuel in both the clear glass Purolator  

filter, and the clear vent line. I only *need* to do this when I know  

that the fuel tanks are getting low, but I check it every so often  

just out of habit. Pucker time comes when I allow myself to get low  

on fuel and have to make a descent. Under these conditions...and I've  

done this maybe 4-5 times (bad, Lynn, BAD)...like Guy suggested, just  

leveling off for a moment will let some fuel fill the header, shut  

off the light, and the pucker relaxes.



Lynn Matteson

Kitfox IV Speedster

Jabiru 2200, 572hrs

Sensenich 62x46

flying again after rebuild, and new Electroair direct-fire ignition  

system



On Oct 17, 2008, at 6:21 PM, Noel Loveys wrote:



[quote] 



 Lynn:



 What you did was one of the things my flight instructor made me  

 practice as

 part of a forced approach.  Even the certified spam cans have  

 issues with

 fuel delivery form the wing tanks on occasion.



 My plane only has a vent to the right wing tank..  The left tank is  

 only

 half the size of the right and yes I do have unequal fuel flow.  I  

 also have

 a clear section in the vent line so I can see when fuel in the  

 header starts

 to run out long before it does.  When I install the 912 I was  

 thinking about

 relocating the header behind the seat.  In that location I will no  

 longer be

 able to see the vent line.



 Noel



 --

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

Float Flyr

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

Posted: Fri Oct 17, 2008 3:18 pm Post subject: Header Tank Venting

I have yet to land a plane with less than an hour of fuel on board.   When I

worked at the AMO ( Canadian equivalent of an FBO) in Gander there was a TC

poster in the Heli part of the hangar which said "Fuel is time"...  Kinda

remembered that.  Also the only time you have too much gas is when you're on

fire 



Most of my flights in the Kitfox I intentionally tried to get the weight up

to the 950 MTOW.  It's a bit harder getting a heavy plane up on step when

flying floats.



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

helili(at)chahtatushka.ne
Guest

Posted: Fri Oct 17, 2008 3:56 pm Post subject: Header Tank Venting

I don't mind flying a half tank of gas...............as long as it's the top

half!



John Hart

KF IV, NSI Subaru

Wilburton, OK

--

pwmac(at)sisna.com
Guest

Posted: Fri Oct 17, 2008 4:33 pm Post subject: Header Tank Venting

Steve.

NO -NO -NO You do not understand.

You are getting advice from someone who has no understanding of the 

physics of fluid flow. You must vent the header. Valves in the header 

tank vents are just plain crazy..

  Follow the instructions in the build manual. The factory guys are 

real engineers and have thought thru many things you may not even 

consider. And if you don't have the latest fuel system version go get 

it. And if you have a flying system that is not the latest system 

change it. As several have pointed out this in not the place to come 

up with something that will kill you.



Remember screwed up fuel systems cause the most downed Kitfoxes of 

any other kind of failure. Probably because the builder did not 

understand the factory setup and changed it to his own design. Or 

just did not follow the instructions.



Please Read Andys message below and try to understand it

Paul

=======

Just as a word clarification, so that terms aren't used 

incorrectly.  The fuel system in a Kitfox is "gravity feed" and fuel 

pressure to the carb or engine fuel pump is "head pressure" from a 

gravity fed fuel tank.  Strictly gravity only.  There is no "siphon 

action".  Designers have to determine that the fuel tank is high 

enough in normal flying/attitudes (nose high/nose low) and fuel line 

size adequate to provide a certain fuel pressure or head pressure for 

the fuel consumption of the engine used.  If your engine installation 

requires additional pressure to the engine pump than head pressure 

can provide, an electric pump must be installed prior to the engine 

pump or carb (ala low wing aircraft).  Fuel line size and head 

pressure to the engine is all that insures that an adequate supply of 

fuel is maintained to the metering device, unless you have a fuel 

pump located at each tank outlet to supply increased fuel flow.  Most 

small aircraft under 140 hp, 3/8" line is used, that will that will 

supply more enough fuel for engine consumption.  As engines get 

larger, fuel line size goes up, 1/2", 5/8", etc.  The only time fuel 

is "sucked" or "siphoned" from a tank is if you have a pump located 

at the tank.



It is extremely important that the fuel lines and the vent lines be 

angled down to the header tank or on a constant slope, problem areas 

are at the wing pivot and the horizontal routing to the header 

tank.  Especially in the vent line.  Air and fuel must have an 

unimpeded path and a way to get out and into the upper wing tank, if 

both lines to one tank have a low or high spot  you could run into a 

fuel lock situation on that side.  Installed correctly and under 

normal flying and fuel conditions, the vent line has fuel in it and 

should correspond to the level of fuel in the tank.  In a long, 

steep, nose down descent with low fuel, your fuel pickup will be 

higher than the fuel level in the tank, as the fuel runs to forward 

to the front of the tank.  The tank is still vented, fuel to the 

header tank is supplied only by the remaining fuel in the fuel line 

from the pickup to the header tank.  Leveling off routinely will then 

raise the fuel level above the fuel pickup/screen and will flow back 

down into the header tank.  The air being displace by the fuel will 

go up the vent line and into the fuel tank.  If the vent were blocked 

then air would have to travel upstream against the fuel going down 

into the header tank.  If it is on a constant slope this should not 

cause a problem other than fuel will not fill the header tank as fast 

as it has to make room for air in the line going up.  This is why the 

vent line is important.



If you look at aerobatic biplanes with a center section upper wing 

mounted fuel tank, you will see a forward fuel pickup. This is for 

nose down attitudes.  Most Cessna's have a forward pick up location, 

we can't because of the folding wing design.  The fuel line would 

have to run down the forward doorpost frame. (Which it does in a Cessna)



There is nothing wrong with a single vent line to one tank or a vent 

line to each tank.  Because we have a folding wing design we cannot 

have a interconnecting vent line (wing tank-to-wing tank) like a 

Cessna that they use to help even the fuel burn from each wing. In a 

perfect world (no slip nor skid, wings level, no turbulence, etc) 

Kitfox dual vent lines are used to keep fuel burn equal.  The fuel 

vents on the "filler caps" provide a very slight positive pressure in 

the tanks, but mainly to fill the void of used fuel.  Make sure the 

caps are on correct and the gaskets are sealing.  One of the reasons 

for the long periscope vent line on the cap is to get the vent into 

static atmospheric air.  The low pressure on top of the wing where 

the fuel cap is can cause siphoning of fuel, which is why a gasket 

check is a good idea.



The reason that the vent line from the header tank needs to be a 

constant slope to the tank vent boss is to ensure that you don't 

create a "trap" for air.  A dual vent line system helps to ensure 

positive flow to the engine just incase one vent line were to become blocked.



Depending on your engine installation it is possible run the fuel low 

enough that there is not enough head pressure to supply the carb, 

even though there may be fuel in the header tank.  I suggest a 

standby electric fuel pump (Faucet 4-6 gph) be mounted below the 

header tank outlet that can be turn on during takeoff/landing and low 

fuel situations.  I installed one in my fuel system.  To insure 

positive pressure.



I would:

I would check the fuel caps first to make sure they are not blocked, 

pointing forward and the gasket seals.

Ensure that the fuel and vent lines to each tank are on a constant 

slope to the tank.

Verify that the fuel level in the vent line corresponds to the level 

of fuel in the tank.



Andy

=============



At 06:29 AM 10/17/2008, you wrote:

 	  Quote: 	
		  



Obviously there are differing thoughts on this issue.  What I am 

getting so far is that it MAY not be necessary to close the venting, 

but closing the venting will not harm anything and MAY actually HELP 

in some instances.  Would that be a accurate summary?



--------

Steve Wilson

Huntsville, UT

Kitfox Model 1- 85DD

912A / 3 Blade Warp Drive

Convertible Nosewheel &amp; Tailwheel





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p 9161#209161

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