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Fuel Flow, continued.
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torgemor(at)online.no
Guest

Posted: Mon Jan 22, 2007 2:01 pm Post subject: Fuel Flow, continued.

The Kitfox tank system with two wing tanks and one header tank, is using  

both the head pressure and the gravity to ensure adequate fuel pressure  

for our engine.



At first this might seem simple and easy, -but is it?



Let's have a look at the system as it is today; with two wing tanks, the  

previous wing tank valves removed and the header vented to the right tank.



Now, can you see that the header tank is filled by the gravity only??



If everything is as it "should" be this system will work fine.



Here is a principle drawing of a "normal" working system;  Fuel_1.jpg



However, what will happen and how -if we forgot to install one of the tank  

cap (let's assume the left) ?



OK., everyone know that our tank will start loosing fuel, but how?  Well,  

remember that our right tank is at "static pressure", in addition it is  

pressurized "a little" by the head pressure entering through our "vent"  

line installed in the fuel cap.



So here's a pressure difference of approx.: (0.2 - 0.3) psi air pressure  

between each wing tank, the high pressure is in the right tank, therefore  

fuel transfer from right to the left tank will take place.



You see, here the left tank will continue overfill until the right tank is  

empty.  After the right tank is exhausted, the level in the header will  

decrease to the "height" position of the input line coming from left main  

tank.



Now, we'll have a continuos airflow from right to the left main preventing  

much fuel from the left tank to flow into the header, soon the header is  

empty -and the engine stop.



This next one drawing show the same system with a missing left fuel cap;  

Fuel_2.jpg



Next time (in a couple of days), we'll have a look at other and more  

interesting failure modes in this same system, and later on the old  

system...



Torgeir



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Michel

Joined: 10 Jan 2006
Posts: 966
Location: Norway

Posted: Mon Jan 22, 2007 3:14 pm Post subject: Fuel Flow, continued.

On Jan 22, 2007, at 11:00 PM, Torgeir Mortensen wrote:

 	  Quote: 	
		   This next one drawing show the same system with a missing left fuel 

 cap; Fuel_2.jpg


	


Torgeir, your second drawing comes as a corrupted file on my computer. 

Could you check and send it again, please?



Med vennlig hilsen,

Michel



do not archive

_________________
Kitfox 3 - Jabiru 2200

Graeme Toft

Joined: 09 Jan 2006
Posts: 123

Posted: Mon Jan 22, 2007 3:34 pm Post subject: Fuel Flow, continued.

Thanks for this excellent description Togier. The senario you described is 

exactly what caused my engine failure.



Regards

Graeme Toft



Do not archive

---

kitfox_robert(at)yahoo.co
Guest

Posted: Mon Jan 22, 2007 3:34 pm Post subject: Fuel Flow, continued.

On my fox I installed valves on the left and right fuel lines going to the header tank and everthing else is the same as Torgeir's nice diagram. What will happen if I turn off one of the valves off? Would there be a difference if I turn off the right side vs left side? Can I remove a cap and shut off the valve and be okay? I take this very serious as I know of a person that left their cap off their fox and had an engine out. After they replaced the cap they were able to fly the again with no extra fuel needed so not sure if they just lost pressure or if they lost fuel while flying.

 Robert N200KF

 0200 Model V

 San Diego

 Do not Archive

 ---

Guy Buchanan

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

Posted: Mon Jan 22, 2007 4:23 pm Post subject: Fuel Flow, continued.

At 02:00 PM 1/22/2007, you wrote:

 	  Quote: 	
		  Now, we'll have a continuos airflow from right to the left main preventing

much fuel from the left tank to flow into the header, soon the header is

empty -and the engine stop.


	


Torgeir,

         Thanks for staying with this. It's important. It's pretty clear 

from your example that we want a cross vent so the tank ullages are both at 

the same pressure, the way Cessna does it. And in retrospect it would have 

been easy to do, too. All you would have had to do was duplicate the tank 

inboard vent on the other side, then run a tube straight across the back 

spar from vent to vent. T off that for the header vent and presto, no fuel 

transfer once the vent transfers vapor.

Guy Buchanan

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

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

aldaniels(at)fmtcblue.com
Guest

Posted: Mon Jan 22, 2007 4:24 pm Post subject: Fuel Flow, continued.

A simple safety that will help in the event of  leaving a fuel cap off is to put a fuel cap fairing on. This also stops or reduces fuel loss around a leaking fuel cap gasket, especially in rough air. I was lucky that I had done this as one of my sons did his first solo cross country in the Kitfox, and in the excitement of the trip and an interruption while fueling with someone wanting to look at the plane he forgot to put one fuel cap on. On the 1 1/2 hour flight back over the mountains he did not loose more than a gallon or so and returned without problems. I did not put them on for that reason, but sometimes you get lucky. On some Cessna high wing planes I understand that it can not only empty the fuel tank in something like 7 minutes, but the sucking also holds up the fuel sensor giving the pilot a full fuel indication until the deafening silence starts.

  I should say that is an assumption I have made about the fuel cap fairing, but I have not done wind tunnel or computer testing. If someone has the capability to do so I would be interested in the results. You know what they say about assumptions.    

 [quote]    	  Quote: 	
		  

	
 [b]

torgemor(at)online.no
Guest

Posted: Tue Jan 23, 2007 11:54 am Post subject: Fuel Flow, continued.

God kveld Michel,



The drawing went through just fine, -but sometimes "Cyber Space" can   

play..



I'll promptly send off list to you.



Torgeir.



do not archive

On Tue, 23 Jan 2007 00:12:32 +0100, Michel Verheughe <michel(at)online.no>  

wrote:



 	  Quote: 	
		   



 On Jan 22, 2007, at 11:00 PM, Torgeir Mortensen wrote:

> This next one drawing show the same system with a missing left fuel  

> cap; Fuel_2.jpg



 Torgeir, your second drawing comes as a corrupted file on my computer.  

 Could you check and send it again, please?



 Med vennlig hilsen,

 Michel



 do not archive


	


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torgemor(at)online.no
Guest

Posted: Tue Jan 23, 2007 12:57 pm Post subject: Fuel Flow, continued.

Hi Graeme, Robert, Guy, Alan and all,



Thanks for the positive response.



Will look more closely at valves etc. next time..



In the mean time, let's assume that we "loose" our right wing tank cap  

(the left one is tight and in place).



Would it make any difference in this case?



Can we do anything about the situ?



Take care.



Torgeir.



On Tue, 23 Jan 2007 00:33:53 +0100, QSS <msm(at)byterocky.net> wrote:



[quote] 



 Thanks for this excellent description Togier. The senario you described  

 is exactly what caused my engine failure.



 Regards

 Graeme Toft



 Do not archive

 ---

Michel

Joined: 10 Jan 2006
Posts: 966
Location: Norway

Posted: Tue Jan 23, 2007 1:31 pm Post subject: Fuel Flow, continued.

On Jan 23, 2007, at 8:53 PM, Torgeir Mortensen wrote:

 	  Quote: 	
		   The drawing went through just fine, -but sometimes "Cyber Space" can  

 play..


	


Yes, it does, sometimes, Torgeir. I got it off-list and it's just fine, 

thank you.

What I find interesting is that your drawing is a true copy of my fuel 

supply system. It confirms again that the original builder of my plane 

(not the one I bought it from) Harald Lien from Stranda (Molde 

flyklubb) did a fantastic job at building it - by the book. Ever since 

I have been on this list, reading all the good tips from builders, I 

see that Harald knew them already in the period 1991-93, when he built 

my plane. She is beautiful, what we call in Norwegian: en klenodium - a 

jewel.



Cheers,

Michel



do not archive

_________________
Kitfox 3 - Jabiru 2200

n981ms(at)yahoo.com
Guest

Posted: Tue Jan 23, 2007 2:12 pm Post subject: Fuel Flow, continued.

I once let myself  get distracted while fueling.  I put the right cap on backward.  ( I twist by the cap not the tube).  About 40 minutes later rpm dropped on the IO240.  I had noticed the fuel seeming to drain from the left only and faster than normal but I had been turning and such.  I was at the point of watching closely.  Shortly after the rpm drop from 2550 to around 1800 ( I think) I turned on the boost pump and all seemed well. Our  destination was only another 5 minutes.  A run up on the ground before shut down obviously seemed well also.  I wish the caps only would go on one way.

  Maxwell



Torgeir Mortensen <torgemor(at)online.no> wrote:

   	  Quote: 	
		  The Kitfox tank system with two wing tanks and one header tank, is using 

both the head pressure and the gravity to ensure  adequate fuel pressure 

for our engine.



At first this might seem simple and easy, -but is it?



Let's have a look at the system as it is today; with two wing tanks, the 

previous wing tank valves removed and the header vented to the right tank.



Now, can you see that the header tank is filled by the gravity only??



If everything is as it "should" be this system will work fine.



Here is a principle drawing of a "normal" working system; Fuel_1.jpg



However, what will happen and how -if we forgot to install one of the tank 

cap (let's assume the left) ?



OK., everyone know that our tank will start loosing fuel, but how? Well, 

remember that our right tank is at "static pressure", in addition it is 

pressurized "a little" by the head pressure entering through our "vent" 

line installed in the fuel cap.



So here's a pressure difference of approx.: (0.2 - 0.3) psi air pressure 

between each wing tank, the high  pressure is in the right tank, therefore 

fuel transfer from right to the left tank will take place.



You see, here the left tank will continue overfill until the right tank is 

empty. After the right tank is exhausted, the level in the header will 

decrease to the "height" position of the input line coming from left main 

tank.



Now, we'll have a continuos airflow from right to the left main preventing 

much fuel from the left tank to flow into the header, soon the header is 

empty -and the engine stop.



This next one drawing show the same system with a missing left fuel cap; 

Fuel_2.jpg



Next time (in a couple of days), we'll have a look at other and more 

interesting failure modes in this same system, and later on the old 

system...



Torgeir



-- 

Using Opera's revolutionary e-mail client: http://www.opera.com/mail/ 	




   Need Mail bonding?

Go to the Yahoo! Mail Q&A for great tips from Yahoo! Answers users. [quote][b]

kitfoxmike

Joined: 05 Dec 2006
Posts: 373

Posted: Tue Jan 23, 2007 2:58 pm Post subject: Re: Fuel Flow, continued.

Those tubes are one tough cookie, just install the caps by the tubes, after awhile that will feel comfortable and you will never put them on backwards again.  I also have a preflight that just before getting in the plane, period, I put my fingers on the tube of each cap and push up and down to make sure they are seated.  There has been a couple times that I forgot to put a cap on after fueling and this habbit found the cap off.

Beemer

Joined: 26 Aug 2006
Posts: 87
Location: Middle Georgia

Posted: Tue Jan 23, 2007 3:24 pm Post subject: Fuel Flow, continued.

I set my system up as two totally seperate, redundant systems. I have no 

interconnect between tanks. I installed a left-off-right valve, so that if 

one tank fouls, my emergency procedure is exactly as I learned in gen av - 

switch tanks, or go back to the good one if I already switched.



My header is my lifeline. It's a closed system with a level light. If the 

wing tanks stop feeding for any reason, the light goes on. I purge the tank 

with a vent overboard, and if 5 minutes pass and it's still on, I land and 

solve the problem. The header alone will sustain 30 minutes of flight at 

2gph. I figure I can get somewhere in that time.



No interconnect means that one fouled vent or cap off will not affect the 

other in any way. The chances of both caps being off are possible, and both 

vents plugging up are nil. It's redundancy.



Bradley



---

_________________
Beemer
KF2 (and now an M3!)
Suzuki G10 three-banger
Middle Georgia

Guy Buchanan

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

Posted: Tue Jan 23, 2007 3:57 pm Post subject: Fuel Flow, continued.

At 12:56 PM 1/23/2007, you wrote:

 	  Quote: 	
		  In the mean time, let's assume that we "loose" our right wing tank cap

(the left one is tight and in place).



Would it make any difference in this case?



Can we do anything about the situ?


	


I'm not sure what you're asking, Torgier. I did some calcs and the dynamic 

pressure at 115 MIAS at sea level equates to about 9" of static fuel head. 

(Assume the static pressure is the same across the open cap and at the vent 

pitot tip, a reasonable approximation.) This appears to mean that as long 

as you're going fast you can empty the left tank. When the fuel level in 

the left tank/line drops to 9" below that in the right tank you'll be at 

equilibrium. This will leave nearly the entire left fuel line and vent line 

full, and the right tank full. Both levels will drop simultaneously, all 

things being equal, with the left level 9" below the right. (This assumes 

the top of your header is more than 9" below the bottom of your tanks. I'm 

pretty sure mine is.)



If you slow down the 9" static fuel head drops as the square of the 

velocity. (E.g. at 57.5 MIAS the head will be 9/4" or 2.25") If you climb 

the static fuel head drops linearly with the air density. So if you find 

you're blowing fuel, slow down, climb high, lift the streaming wing a 

little, and you should be fine. Indeed you should be able to lift the wing 

enough to stop the leak.

Guy Buchanan

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

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

lcfitt(at)sbcglobal.net
Guest

Posted: Tue Jan 23, 2007 10:16 pm Post subject: Fuel Flow, continued.

My numbers are similar to Guy's



Some years ago I used a water manometer to check my airspeed indicator.  It 

doesn't take a lot of Delta Water  to indicate our airspeeds, for esample 

the delta at 30 mph is .74 inches, 90 is 4.13 inches and 6.18 inches at 120 

mph.  Since our fuel is about .75 the density of water, the head of our fuel 

would be .98", 5.49" and 8.21" at the corresponding airspeeds.



I had often heard it said that the pressure from the pitot vents is about 

one or so psi.  Apparently this is not true as the pressure at 120 mph would 

need to be about .3 psi to maintain a 8.21" column of water.



What this means, I haven't a clue really.  This I do know, On a flight from 

Las Vegas to Ely, Nevada a couple of years ago, I noticed the right tank had 

lost most of it's fuel.  The left tank was essentially full.  On landing I 

found that the fuel cap on the right tank had been attached at only one 

side.  For me, at least, I lost fuel apparently from a venturi effect and 

the low pressure on top of the wing from the mis fit cap sucking the tank 

dry and had apparently very little transfilling from the pressurized side.



Lowell



---

Float Flyr

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

Posted: Wed Jan 24, 2007 6:04 am Post subject: Fuel Flow, continued.

Lowell was it the left tank that had the cap partially open?



What I'm thinking is once the left tank is emptied a bit the vacuum caused

by the loose cap will travel along the vent line for the header tank to the

top of the right tank.  Once the fuel in the right tank is below the level

of the vent the vacuum will be broken by air coming in the right forward

facing vent.



If the right cap was the one partially open, the vacuum would have been

ducted to the header tank by both the vent and the right gas line.  That

could allow fuel to be drawn form the left tank faster than normal.



This is just a guess.  When you get into fluid dynamics things get a little

strange a lot of fast.



Noel



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

lcfitt(at)sbcglobal.net
Guest

Posted: Wed Jan 24, 2007 8:06 am Post subject: Fuel Flow, continued.

Noel



It was the right tank that had the fuel cap breach. It was the right tank 

that I noticed the significantly lower fuel level and by the time I landed, 

the right tank had lost fuel to the point I could barely see it in the sight 

gauge.  I never felt at risk as the left tank showed nearly full when I 

noticed the fuel loss with a normal drop thereafter.



There may have been some transfilling from the left tank, but that I can't 

say for sure.  The flight was about 210 miles and the duration was about two 

hours and my lament was that I had lost some expensive fuel - $86 for a two 

hour flight. The trip took 20.4 gallons (yes I still have the receipt) and a 

little over 8 gallons was burned in the two hours, leaving somewhat less 

than 12 gallons lost through the loose fuel cap.



Lowell



---

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Wed Jan 24, 2007 8:33 am Post subject: Fuel Flow, continued.

I have 2  - 6 gals wing tanks  and each has it's own shut off.

Each tank is a pitot tube cap .



They both flow together to a T fitting  then a Clear Fuel filter and I can 

clearly see the fuel flowing throught that filter.   Rivht in line after the 

filter is a Facet pump which I have a manual switch for but only use to 

transfer fuel to Dash tank  (  about 8.5 Gallon  and you can see the level 

in until about 2 gals left and you have to rock the wings to see the fuel 

slosh around)     After the Dash Tank the fuel flows into gascolator then to 

Fuel pump.



I usually fly off the main dash tank only and I only open the independant 

fuel valves from each wing tank  to transfer wing tank fuel  as needed to 

the dash tank .



If I was to loose a cap in flight -what would happen ?  Is this method ok ?

Dave

---

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clint_bazzill(at)hotmail.
Guest

Posted: Wed Jan 24, 2007 8:52 am Post subject: Fuel Flow, continued.

Looks like you were a victim of Mother Natures Vacuum cleaner.

From: "Lowell Fitt" <lcfitt(at)sbcglobal.net>

Reply-To: kitfox-list(at)matronics.com

To: <kitfox-list(at)matronics.com>

Subject: Re: Fuel Flow, continued.

Date: Wed, 24 Jan 2007 08:05:31 -0800

Noel

It was the right tank that had the fuel cap breach. It was the right tank 

that I noticed the significantly lower fuel level and by the time I landed, 

the right tank had lost fuel to the point I could barely see it in the sight 

gauge.  I never felt at risk as the left tank showed nearly full when I 

noticed the fuel loss with a normal drop thereafter.

There may have been some transfilling from the left tank, but that I can't 

say for sure.  The flight was about 210 miles and the duration was about two 

hours and my lament was that I had lost some expensive fuel - $86 for a two 

hour flight. The trip took 20.4 gallons (yes I still have the receipt) and a 

little over 8 gallons was burned in the two hours, leaving somewhat less 

than 12 gallons lost through the loose fuel cap.

Lowell

---

Guy Buchanan

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

Posted: Wed Jan 24, 2007 9:18 am Post subject: Fuel Flow, continued.

At 10:15 PM 1/23/2007, you wrote:

 	  Quote: 	
		  For me, at least, I lost fuel apparently from a venturi effect and

the low pressure on top of the wing from the mis fit cap sucking the tank

dry and had apparently very little transfilling from the pressurized side.


	


That's a tough one to figure out. Yes the wing has low pressure on the top, 

but we only deal in pressure differentials. The question becomes, where was 

the higher pressure coming from? In my system the only source is the fuel 

in the opposite tank, since you can't push fuel uphill with air. Any air 

that came from a high pressure source would percolate through the fuel in 

the right tank and exit at the low pressure vent. To generalize that point 

I don't see how you can push fuel out a cap with a high pressure vapor 

source. So the question remains, how did you push the fuel out your cap? I 

confess that from the facts of the case I'm stuck for an answer.



One possible answer I can imagine is that you reduced the pressure in the 

tank so much the fuel vaporized. Is it possible to vaporize 12 gallons of 

gas in two hours? I confess that's beyond my expertise so someone else will 

have to figure it out. (It also seems rather unlikely you could generate 

enough gas exchange with a cracked cap.)

Guy Buchanan

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

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

lcfitt(at)sbcglobal.net
Guest

Posted: Wed Jan 24, 2007 11:50 am Post subject: Fuel Flow, continued.

Guy,  I don't know what is happening here, but have a friend that lost a 

bunch of fuel from a tank with no fuel cap and it was a Cessna with no pitot 

on the opposite side unless the vent behind the lift strut provides a bit of 

ram pressure.  I don't know how the fuel selector was set.



There is one overriding assumption that seems to be common to all the posts 

and that is that the  fuel essentially sits quitely and overflows the tank 

filler neck because of transfilling.  I don't think that is necessarily the 

case.  Based on what I experienced and the tales of others - granted the 

sample is very small,  Consider that my flight was in Central Nevada over 

the desert and mountains and there is always turbulance there.



Lowell



---

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