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byronmfox(at)gmail.com
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 Posted: Mon Jan 09, 2012 3:42 pm Post subject: Uneven fuel feed CJ6 |
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Keeping the wings level and the ball centered will generally help to keep the tanks in balance. If, like me, however, you're a bit inattentive, purchase Bill Blackwell's fuel vent control kit. This allows you to shutoff the vent to low tank so that the more full tank feeds more rapidly. Works well.
...Blitz
On Mon, Jan 9, 2012 at 3:30 PM, bipolar <bushrat(at)telus.net (bushrat(at)telus.net)> wrote:
| Quote: | --> Yak-List message posted by: "bipolar" <bushrat(at)telus.net (bushrat(at)telus.net)>
Happy New Year all
As a new CJ owner I love the aircraft not crazy about the uneven fuel feed
What is the fix/procedure to even this out?
Thank you
Read this topic online here:
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... Blitz
Byron M. Fox
80 Milland Drive
Mill Valley, CA 94941
415-307-2405
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cjpilot710(at)aol.com
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| Posted: Mon Jan 09, 2012 8:00 pm Post subject: Uneven fuel feed CJ6 |
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Yaw.
In a message dated 1/9/2012 6:33:22 P.M. Eastern Standard Time, bushrat(at)telus.net writes:
| Quote: | --> Yak-List message posted by: "bipolar" <bushrat(at)telus.net>
Happy New Year all
As a new CJ owner I love the aircraft not crazy about the uneven fuel feed
What is the fix/procedure to even this out?
Thank you
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=362888#362888
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[quote][b]
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barryhancock
Joined: 09 Oct 2008
Posts: 285
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| Posted: Tue Jan 10, 2012 9:41 am Post subject: Re: Uneven fuel feed CJ6 |
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3 axis electric trim. Independent fuel vents for left and right tanks. While you're at it may as well do a ground up restoration.  . The above is what I have on my aircraft and the fuel imbalance problem is solved. I realize that's not a workable solutiion for everyone, however. A fuel selector valve would be great if someone would engineer that. Blackwell's vent switch system seems to work, also. Other than that, get used to flying sideways for awhile....
Happy Skidding,
Barry
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Barry Hancock
Worldwide Warbirds, Inc.
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byronmfox(at)gmail.com
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| Posted: Tue Jan 10, 2012 1:11 pm Post subject: Uneven fuel feed CJ6 |
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While still on this subject, a word of caution. Do as I say, not as I did.
I installed Bill Blackwell's fuel vent control system about 6 years ago. And, as mentioned, it works well. Care, however, must be taken not to leave a vent closed for too long. Our CJ fuel tanks are made of light weight aluminum, and will collapse. Shortly after installing the system, I forgot to open the left tank vent and landed. At the gas pump, I was startled when I had to pull the left gas cap off to overcome the vacuum in the tank. The consequent oil-canning noise really got my attention as air rushed back into the tank.
OK, a new procedure -- cycle the vent switch every 5 minutes when balancing the fuel tanks.
I thought I had dodged the bullet, but 6 years hence the left tank developed a leak 3 weeks ago. Sure enough, the outboard end of my old tank had collapsed inward a bit, making it concave instead of convex. Adjacent to the grounding strap tab welded to the end of the tank a crack had developed. The good news is that Doug Sapp had a new tank in stock.
So, either buy fuel bladders to replace the aluminum tanks, or cycle the vent switches very, very frequently.
...Blitz
On Tue, Jan 10, 2012 at 9:41 AM, barryhancock <bhancock(at)worldwidewarbirds.com (bhancock(at)worldwidewarbirds.com)> wrote:
| Quote: | --> Yak-List message posted by: "barryhancock" <bhancock(at)worldwidewarbirds.com (bhancock(at)worldwidewarbirds.com)>
3 axis electric trim. Independent fuel vents for left and right tanks. While you're at it may as well do a ground up restoration. . The above is what I have on my aircraft and the fuel imbalance problem is solved. I realize that's not a workable solutiion for everyone, however. A fuel selector valve would be great if someone would engineer that. Blackwell's vent switch system seems to work, also. Other than that, get used to flying sideways for awhile....
Happy Skidding,
Barry
--------
Barry Hancock
Worldwide Warbirds, Inc.
[url=tel:%28877%29%20869-6458](877) 869-6458[/url]
www.worldwidewarbirds.com
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http://forums.matronics.com/viewtopic.php?p=362945#362945
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... Blitz
Byron M. Fox
80 Milland Drive
Mill Valley, CA 94941
415-307-2405
[quote][b]
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threein60(at)yahoo.com
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| Posted: Tue Jan 10, 2012 1:32 pm Post subject: Uneven fuel feed CJ6 |
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Ken worth trucks makes a pneumatic/electrical toggle switch that allows you to add a panel light to indicate when these vents are closed. This will allow you to know or remind you that a vent is closed. I have seen a CJ with bladders flame out when the cell completely collapsed. Just a little trick that adds safety.
Larry Pine
--- On Tue, 1/10/12, Byron Fox <byronmfox(at)gmail.com> wrote:
| Quote: |
From: Byron Fox <byronmfox(at)gmail.com>
Subject: Re: Re: Uneven fuel feed CJ6
To: yak-list(at)matronics.com
Date: Tuesday, January 10, 2012, 2:08 PM
While still on this subject, a word of caution. Do as I say, not as I did.
I installed Bill Blackwell's fuel vent control system about 6 years ago. And, as mentioned, it works well. Care, however, must be taken not to leave a vent closed for too long. Our CJ fuel tanks are made of light weight aluminum, and will collapse. Shortly after installing the system, I forgot to open the left tank vent and landed. At the gas pump, I was startled when I had to pull the left gas cap off to overcome the vacuum in the tank. The consequent oil-canning noise really got my attention as air rushed back into the tank.
OK, a new procedure -- cycle the vent switch every 5 minutes when balancing the fuel tanks.
I thought I had dodged the bullet, but 6 years hence the left tank developed a leak 3 weeks ago. Sure enough, the outboard end of my old tank had collapsed inward a bit, making it concave instead of convex. Adjacent to the grounding strap tab welded to the end of the tank a crack had developed. The good news is that Doug Sapp had a new tank in stock.
So, either buy fuel bladders to replace the aluminum tanks, or cycle the vent switches very, very frequently.
...Blitz
On Tue, Jan 10, 2012 at 9:41 AM, barryhancock <[url=/mc/compose?to=bhancock(at)worldwidewarbirds.com]bhancock(at)worldwidewarbirds.com[/url]> wrote:
| Quote: | --> Yak-List message posted by: "barryhancock" <[url=/mc/compose?to=bhancock(at)worldwidewarbirds.com]bhancock(at)worldwidewarbirds.com[/url]>
3 axis electric trim. Independent fuel vents for left and right tanks. While you're at it may as well do a ground up restoration. . The above is what I have on my aircraft and the fuel imbalance problem is solved. I realize that's not a workable solutiion for everyone, however. A fuel selector valve would be great if someone would engineer that. Blackwell's vent switch system seems to work, also. Other than that, get used to flying sideways for awhile....
Happy Skidding,
Barry
--------
Barry Hancock
Worldwide Warbirds, Inc.
(877) 869-6458
www.worldwidewarbirds.com
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=362945#362945
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... Blitz
Byron M. Fox
80 Milland Drive
Mill Valley, CA 94941
415-307-2405
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javiercarrascob
Joined: 06 Sep 2009
Posts: 62
Location: Virginia
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| Posted: Tue Jan 10, 2012 1:45 pm Post subject: Uneven fuel feed CJ6 |
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Also Check your tank caps,
My '55 uneven fuel consumption aggravated once the rubber seal in on of the caps came too lose, I switched the tank caps and I can see the transfer issue switch to the other tank. Recently I had both caps refitted and we are back to the normal "unbalance".
It seems that the tank on the side that had the good cap was the one running lower on gas always, switching the caps and the problem switched sides.
JC
--- On Tue, 1/10/12, Byron Fox <byronmfox(at)gmail.com> wrote:
| Quote: |
From: Byron Fox <byronmfox(at)gmail.com>
Subject: Re: Re: Uneven fuel feed CJ6
To: yak-list(at)matronics.com
Date: Tuesday, January 10, 2012, 4:08 PM
While still on this subject, a word of caution. Do as I say, not as I did.
I installed Bill Blackwell's fuel vent control system about 6 years ago. And, as mentioned, it works well. Care, however, must be taken not to leave a vent closed for too long. Our CJ fuel tanks are made of light weight aluminum, and will collapse. Shortly after installing the system, I forgot to open the left tank vent and landed. At the gas pump, I was startled when I had to pull the left gas cap off to overcome the vacuum in the tank. The consequent oil-canning noise really got my attention as air rushed back into the tank.
OK, a new procedure -- cycle the vent switch every 5 minutes when balancing the fuel tanks.
I thought I had dodged the bullet, but 6 years hence the left tank developed a leak 3 weeks ago. Sure enough, the outboard end of my old tank had collapsed inward a bit, making it concave instead of convex. Adjacent to the grounding strap tab welded to the end of the tank a crack had developed. The good news is that Doug Sapp had a new tank in stock.
So, either buy fuel bladders to replace the aluminum tanks, or cycle the vent switches very, very frequently.
...Blitz
On Tue, Jan 10, 2012 at 9:41 AM, barryhancock <bhancock(at)worldwidewarbirds.com (bhancock(at)worldwidewarbirds.com)> wrote:
| Quote: | --> Yak-List message posted by: "barryhancock" <bhancock(at)worldwidewarbirds.com (bhancock(at)worldwidewarbirds.com)>
3 axis electric trim. Independent fuel vents for left and right tanks. While you're at it may as well do a ground up restoration. . The above is what I have on my aircraft and the fuel imbalance problem is solved. I realize that's not a workable solutiion for everyone, however. A fuel selector valve would be great if someone would engineer that. Blackwell's vent switch system seems to work, also. Other than that, get used to flying sideways for awhile....
Happy Skidding,
Barry
--------
Barry Hancock
Worldwide Warbirds, Inc.
(877) 869-6458
www.worldwidewarbirds.com
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=362945#362945
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--
... Blitz
Byron M. Fox
80 Milland Drive
Mill Valley, CA 94941
415-307-2405
| Quote: |
et=_blank rel=nofollow>http://www.matronics.com/Navigator?Yak-List
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[quote][b]
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gill.g(at)gpimail.com
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| Posted: Tue Jan 10, 2012 2:24 pm Post subject: Uneven fuel feed CJ6 |
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The vent control system was never approved for anything but fuel bladders. Do not install on standard metal tanks.
Gill
From: owner-yak-list-server(at)matronics.com [mailto:owner-yak-list-server(at)matronics.com] On Behalf Of Byron Fox
Sent: Tuesday, January 10, 2012 2:08 PM
To: yak-list(at)matronics.com
Subject: Re: Re: Uneven fuel feed CJ6
While still on this subject, a word of caution. Do as I say, not as I did.
I installed Bill Blackwell's fuel vent control system about 6 years ago. And, as mentioned, it works well. Care, however, must be taken not to leave a vent closed for too long. Our CJ fuel tanks are made of light weight aluminum, and will collapse. Shortly after installing the system, I forgot to open the left tank vent and landed. At the gas pump, I was startled when I had to pull the left gas cap off to overcome the vacuum in the tank. The consequent oil-canning noise really got my attention as air rushed back into the tank.
OK, a new procedure -- cycle the vent switch every 5 minutes when balancing the fuel tanks.
I thought I had dodged the bullet, but 6 years hence the left tank developed a leak 3 weeks ago. Sure enough, the outboard end of my old tank had collapsed inward a bit, making it concave instead of convex. Adjacent to the grounding strap tab welded to the end of the tank a crack had developed. The good news is that Doug Sapp had a new tank in stock.
So, either buy fuel bladders to replace the aluminum tanks, or cycle the vent switches very, very frequently.
...Blitz
On Tue, Jan 10, 2012 at 9:41 AM, barryhancock <bhancock(at)worldwidewarbirds.com (bhancock(at)worldwidewarbirds.com)> wrote:
--> Yak-List message posted by: "barryhancock" <bhancock(at)worldwidewarbirds.com (bhancock(at)worldwidewarbirds.com)>
3 axis electric trim. Independent fuel vents for left and right tanks. While you're at it may as well do a ground up restoration. . The above is what I have on my aircraft and the fuel imbalance problem is solved. I realize that's not a workable solutiion for everyone, however. A fuel selector valve would be great if someone would engineer that. Blackwell's vent switch system seems to work, also. Other than that, get used to flying sideways for awhile....
Happy Skidding,
Barry
--------
Barry Hancock
Worldwide Warbirds, Inc.
[url=tel:%28877%29%20869-6458](877) 869-6458[/url]
www.worldwidewarbirds.com
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=362945#362945
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rget="_blank">http://www.matronics.com/Navigator?Yak-List
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http://forums.matronics.com
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le, List Admin.
="_blank">http://www.matronics.com/contribution
===========
--
... Blitz
Byron M. Fox
80 Milland Drive
Mill Valley, CA 94941
415-307-2405
| Quote: | | http://www.matronics.com/Navigator?Yak-List |
01234567
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brian(at)lloyd.com
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| Posted: Tue Jan 10, 2012 3:44 pm Post subject: Uneven fuel feed CJ6 |
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Fuel tank venting is a very interesting subject, especially when you are trying to feed fuel evenly from two wing tanks at the same time. This is one of those things where it pays to do some research into how others have solved this problem before. Perhaps the most interesting source of information on this is Cessna and how they have tried to deal with the uneven fuel flow from the tanks in their aircraft that have a single "both on" position. Reading the service bulletins over the years addressing all the changes and "improvements" is very educational. And I would bet that the Cessna engineers working on the problem probably had more knowledge and experience than we do. Regardless, from what I can tell, they never really found a satisfactory solution other than, "switch to one tank or the other."
You can do a lot but one of the things I would studiously avoid is separate vents for the two (or four) tanks. If you want the two tanks to feed at the same rate then the tank pressure must be exactly equal. The only way you can assure that is to have only one source of tank pressurization for all tanks. Cessna experimented with a single vent and dual vents. I believe they finally settled on a single vent.
Blitz' comment about pulling a vacuum in a tank with the vent off tells me that something else is seriously wrong. That implies that fuel was being sucked from the tank with the vent turned off rather than that tank just not feeding. The vent to the other tank and to the header tank should have been open, allowing free flow of fuel from those tanks with no real suction (other than normal 'head') on the tank with the switched-off vent. Blitz, if that had happened to my plane you can bet your sweet ass that I would ground my airplane and be tearing apart my vent system to figure out why there was enough restriction in the flow of the other tanks to allow ambient pressure to partially collapse the tank. Not good!
So, were it me (and I know that there are those of you who listen very carefully to what I say and then do just the opposite  I would stick with the single-point, high-pressure (belly) vent and then deal with uneven fuel flow the simplest way possible -- fly with the ball toward the emptier tank.
BTW, there is one small problem with the single-point vent that some of you may have experienced -- the fuel siphon. It is possible to actually have fuel siphon out of the vent onto the ground (a LOT of fuel). The fuel vent has a loop in the cockpit that keeps the top of the vent line above the high-fuel point in the tanks. It is possible if the tanks are completely full and the plane is sitting in the hot sun, that the fuel can push up through the vent which can start a siphon and cause a lot of fuel to end up going overboard. The fix for this would be to put a vacuum-breaker valve at the top of the vent loop in the cockpit.
So, my closing comment is -- eschew excessive complexity. Extra switches, valves, indicators, etc., come under the heading of excessive complexity. Proper maintenance of the fuel and vent system coupled with good piloting technique is more than adequate to deal with the problem.
YMMV.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian(at)lloyd.com (brian(at)lloyd.com)
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
[quote][b]
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wlannon(at)shaw.ca
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| Posted: Tue Jan 10, 2012 8:47 pm Post subject: Uneven fuel feed CJ6 |
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I would agree with Brian's closing comments here 100%.
Vent shut off valves are an abomination and any other changes to the vent system are a waste of time and money and could make matters worse..
In fact the vent system is not the problem! It is by no means perfect but (unless it is plugged, partially plugged or a line is kinked) it accounts for a very minor part of the uneven fuel feed and only because of the unequal pipeline lengths to the main tanks.
Before I go any further I must note that I refer only to the CJ6 and none of the Yak series of which I have no knowledge.
The real problem is the design of the header tank flapper valves. There are three of these valves in the aircraft one of which is the fuel feed line non-return valve. In this application the valve design is excellent and it works perfectly.
That is not the case in the header tank.
In the engine fuel line the (very low) head pressure from the weight of the fuel opposing the zero or negative pressure from the fuel pump readily opens the flapper.
In the header tank the same conditions do not exist.
Lets assume full tanks on both sides and further assume that fuel load produces a 1 psi pressure to open each flapper (actually it will be closer to 0.1 psi). Lets also assume a perfectly clean and equal vent system and the aircraft is flying in a vacuum with zero turbulence and zero yaw so there are no other forces involved.
Since the pressure to open both flappers is the same and there is no fuel movement other than that generated by the fuel pump both flappers should be open and the tanks should drain equally.
Well, lets put in a little reality. Only one is open, probably the left side since the vent line and the fuel feed line are shorter and produce slightly less flow resistance.
As the fuel leaves the RH tank the pressure in the header tank is decreasing and the 1psi on the left side should open that flapper. In fact, with the assumptions we have made above, it will not open until the RH tank is near empty.
The reason for this is even though we have approx. equal pressure in psi the actual force on each side of the flapper is nowhere near equal.
The numbers to follow are approx. examples only, I did this work some years ago and do not recall the actual numbers.
The 1 psi acting to open the flapper is applying pressure to an area of 0.125 sq. in. or a force of 0.125 lbs.
The 1 psi holding the valve closed is applying pressure to an area of 0.44 sq. in for a force of 0.44 lbs.
The only factor that allows this system to work is fuel movement due to turbulence, yaw, etc. Fortunately it is difficult to fly in a vacuum.
The fix of course is to modify the valve assy so the force acting on each side is near equal.
I have done five CJ's so far with really excellent results on the 3 flying ones. Doug Sapps and my own are the two exceptions since neither is flying yet. (Who goes first Doug?)
I was able to do a lot of testing with the first one and rarely ever saw an imbalance over 10 lts. except with a point roll or a true slow roll.
With the valves flapping freely that action will give an imbalance but one minute of level flight and it is back to normal.
Theoretically, since there is some vent & feed line difference and it is impractical to get a perfect line contact valve seat, you could expect an imbalance of up to 13 lts in a turbulence and yaw free flight.
If anyone wants further info let me know.
Walt
wlannon(at)shaw.ca (wlannon(at)shaw.ca)
[quote] ---
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wlannon(at)shaw.ca
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| Posted: Tue Jan 10, 2012 9:28 pm Post subject: Uneven fuel feed CJ6 |
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I just proof read my diatribe. Always do that just after I send it!
About half way through I wrote "As fuel leaves the RH tank-----------------and the 1 psi on the LEFT side --------------------------will not open until the RH-----------------------"
Should read LH----------right------------LH.
Oh well!!!
Walt
---
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dave(at)davelaird.com
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| Posted: Tue Jan 10, 2012 10:19 pm Post subject: Uneven fuel feed CJ6 |
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Walt... what would happen with NO flapper valves on the header tank...?
Dave Laird
N63536 1983 CJ6A "Betty"
Dallas * Austin
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Harv
Joined: 01 Jul 2010
Posts: 172
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brian(at)lloyd.com
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| Posted: Wed Jan 11, 2012 8:04 am Post subject: Uneven fuel feed CJ6 |
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On Tue, Jan 10, 2012 at 10:16 PM, Dave Laird <dave(at)davelaird.com (dave(at)davelaird.com)> wrote:
| Quote: | --> Yak-List message posted by: Dave Laird <dave(at)davelaird.com (dave(at)davelaird.com)>
Walt... what would happen with NO flapper valves on the header tank...?
|
Fuel would flow from the high tank, through the header tank, and out to the low tank. This would cause the imbalance to develop twice as quickly and/or be twice as bad. (Well, not twice because it is possible to feed fuel faster than to have it flow back out to a tank -- head pressure and pump draw.) The flapper valves are a good idea, if they are working properly. The trick is making sure that they are always working properly.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian(at)lloyd.com (brian(at)lloyd.com)
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
[quote][b]
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brian(at)lloyd.com
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| Posted: Wed Jan 11, 2012 8:14 am Post subject: Uneven fuel feed CJ6 |
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On Wed, Jan 11, 2012 at 4:46 AM, Harv <martin.harvey(at)kbr.com (martin.harvey(at)kbr.com)> wrote:
| Quote: | --> Yak-List message posted by: "Harv" <martin.harvey(at)kbr.com (martin.harvey(at)kbr.com)>
Chaps
I also wonder what whould happen with no flapper valves (would the problem go away)?
I have an untested idea...
Whilst we have a comparison to the Cessna 152 fuel vent......
An observation I made the other day is that the style of fuel vent on the Cessna differs from the CJ in how it termiates under the aircraft. The Cessna vent is bent into wind like this "J" and the CJ one terminates straight down like this "I".
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They both accomplish the same thing. The vent in the belly of the CJ is in a high-pressure area. The Cessna vent is on the lower side of the wing (high pressure) and it is a pitot tube so it gains from dynamic pressure. The key is that both pressurize the tank above ambient pressure insuring positive flow.
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I would think that the Cessna 'bent vent pipe' will have air forced into it during normal flight and will result in a positive pressure in the fuel tanks (provided the vent tubes are clear) but the CJ 'straight vent pipe' will have air passing over the tube which will create a suction or a vacuum in the tanks.
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Well, flow is not really an issue for the belly vent because the vent is in the boundary layer and there really isn't any flow to produce a pressure reduction. And it is a high pressure area.
| Quote: | Anyone care to try a "bent into wind vent pipe" mod to the CJ and see if the imbalance improves?
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It probably wouldn't help that much, if at all. I suspect that Bushi Cheng and friends took all this into account.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian(at)lloyd.com (brian(at)lloyd.com)
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
[quote][b]
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wlannon(at)shaw.ca
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| Posted: Wed Jan 11, 2012 9:07 am Post subject: Uneven fuel feed CJ6 |
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Hi Dave;
The flapper valves are necessary to ensure there is always a supply of fuel
in the header tank. Without them fuel would move from one tank to the other
with yaw, etc.
---
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byronmfox(at)gmail.com
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| Posted: Wed Jan 11, 2012 10:35 am Post subject: Uneven fuel feed CJ6 |
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Just had a call from Craig Ekberg with the following he asked me to post:
"The CJ's single fuel vent tube on the left side of the fuselage comes from the factory with its end cut at a 45 degree angle facing forward into the slipstream . This pressurizes the vent line and the tanks. Consequently, because of proximity, the left tank more so than the right. Net, net, net the left tank feeds more rapidly than the right. The solution is simple. Trim the end of the vent tube to 90 degrees. It's still vents, but no longer pressurizes. I did this to my CJ and many others for over a decade. No more imbalance problem."
Sent from my iPhone
On Jan 11, 2012, at 9:04 AM, "Walter Lannon" <wlannon(at)shaw.ca> wrote:
[quote]
Hi Dave;
The flapper valves are necessary to ensure there is always a supply of fuel in the header tank. Without them fuel would move from one tank to the other with yaw, etc.
---
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brian(at)lloyd.com
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| Posted: Wed Jan 11, 2012 1:34 pm Post subject: Uneven fuel feed CJ6 |
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On Wed, Jan 11, 2012 at 10:33 AM, Byron Fox <byronmfox(at)gmail.com (byronmfox(at)gmail.com)> wrote:
| Quote: | --> Yak-List message posted by: Byron Fox <byronmfox(at)gmail.com (byronmfox(at)gmail.com)>
Just had a call from Craig Ekberg with the following he asked me to post:
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And I must apologize, but I disagree with this post based on what appears to be a misunderstanding of some physical principles.
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"The CJ's single fuel vent tube on the left side of the fuselage comes from the factory with its end cut at a 45 degree angle facing forward into the slipstream . This pressurizes the vent line and the tanks. |
Given how the layer of air, called the boundary layer, right next to the skin of the airplane does not move (or moves very little), even cutting the line at a 45-degree angle has little effect unless the vent line is extended a significant distance past the skin of the plane.
| Quote: | | Consequently, because of proximity, the left tank more so than the right. Net, net, net the left tank feeds more rapidly than the right. |
Again, my apologies for disagreeing, but this is not the case. Gas pressure in a vessel is equal in all parts of that vessel. If the vent lines between tanks are not blocked then the vent pressure in both tanks is equal. Proximity to one tank or another has no effect. If the fuel is flowing very rapidly giving rise to significant flow of air in the vent line then it is possible that a noticeable difference in length could cause a difference in flow rate but that is not what we are dealing with here.
| Quote: | The solution is simple. Trim the end of the vent tube to 90 degrees. It's still vents, but no longer pressurizes. I did this to my CJ and many others for over a decade. No more imbalance problem."
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Well, you may have solved your imbalance problem but this is not the reason. And the tanks are indeed pressurized anyway, The belly of the airplane is a high-pressure area on the airframe. That is why the vent is terminated there. You want some positive pressure in the tanks to facilitate flow from the tanks to the engine.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian(at)lloyd.com (brian(at)lloyd.com)
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
[quote][b]
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dave(at)davelaird.com
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| Posted: Wed Jan 11, 2012 1:49 pm Post subject: Uneven fuel feed CJ6 |
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makes sense to me... thanks walt and brian...i think the flapper valves like some MMO on occasion to keep them happy...
-dave
On Jan 11, 2012, at 10:02 AM, Brian Lloyd wrote:
[quote]
On Tue, Jan 10, 2012 at 10:16 PM, Dave Laird <dave(at)davelaird.com (dave(at)davelaird.com)> wrote:
| Quote: | --> Yak-List message posted by: Dave Laird <dave(at)davelaird.com (dave(at)davelaird.com)>
Walt... what would happen with NO flapper valves on the header tank...?
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Fuel would flow from the high tank, through the header tank, and out to the low tank. This would cause the imbalance to develop twice as quickly and/or be twice as bad. (Well, not twice because it is possible to feed fuel faster than to have it flow back out to a tank -- head pressure and pump draw.) The flapper valves are a good idea, if they are working properly. The trick is making sure that they are always working properly.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian(at)lloyd.com (brian(at)lloyd.com)
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
[b]
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bipolar
Joined: 16 Apr 2011
Posts: 9
Location: Canada
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| Posted: Sat Jan 14, 2012 4:57 pm Post subject: Re: Uneven fuel feed CJ6 |
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Thanks for all the info guys
Gives me a project to play with while it is to cold to fly
DR
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Pete Fowler
Joined: 07 Jul 2009
Posts: 76
Location: California
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| Posted: Sun Jan 15, 2012 6:49 pm Post subject: Re: Uneven fuel feed CJ6 |
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I had "problems" with asymmetrical fuel flow on my stock CJ. Until, that is, I got a level tie-down. The problem was that no matter what, starting with an asymmetrical fuel level always lead to asymmetrical fuel all the way through the flight regardless of how carefully I filled to "level" it on the ground before I set off.
Never had more than 1/2 a gallon fuel imbalance the rest of the time I flew the plane from the level tie down. I also forward cut the left vent tube as per Craig and all the local guys. That always helps.
Nanchang CJ-6s = 50+ years operating just they way they roll off the factory floor with no issues.
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