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Mark.Napier(at)sciatl.com
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 Posted: Thu Jul 13, 2006 11:32 am Post subject: Low Fuel Warning - Tank venting |
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Hey Dave,
I've still got the forward header tank and rear selector valves. The
builder got around the fuel feed problem with a header pump and it does
work well. But at some point I install a rear header tank to make room
for a radio in the panel.
However the KF rear header system does have a weak point. Since both
tanks drain to the common header the tanks should be cross vented. It's
a requirement for certified planes if they have a selector with a "both"
position or both tanks just feed together like a C152.
With the suggested system if one wing tank vent becomes blocked then
that tank won't feed. Cross venting solves the problem.
Another problem with no cross venting is that if one tank has a faulty
seal on the gas cap then the pressure from the other vent will blow all
the gas in the system out the bad gas cap. There have been some
accidents like this, yes? With cross venting a bad cap will only suck
gas out until the tank vents on both sides are uncovered and then stop.
Of course the lowered pressure might cause a fuel feed problem....
What I don't know is how to add that new vent line to the top inside of
the left wing tank without causing a brand new leak. I'd love to hear
any good ideas or experiences.
FWIW,
Mark Napier
------------------------------------------------------------------------
---
Time: 01:22:52 PM PST US
Lowell,
I learned many years ago as part of my walkaround that when at tail of
plane
to look forward and check gas caps and make sure they are there in in
right
position visually. After a refueling -same thing walkaround look at
tail,
make sure tailwheel still there etc and look forward to gas caps. The
low
pressure on top of wings will drain your tanks very quickly if the cap
comes
off. I would only gues that a poor sealing cap "might " do the same.
Dave
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pwmac(at)sisna.com
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| Posted: Thu Jul 13, 2006 12:49 pm Post subject: Low Fuel Warning - Tank venting |
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Hello Mark,
Not sure I understand what you are saying. The KF design, with the
back of the seat header tank, has no selector valves and only one
vent is necessary. Flow tanks flow to the header and unless the right
tank becomes sealed from the atmosphere venting would be
accomplished. Sealing of the right tank is certainly a possibility
but IMO, quite remote. As you noted the tank wont feed if the supply
to the header is blocked. But, the other one would feed if the vent
is not blocked. The vent line is an important item and must be routed
to prevent any restriction or loops that could trap a slug of fuel
which could restrict or block the venting. Use of a stiff hose might
be called for.
If you have a tank selector valve then you are not following the KF
design, but if there is no failure in the vent system then the tank
that is selected will still feed. No matter what, the KF design works
unless the right tank becomes sealed or the vent becomes blocked.
When that happens your low level sensor in the header tank will tell
you that you are running out of fuel and you have a finite amount of
time to get to the ground.
And yes a cross feed would protect against a missing cap or gasket
or improperly installed gas cap. With one vent the problem is worse
than with both tanks vented. Cessna's I am familiar with have the
leaky/missing tank cap failure mode. Pretty hard to protect.
Having said all the above its not a big deal to add a vent to the
left tank. Here a sound method. Epoxy a plate on the outside of the
tank drill a hole thru it and the tank. Then get one of those trick
fittings and insert it from inside to out and put the nut on it to
squeeze the internal o-ring. The internal o-ring S/B Viton compatible
with the fuel you are using. If you cannot locate the fitting just
find a machinist and have him make you one. It vaguely looks like a
metal valve stem like the ones you see on alloy auto wheels. It has a
groove under the head to capture the o-ring. The metal plate doubler
is required because the fiberglass is too thin for a fitting, IMO
Then just install a tee at the vent outlet on the header tank.
Install the fitting by letting it slide down a wire.
Lots of trouble and work for such a remote failure. Your prop bolts
probably present a higher risk than the failures that prevent venting
form the header. Its your plane and adding a vent to the other tanks
is pretty low risk.
Regards, Paul
PS, I do not like selector valves, R/L/B or R/L/B/O, because its just
not necessary for safe flight. A passive fuel system if the safest.
Then pilot error is eliminated.
==============================
At 01:31 PM 7/13/2006, you wrote:
| Quote: |
Hey Dave,
I've still got the forward header tank and rear selector valves. The
builder got around the fuel feed problem with a header pump and it does
work well. But at some point I install a rear header tank to make room
for a radio in the panel.
However the KF rear header system does have a weak point. Since both
tanks drain to the common header the tanks should be cross vented. It's
a requirement for certified planes if they have a selector with a "both"
position or both tanks just feed together like a C152.
With the suggested system if one wing tank vent becomes blocked then
that tank won't feed. Cross venting solves the problem.
Another problem with no cross venting is that if one tank has a faulty
seal on the gas cap then the pressure from the other vent will blow all
the gas in the system out the bad gas cap. There have been some
accidents like this, yes? With cross venting a bad cap will only suck
gas out until the tank vents on both sides are uncovered and then stop.
Of course the lowered pressure might cause a fuel feed problem....
What I don't know is how to add that new vent line to the top inside of
the left wing tank without causing a brand new leak. I'd love to hear
any good ideas or experiences.
FWIW,
Mark Napier
------------------------------------------------------------------------
---
Time: 01:22:52 PM PST US
Lowell,
I learned many years ago as part of my walkaround that when at tail of
plane
to look forward and check gas caps and make sure they are there in in
right
position visually. After a refueling -same thing walkaround look at
tail,
make sure tailwheel still there etc and look forward to gas caps. The
low
pressure on top of wings will drain your tanks very quickly if the cap
comes
off. I would only gues that a poor sealing cap "might " do the same.
Dave
- - - - - Appended by Scientific Atlanta, a Cisco company - -
- - - This e-mail and any attachments may contain information
which is confidential, proprietary, privileged or otherwise
protected by law. The information is solely intended for the named
addressee (or a person responsible for delivering it to the
addressee). If you are not the intended recipient of this message,
you are not authorized to read, print, retain, copy or disseminate
this message or any part of it. If you have received this e-mail in
error, please notify the sender immediately by return e-mail and
delete it from your computer.
|
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dosmythe(at)cox.net
Guest
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| Posted: Thu Jul 13, 2006 1:27 pm Post subject: Low Fuel Warning - Tank venting |
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I've tried to read all this header venting thing but was lazy and tended to
skip lines so, forgive me if I misread the thread. Standby to throw things
at me. The header vent line only assist in venting off the air in the
header tank and has little or nothing to do with fuel flow from the wing
tanks. Picture this, place a 5 gallon bucket on top of your work bench.
Attach a garden hose via a fitting at the bottom and fill it with water.
The water flows freely on the floor because the top of the bucket is open
and providing air. Gravity does the rest. There is NO vent in this
described system. Take a header that is full of fuel with the vent line
plugged. Fuel will gravity flow down the supply lines as long as the tank
cap is vented to the outside.
I initially installed the second vent to the other tank but removed it
later in a weight reduction binge. Now, if you plug the vent on top of the
wing then you might see some problems but I don't think that's the vent
being discussed.
BTW, I think the Avid used a similar header vent but was closed except for
pre-flight venting or during initial filling of the header. Might be wrong
on that???
Don Smythe
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roncarolnikko(at)hotmail.
Guest
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| Posted: Thu Jul 13, 2006 3:38 pm Post subject: Low Fuel Warning - Tank venting |
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Don I have been fighting vaporlock that forms after folding my wings. The
fuel pushing down (2") in tanks, although above the air in the line, is less
than the 18" lift required to get it up and over the firewall and down to
carb. Once bled out it flows freely, but what about after -g or slips.
Ron NB Or
[quote]From: "Don Smythe" <dosmythe(at)cox.net>
Reply-To: kitfox-list(at)matronics.com
To: <kitfox-list(at)matronics.com>
Subject: Re: Low Fuel Warning - Tank venting
Date: Thu, 13 Jul 2006 17:25:35 -0400
I've tried to read all this header venting thing but was lazy and tended to
skip lines so, forgive me if I misread the thread. Standby to throw things
at me. The header vent line only assist in venting off the air in the
header tank and has little or nothing to do with fuel flow from the wing
tanks. Picture this, place a 5 gallon bucket on top of your work bench.
Attach a garden hose via a fitting at the bottom and fill it with water.
The water flows freely on the floor because the top of the bucket is open
and providing air. Gravity does the rest. There is NO vent in this
described system. Take a header that is full of fuel with the vent line
plugged. Fuel will gravity flow down the supply lines as long as the tank
cap is vented to the outside.
I initially installed the second vent to the other tank but removed it
later in a weight reduction binge. Now, if you plug the vent on top of the
wing then you might see some problems but I don't think that's the vent
being discussed.
BTW, I think the Avid used a similar header vent but was closed except for
pre-flight venting or during initial filling of the header. Might be wrong
on that???
Don Smythe
.
---
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dosmythe(at)cox.net
Guest
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| Posted: Thu Jul 13, 2006 4:15 pm Post subject: Low Fuel Warning - Tank venting |
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Ron,
I'm not sure I understand your setup. After folding the wings back and
out again, the system from the wing tanks to the header should drain and
vent the fuel back to normal. I believe it is ideal for the fuel lines
from the header to the carbs be in a continuous up hill direction without
going up and over then down again to the carb. Any high point could cause a
bubble to form in the line. This is just my opinion but it sounds like you
are going over the firewall then down again. In a gravity drain system, the
fuel lines must be routed in a continuous downhill fashion from the wing
tanks to the header then, a continuous uphill fashion to the carbs. That
is, if the header is at the low point of the system. Auto fuel will "gas
off" anytime it passes through a larger chamber in the fuel system (such as
a filter). Aviation fuel does not "gas off" as easily. Auto manufactures
started placing their electric fuel pumps in the fuel tanks as part of the
cure for this problem. Vapor lock used to be a much bigger problem in autos
before they made this change. All this needs to be taken with a grain of
salt since I obtained all this wealth of knowledge (ha...) from reading a
million web sites on the subject. Many web sites can lead you astray.
Don Smythe
---
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dave(at)cfisher.com
Guest
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| Posted: Thu Jul 13, 2006 5:54 pm Post subject: Low Fuel Warning - Tank venting |
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I just got back from flying and before i went I took the advice on someone
here to blow through the cap vents.
I did all 3 and all clear. Thanks for heads up !
Dave
---
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roncarolnikko(at)hotmail.
Guest
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| Posted: Thu Jul 13, 2006 6:21 pm Post subject: Low Fuel Warning - Tank venting |
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Ahh. Should, but with clear lines it can be seen that the uphill fuel stops
the flow before venting back into wing tank. I installed an electric as a
temporary solution, but need to go forward and down windscreen to alleviate
the low spot beneath seat. Perhaps a vent at the firewal routed up the
windscreen would do. I really would like the gravity system in case of pump
failure. Ron NB Or
[quote]From: "Don Smythe" <dosmythe(at)cox.net>
Reply-To: kitfox-list(at)matronics.com
To: <kitfox-list(at)matronics.com>
Subject: Re: Low Fuel Warning - Tank venting
Date: Thu, 13 Jul 2006 20:14:16 -0400
Ron,
I'm not sure I understand your setup. After folding the wings back and
out again, the system from the wing tanks to the header should drain and
vent the fuel back to normal. I believe it is ideal for the fuel lines
from the header to the carbs be in a continuous up hill direction without
going up and over then down again to the carb. Any high point could cause
a bubble to form in the line. This is just my opinion but it sounds like
you are going over the firewall then down again. In a gravity drain
system, the fuel lines must be routed in a continuous downhill fashion from
the wing tanks to the header then, a continuous uphill fashion to the
carbs. That is, if the header is at the low point of the system. Auto
fuel will "gas off" anytime it passes through a larger chamber in the fuel
system (such as a filter). Aviation fuel does not "gas off" as easily.
Auto manufactures started placing their electric fuel pumps in the fuel
tanks as part of the cure for this problem. Vapor lock used to be a much
bigger problem in autos before they made this change. All this needs to be
taken with a grain of salt since I obtained all this wealth of knowledge
(ha...) from reading a million web sites on the subject. Many web sites
can lead you astray.
Don Smythe
---
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Ben-PA
Joined: 11 Jan 2006
Posts: 44
Location: Berwick, Pa
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| Posted: Sat Jul 15, 2006 4:23 am Post subject: Low Fuel Warning - Tank venting |
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Dave,
You're supposed to suck on the cap vents, then if there is an obstruction in there, you will clear it out ;>)
Ben
DO NOT ARCHIVE
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