The Murphy Builders Site

Ken and All.

Any aircraft I have worked on that is at, or has left, my facilities has
been fitted with a ram air vent to keep a positive pressure on the tanks and
any original holes that were drilled in the tank filler necks, by the
builder, were FILLED with a rivet. I DO NOT drill holes in the filler necks,
as that would negate the whole purpose of the ram air vent in the first
place. Either drill the large holes in the neck (and take your chances) or
use a ram air vent, NOT BOTH. You want the ram air vent to be like a pitot
tube that just holds pressure in the system. There is really no air flow
(other than what matches fuel flow) and this way if flying in the rain you
are not drawing in water either. If you have both vents you would be flowing
the rain in with the air flow that is coming in the ram vent and out the
fuel filler neck vents (oh ya only the air would come out the filler neck,
the water would drop in your tank!). This ram air + pressure is even more
critical in many aircraft I have viewed, due to the fact that the original
builder installed the fuel lines forward, up and around the front door post.
This means that in slow flight attitude (and even level flight for that
matter) when low on fuel all you need is a suction break, from fuel sloshing
away from the outlet, and the fuel will quit flowing. The positive pressure
in the tanks supplied by the ram air vent helps keep this from happening, or
enables the fuel to get flowing again if the suction is broken for an
instant. All I can offer for proof of concept is no fuel starvation
occurrences, hiccups etc. in over 6 years for Howard, myself (and all the
others I have shipped out of here) in any attitude, or fuel levels, with our
Rebels. We have screens installed in the vent tube to keep those pesky mud
wasps (or what ever damn bug does it) from filling the tube with dirt and
larva's.

Everyone's welcome to reinvent the wheel, but I'm sure going to think twice
about flying with you if you do!

Regards,
Wayne G.O'Shea
www.irishfield.on.ca

----- Original Message -----
From: <klehman@albedo.net>
To: <murphy-rebel@dcsol.com>
Sent: Sunday, September 02, 2001 5:12 PM
Subject: Re: Sight guages


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Perhaps this is a statement of the obvious but there must be much more

vent air

flowing than fuel flow for this problem to occur which means that ram air

is

flowing into the J tube and out of the fuel cap vent. Anything that

reduces the

flow has to reduce the error. I put separate guage and vent ports in my

tanks

but I still don't like the idea of flowing air through the tank as it

tends to

increase the likelihood of having a combustible fuel air ratio in the

tank.

Ken

Bob Patterson wrote:

Hi Brian !

Part of the problem might be because the vent tube is pointing
forward into the slipstream. Since it is meant to be just a vent, you
could try a straight vertical tube with a couple of saw cuts on the
back side, or bend the front of the tube down into an inverted "J",
so it doesn't get pressurized by ram air.

As Wayne suggests, you might want to check to see that you are
getting enough air INTO the tanks from the caps. I drilled 1/8" holes
at the front AND back of the filler neck, above the bottom of the
cap, so rain wouldn't get in, but lots of air could ! Lack of

sufficient

air through the caps is the reason for the cross tube & vent in the
first place .... (At least enough air must enter to replace the

volume

of fuel used.)

.......bobp

Wayne, is there a way to redo the vent. Mine is cross vented and if I

blow

into the hole the fuel gets blown out of the sight guages, so when I

get low

it shows no fuel in the tanks. I have already put a restrictor in the

BOTTOM

el of the sight guages and was wondering if there was something else I

could

do to stop the pressure on the guage...Thanks....Brian

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wad'ya mean "Don't Re-invent the Wheel" ?
I never did like those wooden wagon wheels with steel tires. Dem new-fangled
pneumatic tires with the steel wheels was a heck of an idea! Imagine, steel
wheels instead of steel tread. Now I hear someones even gone and put steel cords
in the rubber tires :)

More seriously, my manual still recommends the cross vent AND the filler neck
holes so I appreciate the info. I do like the idea of some kind of secondary
vent though if the gas caps seal tightly.

Ken

"Wayne G. O'Shea" wrote:

Ken and All.

Any aircraft I have worked on that is at, or has left, my facilities has
been fitted with a ram air vent to keep a positive pressure on the tanks and
any original holes that were drilled in the tank filler necks, by the
builder, were FILLED with a rivet. I DO NOT drill holes in the filler necks,
as that would negate the whole purpose of the ram air vent in the first
place. Either drill the large holes in the neck (and take your chances) or
use a ram air vent, NOT BOTH. You want the ram air vent to be like a pitot
tube that just holds pressure in the system. There is really no air flow
(other than what matches fuel flow) and this way if flying in the rain you
are not drawing in water either. If you have both vents you would be flowing
the rain in with the air flow that is coming in the ram vent and out the
fuel filler neck vents (oh ya only the air would come out the filler neck,
the water would drop in your tank!). This ram air + pressure is even more
critical in many aircraft I have viewed, due to the fact that the original
builder installed the fuel lines forward, up and around the front door post.
This means that in slow flight attitude (and even level flight for that
matter) when low on fuel all you need is a suction break, from fuel sloshing
away from the outlet, and the fuel will quit flowing. The positive pressure
in the tanks supplied by the ram air vent helps keep this from happening, or
enables the fuel to get flowing again if the suction is broken for an
instant. All I can offer for proof of concept is no fuel starvation
occurrences, hiccups etc. in over 6 years for Howard, myself (and all the
others I have shipped out of here) in any attitude, or fuel levels, with our
Rebels. We have screens installed in the vent tube to keep those pesky mud
wasps (or what ever damn bug does it) from filling the tube with dirt and
larva's.

Everyone's welcome to reinvent the wheel, but I'm sure going to think twice
about flying with you if you do!

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Good to see you still have a sense of humour Ken!

Yes, you definitely want the cross vent tube to keep both tanks evenly
pressured/vented for even fuel flow from the tanks, you just need to decide
if it's ram air or filler neck vent holes to go with the cross vent tube.
The holes in the filler necks may be sufficient venting for a properly
fitted fuel line installation, but I figure why take the chance when the ram
air is a better guarantee and a proven installation that hasn't let me (and
others) down (that was the "wheel" I was taking about). No reason you
couldn't put one small 1/4" ram air tube on each side of the cross vent
tube, up through each wing root fairing. That way if one plugs, the other
will still provide the venting/pressurizing, or go with ram air tubes on the
fuel caps (as I think it was Brian C. or Curt that said) "so you can blow
through them to make sure they are open".

Wayne

----- Original Message -----
From: <klehman@albedo.net>
To: <murphy-rebel@dcsol.com>
Sent: Monday, September 03, 2001 3:49 PM
Subject: Re: Tank Venting


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wad'ya mean "Don't Re-invent the Wheel" ?
I never did like those wooden wagon wheels with steel tires. Dem

new-fangled

pneumatic tires with the steel wheels was a heck of an idea! Imagine,

steel

wheels instead of steel tread. Now I hear someones even gone and put steel

cords

in the rubber tires :)

More seriously, my manual still recommends the cross vent AND the filler

neck

holes so I appreciate the info. I do like the idea of some kind of

secondary

vent though if the gas caps seal tightly.

Ken

"Wayne G. O'Shea" wrote:

Ken and All.

Any aircraft I have worked on that is at, or has left, my facilities has
been fitted with a ram air vent to keep a positive pressure on the tanks

and

any original holes that were drilled in the tank filler necks, by the
builder, were FILLED with a rivet. I DO NOT drill holes in the filler

necks,

as that would negate the whole purpose of the ram air vent in the first
place. Either drill the large holes in the neck (and take your chances)

or

use a ram air vent, NOT BOTH. You want the ram air vent to be like a

pitot

tube that just holds pressure in the system. There is really no air flow
(other than what matches fuel flow) and this way if flying in the rain

you

are not drawing in water either. If you have both vents you would be

flowing

the rain in with the air flow that is coming in the ram vent and out the
fuel filler neck vents (oh ya only the air would come out the filler

neck,

the water would drop in your tank!). This ram air + pressure is even

more

critical in many aircraft I have viewed, due to the fact that the

original

builder installed the fuel lines forward, up and around the front door

post.

This means that in slow flight attitude (and even level flight for that
matter) when low on fuel all you need is a suction break, from fuel

sloshing

away from the outlet, and the fuel will quit flowing. The positive

pressure

in the tanks supplied by the ram air vent helps keep this from

happening, or

enables the fuel to get flowing again if the suction is broken for an
instant. All I can offer for proof of concept is no fuel starvation
occurrences, hiccups etc. in over 6 years for Howard, myself (and all

the

others I have shipped out of here) in any attitude, or fuel levels, with

our

Rebels. We have screens installed in the vent tube to keep those pesky

mud

wasps (or what ever damn bug does it) from filling the tube with dirt

and

larva's.

Everyone's welcome to reinvent the wheel, but I'm sure going to think

twice

about flying with you if you do!

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Hi Guys

I have the ram air caps with NO vent holes drilled into the filler necks. I
agree with Wayne that to do so would negate the effect of ram air. Every
time I refill the tank I simply blow through the vent tube to double check
they are not blocked. With two vents (1 per cap) & cross venting from tank
to tank, I think my chances are very low of fuel starvation due to poor
venting.

At low cruise, I calculated some time ago that it will give you about 0.4
psi fuel pressure boost. That is significant when you consider how small
the fuel head is overall due to gravity alone & it is there no matter what
attitude (within limits) the aircraft is in.

The Rebel is a great airplane & these small points can make it an even
greater & safer aircraft.

Cheers

Brian #328R

-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of
klehman@albedo.net
Sent: Monday, September 03, 2001 3:50 PM
To: murphy-rebel@dcsol.com
Subject: Re: Tank Venting


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wad'ya mean "Don't Re-invent the Wheel" ?
I never did like those wooden wagon wheels with steel tires. Dem new-fangled
pneumatic tires with the steel wheels was a heck of an idea! Imagine, steel
wheels instead of steel tread. Now I hear someones even gone and put steel
cords
in the rubber tires :)

More seriously, my manual still recommends the cross vent AND the filler
neck
holes so I appreciate the info. I do like the idea of some kind of secondary
vent though if the gas caps seal tightly.

Ken

"Wayne G. O'Shea" wrote:

Ken and All.

Any aircraft I have worked on that is at, or has left, my facilities has
been fitted with a ram air vent to keep a positive pressure on the tanks

and

any original holes that were drilled in the tank filler necks, by the
builder, were FILLED with a rivet. I DO NOT drill holes in the filler

necks,

as that would negate the whole purpose of the ram air vent in the first
place. Either drill the large holes in the neck (and take your chances) or
use a ram air vent, NOT BOTH. You want the ram air vent to be like a pitot
tube that just holds pressure in the system. There is really no air flow
(other than what matches fuel flow) and this way if flying in the rain you
are not drawing in water either. If you have both vents you would be

flowing

the rain in with the air flow that is coming in the ram vent and out the
fuel filler neck vents (oh ya only the air would come out the filler neck,
the water would drop in your tank!). This ram air + pressure is even more
critical in many aircraft I have viewed, due to the fact that the original
builder installed the fuel lines forward, up and around the front door

post.

This means that in slow flight attitude (and even level flight for that
matter) when low on fuel all you need is a suction break, from fuel

sloshing

away from the outlet, and the fuel will quit flowing. The positive

pressure

in the tanks supplied by the ram air vent helps keep this from happening,

or

enables the fuel to get flowing again if the suction is broken for an
instant. All I can offer for proof of concept is no fuel starvation
occurrences, hiccups etc. in over 6 years for Howard, myself (and all the
others I have shipped out of here) in any attitude, or fuel levels, with

our

Rebels. We have screens installed in the vent tube to keep those pesky mud
wasps (or what ever damn bug does it) from filling the tube with dirt and
larva's.

Everyone's welcome to reinvent the wheel, but I'm sure going to think

twice

about flying with you if you do!

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Brian,

I must agree with your analysis of the venting issue. Skystar's Kitfox tanks
are cross vented with ram air caps and I have never heard of a single Kitfox
suffering fuel starvation do to fuel venting problem. That would include my
own. I have vented my Rebel the same.

Bruce 357R



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