The Murphy Builders Site

All,

I am nearing the point in the construction of the right wing where I will be
placing fuel fittings into the root rib. Before I start cutting holes, I
wanted to get some opinions about cross venting the fuel tanks.

A couple points first. I will be using the standard fuel caps which I
understand are a vented cap. I do not intend to use the sight guages, opting
for a float type, resistance sending unit.

In my manual there is a page which discusses fuel tank cross venting which
says in part "Although not necessary, we strongly recommend cross venting of
fuel tanks when using the standard fuel cap as well".

I'm wondering how important the rest of the 'Rebel community' feels about
this aspect of the construction. I'm not seeing the cross vent in any of the
photographs of Rebels I find on the various websites, but maybe the vent is
not large enough to show up in a photograph?

And, if builders are cross venting, are you placing the vent through the
cabin roof as shown in the builder's manual sketch? Or is there an alternate
method of venting rather than cutting a hole in the roof?

Thanks for any advice,

R Hoffman #687R
Eugene, OR USA

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Roger
In addition to what Drew said, a cross vent should also help your tanks
feed evenly. On mine, I even went as far as extending the vent lines
(inside the tank) to the top outboard corner of the tank. That was to
also stop drainage from one tank to the other in case of something like
a flat tire. I will vent through the top right side of the fuselage but
using larger diameter tube and arranged to try and prevent rain entering
while parked or in flight.
Ken

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I think most builders are cross venting because it is possible with full
fuel and both tanks turned on for the fuel to siphon from one tank to the
other and escape through the gas cap vent. I know of one rebel accident
from fuel starvation where this is the suspected cause. The cross vent is
there to break the siphon. On my plane I didn't drill a hole in the roof I
just replaced the elbow at the top of the fuel sight guage with a tee
fitting and ran a line along the bulkhead to the other side. If you're not
using sight guages you could still instal the fitting at the top of the
tank and run a line straight off the nipple. plastic or aliminum would work

Drew

At 05:20 AM 1/19/01 -0800, you wrote:

All,

I am nearing the point in the construction of the right wing where I will be
placing fuel fittings into the root rib. Before I start cutting holes, I
wanted to get some opinions about cross venting the fuel tanks.

A couple points first. I will be using the standard fuel caps which I
understand are a vented cap. I do not intend to use the sight guages, opting
for a float type, resistance sending unit.

In my manual there is a page which discusses fuel tank cross venting which
says in part "Although not necessary, we strongly recommend cross venting of
fuel tanks when using the standard fuel cap as well".

I'm wondering how important the rest of the 'Rebel community' feels about
this aspect of the construction. I'm not seeing the cross vent in any of the
photographs of Rebels I find on the various websites, but maybe the vent is
not large enough to show up in a photograph?

And, if builders are cross venting, are you placing the vent through the
cabin roof as shown in the builder's manual sketch? Or is there an alternate
method of venting rather than cutting a hole in the roof?

Thanks for any advice,

R Hoffman #687R
Eugene, OR USA

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Hi Roger !

Here's my 2 cents .....

I've flown around for many years with just the standard caps
- BUT - they had a 1/16" drill run through the stock vent holes,
AND - I would drill 1/8" holes front and back, at the top of the
filler necks - high enough up so the holes are sheltered from rain
by the lip of the cap. This allows lots of airflow into the tank.

I would also suggest you install (at least) the top nipples
for the sight guages & run plastic tubing across the top of the
cockpit to cross vent the tanks. If you want, you could also add
an external vent - <I> would do this as a metal pipe bent into
an inverted "J" shape, fastened onto the right side FAIRING between
the wing root & fuse. The inverted J will keep rain out, and putting
it on the fairing strip will make it easy to service or remove,
and, if fuel should overflow through it, it will not drench the
cockpit !!

My inclination would be to install separate fuel valves at
the back bottom of the tank, so you <could> hook a tube to them
as a sight guage. This will give you a quick, easy way to drain
the tanks if you ever want to remove the wings - AND - allow
you to go to a sight guage, when the capacitance float sender
fails .... ;-`)

FWIW - if you don't want a sight guage, I would use either
a mechanical guage with float that mounts in the tank root, OR
a straight, tube-type capacitance sender (although these can be
fun to calibrate !). A remote float & capacitance sender sounds
like the worst of both worlds !! (just MHO ...)

.....bobp

------------------------------orig.--------------------------------------
At 05:20 AM 1/19/01 -0800, you wrote:

All,

I am nearing the point in the construction of the right wing where I will be
placing fuel fittings into the root rib. Before I start cutting holes, I
wanted to get some opinions about cross venting the fuel tanks.

A couple points first. I will be using the standard fuel caps which I
understand are a vented cap. I do not intend to use the sight guages, opting
for a float type, resistance sending unit.

In my manual there is a page which discusses fuel tank cross venting which
says in part "Although not necessary, we strongly recommend cross venting of
fuel tanks when using the standard fuel cap as well".

I'm wondering how important the rest of the 'Rebel community' feels about
this aspect of the construction. I'm not seeing the cross vent in any of the
photographs of Rebels I find on the various websites, but maybe the vent is
not large enough to show up in a photograph?

And, if builders are cross venting, are you placing the vent through the
cabin roof as shown in the builder's manual sketch? Or is there an alternate
method of venting rather than cutting a hole in the roof?

Thanks for any advice,

R Hoffman #687R
Eugene, OR USA

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Hi

I did cross vent my Rebel tanks per MAM recommendations but I did not put a
hole in the roof & put an 'into wind' as they suggest. I vented the caps
only. By cross venting, it guards against a single vent blockage from
becoming a serious problem. I also check each vent as part of my preflight.

Brian #328R

-----Original Message-----
From: Roger and Alice Hoffman [mailto:rognal@continet.com]
Sent: Friday, January 19, 2001 8:21 AM
To: Murphy Rebel Builders List
Subject: Fuel Tank Cross Venting


All,

I am nearing the point in the construction of the right wing where I will be
placing fuel fittings into the root rib. Before I start cutting holes, I
wanted to get some opinions about cross venting the fuel tanks.

A couple points first. I will be using the standard fuel caps which I
understand are a vented cap. I do not intend to use the sight guages, opting
for a float type, resistance sending unit.

In my manual there is a page which discusses fuel tank cross venting which
says in part "Although not necessary, we strongly recommend cross venting of
fuel tanks when using the standard fuel cap as well".

I'm wondering how important the rest of the 'Rebel community' feels about
this aspect of the construction. I'm not seeing the cross vent in any of the
photographs of Rebels I find on the various websites, but maybe the vent is
not large enough to show up in a photograph?

And, if builders are cross venting, are you placing the vent through the
cabin roof as shown in the builder's manual sketch? Or is there an alternate
method of venting rather than cutting a hole in the roof?

Thanks for any advice,

R Hoffman #687R
Eugene, OR USA

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All,

Thanks to all who helped me with advice about cross venting the fuel tanks.

R Hoffman #687R
Eugene, OR USA

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