The Murphy Builders Site

Hi Mike !

The vents in the caps are pretty minimal, and likely easily
blocked. The holes in the filler neck were right near the top,
on the flat sides, just under the top rim, so they would
be sheltered by the overhanging cap.

I would do the cross vent - it's easy ! Just run a piece of
fuel line across between the two top sight guage outlets -
use a tee with the guage tube - and fasten to the cross
bulkhead. Might help avoid a problem later ... and can help
if you ovefill one tank - it'll cross-flow to the other side...

--

......bobp
bobp@prosumers.ca
bobp@pattersys.com
http://www.Pattersys.com
http://www.amway.ca/BobPatterson


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On October 9, 2010 05:08:40 am mikeh@dcsol.com wrote:

Hi Bob,
I did my wings with the cap vents to the sides as you have done, and
will need to decide on cross venting in the forseeable future. I have been
wondering if it is really necessary if I already have 2 vents in each cap.
I like what you say about the cap vents and extra holes in the fillers. Can
you tell me if you have the standard caps like mine, and where you drilled
the holes in the fillers please? (I guess as high up as you could?)
Thanks for your input to the site, it's all very useful to this
builder. Cheers Mike

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Yes a couple of builders have installed the cross vent after discovering
they could not draw fuel from one wing due to one vent being plugged.
Fuel is still about the largest cause of unintended landings though so I
think we are well advised to follow the manual as much as possible.

With both tank valves open the fuel can still flow from one tank to the
other which is why I keep at least one tank valve closed when parked. A
normal cross vent can let fuel flow to the low side and perhaps
overboard if parked on a slope or with a flat tire and full tanks. Cross
venting from the forward outboard corners of the tanks solves that if it
is a concern.

The concept of cross venting for equal tank pressure and feed only works
if the aircraft is perfectly trimmed. Other wise a minor rudder or
aileron mistrim still determines which tank feeds fastest. Cross venting
to equalize the pressure probably helps minimize this in flight but my
tanks never feed equally.

Ken

Bob Patterson wrote:

Hi Mike !

The vents in the caps are pretty minimal, and likely easily
blocked. The holes in the filler neck were right near the top,
on the flat sides, just under the top rim, so they would
be sheltered by the overhanging cap.

I would do the cross vent - it's easy ! Just run a piece of
fuel line across between the two top sight guage outlets -
use a tee with the guage tube - and fasten to the cross
bulkhead. Might help avoid a problem later ... and can help
if you ovefill one tank - it'll cross-flow to the other side...

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When I had my 0-290 engine I often flew with minimum fuel while on floats
due to marginal performance. I had some very scary moments with slow
restarts after running a tank dry and losing power when manuvering if the
tank in use came unported. All these problems were cured by installing an
inverted J tube and blocking off both filler vents. 1/4" aluminum tube
vents are in my mind the only acceptable way to go.

P.S. Last Sunday Ken and I looked at the rebuilt fuel system on a sherpa
knock off. This plane has already had one fuel starvation engine out off
airport hard landing. ( unreported crash ) The non builder student pilot
owner has hired the local AME to fix it and as far as I can tell the new
system can't work any better than what was there before. Short of calling
the AME a fucking idiot I've used the strongest language I can with a
friend to express my doubts. Please don't take any shotcuts with your fuel
delivery and venting system.

P.P.S. The last 2 fly-ins that I've been at the Rebels have out numbered
the RVs. At Parry Sound we had 5 rebels (4 on floats) plus a Moose on
floats and at Centralia we had 3 rebels (2 on floats)


At 10:15 PM 09/10/2010 -0400, you wrote:

Yes a couple of builders have installed the cross vent after discovering
they could not draw fuel from one wing due to one vent being plugged.
Fuel is still about the largest cause of unintended landings though so I
think we are well advised to follow the manual as much as possible.

With both tank valves open the fuel can still flow from one tank to the
other which is why I keep at least one tank valve closed when parked. A
normal cross vent can let fuel flow to the low side and perhaps
overboard if parked on a slope or with a flat tire and full tanks. Cross
venting from the forward outboard corners of the tanks solves that if it
is a concern.

The concept of cross venting for equal tank pressure and feed only works
if the aircraft is perfectly trimmed. Other wise a minor rudder or
aileron mistrim still determines which tank feeds fastest. Cross venting
to equalize the pressure probably helps minimize this in flight but my
tanks never feed equally.

Ken

Bob Patterson wrote:

Hi Mike !

The vents in the caps are pretty minimal, and likely easily
blocked. The holes in the filler neck were right near the top,
on the flat sides, just under the top rim, so they would
be sheltered by the overhanging cap.

I would do the cross vent - it's easy ! Just run a piece of
fuel line across between the two top sight guage outlets -
use a tee with the guage tube - and fasten to the cross
bulkhead. Might help avoid a problem later ... and can help
if you ovefill one tank - it'll cross-flow to the other side...

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Drew



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You make a point that I avoided mentioning but agree with. If you add
the inverted J vent(s) it means lots of airflow out any cap vents or
filler neck holes. That bleeds off any ram pressure (about 5 inches of
head), vents expensive hydrocarbons to the atmosphere, brings in dirt,
and potentially keeps enough oxygen in the tank to have a combustible
mixture instead of the desired and normal 'too rich to burn' situation.
I hate to counsel any change from the manual but with two J tubes I
don't agree with drilling holes in the filler necks. Both my caps have
small vents and I've had to point my single J tube almost straight down
to minimize airflow through the tanks. (I have a header tank and don't
need any ram pressure) My cross vent is transparent and I was surprised
to see how fast the air flows in from the J tube as evidenced by the
bubbles going into each tank even when the outflow valve is closed. If I
had two J tubes I think I would fit non vented caps but in my case the
original cap vents are my secondary vents.

Another thing I did with the J tube was to epoxy an inch of 3/8" tubing
at the inlet so that I could fit a screen in the inlet to keep bugs from
nesting in the tube. That is what plugged Jim's J tube.

Ken

Drew Dalgleish wrote:

When I had my 0-290 engine I often flew with minimum fuel while on floats
due to marginal performance. I had some very scary moments with slow
restarts after running a tank dry and losing power when manuvering if the
tank in use came unported. All these problems were cured by installing an
inverted J tube and blocking off both filler vents. 1/4" aluminum tube
vents are in my mind the only acceptable way to go.

P.S. Last Sunday Ken and I looked at the rebuilt fuel system on a sherpa
knock off. This plane has already had one fuel starvation engine out off
airport hard landing. ( unreported crash ) The non builder student pilot
owner has hired the local AME to fix it and as far as I can tell the new
system can't work any better than what was there before. Short of calling
the AME a fucking idiot I've used the strongest language I can with a
friend to express my doubts. Please don't take any shotcuts with your fuel
delivery and venting system.

P.P.S. The last 2 fly-ins that I've been at the Rebels have out numbered
the RVs. At Parry Sound we had 5 rebels (4 on floats) plus a Moose on
floats and at Centralia we had 3 rebels (2 on floats)


At 10:15 PM 09/10/2010 -0400, you wrote:

Yes a couple of builders have installed the cross vent after discovering
they could not draw fuel from one wing due to one vent being plugged.
Fuel is still about the largest cause of unintended landings though so I
think we are well advised to follow the manual as much as possible.

With both tank valves open the fuel can still flow from one tank to the
other which is why I keep at least one tank valve closed when parked. A
normal cross vent can let fuel flow to the low side and perhaps
overboard if parked on a slope or with a flat tire and full tanks. Cross
venting from the forward outboard corners of the tanks solves that if it
is a concern.

The concept of cross venting for equal tank pressure and feed only works
if the aircraft is perfectly trimmed. Other wise a minor rudder or
aileron mistrim still determines which tank feeds fastest. Cross venting
to equalize the pressure probably helps minimize this in flight but my
tanks never feed equally.

Ken

Bob Patterson wrote:

Hi Mike !

The vents in the caps are pretty minimal, and likely easily
blocked. The holes in the filler neck were right near the top,
on the flat sides, just under the top rim, so they would
be sheltered by the overhanging cap.

I would do the cross vent - it's easy ! Just run a piece of
fuel line across between the two top sight guage outlets -
use a tee with the guage tube - and fasten to the cross
bulkhead. Might help avoid a problem later ... and can help
if you ovefill one tank - it'll cross-flow to the other side...

-----------------------------------------------------------------
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Drew



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Ken

I fly a Luscombe with wing tanks. Each tank has two fuel ports (front &
rear) that connect together just before the shut off valves and each tank
cap has a periscope pointing forward and the tanks are not cross vented.

The operation manual says other then the time it takes to switch from one
tank to the other one should not fly with both tanks "ON".

To days consciences is that cross venting the tanks would be a good idea but
all those regulatory requirements and the cost of testing make it
economically prohibitive.

Charlie E. 802R

----- Original Message -----
From: "Ken" <klehman@albedo.net>
To: <rebel-builders@dcsol.com>
Sent: Sunday, October 10, 2010 7:42 AM
Subject: Re: [rebel-builders] Fuel tank vents 818R

You make a point that I avoided mentioning but agree with. If you add
the inverted J vent(s) it means lots of airflow out any cap vents or
filler neck holes. That bleeds off any ram pressure (about 5 inches of
head), vents expensive hydrocarbons to the atmosphere, brings in dirt,
and potentially keeps enough oxygen in the tank to have a combustible
mixture instead of the desired and normal 'too rich to burn' situation.
I hate to counsel any change from the manual but with two J tubes I
don't agree with drilling holes in the filler necks. Both my caps have
small vents and I've had to point my single J tube almost straight down
to minimize airflow through the tanks. (I have a header tank and don't
need any ram pressure) My cross vent is transparent and I was surprised
to see how fast the air flows in from the J tube as evidenced by the
bubbles going into each tank even when the outflow valve is closed. If I
had two J tubes I think I would fit non vented caps but in my case the
original cap vents are my secondary vents.

Another thing I did with the J tube was to epoxy an inch of 3/8" tubing
at the inlet so that I could fit a screen in the inlet to keep bugs from
nesting in the tube. That is what plugged Jim's J tube.

Ken

Drew Dalgleish wrote:

When I had my 0-290 engine I often flew with minimum fuel while on floats
due to marginal performance. I had some very scary moments with slow
restarts after running a tank dry and losing power when manuvering if the
tank in use came unported. All these problems were cured by installing an
inverted J tube and blocking off both filler vents. 1/4" aluminum tube
vents are in my mind the only acceptable way to go.

P.S. Last Sunday Ken and I looked at the rebuilt fuel system on a sherpa
knock off. This plane has already had one fuel starvation engine out off
airport hard landing. ( unreported crash ) The non builder student pilot
owner has hired the local AME to fix it and as far as I can tell the new
system can't work any better than what was there before. Short of calling
the AME a fucking idiot I've used the strongest language I can with a
friend to express my doubts. Please don't take any shotcuts with your
fuel
delivery and venting system.

P.P.S. The last 2 fly-ins that I've been at the Rebels have out numbered
the RVs. At Parry Sound we had 5 rebels (4 on floats) plus a Moose on
floats and at Centralia we had 3 rebels (2 on floats)


At 10:15 PM 09/10/2010 -0400, you wrote:

Yes a couple of builders have installed the cross vent after discovering
they could not draw fuel from one wing due to one vent being plugged.
Fuel is still about the largest cause of unintended landings though so I
think we are well advised to follow the manual as much as possible.

With both tank valves open the fuel can still flow from one tank to the
other which is why I keep at least one tank valve closed when parked. A
normal cross vent can let fuel flow to the low side and perhaps
overboard if parked on a slope or with a flat tire and full tanks. Cross
venting from the forward outboard corners of the tanks solves that if it
is a concern.

The concept of cross venting for equal tank pressure and feed only works
if the aircraft is perfectly trimmed. Other wise a minor rudder or
aileron mistrim still determines which tank feeds fastest. Cross venting
to equalize the pressure probably helps minimize this in flight but my
tanks never feed equally.

Ken

Bob Patterson wrote: -----------------------------------------------------------------
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