Citabria Fuel-Flow Problem

"Maxwell" luv2^fly99@cox.^net wrote in news:BLjVj.72955$y05.14344
@newsfe22.lga:


"Stealth Pilot" wrote in message
...
On Fri, 9 May 2008 17:34:02 +0000 (UTC), Bertie the Bunyip
wrote:

Stealth Pilot wrote in
:

On Wed, 7 May 2008 11:17:24 -0700 (PDT), quietguy
wrote:

The A/C in question is a 1974 Bellanca 7ECA, re-engined with an O-
320
so it's effectively a 7GCAA. It belongs to the Offutt AFB Aero
Club
and has seen very little use, often sitting for weeks at a time
until
a week ago when I began taking dual in it 2-3 times a week to get
my
tailwheel endorsement. The fuel system is not for inverted flight,
so
no header tank -- two 18-gallon wing tanks with check valves to a
single vent on the left, crossflow pipes to the aft fuel manifold
under the baggage compartment and crossflow pipes to the forward
fuel
manifold on the firewall. Caps are non-vented and the gaskets are
like new.

This A/C is drawing 3-4 times as much fuel from the left tank as
from
the right and it's not crossflowing on the ground, even overnight.
We've made right patterns as well as lefts -- makes no difference.
We
haven't done any extended S&L flight, just 11 NM to Plattsmouth, NE
for pattern work. The club's A&P has blown out the feed and vent
lines and got a good blast into the right tank from both. We're
getting a free flow of clean gas out of all four drains.

So what's our next move? Anybody had this problem?

does the fuel situation change if you swap the caps to the other
tank?


Citabria caps aren't vented.


Bertie

that is what I was getting at bertie. looking as though they seal
isnt
necessarily sealed.
if one is leaking and you swap the caps around the pattern of the
problem should change.
a cheap check

Stealth Pilot

You would probably find it easier to explain to MX.


Awww, he;'s giving me another lashing there.

Ouch.


Bertie

The Citabria's fuel system is okay now; those who guessed "filler
caps" have the satisfaction of being right. The A&P had time to give
the system a good look late last week and we tested the fix with some
local and cross-country flying over the weekend. The left tank still
tends to contribute a bit more than the right in flight, but "it's
always done that." And the system now crossflows on the ground when
the wings are not level, which it had stopped doing.

The A&P didn't find any soft or swollen hoses so he took a close look
at the cap gaskets and found that looking like new and performing like
new aren't the same thing. There were no cracks or other obvious
flaws but both gaskets were equally bad at sealing; that's why a
simple cap-swap didn't change anything. It seems that the left tank
just isn't as sensitive to venting/sealing problems as the right. To
seal well, even with good gaskets, the caps have to be difficult to
screw down tight.

Thanks to all who contributed ideas.

On May 19, 5:27 pm, quietguy wrote:
There were no cracks or other obvious
flaws but both gaskets were equally bad at sealing; that's why a
simple cap-swap didn't change anything. It seems that the left tank
just isn't as sensitive to venting/sealing problems as the right. To
seal well, even with good gaskets, the caps have to be difficult to
screw down tight.

The LH tank vents directly outside, while the RH tank vent into
the left, so a leaking RH cap would hold back the flow in flight
somewhat due to the small resistance of airflow through the vent
crossover. But leaking caps still don't explain the lack of crossflow
overnight; only a totally plugged vent system or plugged fuel lines
would do that.
Those cap gaskets compress with age and get hard, and won't seal
unless they're really clamped down tight. New gaskets fix that, but
they can be so tight that the cap doesn't get screwed on all the way
and can come off in flight. I painted red stripes on our caps so that
the stripes are lined up fore-and-aft when the caps are all the way
on. And I use a little tiny bit of Dow DC-4 silicone grease between
the cap and gasket so the cap doesn't have to grind the gasket against
the filler neck; the cap goes on really nice after that.

Dan

wrote in news:6cbe76a7-0b6a-4d7c-a352-
:

On May 19, 5:27 pm, quietguy wrote:
There were no cracks or other obvious
flaws but both gaskets were equally bad at sealing; that's why a
simple cap-swap didn't change anything. It seems that the left tank
just isn't as sensitive to venting/sealing problems as the right. To
seal well, even with good gaskets, the caps have to be difficult to
screw down tight.

The LH tank vents directly outside, while the RH tank vent into
the left,

Not according to my manual, which has a T fitting feeding air to both
tanks from the one vent on all models. It wouldn't be the first time the
reality differed from the manuals, of course.


Bertie

"Bertie the Bunyip" wrote in message
...

Not according to my manual, which has a T fitting feeding air to both
tanks from the one vent on all models. It wouldn't be the first time the
reality differed from the manuals, of course.


Bertie


Or the first time reality differed from your recollection.

"Maxwell" luv2^fly99@cox.^net wrote in news:FIqYj.87799$y05.56401
@newsfe22.lga:


"Bertie the Bunyip" wrote in message
...

Not according to my manual, which has a T fitting feeding air to both
tanks from the one vent on all models. It wouldn't be the first time
the
reality differed from the manuals, of course.


Bertie


Or the first time reality differed from your recollection.


True enouogh, but then I do still remember where I left the manuals, so
it doen't matter.



Bertie

On May 19, 7:00 pm, Bertie the Bunyip wrote:
wrote in news:6cbe76a7-0b6a-4d7c-a352-
:

On May 19, 5:27 pm, quietguy wrote:
There were no cracks or other obvious
flaws but both gaskets were equally bad at sealing; that's why a
simple cap-swap didn't change anything. It seems that the left tank
just isn't as sensitive to venting/sealing problems as the right. To
seal well, even with good gaskets, the caps have to be difficult to
screw down tight.

The LH tank vents directly outside, while the RH tank vent into
the left,

Not according to my manual, which has a T fitting feeding air to both
tanks from the one vent on all models. It wouldn't be the first time the
reality differed from the manuals, of course.

Bertie

Must have changed at some point. Both of ours have the vent
feeding through a check valve into the LH tank, and a crossover vent
connection between the inboard walls of both tanks.

Dan

wrote in message
...
On May 19, 7:00 pm, Bertie the Bunyip wrote:
wrote in news:6cbe76a7-0b6a-4d7c-a352-
:

On May 19, 5:27 pm, quietguy wrote:
There were no cracks or other obvious
flaws but both gaskets were equally bad at sealing; that's why a
simple cap-swap didn't change anything. It seems that the left tank
just isn't as sensitive to venting/sealing problems as the right. To
seal well, even with good gaskets, the caps have to be difficult to
screw down tight.

The LH tank vents directly outside, while the RH tank vent into
the left,

Not according to my manual, which has a T fitting feeding air to both
tanks from the one vent on all models. It wouldn't be the first time the
reality differed from the manuals, of course.

Bertie

Must have changed at some point. Both of ours have the vent
feeding through a check valve into the LH tank, and a crossover vent
connection between the inboard walls of both tanks.

Dan

You're just feeding a troll. All he does is repeat what he is told. Very
much like MX.

wrote in news:d3672a56-fbb0-4eac-bb4a-
:

On May 19, 7:00 pm, Bertie the Bunyip wrote:
wrote in news:6cbe76a7-0b6a-4d7c-a352-
:

On May 19, 5:27 pm, quietguy wrote:
There were no cracks or other obvious
flaws but both gaskets were equally bad at sealing; that's why a
simple cap-swap didn't change anything. It seems that the left
tank
just isn't as sensitive to venting/sealing problems as the right.
To
seal well, even with good gaskets, the caps have to be difficult
to
screw down tight.

The LH tank vents directly outside, while the RH tank vent
into
the left,

Not according to my manual, which has a T fitting feeding air to both
tanks from the one vent on all models. It wouldn't be the first time
the
reality differed from the manuals, of course.

Bertie

Must have changed at some point. Both of ours have the vent
feeding through a check valve into the LH tank, and a crossover vent
connection between the inboard walls of both tanks.



Might depend on the year of manufacture 9 my books are for the mid
seenites airplanes) and /or the manufacturer.


Bertie

quietguy wrote:

The Citabria's fuel system is okay now; those who guessed "filler
caps" have the satisfaction of being right. The A&P had time to give
the system a good look late last week and we tested the fix with some
local and cross-country flying over the weekend. The left tank still
tends to contribute a bit more than the right in flight, but "it's
always done that." And the system now crossflows on the ground when
the wings are not level, which it had stopped doing.

Thanks for startingthe topic. This is good stuff to know. One recently
checked out on a Citabria at one of my FBO's and I'll keep what you found
out in mind.