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Point to consider. The little squiggling,vibrating, pressure
changes the plane sees can easily cause a micro hole to develop where none
showed in static tests. Not uncommon to have leak develop a year later with
avgas.
Weave showing may be fuel sensitive paint,primer, or filler. Not epoxy or
other component. I used a paint that was fuel sensitive. Had similar symptoms.
When I sealed the leak, the paint returned to normal.
I tested all of the foams near tank, glass, epoxy. None fuel sensitive. So,
yes, I too have that foam sandwich.
I noticed pattern to surface symptoms. That's how I selected locations to
drill. Drilling into outer skin allowed fuel to dribble out. Epoxy cured fine
apparently, as I no longer have leaks.
Just offering my test results and findings. I SUSPECT your issues
have nothing to do with fuel type (except plastic fuel gauge). Lot's of evidence
supports my theory, but not conclusive.
If you read the archives from canard
builders you will find it's extremely common to have such pinhole leaks. If I
had to guess, I'd say 50% have this problem. Regardless of type of
fuel
I agree that could
well be that the leak in the bottom strake inner skin has been there and has
nothing to do with the type of fuel. I had leak tested with air after
strake closure, and it held about an 8 – 10” head of water pressure for
days.
If you had any mushiness near leaks, then
I'd be concerned. I tested non-compatible epoxy and it just gradually got
mushy.
What I have now is
a roughly oval area about 6” by 4” where the weave of the glass cloth is
showing through the paint finish, and it feels/looks like there maybe some
dis-bonding of the outer skin from the foam. My guess is that somewhere in
that area there is a pinhole leak in the inner skin, and the fuel has
permeated the foam. There is no fuel leak on the outside. Because
of the roughness/weave showing, and the dis-bonding, it seems clear that the
fuel (or something) is doing something to the epoxy. It was my
understanding that fuel (avgas, I suppose) would not permeate the closed cell
PVC foam, and not effect the epoxy.
I drained tank, then drill 1/16" hole at leak
location. Hole only goes part way into tank wall. Fuel came burbling out. I
then used syringe with no needle to inject epoxy. Totally solved problem, no
leaks for years now.
Do you also have a
foam core sandwich tank wall? How did you decide where to drill the
outer skin? What epoxy did you use; I’d think the presence of fuel would
mess up the epoxy before it cured?
Leaks take a long time to show on surface, fuel has to
migrate from interior hole to exterior hole. That also makes it tough to find
leak source.
I’ve drained the
fuel on that side, and for now I’m leaving it as is since we are trying to get
first flight done Friday/Saturday. I’ll probably put some avgas in on
that side for balance, and deal with the apparent leak
later.
Thanks,
Al
Not sure where to
go with this because there are only a few here with epoxy fuel tanks, and on
the Velocity list very few interested in the use of mogas. I’m
suspecting fuel compatibility isses.
I first put fuel
in the tanks nearly 2 years ago and used Chevron regular. Everything was
fine. When I moved the plane to the airport 3 months ago (tanks empty)
I filled with Exxon-Mobile. Four troubling things have come up in the
past few weeks.
1.
I have Vance Atkinson site
gauge that has a white plastic back plate for easier reading of the fuel
level. The small hole through the backing has been swelling shut so the
sight gauge no longer works. I contacted Vance who said that there are
hundreds of these gauges in EZs using mogas without problems, but he has had
3 incidents like mine in the last three months.
2.
A couple of weeks ago there
was suddenly a pinhole leak in one of the gear well enclosures. These
enclosures are part of the fuel tank wall, and are parts that come with the
Velocity kit. These are also made and coated with
EZ-poxy.
3.
Looking in through the filler
cap I see reddish-purple splotches and streaks on those gear leg
enclosures. Poking and scratching with some safety wire on a stick
does not indicate any softness of the surface.
4.
Yesterday, under the leading
edges of one of the strakes, I noted an area with some slight surface
irregularity. Pushing on it suggests some sponginess. This is ½”
foam core material, and indicates the possibility of a pinhole leak in the
inner skin, and fuel softening the PVC foam. PVC foam is supposed to
be unaffected by fuel.
My tanks
(strakes) were made and coated with EZ-poxy back in 1998. At the time
I polled EZ flyers about there experience, and talked to reps of various
epoxy manufacturers about auto fuel compatibility. All the evidence
said go with the EZ-poxy.
Any others with
composite tanks having any trouble? Anybody using Exxon-mobile fuel?
Know of any new additives that are an issue?
I’m thinking I
should drain this fuel ASAP, but then what? Other brand? That
expensive Avgas? Regardless I may be faced with cutting open a strake
at some point, but right now we are trying to get first flight done this
coming weekend.
-al wick
Artificial intelligence
in cockpit, Cozy IV powered by stock Subaru 2.5
N9032U 200+ hours on
engine/airframe from Portland, Oregon
Prop construct, Subaru
install, Risk assessment, Glass panel design
info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html
-al wick
Artificial intelligence in
cockpit, Cozy IV powered by stock Subaru 2.5
N9032U 200+ hours on
engine/airframe from Portland, Oregon
Prop construct, Subaru install, Risk
assessment, Glass panel design
info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html
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