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 ˝” 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.