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Thanks Al W. Good info.
Al G.
-----Original Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of al p wick
Sent: Wednesday, August 02, 2006
10:08 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Auto Fuel
- composite tanks
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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