Willy
Short answer:
The dent is caused by fiberglassing the plastic neck to the skin directly.
As the fuel vents vapor, the neck cools and shrinks, deforming the outer
skin. Techniques to allow the skin and neck to move independently are time
consuming and must be made to keep the neck secure in all directions yet
movable... To prevent damage during refueling one has to consider making
the neck firmly attached to the fuselage, in the event a line boy sticks the
filler in the fuel neck and hang on it. Failure here would be a disaster.
It is necessary to secure the neck hard to a reinforced fuselage side.
Techniques:
We prefer to heavily reinforce the fuel neck skin attach area as a safety
precaution.
On a new build, simply put a 1/4 inch piece of blue foam just larger than
the cobra neck width by at least 1/2 inch. Bevel the edges at a 45. It
should be from 1/2 to one inch shorter than the curved flat cobra section.
On a used aircraft, cut the straps off carefully (you will find that epoxy
sticks to the PTFE plastic very well). We often cut the FS18 neck
completely off. Then heat the metal ring and remove. Consider installing
the new style cap at this time. The outside dent will be a problem. All I
can say is de-paint, fill, glass over, fill again, and repaint.
We at Custom Flight Creations simply fit our neck and filler and mark the
skin. Remove and add the foam and put two layers of glass over it. Use
micro and flox as appropriate. Many have asked how we curve the foam to the
skin. In the past we used large clamps that reach in, however, you can also
score the foam, use micro to stick the foam and simply use long sticks to
hold it in place. To be honest we now use blue foam safe super glue to
tack the foam at the top and bottom and hold it secure until the micro
cures. Obviously, one must leave the foam free of micro in the superglue
tack areas. Once it is stuck we then smear micro and flox over the foam and
put two layers of glass over the foam and peel ply down the sides and across
the bottom. Done in a day.
Reinstall the cobra neck and cap in place over the reinforced skin (Redux
the cap area). Apply glass straps as per the manual over the plastic and
lap only to the foam reinforcement area. No problems encountered in 16
aircraft.
On another note.
To prevent line boys from messing up our aircraft, we supply our current
owners with 1 inch clear PVC flexible tube to fit over the fuel filler tube,
and long enough to go down into the neck to fill. That way the shutoff on
the nozzle (if it works) will kick the fuel off before a fuel explosion on
an over fill. I have the line guys keep it on low flow and watch the fuel
in the hose. When the hose fills with fuel, stop. Once the fuel burps
down, you can fill some more until it fills again. Now, it is typically
full. Unfortunately, seeing exactly how much fuel you have is difficult.
You just can't dip the tank in a Europa XS or Classic. So often, guys fill
to the neck.
I use a sight gauge, (see my website) but if over fueled it is not uncommon
to fill the top of the sight gauge also. Then you have to clear the fuel
out of the top vent portion of the sight gauge. So a vent clearing
technique has to be used by attaching a 1/4 inch tube to a nipple inside the
fuel neck. Yea, that's convenient on a hot day. But better than not
knowing how much fuel you have at all or depending solely on an electrical
gauge. It is very difficult to keep an overfull fuel tank from venting and
often once you have filled your tank, the fuel expands and drips out over
the top staining the paint) or if your vent is underneath, then on the ramp.
If your vent for your sight gauge is tucked just on top the tank fuel filler
tube the fuel will expand into the vent side of your fuel sight gauge unless
the tank has a vent lower than the sight gauge vent. No matter what you
do, on takeoff, the fuel still can slosh and fill your sight gauge vent side
(especially in a mono). Your fuel flow and wrist watch is all you have for
sure.
Best Regards,
Bud Yerly
Custom Flight Creations
Tech Counselor
www.customflightcreations.com
--------------------------------------------------
From: "willydewey" <willydewey@gmail.com>
Sent: Saturday, December 27, 2014 2:53 PM
Subject: Europa-List: Warping or shrinkage of fuselage around and below fuel
fille
>
> I have seen some severe distortion in the skin below the filler cap on a
> TRI gear and would welcome independent advice why it happened and what
> method of repair is recommended for a permanent repair?
>
> --------
> Give a wise man knowledge and he will be yet wiser
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=436326#436326
>
>
>
|