On Saturday, I praised the cowling flange mod mentionded in Europa News 4
years ago. A reader asked:
>What is the Europa's flange mod? I'm rapidly getting to that point of the
build.<
For those not having that old issue of Europa News, I quote the description
below. As it is not possible to send attachments, I hope the below "sketch"
will suffice to replace the drawing accompanying Europa's text. It will
perhaps be more clear if you draw one line through all the "u"s (upper
cowling half), one line through all the "l"s (lower cowling half) and one
line through all the "a"s (additional flange) (55 years since I last did
this - remember the childrens' drawing books!).
u
u
u a
u a
u a
OUTSIDE u l a INSIDE
u l a
u l a
l
l
l
l
quote
As called up in the build manual, a total of 19 bolts are used with which to
fasten the upper cowling to the aircraft. Adding a glassfibre flange to the
inside of the upper cowling will enable you to reduce the number of bolts
required down to 11.
The additional flange holds the two cowlings together and prevents
"quilting" or bulging between where the bolts are. To make the flange, tape
the two cowlings halves together and set them such that you can get access
to the inside. Scuff sand the upeer cowling where you will be laying up the
glassfibre flange and apply some adhesive backed plastic tape to the lower
cowling flange to act as a release agent.
Lay-up two 3 bid strips at +-45 degr, about 1 m long and 5 cm (2") wide.
Apply each strip to overlap half on the upper cowling and half on the lower
cowling flange and allow to cure. Turning the edge of the flange away from
the lower cowling will aid fitting the two cowlings together but it's not
essential.
The flange should be interrupted where the fasteners are on the joint line.
Dimensions are measured around the cowling's perimeter. See below figure.
unquote
My substitute "sketch" )o = fastener):
FRONT o 5" (127 mm) o 11" (280 mm) o 20" (508 mm)
o REAR
There must be misprint in the newsletter - the new number of fasteners will
be 15, not 11, between the upper cowling and fuselage/lower cowling. You
may wonder why all this effort to save just 4 bolts and fasteners. The main
advantage is not this, but that you avoid the bulging - it is really
significant if the new flange is not added.
I did not figure out an easy way to make the edge turn away from the lower
cowling, as called for in the above quote. Instead I cut the new flange back
5 mm after cure. I can then press gently on the outside of the upper
cowling and it enters over the lower cowling.
Another recommendation: When you apply the plastic tape to the lower
cowling flange to act as a release agent, do this AFTER you have placed the
two cowling halves together, and let the tape go 1-2 mm onto the upper
cowling. This seals off the joint and no epoxy gets in between the two
original flange surfaces and bond them together. If that should happen, it
would not be easy to pry them apart after the new flange is made.
I don't think tape will hold the two cowling halves nicely together, as the
text suggests, with the tendency for the cowlings to bulge and mechanical
stress when handling the thing during this work. I used thin self-tapping
screws with washer head, placed where I intended to have the fasteners and
some in between - easy to fill the holes later.
Regards,
Svein
A225 - now in Norway
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