> Wonder if you experienced builders can lend a bit of advice to a confused and
> just about to start building first-timer?
Barry,
To peel ply or not to peel ply? that is the question. Whether 'tis better to
suffer the slings and arrows of outrageous criticism, or just follow the herd
like everyone else.
In contrast to just about everybody else, I elected to use full peel ply
coverage over all flying surfaces, and the benefits have been truly outsanding.
I will try to justify my decision, and let you make up you own mind whether you
should adopt this technique or not.
If you have followed these postings for long, you will notice that there has
been a significant unrest concerning
1. Build time of flying surfaces
2. core warping (particularly ailerons)
3. Amine Blush
4. The possibility of vacuum bagging.
Peel plying can significantly reduce 1. virtually eliminate 2. & 3. and
emulate 4.
There is a popular misconception that peel plying always results in heavy
layups....not so. There IS a very real risk that the structure can become resin
starved if not laminated correctly. For this reason, kit aircraft factories
tend to dissuade amateur (less experienced) builders from using the technique.
Interestingly it is commonly used in the boat building industry. If however,
you can guarantee the uniformity and resin/reinforcing ratio, then peel ply can
offer significant advantages. The biggest mistake people make is to squeegee
the laminate to perfection and then add the peel ply and squeegee some more,
this sucks out the resin, compromising the resin/reinforcement ratio. The
result is a weak structure. If however, a laminate with a perfect
resin/reinforcement ratio has a layer of peel ply added and a small amount of
extra resin is added to wet out the peel ply, the laminate is not affected.
I used Dacron peel ply supplied on rolls 75mm wide by 100m long from my local
ships chandler. Unlike the blue stuff supplied by Europa Aviation as part of
your kit, this is a white materiel with a fine red tracer (to aid alignment)
every 25mm. It turns transparent when impregnated with resin and this is
crucial to allow good inspection during squeegeeing, allowing air bubbles to be
spotted. Once laminating is mastered, the real benefits begin.
CORE WARPING
One of the inherant problems with blue foam is that internal stresses can
cause long thin components to distort once they are hot wire cut. Particularly
vulnerable are the Europa's ailerons and rudder (witness the number of
complaints). The factories inelegant solution is to glue the component into its
lower jig block during lamination. Once you have elected to ride with the
outlaws and use peel ply, your solution is far more elegant.
1. Lay a sheet of new polythene into the lower jig block. I used Damp Proof
Membrane from a builders merchant.
2. Place the workpiece on top and lay up according to instructions, but
using peel ply.
3. Lay another sheet of new polythene on top of the peel ply.
4. Place the other jig block on top. Since one was cut from the other they
will fit perfectly.
5. Lay a flat board on top to spread the load and add any suitable weights.
The even distribution of pressure over the entire surface will create
an effect similar to vacuum bagging. Excess resin will run out, exactly
like vacuum bagging. The workpiece is held perfectly flat while the
resin cures, countering any tendency to distort. Providing the
cores were cut correctly (not all were) you are guaranteed a perfectly
true finish.
AMINE BLUSH
Amine blush can occur under certain atmospheric conditions and manifests its
self as a sticky surface coating . It is quite normal but require a lot of
messy and time consuming work using warm water and detergent to remove. Since
it only occurs at the interface of resin and air and we don't have any air in
contact.........we don't get the problem. When you look at the surface area of
your wings, you will appreciate the saving in time.
ALLERGIC REACTION
Some people (me included) have developed an allergic reaction to the hardeners
used in the epoxy system. Since polythene covers 95% of the resin on the
workpiece, I have found the reaction to be significantly reduced. Another
bonus.
FINISHING
Once cured, the jig blocks simply lift off. The polythene is stripped of to
reveal a horrible claggy looking mess....don't worry, all this resin is on the
waste side of the peel ply. Don't be in a hurry to remove the peel ply, leave
it there until you are ready to fill the surfaces. It will withstand post
curing quite happily and will protect the part. When ready to fill, lift a
corner, and strip the ply back. It's as easy as stripping off wet wallpaper.
The clag will be removed with the peel ply and your ugly duckling will turn
into a swan. Compare the time taken to do that with the hours it would
otherwise take with a wire brush water and detergent. And this won't risk
damaging the glass weave...unlike a wire brush.
So much for my experiences. I would not recommend that you take any of this
for granted. Experiment yourself and make your own mind up and get your
inspector involved, he will give you invaluable feedback.
I made a test piece 1ft by 2ft out of about 4 layers of BID . After
squeegeeing, I added peel ply to exactly half the layup, adding just sufficient
resin where needed to wet out the peel ply. After cure I cut the test piece in
half, one with, one without ply, trimmed both to exactly the same size,
stripped off the ply then weighed them. The difference was negligible. If I was
to prepare them for filling, the difference (in time) would be significant.
Then jump on them to destruction to give yourself confidence!
To peel ply, or not to peel ply?..........the choice is yours
Nigel
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