Re: Why hard shelling is a dumb idea


Dave Dugas
 

John,

Could you post some pictures of your Q? Dave D.

johntenhave <johntenhave@...> wrote:
Paul,

no offence taken, and there is nothing like a healthy, reasoned debate.

Rather than clutter the bandwidth, let your comments stand. Let me
comment briefly on incorrect assumptions and may I direct you and
anyone else how is interested to the composite finishing presentation
I have posted. I was asked to explain to the SAAA how the finish on VH
XMX was achieved, so I did.

A Long Ez has 195 sq ft of wetted area. All of it has to be finished
from foam to paint. A Q2XX is a much smaller, simpler area subset.

I have seen the hardshelling method and you are right - I have not
tried it. Its shortcomings were apparent by inspection, my teachers
(mentioned in the presentation) were masters of the faster method and
that is how I decided which was best.

Yes I am advocating peel plying every square inch of the external and
internal glass work. I will explain my reasoning why in another
posting- if it is not apparent from the presentation.

Regards

John

P.S. Re practical experience? I built and surface finished the Long
Ez used as the example in the presentation - single handed.

As one wry Vari Eze builder once noted : "more like moderately
f**king difficult!"

--- In Q-LIST@..., "Paul Buckley" <paulbuckley@...> wrote:

John

Without malice, I disagree with almost everything that you have
said, except maybe the dust!

It is quite obvious that you have never tried or seen this method,
which is well documented.

I reiterate that my wings are as perfect as they could possibly be,
with virtually no micro filler, and that they only require a primer
surfacer to finish.

So the substrate has to be your very best work so do it once
and do it right.<<<<

Exactly!

you have done far more
work than you need to do, will most likely have a heavier
wing and may have a less accurate product <<<<<

Why more work? By all accounts, most builders spend an inordinate
amount of time sanding-filling, sanding-filling, creating copious
amounts of dust in the process.

Why heavier? Using the hard shell method, most of the micro is
sanded away and is only there to provide a straight, hard surface on
which to lay the glass, the resultant cured surface of which is nigh
on perfect.

Why less accurate? You talk about sanding the bare, foam cores.
Surely, doing that destroys any accuracy that you have tried to
achieve by making accurate 'thin' templates!
(and talking about your reasons for using a thin template is rather
like saying that if your pitot head is on the port wing tip, turning
left will give you an ASI reading that is lower than a right turn.
No doubt it will, but it is both academic and unreadable)

You talk about 'only a mechanical bond' between the glass and the
hard shelled surface. Isn't virtually all of the airframe built
relying on mechanical bonds? Have you ever tried to separate two
mechanically bonded surfaces?
The 'mechanical' bond is every bit as strong as any other bond on
the airframe, which I believe holds together pretty well, provided,
like everything else, it is done using the correct techniques.
In any case, the weakest link in the 'skin to foam' bonding is the
foam itself, and I have built test pieces (documented some time ago)
using both methods of construction, and there was no discernable
difference
in the bonding strengths.

Break though the shell whilst sanding and the foam is gone in a
heartbeat - more repairs needed, more weight, more wait<<<<

Rubbish! Are you going to use a belt sander??
When sanding the shell, using a spline, you can clearly see when the
micro is becoming thin, and that is when you stop.
And as the foam cores have been accurately cut and jigged in the
first place, there will be no high spots to break through!
But even if you do break through, it is neither catastrophic or a
problem.

And what shape do you finish the hard shell to? If you use the
final finish
template (and there is is no other option) by definition when you
finish the construction process, you will be adding additional
material unevenly on top of what you have tried to make the correct
shape. Result? An inescapably incorrect shape. <<<<<<<

Really John? I must have missed something. In my 24 years of being
on the 'Quickie' scene, I have never yet seen a 'final finish' template.
Have you? Has anyone?
The hard shell is finished to the same shape as the underlying foam
cores.
Well, to 25thou. anyway! Hopefully, that is good enough!

And it gets worse. Now you have to sand the glass surface
to dull to
bond the micro, so off comes structural strength. The glass bundles
are not as straight as they could be and then we deliberately sand
through them...<<<<<<<<<<

Tell me John, do you not have to sand the glass wing surface in
order to bond the micro filler when using the 'conventional' technique??
Surely you are not advocating the use of peel ply over the whole
wing area? It is a well know fact that doing so is a no-no because it
adds a lot of weight..........
And, using the hard shell method, it is easy to get the glass fibres
dead straight......and I mean, dead straight!

There is no doubt that you are a clever and intelligent man, John,
but I think that you are neither practical or experienced in the
building of glass fibre aeroplanes.
You suffer from what a lot of engineers suffer from, the addiction
to minutia.
You are not building a Swiss watch.........I pay avid attention to
detail and am a perfectionist, but you take your arguments beyond
sensible reason and practicality.

I could go on (and on and on) but I haven't the time or the
patience.......if anyone would like to discuss the pros and cons I am
available off list...... with lots of photos!

Paul Buckley
Cheshire
England

TriQ-200
Still building............





----- Original Message -----
From: johntenhave
To: Q-LIST@...
Sent: Thursday, November 15, 2007 8:54 AM
Subject: [Q-LIST] Why hard shelling is a dumb idea


OK, Paul

before I go any further I am going to spell out the reasons why hard
shelling is dumb and my comments are only directed at the method NOT
at those who choose to use it. This is not a personal attack, please
do not take it as such. I am also not saying that you cannot get a
wing from using the process but rather that you have done far more
work than you you need to do, will most likely have have a heavier
wing and may have a less accurate product. For reasons I will expand
upon in a moment you may well also finish up with an inferior level of
finish.

Firstly lets clearly define what we are trying to achieve:

a smooth, straight, accurate, structurally efficient aerodynamically
correct airfoil with the best possible finish in the shortest possible
time.

The final shape is the outside. The outside is the resultant of (
starting at the bottom surface) paint, primer surfacer, micro/filler
,glass, glass foam interface, foam ...center line and then the same
series in reverse.

All of us only have so much sanding in us. Eventually the most
diligent and persistent of us will give up and go fly so let me submit
that the smart thing to do is to spend that resource wisely.

Finishing occurs at the point in a project when our physical,
financial, energy and enthusiasm resources are at an ebb.
Unfortunately, two factors conspire to get us. The first factor is
that the last thing we do is the first thing that everyone sees and
unfortunately the total quality is often judged by the finish. It
behooves us to get the finish to the highest possible standard (but
not at any cost or weight). What is the acceptable standard? Short
answer - luxury car paint finish is a good standard to aim for.

The second factor is that not everyone realises that the top coat is
best regarded as colour and shine on the substrate. Spraying 30
microns of paint on a cheese grater will not transform it into a
mirror. So the substrate has to be your very best work so do it once
and do it right.

Finishing is a progressive process. First flat, then increasingly
smooth. And there is a difference - a pool ball is smooth but it is
not flat, the billiard table is flat but it is not smooth. Polishing
the slate under the felt will not make the fabric finish any smoother.

All the issues that Paul as identified as being rectified could and
should have been rectified by sanding the foam. Foam is much easier
to sand than micro (we will get to glass in a moment). It is also of
uniform density so it sands evenly and quickly. You are subtracting
weight. The process is fast, easy and you are working below the final
profile.

You are neither micro cure cycle time dependent nor faced with having
to spread, smooth, cure fill, sand, fill,each time adding weight,
making dust.

Break though the shell whilst sanding and the foam is gone in a
heartbeat - more repairs needed, more weight, more wait. And what
shape do you finish the hard shell to? If you use the final finish
template (and there is is no other option) by definition when you
finish the construction process, you will be adding additional
material unevenly on top of what you have tried to make the correct
shape. Result? An inescapably incorrect shape.

But that is not all.

All that work and you have achieved a surface finish which is
inappropriate and unnecessary for that stage in the finish.

You have a surface which provides a poorer bond interface between the
glass and the foam than the chemical and mechanical bond provided
using the original approach. More resin is then required to bond the
glass to the micro surface and again it is only a mechanical bond.

The glass bundles have a rigid under surface - which means that they
do finish up lying under and over to a greater degree than the wet on
wet method combined with peel ply (which should be applied to every
square inch of the surface.) The net result is that the glass surface
is a raised mesh which is less securely bonded to the micro below and
is located above the the correct profile.

And it gets worse. Now you have to sand the glass surface to dull to
bond the micro, so off comes structural strength. The glass bundles
are not as straight as they could be and then we deliberately sand
through them...

Lets summarise then.

Hard shelling adds weight, is slower, results in the wrong profile,
degrades bond strength between glass and foam, results in a weaker
glass structure - and then you have to do it all again!! Remember the
sanding effort is a finite resource and you have spent half of it
already...

Hardshelling makes as much sense as practice bleeding..

Hope that explains the one liner a little more clearly..

John


--- In Q-LIST@..., "Paul Buckley" <paulbuckley@> wrote:

Me too!

I actually aligned the two outer wing cores vertically on my bench,
shearweb down, between two long straight edges which matched the taper
of the wings, thus ensuring that the shearweb was flat and straight,
as were all other joined surfaces. I also pinned the joint with short
wood dowels located on the level lines, but that isn't really
necessary as you can simply lightly clamp two straight boards on each
side of the wing surfaces across the joint (as they are sitting
vertically, on the shearweb), which will ensure that the panels are
aligned accurately.
When cured both wings were then offered up to the center section,
which was firmly fastened to the wing jig.
Result:- perfectly straight and aligned wings.
Easy peasy!

As far as 'hard shelling' is concerned, I have made two sets of
wings this way, after building a set the 'wet' way.
It is much easier to make an accurate wing by 'hard shelling' with
no bumps, hollows etc, and with the glass perfectly straight, with no
micro contamination between plies, and it is much quicker to lay the
glass down on a previously prepared, smooth, surface, not to mention
being much less messy!
The only filling required on my wings were to fill the weave and the
glass spar-cap 'steps', and I would never do it any other way, now.
Hardly a 'moronic' process!

The glass bonds to the cured micro without any problems, and is just
as strong as any other bonding providing that normal 'clean' building
practices are observed. (all of the airframe is glued together)
In any case, the weakest link is in the strength of the foam,
whichever way you do it.

Paul Buckley
Cheshire, England.

Waddelow TriQ-200.....still building.



----- Original Message -----
From: Sam Hoskins
To: Q-LIST@...
Sent: Thursday, November 15, 2007 12:26 AM
Subject: Re: [Q-LIST] Re: Initial foam alignment


Re your comment: "I am inclined to "build" the exterior BL
100-51) *to
center section (BL 51-0)* on a flat surface - let the micro dry.
Then take
the two completed wings and butter up the center (at BL00) and all
the given
jigs "work" per the plans.."

I did exactly that on the last wing I built and it was sooo much
easier.

Sam Hoskins
Murphysboro, IL

On Nov 14, 2007 6:21 PM, Michael Quinn <mquinn6@> wrote:


John, Everything makes sense after you do it... I just have not
done this
before. I wish there was someone local to Charlotte that is a
few steps
ahead of me so I could work w/ them and learn - then mine would
be better by
one generation of build experience! I think thru the process
many times
before attacking it so that I can reduce the "damn I did it the
hard way..."
I am certain w/ pracitce/experience it will become easier. I
re-re-reread
the plans and they talk about the jig - but the female jigs only
were
supporting one section of foam or the other (or are they
bridging it?!?! - I
have female jigs of 3/4 plywood (scared b/c of the which hat
potential since
they are cut square and "should" only make contact with the wing
in one
point (lowest side of the wing). Do you micro and pin the
joints? I look at
jigs from the picts sent to me from others and they look nothing
like the
plans. I just am running thru the build process of the main wing
and it goes
like - check everything for fit and alignment - recheck this at
least 100
times. assemble the center joint less than 1/16 gap (I do not
have the plans
in front of me - but the purpose is for complete bond and reduce
the risk of
exothermic and melting foam and making a non bonded gap
(yes?)). Ok,
assuming gravity still is working in the downward direction -
doesn't it
make the center section of the main wing "want" to pull apart. I
noticed the
5min. epoxy between the foam and female jigs - assume that give
you enough
time to work the foam into final resting place after lathing -
then it hold
until the micro cures. Continuing on, the external two foam wing
cores
(already check fitted 100 times) are buttered with micro and put
onto the
assembly that I just completed (5 min. epoxy should hold it
right?). Now -
the female wing jig is on the center section (the plan show it
on the
external foam cores! this would change the angles of dihedral
and make
"curved" wings....), thus I scratch my brain (but not thru the
nose)... If
they are on the exterior part of the wing - I am inclined to
"build" the
exterior BL 100-51) *to center section (BL 51-0)* on a flat
surface - let
the micro dry. Then take the two completed wings and butter up
the center
(at BL00) and all the given jigs "work" per the plans....
Hardshelling =
slathering and curing, sanding micro prior to starting to glass?
I have read
several success stories about this method - my fear is the less
than optimum
bond between the hardened micro and the glass lay-up. And weight
(which the
argument is you will have to use that micro on the outside
otherwise). Since
one does not peel ply the micro (since it is sanded down to
true) - the last
sanding would be done with 60 grit to leave connection points of
pure epoxy
prior to glass. Please be gentile I am a virgin with regards
to the
quickie.... M. *Not certain on BL measurements - just pulling
these numbers
from what I thought I remember reading...

To: Q-LIST@ <Q-LIST%40yahoogroups.comFrom>:
johntenhave@ <johntenhave%40yahoo.comDate>: Wed, 14 Nov 2007
08:25:38 +0000Subject: [Q-LIST] Re: Initial foam alignment

M,you are attempting to partially fix one problem whilst
ignoring therest
of the process. The problem you are trying to fix will
beunlikely to exist
if you follow a very well worn path.Let me add the following
suggestions
and forgive me if some of thesethings seem so trivial as to be
too obvious
to state.1. The final product accuracy will be dependent upon
the sum of
theerrors in each of the steps leading to the final product. i.e.
jig,templates, hot wiring, joining, glassing, filling.2. Get
your jig
right, and spend as much time on it as is needed toget the
desired level of
accuracy. Remember that a jig is a devicedesigned to permit
ordinary levels
of skill to achieve levels ofaccuracy higher than normally
possible. 3. Get
your hot wire templates spot on, make them as thin as
possibleand make sure
that they permit a smooth passage of the the hot wire.errors
come from
snagging wires, dragging drooping wires, cooling ofthe wires,
and hidden
obstructions. Why thin? remember that you are cutting a taper
and if you use
eachtemplate twice you will cut foam matching faces. Each face
will usethe
same face/edge of the template. One face/edge will be adjacent
tothe foam
but the other foam block will be spaced out by the thicknessof
the template
and will cut oversize. To better visualise this, thinkabout
cutting a
witches hat out of foam in two parts. Imagine a 1"thick template
halfway up
the hat. with the hat upright, the top halfwill use the top edge
of the
template. Cutting the bottom half willstill use the top edge of
the template
but the taper will mean thatthe wire meets the top of the foam
on an angle
and will cut over size. 4. Smooth passage of the wire means
smooth templates
and smoothoperators. 5. Snagging comes from :a. the nails
holding the
templates to the foam at an angle whichintersects the wire path
- so point
them inwards and locate them aninch or so from the cut
surface.b. the wire
hitting blobs of micro joining blocks prior to hot wiring- so
use very
little, and leave the edges free of micro ~ 1/4" or so.You can
fill this
gap later and there is no point in making thejoint any stronger
than the
parent foam. The foam is a mold, thestructure is the glass. 6.
Drooping
comes from wire lengthening, wire dragging and unevenheating and
poor
technique.7. When cutting the second half of a wing block put
the core
back intothe block from which you have just cut it.Some
suggestions : use
0.032" stainless steel mig welding wire whichis orders of
magnitude
stronger than lockwire, use a good power supplywhich you can
control quickly
and easily, build a strong light hotwiresaw and heat and tighten
the wire
till your eyes bleed.. Plucking thewire will tell you when you
have reached
yield. Practice at different temps and speed until you get dogbone
freeshapes. This means slow on sharp curves, faster on shallow
curves,tight
hot wires and smooth accurate number following - at both ends.8.
Choreograph each cut before you make it and make sure the saw
canreach the
whole cut, the weights used to hold everything down can
becleared, and the
saw power supply cable is long enough - remember thatif you snag
you stop,
if you stop you burn and cut over size - sothe immediate action
if you snag
is out at right angles to the template.9. store your cores in
the cut out
portions.10 join the cores in the jig and run a straight edge
along
theleading edge to maximise alignment. Split differences and aim
to makeany
error a hollow rather than a hump.11. When glued remember this -
0.020" of
glass over corrugated ironwill not change the surface into an
ice rink so
sand your foam with along sanding block, a long straight edge
and along the
lines whichjoin the talking lines spanwise. Foam is much much
easier to sand
thaneither micro or glass. and get it to within 0.030" or so.
Use lightand
sand intelligently. One stroke of the sanding block will make
adifference.
Do not hard shell - this is a moronic process. Lets continue the
conversation when you get to glassing, there arelots of ways to
make that
simpler and easier as well. Hope this helpsJohn--- In
Q-LIST@... <Q-LIST%40yahoogroups.com>, "mtyquinn665"
<mquinn6@> wrote:>> I am trying VERY hard not to reinvent the
wheel but I
am attempting to > build the wing on a jig and see posting where
washout and
wing > alignment (of the foam) caused the final product to not
be as perfect
as intended. (any sanding to match the other foam indicates an
inacuracy
in following the template when hot wiring - then one sands to >
match and
you are left with an "original" airfoil)> > My thought is to
make a slot cut
(90 degrees perpendicular to the > surface) 1/2 inch deep at the
WL between
the foam sections and use a > 1/16" x 1" ( x width of the wing
at that point
minus 1 in or so) strip > of plastic as a key (this concept is
from years of
woodworking and what > we call "biskets"). > > To test for
levelness a equal
length wood skewer could be inserted > (using a small square to
insure
perpendicular to skin in 2 planes) > until it makes contact w/
the plastic
(prior to glassing)and a level > could be placed on top of the
skewers. > >
Does this make any sense?> > M.>

__________________________________________________________
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--
Sam Hoskins
www.MistakeProofing.Net
www.MistakeProofing.net/blog/
618-967-0016 ph.
312-212-4086 fax








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