Re: Why hard shelling is a dumb idea

Michael Quinn


All this makes sense. I still think the bond between hardshell or micro-wet layup the weak point is between the micro (whether hard or wet) and not the rough sanded hard and glass. Yes the chemical bond on the wet lay-up will be stronger - but the chain is only as strong as the weakest link (whichever way and the foam).

The only way I see to make this better would be to take and put negative "teeth" in the foam with a nail every 1/2" (or so) to provide a better "bite" for the micro slurry to get into - IF you could be assured of getting down into the cavities. This of course would add weight.

Did you modify the original LS1 templates and EP1212 templates to account for the thickness of the glass layup? Or did you draw out the spar cap and sand down the foam where the thicker layers go? Good point about the final profile! I am curious how many true profiles after either technique are out there!!!


To: Q-LIST@...: johntenhave@...: Thu, 15 Nov 2007 08:54:41 +0000Subject: [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 hardshelling is dumb and my comments are only directed at the method NOTat those who choose to use it. This is not a personal attack, pleasedo not take it as such. I am also not saying that you cannot get awing from using the process but rather that you have done far morework than you you need to do, will most likely have have a heavierwing and may have a less accurate product. For reasons I will expandupon in a moment you may well also finish up with an inferior level offinish.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 possibletime.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 line and then the sameseries in reverse. All of us only have so much sanding in us. Eventually the mostdiligent and persistent of us will give up and go fly so let me submitthat 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 isthat the last thing we do is the first thing that everyone sees andunfortunately the total quality is often judged by the finish. Itbehooves us to get the finish to the highest possible standard (butnot at any cost or weight). What is the acceptable standard? Shortanswer - luxury car paint finish is a good standard to aim for. The second factor is that not everyone realises that the top coat isbest regarded as colour and shine on the substrate. Spraying 30microns of paint on a cheese grater will not transform it into amirror. So the substrate has to be your very best work so do it onceand do it right.Finishing is a progressive process. First flat, then increasinglysmooth. And there is a difference - a pool ball is smooth but it isnot flat, the billiard table is flat but it is not smooth. Polishingthe slate under the felt will not make the fabric finish any smoother.All the issues that Paul as identified as being rectified could andshould have been rectified by sanding the foam. Foam is much easierto sand than micro (we will get to glass in a moment). It is also ofuniform density so it sands evenly and quickly. You are subtractingweight. The process is fast, easy and you are working below the finalprofile.You are neither micro cure cycle time dependent nor faced with havingto spread, smooth, cure fill, sand, fill,each time adding weight,making dust. Break though the shell whilst sanding and the foam is gone in aheartbeat - more repairs needed, more weight, more wait. And whatshape do you finish the hard shell to? If you use the final finishtemplate (and there is is no other option) by definition when youfinish the construction process, you will be adding additionalmaterial unevenly on top of what you have tried to make the correctshape. Result? An inescapably incorrect shape. But that is not all.All that work and you have achieved a surface finish which isinappropriate and unnecessary for that stage in the finish. You have a surface which provides a poorer bond interface between theglass and the foam than the chemical and mechanical bond providedusing the original approach. More resin is then required to bond theglass to the micro surface and again it is only a mechanical bond. The glass bundles have a rigid under surface - which means that theydo finish up lying under and over to a greater degree than the wet onwet method combined with peel ply (which should be applied to everysquare inch of the surface.) The net result is that the glass surfaceis a raised mesh which is less securely bonded to the micro below andis located above the the correct profile.And it gets worse. Now you have to sand the glass surface to dull tobond the micro, so off comes structural strength. The glass bundlesare not as straight as they could be and then we deliberately sandthrough 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 weakerglass structure - and then you have to do it all again!! Remember thesanding effort is a finite resource and you have spent half of italready...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 taperof the wings, thus ensuring that the shearweb was flat and straight,as were all other joined surfaces. I also pinned the joint with shortwood dowels located on the level lines, but that isn't reallynecessary as you can simply lightly clamp two straight boards on eachside of the wing surfaces across the joint (as they are sittingvertically, on the shearweb), which will ensure that the panels arealigned 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 ofwings this way, after building a set the 'wet' way.> It is much easier to make an accurate wing by 'hard shelling' withno bumps, hollows etc, and with the glass perfectly straight, with nomicro contamination between plies, and it is much quicker to lay theglass down on a previously prepared, smooth, surface, not to mentionbeing much less messy!> The only filling required on my wings were to fill the weave and theglass 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 justas strong as any other bonding providing that normal 'clean' buildingpractices 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 allthe given> jigs "work" per the plans.."> > I did exactly that on the last wing I built and it was sooo mucheasier.> > 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 notdone this> > before. I wish there was someone local to Charlotte that is afew steps> > ahead of me so I could work w/ them and learn - then mine wouldbe better by> > one generation of build experience! I think thru the processmany times> > before attacking it so that I can reduce the "damn I did it thehard way..."> > I am certain w/ pracitce/experience it will become easier. Ire-re-reread> > the plans and they talk about the jig - but the female jigs onlywere> > supporting one section of foam or the other (or are theybridging it?!?! - I> > have female jigs of 3/4 plywood (scared b/c of the which hatpotential since> > they are cut square and "should" only make contact with the wingin one> > point (lowest side of the wing). Do you micro and pin thejoints? I look at> > jigs from the picts sent to me from others and they look nothinglike the> > plans. I just am running thru the build process of the main wingand it goes> > like - check everything for fit and alignment - recheck this atleast 100> > times. assemble the center joint less than 1/16 gap (I do nothave the plans> > in front of me - but the purpose is for complete bond and reducethe 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. Inoticed the> > 5min. epoxy between the foam and female jigs - assume that giveyou 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 wingcores> > (already check fitted 100 times) are buttered with micro and putonto the> > assembly that I just completed (5 min. epoxy should hold itright?). Now -> > the female wing jig is on the center section (the plan show iton the> > external foam cores! this would change the angles of dihedraland make> > "curved" wings....), thus I scratch my brain (but not thru thenose)... 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 flatsurface - let> > the micro dry. Then take the two completed wings and butter upthe 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 lessthan 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 outsideotherwise). Since> > one does not peel ply the micro (since it is sanded down totrue) - the last> > sanding would be done with 60 grit to leave connection points ofpure epoxy> > prior to glass. Please be gentile I am a virgin with regards to the> > quickie.... M. *Not certain on BL measurements - just pullingthese 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 whilstignoring therest> > of the process. The problem you are trying to fix willbeunlikely to exist> > if you follow a very well worn path.Let me add the followingsuggestions> > and forgive me if some of thesethings seem so trivial as to betoo obvious> > to state.1. The final product accuracy will be dependent uponthe sum of> > theerrors in each of the steps leading to the final product. i.e.> > jig,templates, hot wiring, joining, glassing, filling.2. Getyour jig> > right, and spend as much time on it as is needed toget thedesired level of> > accuracy. Remember that a jig is a devicedesigned to permitordinary levels> > of skill to achieve levels ofaccuracy higher than normallypossible. 3. Get> > your hot wire templates spot on, make them as thin aspossibleand make sure> > that they permit a smooth passage of the the hot wire.errorscome from> > snagging wires, dragging drooping wires, cooling ofthe wires,and hidden> > obstructions. Why thin? remember that you are cutting a taperand if you use> > eachtemplate twice you will cut foam matching faces. Each facewill usethe> > same face/edge of the template. One face/edge will be adjacenttothe foam> > but the other foam block will be spaced out by the thicknessofthe template> > and will cut oversize. To better visualise this, thinkaboutcutting a> > witches hat out of foam in two parts. Imagine a 1"thick templatehalfway up> > the hat. with the hat upright, the top halfwill use the top edgeof the> > template. Cutting the bottom half willstill use the top edge ofthe template> > but the taper will mean thatthe wire meets the top of the foamon an angle> > and will cut over size. 4. Smooth passage of the wire meanssmooth templates> > and smoothoperators. 5. Snagging comes from :a. the nailsholding the> > templates to the foam at an angle whichintersects the wire path- so point> > them inwards and locate them aninch or so from the cutsurface.b. the wire> > hitting blobs of micro joining blocks prior to hot wiring- souse very> > little, and leave the edges free of micro ~ 1/4" or so.You canfill this> > gap later and there is no point in making thejoint any strongerthan the> > parent foam. The foam is a mold, thestructure is the glass. 6.Drooping> > comes from wire lengthening, wire dragging and unevenheating andpoor> > technique.7. When cutting the second half of a wing block putthe core> > back intothe block from which you have just cut it.Somesuggestions : use> > 0.032" stainless steel mig welding wire whichis orders of magnitude> > stronger than lockwire, use a good power supplywhich you cancontrol quickly> > and easily, build a strong light hotwiresaw and heat and tightenthe wire> > till your eyes bleed.. Plucking thewire will tell you when youhave reached> > yield. Practice at different temps and speed until you get dogbone> > freeshapes. This means slow on sharp curves, faster on shallowcurves,tight> > hot wires and smooth accurate number following - at both ends.8.> > Choreograph each cut before you make it and make sure the sawcanreach the> > whole cut, the weights used to hold everything down canbecleared, and the> > saw power supply cable is long enough - remember thatif you snagyou stop,> > if you stop you burn and cut over size - sothe immediate actionif you snag> > is out at right angles to the template.9. store your cores inthe cut out> > portions.10 join the cores in the jig and run a straight edge along> > theleading edge to maximise alignment. Split differences and aimto 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 anice rink so> > sand your foam with along sanding block, a long straight edgeand along the> > lines whichjoin the talking lines spanwise. Foam is much mucheasier 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 makeadifference.> > Do not hard shell - this is a moronic process. Lets continue the> > conversation when you get to glassing, there arelots of ways tomake that> > simpler and easier as well. Hope this helpsJohn--- In> > Q-LIST@... <>, "mtyquinn665"> > <mquinn6@> wrote:>> I am trying VERY hard not to reinvent thewheel but I> > am attempting to > build the wing on a jig and see posting wherewashout and> > wing > alignment (of the foam) caused the final product to notbe 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 tomake a slot cut> > (90 degrees perpendicular to the > surface) 1/2 inch deep at theWL between> > the foam sections and use a > 1/16" x 1" ( x width of the wingat that point> > minus 1 in or so) strip > of plastic as a key (this concept isfrom years of> > woodworking and what > we call "biskets"). > > To test forlevelness a equal> > length wood skewer could be inserted > (using a small square toinsure> > 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 theskewers. > >> > Does this make any sense?> > M.>> >> > __________________________________________________________> > Climb to the top of the charts! Play Star Shuffle: the word scramble> > challenge with star power.> >> >> >> > [Non-text portions of this message have been removed]> >> > > >> > -- > Sam Hoskins> www.MistakeProofing.Net>> 618-967-0016 ph.> 312-212-4086 fax> > [Non-text portions of this message have been removed]> > > > > > >----------------------------------------------------------> > > No virus found in this incoming message.> Checked by AVG Free Edition. > Version: 7.5.503 / Virus Database: 269.15.31/1129 - Release Date:13/11/2007 21:22> > > [Non-text portions of this message have been removed]>

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