Which carbon fiber tape?

I am working on my RV-8 canopy windscreen and would like to add some carbon fiber tape to the canopy bow. I am sure that at some point in time i will grab it getting in or out of the plane and I would like to strengthen the glassed area.

After reading all the specs, I am even more confused as to which weave and weight would work best.

US Composites seems to have the best selection. For those who are familiar with carbon fiber, which cloth tape would you suggest? Should I consider Kevlar as well?

choices are: http://www.shopmaninc.com/carbonpage.html

Thanks in advance for your suggestions.

Mike Draper
RV-8 N468RV
-working on the canopy

Depends - but don't use Kevlar!

Do you want an outer cosmetic layer or do you want stiffness and plan to paint the bow? The unidirectional carbon tape will provide stiffness parallel to the bow, but will provide no strength perpendicular to the bow. It will easily crack parallel to the fibers when gripping it with your hands. This material is parallel graphite tows tied together with non-structural fibers.

Any of the other fabrics can be used depending on your preference for thickness. The thinner fabics allow a mixing of glass and graphite without making the bow layup too thick. A good basic weave is the plain weave. It should drape fine for the bow contours.

If you want a cosmetic finish, just pick the weave that you like the best.

Don't use Kevlar. Epoxy does not bond well to Kevlar and can easily be delaminated. Plus you can't sand it, and it is not as stiff as the graphite. A kevlar laminate can easily be peeled abart ply by ply.

One other tip, if you use carbon fiber with fiberglass, make the material layup symmetric about the center of the layup stack by both material type and orientation. In other words, if you want a 0/90 carbon last ply, put a 0/90 ply down also as the first ply. Otherwise, as the cured laminate changes temperature, the different materials and fiber directions will cause the laminate to warp due to the mismatch in coefficients of thermal expansion.

Mike, in that application I'd suggest carbon is a lot of trouble/expense for very little gain.

Tips FOR kevlar?

BJohnson said:

Don't use Kevlar. Epoxy does not bond well to Kevlar and can easily be delaminated. Plus you can't sand it, and it is not as stiff as the graphite. A kevlar laminate can easily be peeled abart ply by ply.

Click to expand...

Brice,
It's obvious that you have direct experience with composites. Since I have a "free" roll of plain weave Kevlar sitting in the shop, I am curious if there are techniques to successfully use it. Heck, I already forked over the cash for the good scissors!

make bulletproof clothes!

Other uses of Kevlar

Other that ballistics, including fan containment structures for turbofan engines, the best use of Kevlar I have seen is as a peel ply. I have placed Kevlar/epoxy prepreg between two stacks of carbon/epoxy prepreg with the intent to later separate the two carbon laminates after cure. Once cured, the two pieces separate very easily at the Kevlar layer by starting peel with a knife wedge at the Kevlar. The Kevlar ply can then be removed without tearing as a single piece.

Kevlar is great for energy absorption..... when used in tension where one does not have to rely on the shear properties for resin to fiber adhesion.

Overkill?

Brice, thanks for the briefing, it was very helpful.

Dan, you raise an excellent question. Is it really necessary to reinforce the canopy bow on the RV-8?

For those RV-8ers who *haven't* added any carbon fiber to the canopy bow, have you ran into any issues?

Mike Draper
RV-8 N468RV
- working on the canopy

I have a four year old -8 with the canopy bow made of plain old fiberglass. It is plenty strong. No cracks. Just use enough layers to make it stiff without getting to thick.

David

BJohnson said:

One other tip, if you use carbon fiber with fiberglass, make the material layup symmetric about the center of the layup stack by both material type and orientation. In other words, if you want a 0/90 carbon last ply, put a 0/90 ply down also as the first ply. Otherwise, as the cured laminate changes temperature, the different materials and fiber directions will cause the laminate to warp due to the mismatch in coefficients of thermal expansion.

Click to expand...

Have you seen this happen? I ask because this is the first i have heard of it, and i've worked on some legacys, which often have fiberglass and carbon mixed. I don't have years of experience with composites, just months (albeit full time ) and i think i would have remembered something like this if someone told me. maybe no-one ever told me ; )

<<Brice, thanks for the briefing, it was very helpful.>>

Yeah, and I wish you would write more often. I very much enjoy professional input.

<<Dan, you raise an excellent question. Is it really necessary to reinforce the canopy bow on the RV-8? >>

.....or any other slider? Depends. Some folks can break a bowling ball in a rubber room.

Here's why I said you were going to a lot of trouble for not much gain. Carbon tends to be seen as some sort of super fabric. It's not; it merely has different properties as compared to the other choices. Quantifying those properties and applying them is important.

Brice, check me here. A bi-directional carbon/epoxy laminate is stiffer than glass/epoxy (roughly 3 to 4 times). However, it is not vastly stronger (maybe 1.5 times).

So, a little country-boy analysis for the windshield lip. Assume the plans version is 6 plies of 9 oz glass tape (I dunno, is it?). The fabrics you're likely to use are all about 0.010 inch thick.

Maybe you use 9 plies of glass tape instead of 6 plies. Three additional plies of 9oz glass in 3" tape 3 feet long would be 2.25 oz. A 50/50 glass-to-resin ratio doubles that, so you're adding something less than 5 ozs total and 0.030 thickness if you're convinced you need a tougher, stronger lip.....and there is very little cost/hassle factor.

Or add a carbon tape layer inside and outside. 2 plies carbon and 4 plies glass would save a grand total of 1/2 oz compared to the original 6 plies glass. It would be roughly the same strength as the 9 ply glass lip and .030" thinner.

I'm not the least bit opposed if you want to incorporate the carbon tape (education and recreation, right?). For me, 5 oz and .030 thickness vs the additional cost and hassle wouldn't be worth it. The application is small, non-structural, and not dimensionally critical.

The basics

Danny7,

Balanced and symmetric laminates are rule #1 for composite materials. If it is not symmetric (about the mid ply be material type and orientation) it will warp with changes in temperature. If it is not symmetric (for every positive fiber angle there is a negative fiber angle) the laminate will twist while bending. Classical laminate theory predicts the behavior quite nicely, but if you want to experiment, laminate a ply of carbon to a ply of fiberglass and cure it flat (assuming at room temperature). Once cured, heat it up. The different coefficients of thermal expansion will warp it like a potato chip. THis is more critical with elevated cure composite materials where just cooling down from the cure cycle will warp the part. If t-here is no change in temp, then nonsymmetric layups are not as critical.

Dan,

I agree, the carbon is much stiffer but about the same strength, except as with E glass, S glass, and quartz, there are many different types of cabon fibers with dramatically different stiffness and strengths. Whole families of standard modulus, intermediate modulus, and high modulus fibers exist allowing designers to pick optimal properties for their needs. Most fabrics are typically standard modulus fibers. Adding some carbon fiber will add some stiffness without adding thickness that fiber glass would add.

When I get to that point, I am leaning towards composite skirts with cosmetic carbon fiber outer plies, if i can get them to come out smooth, and left clear coated. I Need to get more composite content on my RV because I got in trouble at work for building a metal airplane.

BJohnson said:

Danny7,

Balanced and symmetric laminates are rule #1 for composite materials. If it is not symmetric (about the mid ply be material type and orientation) it will warp with changes in temperature. If it is not symmetric (for every positive fiber angle there is a negative fiber angle) the laminate will twist while bending. Classical laminate theory predicts the behavior quite nicely, but if you want to experiment, laminate a ply of carbon to a ply of fiberglass and cure it flat (assuming at room temperature). Once cured, heat it up. The different coefficients of thermal expansion will warp it like a potato chip. THis is more critical with elevated cure composite materials where just cooling down from the cure cycle will warp the part. If t-here is no change in temp, then nonsymmetric layups are not as critical.

Dan,

I agree, the carbon is much stiffer but about the same strength, except as with E glass, S glass, and quartz, there are many different types of cabon fibers with dramatically different stiffness and strengths. Whole families of standard modulus, intermediate modulus, and high modulus fibers exist allowing designers to pick optimal properties for their needs. Most fabrics are typically standard modulus fibers. Adding some carbon fiber will add some stiffness without adding thickness that fiber glass would add.

When I get to that point, I am leaning towards composite skirts with cosmetic carbon fiber outer plies, if i can get them to come out smooth, and left clear coated. I Need to get more composite content on my RV because I got in trouble at work for building a metal airplane.

Click to expand...

when you are talking symmetric in your response to me, would this be addressed by cutting materials on a 45 degree bias, that have the same thread for the material in the warp and weave (is that the correct terminology?)

and re your reply to dan, what is quartz?

i found this for quartz http://www.freepatentsonline.com/6979172.html, it references quartz as being particulary well suited for impact resistance. is that how it is used on airplanes?

So I happen to have some carbon uni tape on hand I was thinking about using for this canopy bow, however I was looking at coefficient of thermal expansion, and this raises a question. The coefficient of thermal expansion for fiberglass is about half that of Perspex. The coefficient of thermal expansion of carbon fiber is virtually nothing. Thus if I use carbon, in temperature extremes should I be expecting my slider to get stuck under the windscreen bow, and worse still, crack, or for some reason is this just a non issue. Anyone input from those with field experience of carbon bows would be appreciated.
Cheers.
Tom.
RV-7 slider.

canopy

I used 3 bids of carbon on my RV6 over base of fiberglass because everyone getting in and out grabs it. After screwing windshield to rollbar and finishing with fiberglass cloth then the carbon I added a layer of dynel over the top for smoothness and easy final filling less pin holes.This leaves a big gap between rollbar and skirt which filling with West epoxy in the caulking premixed tube really stiffens the top skirt so grabbing it for getting in and out works.Took about 1 1/2 tubes to fill.
Bob

I'd seen several sliders where the paint was cracked on the bow, so wanted to prevent that. I used CF on my -6A the canopy bow not for the strength but for the stiffness: passengers do grab it and I didn't want it flexing and cracking the paint. It's just a layer of CF cloth sandwitched between two layers of bidi FG cloth.

My first experience with this FG stuff was building this plane, so, no experience here, but on the top bow of the slider WS I did, 4 FG, 1 CF, and 2 FG, the 2" CF tape had the strands going the wrong way for the strength I wanted for the bow, so I cut them into squares and laid them in, what a pain, but al in all it came out great and no paint chipping or cracking.

Thanks.

So the general concensis seems to be that carbon is fine and doesn't lead to Perspex cracking. I guess in my mind I still do not fully understand the mechanisms at play given that we go to all the effort to make these 1/8" spacers for the sikaflex application, but then bond a product like carbon to the outside that has virtually no coefficient of thermal expansion.
I guess this is one of those situations where I need to stop thinkin and get moving.
Tom.

tgmillso said:

So the general concensis seems to be that carbon is fine and doesn't lead to Perspex cracking. I guess in my mind I still do not fully understand the mechanisms at play given that we go to all the effort to make these 1/8" spacers for the sikaflex application, but then bond a product like carbon to the outside that has virtually no coefficient of thermal expansion.
I guess this is one of those situations where I need to stop thinkin and get moving.
Tom.

Click to expand...

Ah, great clarifying statement!

I bonded my canopy with Sikaflex, and likewise ended up bonding the composite bits (skirts, etc.) to the plexi using Sikaflex as well after finding epoxy to be less than satisfactory.

An entirely different perspective........

One problem that can occur with these fiberglass fairings is abuse from people kicking / banging into them while climbing in or out.
They rarely suffer damage that would be prevented by having carbon cloth in the lay-up, but it does often cause the start of a de-lamination from the surface the fairing is bonded too.
The stiffer the fairing, the more that any impact on the fairing will get focused on the bond zone and start a delamination
Adding carbon cloth to the lay up does add stiffness.

rvbuilder2002 said:

One problem that can occur with these fiberglass fairings is abuse from people kicking / banging into them while climbing in or out.
They rarely suffer damage that would be prevented by having carbon cloth in the lay-up, but it does often cause the start of a de-lamination from the surface the fairing is bonded too.
The stiffer the fairing, the more that any impact on the fairing will get focused on the bond zone and start a delamination
Adding carbon cloth to the lay up does add stiffness.

Click to expand...

Certainly that's true. But that doesn't mean that you need to accept cracking or delamination - I chose to accept neither after seeing enough damaged fairings and talking to multiple builders who wished they had done something differently. So I learned from their experience and used CF + sikalfex. Almost 5 years and 700 hours later, no issues to date and it's been kicked (accidentally, of course) multiple times. The sika is still holding strong and no cracks on the paint.

ChiefPilot said:

Certainly that's true. But that doesn't mean that you need to accept cracking or delamination - I chose to accept neither after seeing enough damaged fairings and talking to multiple builders who wished they had done something differently. So I learned from their experience and used CF + sikalfex. Almost 5 years and 700 hours later, no issues to date and it's been kicked (accidentally, of course) multiple times. The sika is still holding strong and no cracks on the paint.

Click to expand...

Any photos of your process and result? Sounds interesting.

ChiefPilot said:

Certainly that's true. But that doesn't mean that you need to accept cracking or delamination - I chose to accept neither after seeing enough damaged fairings and talking to multiple builders who wished they had done something differently. So I learned from their experience and used CF + sikalfex. Almost 5 years and 700 hours later, no issues to date and it's been kicked (accidentally, of course) multiple times. The sika is still holding strong and no cracks on the paint.

Click to expand...

Coming back full circle to my primary point.....

There is little if any structural benefit in using carbon fiber cloth and the extra stiffness (along with higher cost, higher difficulty to work with, etc.) can be a detriment......

rvbuilder2002 said:

Coming back full circle to my primary point.....

There is little if any structural benefit in using carbon fiber cloth and the extra stiffness (along with higher cost, higher difficulty to work with, etc.) can be a detriment......

Click to expand...

Sigh.

And coming back to my primary point - the CF wasn't there for structural benefit, but rather finish benefit: no paint cracking due to flexing of the underlying structure. Was it extra work? Hard to tell, but it was nothing compared to the rest of the canopy work.

ETA: I don't think the two points are incompatible - it comes down to what the builder wants.

ChiefPilot said:

Sigh.

And coming back to my primary point - the CF wasn't there for structural benefit, but rather finish benefit: no paint cracking due to flexing of the underlying structure. Was it extra work? Hard to tell, but it was nothing compared to the rest of the canopy work.

Click to expand...

No problem..... The aft targa strip on my personal airplane has 1 layer of carbon for cosmetic purposes on the portion that is not painted.
One layer has very minimal impact on overall stiffness.
I should have been more specific to say that I would recommend not using carbon for the entire thing.

So I think I have this thing worked out, at least I hope I have because I'm about to go and lay some composites down. If the coefficient of thermal expansion of perspex is 0.000075mm/mm per degree kelvin, and assuming the canopy side is 1000mm long (round figures here) then for a 40 degree celsius maximum desired temperature and assuming I bond at 20 degrees celsius, the canopy will expand by 1.5mm. Sikaflex has a 500% elongation to break per the data sheets, and IIRC a working elongation up to 300%, thus of this canopy can shear expand up to 1.5mm compared to the skirt, then basic trig suggests that a 0.5mm spacer should be adequate to allow the bond to shear this amount (ok, the hypotenuse of a 1.5mmx0.5mm triangle is 1.58mm, but close enough).
Thus, in summary, I intend to lay up some electrical tape first to a 0.5mm thickness to fill the void where the sikaflex will be in the future (this step may not even be necessary as you should get enough flex in the skirt even with carbon in the mix), then cover the tape and the void between the canopy and the fuselage with packing tape tape, lay up the glass/fiber skirt, pop it off when cured, tear off the electrical tape spacer (if I decide to use it), replace this with some 0.5mm small spacers (fishing line perhaps) then finally bond the canopy in place with sikaflex. At least in theory. The only downside I can see to this is the fact that you will have a 0.5mm thicker layup than you would otherwise., but there's no reason why you can't put a nice slope on the sikaflex bead. Time to put this into practice.
Tom.

I'd put a large factor of safety on that elongation. That 300% isn't a "working" number, it's elongation to failure. You don't want it to fail. Do search in VAF for the thickness that other people are using even without the carbon, and I think that you'll find that the gap really ought to be considerably larger.

Dave

Hi Dave. The elongation to failure for 295 UV is definitely 500%. I checked VAF threads and it appears that many are using no spacers at all for joining the skirt to the canopy.
http://www.vansairforce.com/community/showthread.php?t=98485
Thus I fail to see why 0.5mm won't be better than nothing. I just don't want an unnecessarily high step up to my already thick skirt and targa strip. Although there is little linear elongation in the carbon/fiberglass skirt, it does have the ability to flex outward to some degree. The spacing specs issued by Sika are assuming mounting to a far more rigid marine structure.
The world has 10 minutes to convince me otherwise, as I'm about to lay down the last layer of tape.
Tom.

But thanks for your feedback anyway Dave. That's the whole reason I'm hashing this out on the forum and not making the decision in complete isolation.
Tom.

I increased the thickness by 50% to 0.75mm. Don't say I'm not good to you Dave.

Glue

Put a few screws in and it will be alright.
Bob

Tom, it's not my job to convince anyone to do anything. Especially on someone else's schedule, and across multiple time zones. You're free to do as you think best, and I'm glad that you're documenting what you're doing and your reasons. I hope that in a few years you'll return to this thread and let us all know how it worked out.

In general, when someone uses an elastomer to manage a difference in thermal expansion, adding thickness to the elastomer is the way to improve the joint. To a degree, the thicker the better - thickness reduces the shear stresses as the other materials expand and contract relative to each other. Generally speaking there's no structural merit to making the elastomer thinner for this sort of joint, although as you suggested, there might be a cosmetic benefit. With canopies, since they're a PITA, I'd put the emphasis on having a good structure and deal with the cosmetics elsewhere.

Dave

So Dave, I think I have worked out why you are right and I am wrong. When a tensile test to failure is performed, the material is allowed to "neck" in the middle. In our case the structure is purely under shear, so the material can not neck to the same degree (essentially not at all). This why what we really need to do is test a sample in shear, increasing the bond thickness until we achieve our desired 1.5mm elongation before failure. This still doesn't tell us much about the stresses within the Perspex at this point, but it will at least tell us what bond thickness is required to sustain the temperature range. That said, I've spent the best part of the day prepping this canopy ready for the layup, and I have only allowed for 0.75mm, so it will be a major PITA to go back and change everything now, thus I'll be the sacrificial lamb in the testing for this one. I can only hope that what I haven't allowed for will be taken up by the complex curve nature of the canopy. At the end of the day 0.75mm spacing on the top and 1/8" spacing beneath is a load better that directly bolting to a steel frame and bonding the skirt with straight epoxy!
Tom.

The acrylic has some compliance and can absorb some of the differential expansion, as can the fiberglass, if you didn't use carbon. Carbon, being stiffer and having that near-zero CTE, is both the cause of the issue and not a contributor to the solution.

Who knows- maybe you'll get away with it. I hope so, but will take a different, more conservative, approach on mine, when I get that far.

Dave
RV-3B, now skinning the fuselage

I just finished the layups, and I'm having my regrets already.
I used 22oz triax glass on the bottom, 14oz carbon uni in the middle, and 22oz traix on the outside. I suspect this is thicker than what I need.
It was recommended to me to use the triax as it is stronger than the weave for the same weight. I had a dog of a time getting it around the aft bow on the canopy, as the weave was just too stiff, so I had to cut it and double it back over itself in sections. I also had an appalling time getting this heavy weight triax to comply to the profile of the doghouse. The carbon too was also so wide as it didn't conform either around the aft canopy bow, so I had to make some cuts through it and double it over itself. I at least made sure these cuts didn't occur in the same location, so my resulting bulges should be minimized. Total weight was about 950g for material, and 950g for resin, which after edge trimming should come to 1475g combined. I suspect there will be another 100g of filler as the traix was pretty coarse and will require filling. There will be 90g of sikaflex required to fill the 0.75mm gap, giving a grand total of 1.66kg. This compares to approximately 1.2kg for the aluminium fairing, so there's almost exactly a pound difference there.
If I was to do this again (which I hope I never will), I think I would forgo the stiffness of the triax glass, or at least lay down some more conformant woven cloth of lighter weight first and do the layup in thinner layers. This should help conform around the rear bow curves and the doghouse. I may sandwich in the middle some uni glass, but thinner widths so that it conforms better around the rear bow. This super thick triax was tough to handle and wet out. For all the reasons Dave has pointed out, I think I'd also skip the carbon. Time will tell, and I will be sure to report back of this doesn't work out. Great excuse I guess to get out of Tasmania and head to some hotter places, all in the name of science.
Tom.

tgmillso said:

I used 22oz triax glass on the bottom, 14oz carbon uni in the middle, and 22oz traix on the outside. I suspect this is thicker than what I need.

Click to expand...

Holy heavy cloth Batman! I think I used one layer of 6oz CF BIDI sandwiched between two layers of 8oz FG BIDI. Then again I was just making a cosmetic/fairing thing. I think you made a roll bar

The heavier weight + uni weave would make it more difficult to deal with any compound curves I think. I've never worked with triax so I'd be interested in commentary from someone more knowledgeable than me around that.

Looking forward to seeing how it all turns out!

Tom, thanks for an informative report on the build-up. Very interesting.

Dave

Complete

Hi Dave/Brad and the 50,000 or so other VAF geeks,

So I finally finished the canopy. Talk about one monster of a project. No wonder it had an entire section of the instruction manual dedicated to it. I started work on March 8th, and finished a day ago, working on it almost every day. Admittedly some days were only a couple of hours of work, because I'd have to wait a full 24hrs before I could sand the West 407 filler back due to the low temperatures (even with 205 fast hardener).
So the canopy skirt (or rear roll bar as Brad refers to it) came in at 1.8kg total after surface filling then priming the interior with Wattyl (Valspar) UC230 high build primer, and top coating with a couple of coats of Colourthane Polyurethane. Heavier than I would have liked, but crikey it is stiff. I had just bridged between the canopy and the fuselage with packing tape, so like others, I experienced a bit of sagging when the layup cured, so I had to use more fill than I would have liked, which I suspect lead to the higher than calculated weight, although I still don't know a better way of bridging this gap. I used the proscribed MK319-BS rivets to attach the fairing to the canopy frame, so I had to countersink pretty deep, then filled over the top with West 407. I went with the monel rivets instead of the longer aluminum CS4-4 due to Dan Horton's concerns about corrosion with the carbon fiber. I suspect given that these will be completely sealed, then the risk of corrosion should be very low. The canopy skirt brace is riveted to the skirt using soft -A instead of -AD rivets, and on the inside of the steel canopy frame using the regular LP4-3 rivets. The top slider dog house was laid up over the supplied aluminium part (it was taped down to the aft fuselage when the packing tape was laid as the release agent) then much later in the fabrication the C-679 slider seal was shaped, then taped with packing tape so a tighter mould could be taken to ensure an airtight seal. The skirt was attached to the perspex using Sikaflex 295UV (and 209 primer of course). 0.75mm spacers were fabricated from layers of black electrical tape and places at 2-3" intervals When the original layup was completed, 0.75mm thick layers of electrical tape were run all the way around to simulate the future sikaflex layer. The big issue faced when bonding the skirt to the canopy was getting the sikaflex to squeeze out of the layer. The problem was the sikaflex was so thick and I didn't have clamps deep enough to clear the aft of the skirt, so I had to squeeze using my hands as hard as I could and progressively work from one side ot the other. It came up fine, but in hindsight I was just lucky I got it down before things cured with an overly large gap. I probably should have fabricated some deep clamps for this purpose.
Once the canopy was complete, I then laid up a coating of West G-Flex epoxy and West 407 filler and placed it around the windscreen. My windscreen is also a bit non conventional. The windscreen was originally bonded to the fuselage using West G-Flex and flox, on both the inside and outside, with Sikaflex 295UV around the roll bar portion. I then I added more flox and G-Flex around the front of the windscreen and sanded this into a smooth transition, before laying up just one layer of 12 oz double bias glass cloth. This glass was laid onto a coat of G-Flex but was wetted out using West 105 resin, as G-Flex isn't much good for wetting out (but bonds well to Aluminium and Perspex). A couple of final layers of West 407 filler was progressively laid down and sanded accordingly. Around the roll bar I laid a transitionary coat of G-Flex mixed with 407 filler so I could have a smooth aerodynamic flow from the windscreen to the canopy. My canopy didn't match the windscreen perfectly, as I had clamped the windscreen down a little hard in places when the sikaflex was setting, so this 407 filler masked my incompetence. The gap between the windscreen and the canopy is very consistent (I spent a day and a half sanding it, so I guess it should be) thus I have decided to do without the 1" lip that normally extends from the windscreen over the canopy, and instead will just add a foam seal, as it the practice on aircraft like the Grumman Tiger. I can always add something in the future should I deem it necessary, however this got around the problem of people leaning on the strip when entering and exiting the aircraft and potentially causing cracks, or making something so stiff (carbon) that it causes thermal coefficient of expansion problems and subsequent perspex cracking. It also buys back some of the weight I added with my overly massive canopy skirt! Anyway, I'm glad that's a chapter of this build completed, and I'm definitely looking forward to the engine installation as a change of pace from sanding fiberglass.
Tom.
PS. Having trouble uploading pics, so will try to add more tomorrow.

tgmillso said:

I used 22oz triax glass on the bottom, 14oz carbon uni in the middle, and 22oz traix on the outside. I suspect this is thicker than what I need.

Click to expand...

It's also bass ackwards. The carbon cannot add much stiffness when placed at the neutral axis of the layup.

Hi Dan,
I too was a little sceptical about this at the start, as I am in agreement that the moment of inertia and benefit of the carbon would be greatest when it is out at the geometrical extremities of the layup, but was told that the intent wasn't to transfer the bending load at a point directly back to the canopy frame, but to add hoop strength and transfer the subsequent load from the load point around the curved surface of the rear hoop under compression, hence the reason that it didn't matter that it sat in the middle of the layup. The composites engineer that came up with the layup for me said that this would be the most cost effective application of the carbon and the easiest to apply. I didn't argue, as I frankly wasn't keen on having the carbon layup on the outside that I had to sand. I see carbon as simply high strength asbestos. I can give you this engineers number and you two can hash it out, but at the end of the day, it's done and **** is it stiff. I think if I were to do it again however, I would have skipped the carbon layer as the stuff is a-- expensive and a pain to cut, and would have used thinner and narrower layers of triax glass (but probably close to the total thickness I used) as the thick stuff I used was tough to work with. All part of the education I guess.
Tom.