I’m planning one of my first resin infusion projects and I’m looking for some advice/guidance from someone with experience with vac infusion. FYI, I can’t figure out how to upload a drawing (in PDF format) of the project that I created but I’d be happy to email it anyone who’s interested (I also have a pic of the wing skin cut-out). Essentially I’m reinforcing the upper wing skin on an experimental aircraft. The wing skin is constructed of a 1/2" foam core sandwiched between two layers (4 plies each) of glass/vinylester. I’ve removed (a.) the inner 4 layers of glass/vinylester and the 1/2" foam core in a 14" circle to provide extra clearance for the wheel when retracted. I now want to bond in one Uni 9oz Carbon layer (fibers running front to back) and two close out layers of 5.7oz twill carbon to stiffen outer wing skin laminates where the foam core and inner skin laminates have been removed. The Uni cloth will only be bonded to the inside of the outer wing skin laminates where the foam core has been removed… the two close out layers will then go over the uni layer and lap up over the exposed foam core and onto the inner wing skin laminates approx 1". I’d really like to try vac infusion for this project but would like to hear from some of you experts on exactly how you’d plan/set up the project (describe the consumables, sequence of consumable layers, size of infusion tubes, layout/position of resin feed tube and vac line(s). Am I going to run into problems trying to infuse a three ply laminate where the bottom layer is 9oz uni? Should I use a standard vac bag or the stretchable type (the stretchable type looks pretty cool), peel ply only or peel ply then release fabric then infusion mesh? I was planning on using infusion epoxy for a better bond to the carbon but could use a vinylester that bonds well to Derkane 411-45 if you think the bond would be sufficiently strong. Any advice/guidance you can provide will be much appreciated! Oh and BTW: I’d like to seal the bag no more than 1.5-2" around the perimeter of the 14" cutout. Thx!
Canyon, can you unleash all forum options for this guy, so we can take a look at his PDF?
in short, you cut a hole in a foamcored laminate, and want to reinfuse carbon into the hole (and over the existing skin)?
If so. Yes.
If simple geometry, you can bag around the hole, with lots of pleats, with a small spiral tube around the hole on the outside, and infuse in the middle of the hole. (think a bowl, where you pour water in the middle, and it flows out around the edges). I would go with peelply (or perf. release film), flow media over 90% of the bowl, and bag. Vacuum spiral/line can have peelply over it just to guard agasint bag ripping.
Maybe take a screen shot or 2 of the PDF, and upload the images?
He should be able to upload the PDF as an attachment or take a screenshot and upload that as an image. Attachments aren’t restricted for new users.
jbocek
Try using the little paperclip to attach the pdf or the picture. If that fails take a screenshot of the PDF and upload it to flickr or photobucket and post the link
If you still can’t do it just email me through the contact us form and I’ll help you out.
==Edit===
What Riff said
Thanks for the help guys! I’ve posted pics to photobucket, here is the URL: http://s1095.photobucket.com/albums/i477/jbocek/Glasair%20project/
Questions:
-
If I place my resin feed line in the middle of the cutout and spiral wrap t’d into a vacuum line around the perimeter of the hole, is there any danger of the resin racing down the UNI and failing to spread to the sides? If so, how would you set up your vac lines, flow media to best address this issue?
-
Would you also add a small extra peice of flow media under the feed line to keep the feed line from printing through?
-
Re #2 above, would an extra strip (1" to 1.5" wide… placed perpendicular to the UNI fibers) help to get the resin to the sides of the hole and accross the UNI fibers before the resin raced down to the other ends of the hole (parallal to the UNI fibers)?
-
Is the 5.7oz carbon twill a good choice for closing out the hole over the UNI? For finish, I’m thinking of clear coating the carbon in the just the cutout area to show off the cool looking carbon for anyone interested enough to look up inside the wheel well.
Thanks for all the help… I’m brand new at this and I really dont want to screw it up! BTW: I dont have a paperclip option for uploading attachments…
1: mix your resin for a long gel time. infuse slowly. Allow the resin to flow down. You CAN try infusion from the side, but I’m not sure how a round shape would work. Might race track and close off? The best I can say, is cut a circular flow media just smaller than the flat bottom. This will force the resin on the bottom of the laminate to catch up, and flow evenly through the stack to the vent line. ps: not a thick laminate anyway, so I would not have worries.
2: yes. You can build up a few layers of peelply and flow media
4: Yes. It will give added 0/90 strength over just the uni. it will also close off the core and prevent delam and foam damage.
Thanks for the great advice! A few more quick questions:
- What size of infusion feed tube (ID) woudl you use? 3/8", 1/4"?
- What do you think of laying a peice of spiral wrap (either 3/8" or 1/4" to match the feed line) on top of the flow media (perpendicular to the UNI fibers accross the cut out) to help the resin migrate accross the UNI fibers? Perhaps stop the spiral a couple of inches short of each side of the bottom of the cut out (feed line connected via “T” in the middle)?
- Would you recommend using an infusion vinylester or infusion epoxy resin? I’ve heard carbon doesnt wet out too well with vinylesters.
- When you say “added 0/90” do you mean one layer of closout carbon twill layed on a 0 degree and the 2nd layer on a 90 degree bias? To clarify, you’re thinking I shouldnt lay the two closout layers of carbon on a 45 degree bias?
Thanks !!!
Oh… since I’d like to show off the carbon (clear coat the carbon in the dished out area where the closout carbon layers will be) do you guys recommend infusing only the UNI first, then filling if necessary the are between where the UNI stops and the dished out inner skin foam so the closout carbon (when infused) will have a smooth raduis from the bottom of the dished out area up to the top wing skin layer? Is there a specific type of peel ply that I should use when infusing the close out layers of carbon to reduce the sanding required for clear coating? Can I spray clear directly on the infusion vinylester? What about infusion eoxy? If primer is needed do they make it in clear?
Jbocek,
I leave the experts to explain the tips&tricks of infusion but I feel that add some other suggestion could be helpful in this delicate job.
- You can’t remove plies and make repair/modification without knowing which material and ply angles were present in that area
- Plies must be always overlapped, that is, their edges must not be coincident; you have to increase progressively their size in you patches; then the two inner plies, that are visible in the picture with the sketch, must have increasing size from the outermost (outer mold line) to the inner. Leave a conservative extra edge of 30 mm for the innermost ply.
- The aim of that core (that you removed…!!!) is to stabilize the skins in a very high stress area; in particular , right there , you have torsion and compression, therefore ±45 deg material is necessary. If it is woven fabric, it’s better since it resists better delamination, but before remember point 2)
- Forget that carbon uni running along the wing chord ( from a reference system for the wing loads it is placed at 90 deg) …you are placing it exactly where it will risk to delaminate !
If external wing skin are fabrics, then use fabrics; - Remove that round chamfer at the base of the foam core, it only helps to detach the skins form the foam once the wings bends up; use an edge with an angle of 30 deg, or , if you have difficulties, try to keep 45 deg but not more ( 25-30 deg are the optimum).
…and now back to infusion experts.
Good reply wings, especially for this topic good points all around I would have missed!!!
1: I’d stick with 1/4" for infusion, vent can be similar, or larger.
2: might be a non-topic if wings is right about not using the Uni. However, place the vent spiral on the OUTSIDE perimeter of the bonding area. You have to let the resin travel, and equalize in the stack before it hits the vent, else you can cause dry spots on the edges. See several infusion threads on here about adding a delay line. I know you have limited room, but something might work out for you.
3: good point, missed that. I have used 530 Momentum, 510-a, and 8084 on carbon (never used 411), and while it HAS worked, you are right. Most carbon fibers are sized(treated) for epoxy, not VER. It will wet out, but the actual resin bonding to the fibers will not be as strong. However, you are not cutting your part, so you might be ok.
4: Was just saying, the twill is a good choice for closing out a skin. It has equal strength in both directins. Whether or not you should be adding a 45 in there…I do not know.
Per your questioning on surface finish. Not sure how much detail people will see, laying on the ground with flashlights jsut to see a show-perfect surface. Unless this IS a show plane, don’t bother. You can use perforated release film, and it will leave a wavey, but shiny finish. You can use peelply (stick with release coated nylon, it’s just easier to peel off), and then brush on a layer of clear (after infusion, won’t matter much, either more VER, or a PUR clearcoat.) I don’t see a need to sand it, UNLESS you going to have lights, and make this thing a showpiece, then others will chime in on how to finish to show quality (clearcoating, sanding, recoating, sanding, buffing, etc)
-
Thanks guys for the great points! Please keep em coming!!! Re the direction of the UNI: The wing itself is super strong and likely wouldn’t have a problem even without any internal closeout reinforcements. I'm placing the UNI there because the top of the wing that corresponds with the inner skin cut-out is right where passengers stand on the wing to climb into the xxxxpit (low wing) and I don’t want to risk someone putting their foot through the wing skin when they climb in. A local composites kit aircraft company recommended the UNI and running the fibers front to back (that’s where I got the idea). I assume the reason they recommended front to back vs side to side is because they were more concerned with the stress of someone standing on the wing in that area vs flight loads. I believe the UNI would be resist someone standing in that area better if the UNI fibers run front to back due to the fact that the airfoil has a curved upper surface front to back (not much in that area, but still curved) vs side to side (perfectly flat on my wing). I agree this places the strands of the UNI perpendicular to the flight loads on the wing but again the wing is super strong and has virtually no flex even when pulling 4-6 g's (yes, it's stressed for that). Re the camber at the foam core vs a 30 degree angle… do you still think this is a concern with such a strong wing with virtually zero flex? Thanks again for the great tips.. this site (members) is great!
Re the finish… Yes, I want the carbon to have a smooth high gloss mirror finish that looks beautiful when someone lays on their back and looks up in the wheel well. I actually spent a lot of time detailing the inner wheel wells this summer (they were plain, unfinished glass with rough layer overlaps, etc). I spent many hours sanding, priming and painting the area and you could now eat off the inner surface… looks really awesome!
Well ok, you are crazy, but…i would go with peelply, then you can clearcoat the surface without sanding. After the clearcoating, see how it is to your liking, and then sand/buff as needed to finish it off. Add some LED’s there to highlight it 
I can’t say if and how (super) strong is the aircraft, even if i know the model. My suggestion belong to the “good practice and engineering sense” that should be considered for such application, then take my posts as add-on to the knowledge about composites…i’m sure your work will give the expected results 
Passengers ““walking” on the upper side of the wing exert local pressure due to their weight ; this force must be spread into the surrounding material in order to avoid delamination. This can be done if you cover the most of the ply angles but the ±45 fibers are those that should be always present; Unidirectional ( unless you have thick laminates, but this is not the case) splits !! Usually this area is limited ( and walk areas should be indicated on the upper surface of the wing) then their contribute to the"super strenght” is very limited ( for this reason those guys were worried much about people rather than flight loads)
About the edge of the foam ( and in general): one composite structure can safely support heavy loads but fail under a low energy impacts (e.g your mobile phone “flying” out of your pocket and hitting a composite surface…). Therefore don’t base your judgement exclusively on your feelling about the strenght or striffness. Angle of 30 deg and doublers spread the stresses around the holes (holes are the nightmares of composite structures designers…)