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Need help reinforcing fiberglas (with Carbon Fiber?)

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Harvey

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I’m working on a little two-seat Cessna 150 and its fiberglass nosewheel pant has damage at two of its attachment holes. The pant is predominately held on by the wheel’s axle but is prevented from rotating around the axle by an “anti-rotation” bolt at the top (see picture 1). It’s the two anti-rotation boltholes in the pant that are damaged (see pic 2).

The wheelpant is constructed of common (i.e. mid-1970s, non-exotic) fiberglass that is, otherwise, in very good condition. The 7/16 diameter axle holes are about 1/4” thick and in good shape but the thinner (~ 1/16” thick) 1/4” dia anti-rotation boltholes have broken out at their tops. (Picture 2) I only have room for a 1/16” thick reinforcement and originally figured that a metal doubler (temporarily held in place by clecos in picture 3) would be stronger than 1/16” more fiberglass; however, I've since heard that trying to bond a steel or aluminum reinforcement to fiberglas wouldn't work as well as I thought, according to a local boat repairer.

A stiffener made out of carbon fiber has been suggested but I know almost nothing about working with CF. Can anyone here teach this old guy a new trick?

Thanks,

Harvey
 

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Bob Korves

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#2
The correct way to repair that is to scarf the area with a long taper and then lay up new fiberglass into the scarfed areas:
http://epoxyworks.com/index.php/common-errors-in-fiberglass-repair/
12:1 scarf, do not cheat, bubble gum repairs will not last on fiberglass, and that wheel pant can have lots of vibration at certain engine RPM settings. You can probably do that repair legally as an owner, but I would at least ask an A & P about the repair before taking it on. You will end up needing to paint the entire pant.
 

woodchucker

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I used to work with carbon fiber and glass all the time.
These days the carbon can be had so many ways. you will want a biderectional weave. The fiberglass you are working with was not done with epoxy. Epoxy is common these days.
Your's was molded with polyester most likely. Which is good. Polyester while stinky has excellent repair capabilities. The polyester has open chemical links that will bond well to new polyester (not so with epoxy) btw that's why polyester stinks, because of the open ended molecule.
There's little difference in working with carbon vs glass, the direction is important for strength, but is also important for flexibility. on a bias creates the most flexible so you can move it to shape.
you do the same thing with carbon that you do for glass. Recommendation. use a small 2 or 3 inch roller with a short nap to wet out the carbon. Wet it out on a polyethlene sheet. think milk container.. I have a fabric cutting sheet that is polyethlene I don't cut on it but use it for wetting out. I used to keep the layup as light as possible, as carbon soaks up more resin than glass. So I might recommend putting glass under, and over the carbon.. wet them out as a sandwich squeegee it out with a body tool. The glass top and bottom will prevent the carbon from going all over the place and losing its shape. place it on the repair (as prepped like Bob said). Now you can use whatever filler you want, include carbon filler too with you filler.. you can buy it, its chopped up strands...
Sand to shape when hard. Then Coat over with another sandwich of glass, and carbon. as your finish layer. you have now made a super strong repair as it is strong on the inside and outside. It's lightweight because you use a filler paste with carbon reinforcement. There are many fillers, the choice would be yours. The weight of the carbon is something you will have to talk to a dealer about. Explain the issue, show pics. The dealers are very good at how to, and many have videos, and technical expertise. Good luck, it's not hard. Take the wheel pant off to work on it. Use release cloth to be able to put a backing on it. for shaping if needed. Talk to the dealer.
You may need more layers on top of the original repair b4 adding filler, or may chose to do it using all layers (heavier). In that case keep changing the direction to get the most strength. Think 45 degree biases.

EDIT: unlike Emilio, I recommend soaking the carbon. There is nothing worse than a dry layup. Which is why I say squeegee it after. That assures that the carbon is wetted out, and the squeegee will remove the excess resin (weight).
 
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EmilioG

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I've been working with FRP's for over 20 years. I would look at Epoxy/FG from West Systems. There is lot's of good info on their website.
Carbon fiber is used mainly for parts. Not as good for repairs over old polyester resin. I've also used Epoxy, cloth and filler combos that are as strong as steel.
Kevlar pulp mixed in to epoxy resin for example. I'd look into epoxy resin instead of polyester resin in your case.
 
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EmilioG

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Lot's of good info here too: http://www.fibreglast.com/category/Carbon_Fiber

If you decide on CF, take a look at the CF tape., or kevlar hybrid cloth. Both super strong.
There are also UV cured resins, polyester, but I would use Epoxy resin/cloth. Remember, strength comes from the cloth and not so much the resin.
Cloth to resin ratio. You don't need to over-saturate the cloth. Another thing to keep in mind, is ambient temp. If you do the work on a very cold day, the resin will take forever to cure. I would choose a day that isn't too cold or too warm, if possible.

Here is another good supplier>> https://www.freemansupply.com/
 
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Harvey

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Good Mornin' Guys, thanks for your inputs. Unfortunately, while it probably wasn't your intent, the process sounds very complicated; especially since my fiberglas/epoxy/polyester/carbon fiber experience is practically nil. Therefore, instead of trying to do it myself, I'm wondering where I can HAVE it done.

Here on the Gulf Coast, we have boat repair shops everywhere, ranging from award-winning to fly-by-night. What do I need to look for or ask in order to find a shop that can do what I need?

You can probably do that repair legally as an owner, but I would at least ask an A & P about the repair before taking it on.
Hi Bob, thanks for the warning but I'm an A&P-IA.

Bob Korves said:
You will end up needing to paint the entire pant.
All three wheel pants came from another C150 that was a different color (they were an eBay purchase) and will need repainting anyway to match my 150.
 

David S

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You might ask if they have any experience repairing fiberglass motorcycle parts. They are more delicate and intricate, similar to your wheels pants. Or perhaps contact a motorcycle place and see if they have any recommendations.

David
 

woodchucker

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It really hard to mess it up. There's plenty of video. You just have to mix the proper ratios of resin and hardner(catalyst).
The rest is like playing with clay so to say. Really take a look at a few videos before you give up.
And if you really don't want to do it, most marine places will do a fine job. That area will be treated like the engine/transom area and get a strong repair.
Anything taking in structure/ bulkheads, bolts, mounting areas get a heavier weave, and a few extra layers.
If you decide to go the marine route, don't worry even the fly by night guys have experience. Just go to someone who has a shop that looks as old as you and I and you'll be fine. ;)
 

dlane

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Is the pant gel coated ?
 

EmilioG

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It may look simple and easy but a small repair like this can be tricky. You're reconstructing a part that has two sides, not just a simple fill.
You're duplicating an existing or pre existing part, from what I can see. And in order for the new repair to stay fixed, part of the broken piece may have to
be ground back and some type of form needed for the back of the repair piece.

Simple but you need a pro with a some finesse. Sloppy work and you'll be sanding for days. I would consult a few places in your area
first. Woodchuck: I never suggested a dry lay up. Only a proper resin to cloth ratio, which is fundamental to any glass work. Strength comes from the cloth and not the resin. Check out the West Systems website, they have a support line and a blog. Good luck.
 

woodchucker

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first. Woodchuck: I never suggested a dry lay up. Only a proper resin to cloth ratio, which is fundamental to any glass work. Strength comes from the cloth and not the resin. Check out the West Systems website, they have a support line and a blog. Good luck.
I know you didn't suggest a dry layup, you suggested not over saturating. There's a bigger danger to that. So over-saturating and removing is a better way, than less and risking a dry layup. Carbon absorbs way more than glass. Also this is not a hard repair at all.
 

Bob Korves

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#13
Good Mornin' Guys, thanks for your inputs. Unfortunately, while it probably wasn't your intent, the process sounds very complicated; especially since my fiberglas/epoxy/polyester/carbon fiber experience is practically nil. Therefore, instead of trying to do it myself, I'm wondering where I can HAVE it done.

Here on the Gulf Coast, we have boat repair shops everywhere, ranging from award-winning to fly-by-night. What do I need to look for or ask in order to find a shop that can do what I need?


Hi Bob, thanks for the warning but I'm an A&P-IA.


All three wheel pants came from another C150 that was a different color (they were an eBay purchase) and will need repainting anyway to match my 150.
Ah, the rest of the story! Use your A&P/IA good judgement... ;) This is not really a safety of flight issue, just needs a repair that will last...
 

Glenn Brooks

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Harvey, I did fiberglass and epoxy repair on boats for decades in the marine and commercial fishing industry. this looks like a really simple and easy repair. I great project for you to learn FG work, if you choose to do so!

I think the only two things I would ask a shop are: how much and when can I get it back. :) The job is going to be dead simple for any FG shop to accomplish.

If you choose to do the work yourself, here's a method you could use. The damage looks minor along the top of the fairing and around the broken area where a bolt and washer were used to secure the top of cowing to the wheel strut. I would to grind off and fair back the gel coat using a 4" angle grinder and fine wire wheel, then build up 1/4" or 5/16" of matt and resin to reconstruct the countour of the part. Use a backing block made out of plywood taped to the fairing and a small separator sheet of plastic garbage bag if you want to form the inside edge. Make the bolt area at the top it a bit thicker, say 1/8" oversize, for extra strength around where the bolt and washer impart crushing stress to the fairing. Also add an inch or two excess lapped up over the top. This to ensure equal thickness around the edge when you trim it off. Then when dry, cut off the excess with a jig saw or grind down with a belt sander, and sand to shape. All done. You can always add one or two finish coats of resin to achieve a nice smooth and blended top surface.

I like to paint raw fiberglass with one part marine primer, usually Interlux Pre-kote. then finish with a couple of coats of any good grade polyurethane.

My .02 worth is that epoxy and carbon is way overkill for the repair. FG resin and cloth will give you more than enough strength and last litterly for ever in an operable condition, and be very cost effective. If you do elect to do the job yourself I would think you could do this in an afternoon for $50 worth of materials, and have a repair that would last for decades. Carbon fiber and epoxy would work but will cost you 3x or 4x as much and take three or four times as long to apply -with no added benefit in part serviceability when your done.

The main thing I like about fiberglass, versus epoxy is that you can control pot life with FG resin by altering the amount of catalyst you mix in - anywhere from 10 minutes to upwards of an hour before it sets off. This means you can add layers of cloth at a very rapid rate , and finish off with a few nice skim coats of resin in no time. Most epoxy takes a looong time to set up, sometimes overnight - turning a simple job into an endless train of "watching paint dry" before you can apply another layer.

Cheers! I would urge you to try it! Let us know how it comes out.

Glenn
 
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EmilioG

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I recently used a mix of Bondo paste and Bondo fiberglass resin, mixed together to form a strong lasting patch material. Lay up regular cloth and resin, then. Add hardener to each material first, then mix together. 1 2 3 easy. Sand, paint, done. You can use a piece of waxed PVC to form the ID if it's the same ID as available PVC tube, or something else suitable. Home Depot has all this stuff.

West Systems has a fast setting epoxy >> http://www.westsystem.com/fiberglass-boat-repair-kit/

There are UV cured resins. Many modern materials are not like your Grandfathers stuff. Detailed info on the website. Great epoxy. Used it many times. Sets in 15-20 minutes. Test it out on a piece of lumber or scrap FG part. Very easy once you do it a few times.
 
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Harvey

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Thanks for your inputs guys. I'll keep you posted on how it turns out.

Harvey
 

Harvey

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I learned that a new neighbor has composite construction experience and I met with him yesterday morning. He identified my nosewheel pant as not being fiberglas at all but a form of plastic. (The hint of layed-up fibers under the paint had me thinking it was a form of 'glas.) Anyway, we found a trial-sized PolyFix kit in the latest Aircraft Spruce and Specialty catalog and it should be here before next weekend. Supposedly, PolyFix is effective on PVC and all kinds of "plastics" common in the aircraft industry. At $22 for the kit (+another $16 for friggin' hazmat mailing fees), I figured it'll be worth a try. I'll let you know how it turns out.

Harvey
 

Harvey

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Well, my neighbor and I repaired my wheelpant with the PolyFix yesterday evening and I'm happy to report that it worked out very well. I've got a bit of sanding to do before I get the pant's paint touched back up but I'm pleased with the repair so far!

Harvey
 
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