Kodiak Flyer

Just noticed this composite repair forum...

Out flying my Skywave today, finally had some good weather. If you don't know, the Skywave is almost exactly like the Firebird series of planes...a pusher prop with pod and boom construction. The boom is made of carbon fiber on the Skywave.

Coming in for a landing, I hit tail first (pulled up too hard) and the carbon fiber boom (pushrods are inside the boom) snapped, right below the prop. You can see the tip of the prop in the picture, with the broken boom below.

I'm NO expert, but I'm pretty sure that carbon fiber can't just be glued together. Anyone have any suggestions for repair, or do I call this a total loss and move on to my next destruction....errr....project?

Thanks!

Andy

Jetman007

My Feedback: (6)

Easiest thing I can think of is push it back together and apply a popsicle stick splint to the outside area of the break. Use packing tape to hold the splint firmly to the broken boom. Maybe use two splints, one on right side and one on the left.


Be sure to check the balance after the repair. You've added weight just behind the balance point. You'll need to add some in front now.

Giant Scale

Carbon fiber can be repaired using epoxy and carbon fiber cloth for reinforcement. You could also use CF tape. Clean the area with acetone to remove any dirt or oil. If the tube has a thick wall I would epoxy the tube back together. After this sets up, scuff the area with some sandpaper(wear a mask since CF fibers are nasty stuff) and laminate the area with epoxy and CF cloth, wet the cloth out a couple of inches on either side of the break. When dry you should have a very durable repair. If you need additional reinforcement I would epoxy some small pieces of CF rod on either side of the break and then wrap the cloth around. I am not familiar with the plane so am not sure how thick it is or it's dimension. If the boom is a very thin wall, I would laminate a piece of cloth around the inner perimeter of one side of the tube to form a sleeve, let it dry. Then apply epoxy to the entire area and slide the tube back together. Then reinforce the area with more CF cloth and epoxy. CF cloth and epoxy is a very stiff and durable material. I cover all my plywood engine boxes with it. Have had an entire fuselage destroyed,the motor box remained intact, all the other plywood in the fuse shattered.

SoarNeck

Hey Andy,

Sorry to hear about your loss...but these things happen. First off...I'd put money on that boom not being actual carbon fibre. Your photo isn't clear enough to be sure, but the frayed ends look very white...which indicates pigmented fibreglass, not carbon. You can check whether a boom is actually carbon by using a voltmeter set to check continuity - carbon is electrically conductive. Most carbon booms have a surface coat of resin or fibreglass, so you might have to scrape an undamaged boom to get down to the carbon fibres.

Anyway, that said, the easiest way to repair any boom is with carbon or glass woven tube. It acts like a chinese finger puzzle...pull on it longitudinally and the diameter shrinks, push on it and it expands. ACP and CST are the easiest places to find the material if your local shop doesn't carry it (http://www.acp-composites.com/acp-bcs.htm).

I've repaired heavy carbon booms with this method with good success. Glue the boom back together with medium CA (MAKING SURE TO KEEP IT STRAIGHT), then sand the boom to about 2" away from the break on either side. The sanding willl remove any dirt or mold release used in the mfg process, and the scratches from the sandpaper give the epoxy (or thick CA) something to "key" into.

I used laminating epoxy and a vacuum pump to set the joint and get a smooth finished surface, but you could do the same thing by wrapping the wet splint with wax paper and tensioned tape (heat shrink tube for batteries would be a slick way to do it, now that I think about it....even finish-wise).

Just remember that your boom isn't likely to be quite as strong as a new one, which you might be able to find at the local kite shop.

Until later,
Adam

Kodiak Flyer

Thanks for the help guys. I went ahead and cut one of my aluminum arrows down to length, cut some slits in it for the control wire, put the tail section back on, and it flies great! Looks cool too, with the camoflauge pattern...not to mention all the duct tape on the wings...and it still flies magnificently!

TT2

My Feedback: (13)

Great idea!

-Tom