RV10 cowl cut too short. Advice on repairs please

[amerkarim]

Hi All,

I had a super frustrating day yesterday evening that was topped off with lots of shouted 4 letter words !!

I was fitting the cowl on my RV10 and despite measuring twice and following the plans, I made a mistake with my pen marks and have cut the cowl too short by an inch all around, top and bottom.

I am planning to fit Skybolt ? turn fasteners.

I was going to sand the inside of the cowl and then lay down some new fibreglass cloth and try and blend it all in. Sand and then recut and refit.

Any advice or tips on the way forward would be much appreciated.

In addition, any tips on fitting the sky bolt fasters would be appreciated. My cowl is dark grey in colour so I cant shine a light through it to find the holes. Is there another way to do it?

Thanks in advance

Amer

[rocketman1988]

Make sure that you properly layout the skybolts. If you are not
paying attention, you will find that four of them will end up right behind the engine mounts and you won?t have adequate clearance.

[Bavafa]

Sorry for the mishaps, it is part of the build experience that almost everyone goes thru it in different degree.
First to your second question which is the easy one. VANs provide a group of round magnets that can be used to locate the holes thru fiberglass that is gel coated. But a more accurate way, at least for me, is to align and shine a laser light to your spot that you want to match drill, then install the cowl without and disturbance to the laser light which will shine and locate your hole to be drilled.

As for the first part. I would imagine you could put the cut piece back and attach it with a few layer of glass. Perhaps a couple of strip of s 1? aluminum riveted to both sides can be used to reinforce it.

[BillL]

If you have the 1" strips cut off and have not sanded, they will fit perfectly back in place. If so, I would match them back up, and use some packing tape on the outer surface to tape them in place. Check for flatness with parent surface. Then Use a 2" coarse sanding disc (roloc) with an angle die grinder and carefully dish thickness along the cut line. The first objective is to restore the piece and have it held in place for subsequent glass layers. If the dish is more than 50% of the thickness and at least 1.5" wide, make strips of glass cloth to fill the dish. start with 1/2 - 3/4" wide and progressively make strips wider, maybe 1/2" at a time. You could make one long and wide strip then add your resin and cut the strips with a roller razor. This would act like a prepreg, DanH style. More details might help, but this should convey the idea. [edit: Like Mike, wide strip first, describes below is much easier.]

Fill the inner side and let it cure, then duplicate the same process for the outer surface.

I was once told craftsmanship is not about being perfect, but knowing how to correct the mistakes for a nice finished product.

[Mike S]

Originally Posted by BillL

If you have the 1" strips cut off and have not sanded, they will fit perfectly back in place. If so, I would match them back up, and use some packing tape on the outer surface to tape them in place. Check for flatness with parent surface. Then Use a 2" coarse sanding disc (roloc) with an angle die grinder and carefully dish thickness along the cut line. The first objective is to restore the piece and have it held in place for subsequent glass layers. If the dish is more than 50% of the thickness and at least 1.5" wide, make strips of glass cloth to fill the dish. start with 1/2 - 3/4" wide and progressively make strips wider, maybe 1/2" at a time. You could make one long and wide strip then add your resin and cut the strips with a roller razor. This would act like a prepreg, DanH style. More details might help, but this should convey the idea.

Fill the inner side and let it cure, then duplicate the same process for the outer surface.

I was once told craftsmanship is not about being perfect, but knowing how to correct the mistakes for a nice finished product.

Pretty much agree with Bill, except I would lay full width pieces in the scarff, not start with narrow ones------the way Bill described leaves small voids at the edge where each wider layer is added. Minor difference maybe not a factor-----???? Lay up full width and then sand down the outer surface as in the image below.

For the scarff you want at least a 1 to 7 taper, as much as 1 to 12.

Google "Fiberglass scarf joint" for more info, or go to a local boat repair shop ----I suspect Houston has a few-----



If you have cut into the honeycomb-----the above info is going to need a bit of modification-----you need to get back the strength by tying the two glass layers together before you do the repair.

[amerkarim]

Thanks guys

For all your help and advice.

Will start the repair tomorrow

Kindest regards

Amer

[DanH]

Originally Posted by BillL

If you have the 1" strips cut off and have not sanded, they will fit perfectly back in place. If so, I would match them back up, and use some packing tape on the outer surface to tape them in place.

Good thinkin' Bill.

One tweak...instead of tape, fixate the strips back in place using some scrap aluminum and clecos. It's easy to fill the cleco holes later, and the aluminum can be bent and shimmed to get the joint absolutely flush.

Something like this:

http://www.vansairforce.com/communit...d.php?p=276028

Post #11 describes how to wet the scarf ply strips and place them, no mess, no fuss.

Then Use a 2" coarse sanding disc (roloc) with an angle die grinder and carefully dish thickness along the cut line.

Using the cleco method, you can fit the strips, then take out the clecos, separate the parts, sand a nice scarf on the strips and the cowl, then reassemble and lay up scarf plies.

After it cures, remove the aluminum tabs and clecos. Then, as Bill said, cut a shallow dish on the opposite side and lay in more scarf plies. Block sand both sides until dead flat.

I was once told craftsmanship is not about being perfect, but knowing how to correct the mistakes for a nice finished product.

Right. it's not a mistake. It's an opportunity to become a craftsman

[StressedOut]

I just wanted to add a comment about Mike S. recommendation on a scarf repair. What that graphic shows with a 12:1 scarf is more commonly done in a boat repair where strength isn't the primary issue. This isn't a shallow enough aspect ratio to get good load transfer to the repair plies. Also the single ply laid down across doesn't provide interlaminar shear transfer as well as a traditional scarf ply repair with different size plies in the stack up.

It's more common to use a 30:1 or even a 50:1 scarf joint. This exposes enough of each individual ply so that you can lay a repair ply down and bond the ends together. Look at this link for the scarf patch repair to see what I mean. The final overlay ply above the original OML surface is structural and completes the repair.

I realize if the repair fails the cowling probably won't come off the airplane. If the entire edge band separates, you may overheat your engine though because you've lost pressure sealing.

Just something to think about.

[penguin]

The additional layer is not required - see most sailplane repair manuals. 30:1 scarf is certainly more usual than 12:1 (50:1 only with carbon). However...if only an inch has been cut off a (say) 2mm layup then it's not possible to achieve a 30:1 scarf using the removed piece. The thickness of the repair is important to achieve a flush fitting cowl. Maybe the cut off piece is too narrow to be useful. Perhaps fit some ally sheet to the outside as a mould (as Dan suggests with clecos). Scarf and layup the inside - will probably result in a better outer contour.
Pete

[Capt]

Originally Posted by Mike S

Pretty much agree with Bill, except I would lay full width pieces in the scarff, not start with narrow ones------the way Bill described leaves small voids at the edge where each wider layer is added. Minor difference maybe not a factor-----???? Lay up full width and then sand down the outer surface as in the image below.

For the scarff you want at least a 1 to 7 taper, as much as 1 to 12.

Google "Fiberglass scarf joint" for more info, or go to a local boat repair shop ----I suspect Houston has a few-----



If you have cut into the honeycomb-----the above info is going to need a bit of modification-----you need to get back the strength by tying the two glass layers together before you do the repair.

Gee I like that layup detail, must put that in the memory bank for another time, thanks