fiberglass repair?

[[email protected]]

When attempting to modify my battery tray (and suffering from dehydration) I mistakenly cut through the outer skin of the fuselage.

The damage is approx 2" x 1/32nd".

Is this structural or cosmetic?

https://drive.google.com/file/d/0B79vbVufUPnLZndHWUMxUWJzZzlia2cwUmZzR3VEWUl5N1FR/view?usp=sharing

https://drive.google.com/file/d/0B79vbVufUPnLWWgySms0OXpmRVdaR3FDamQ1V1VIZ1dxYzBj/view?usp=sharing

How would the fiberglass guru's here repair the damage?

Advice is much appreciated,

Nick

[Bill T]

I'm not a fiberglass expert. But a through and through cut needs to be repaired properly just like an impact that would have cracked the hull.
Directions are in the maintenance manual, to include scarfing to widen the repair area, laying in epoxy, cloth, etc. Sanding and refinishing.

A simple repair, not done properly, could crack and get longer as the fuselage flexes in turbulence and with temperature changes.

BillT

[[email protected]]

I respectfully suggest that someone who cuts through the fuselage in an attempt to repair a batter tray should not be repairing the fuselage.
Just a thought.

[[email protected]]

Lots of people have done it jackass. Ask around. It ain't that uncommon

[Eric Munk]

And don't forget the correct curing temperatures of the repair. Cutting
corners there significantly reduces strength in the affected area.

[[email protected]]

On Sunday, August 9, 2015 at 7:55:42 PM UTC-4, Bill T wrote:
> I'm not a fiberglass expert. But a through and through cut needs to be repaired properly just like an impact that would have cracked the hull.
> Directions are in the maintenance manual, to include scarfing to widen the repair area, laying in epoxy, cloth, etc. Sanding and refinishing.
>
> A simple repair, not done properly, could crack and get longer as the fuselage flexes in turbulence and with temperature changes.
>
> BillT

What is the context of this thread?
UH

[Andreas Maurer]

On Sun, 9 Aug 2015 16:47:43 -0700 (PDT), wrote:

>When attempting to modify my battery tray (and suffering from dehydration) I mistakenly cut through the outer skin of the fuselage.
>
>The damage is approx 2" x 1/32nd".
>
>Is this structural or cosmetic?

Definitely structural. Major. Pretty bad spot for such a damage.

>
>https://drive.google.com/file/d/0B79vbVufUPnLZndHWUMxUWJzZzlia2cwUmZzR3VEWUl5N1FR/view?usp=sharing
>
>https://drive.google.com/file/d/0B79vbVufUPnLWWgySms0OXpmRVdaR3FDamQ1V1VIZ1dxYzBj/view?usp=sharing
>
>How would the fiberglass guru's here repair the damage?

A proper repair is going to require about one square ft of multilayer
skin replacement and some practice.

Get the glider into a repair shop if you haven't done such a major
repair yet.


Best of luck
Andreas

[Charlie M. (UH & 002 owner/pilot)]

On Monday, August 10, 2015 at 3:12:54 PM UTC-4, Andreas Maurer wrote:
> On Sun, 9 Aug 2015 16:47:43 -0700 (PDT), wrote:
>
> >When attempting to modify my battery tray (and suffering from dehydration) I mistakenly cut through the outer skin of the fuselage.
> >
> >The damage is approx 2" x 1/32nd".
> >
> >Is this structural or cosmetic?
>
> Definitely structural. Major. Pretty bad spot for such a damage.
>
> >
> >https://drive.google.com/file/d/0B79vbVufUPnLZndHWUMxUWJzZzlia2cwUmZzR3VEWUl5N1FR/view?usp=sharing
> >
> >https://drive.google.com/file/d/0B79vbVufUPnLWWgySms0OXpmRVdaR3FDamQ1V1VIZ1dxYzBj/view?usp=sharing
> >
> >How would the fiberglass guru's here repair the damage?
>
> A proper repair is going to require about one square ft of multilayer
> skin replacement and some practice.
>
> Get the glider into a repair shop if you haven't done such a major
> repair yet.
>
>
> Best of luck
> Andreas

"Major ARRRRGGGHHHHH......"

Where did your text come from?
This thread showed very little.

"Prepare for sanding/grinding...... glass & resin, more sanding, Gelcoat, finishing & polish/wax......

"Ehhhh..... cover it in '150 MPH tape', placard the ASI to 149MPH and call it a day......"

Just kidding folks......

[Brad[_2_]]

the OP should seriously consider finding a wrecked ASW-19 with a good forward fuselage, and graft it on to the tail boom of the original glider. everybody knows that older generation glass used such skimpy and poor quality materials......and a 2" x 1/32" slit is asking for severe structural failure......perhaps even causing the fuselage to buckle by just rolling it out of the trailer.

Brad

[[email protected]]

On Monday, August 10, 2015 at 3:12:54 PM UTC-4, Andreas Maurer wrote:
> On Sun, 9 Aug 2015 16:47:43 -0700 (PDT), wrote:
>
> >When attempting to modify my battery tray (and suffering from dehydration) I mistakenly cut through the outer skin of the fuselage.
> >
> >The damage is approx 2" x 1/32nd".
> >
> >Is this structural or cosmetic?
>
> Definitely structural. Major. Pretty bad spot for such a damage.
>
> >
> >https://drive.google.com/file/d/0B79vbVufUPnLZndHWUMxUWJzZzlia2cwUmZzR3VEWUl5N1FR/view?usp=sharing
> >
> >https://drive.google.com/file/d/0B79vbVufUPnLWWgySms0OXpmRVdaR3FDamQ1V1VIZ1dxYzBj/view?usp=sharing
> >
> >How would the fiberglass guru's here repair the damage?
>
> A proper repair is going to require about one square ft of multilayer
> skin replacement and some practice.
>
> Get the glider into a repair shop if you haven't done such a major
> repair yet.
>
>
> Best of luck
> Andreas

Original poster- contact me off line and I will give you some guidance without the panic mongering.
UH

[Bob Kuykendall]

On Monday, August 10, 2015 at 4:59:42 PM UTC-7, wrote:

> Original poster- contact me off line and I will give
> you some guidance without the panic mongering.

Seconded. This looks like it'd be a pretty straightforward repair, nothing to get too bent out of shape about. Hank will set you straight.

Thanks, Bob K.

[BruceGreeff]

That really does look relatively minor.
I have seen much bigger, and very poorly repaired damage where they were
discovered under decades old bondo and gelcoat. Having not caused any
problems for all of those many years of abuse and neglect...

I suspect most older glider structures are way over strength, because
they did not have the finite element analysis to say how strong to make
it - and newer ones are also over strength to get the required
stiffness/ crashworthiness.

That looks like it needs to be cleaned up over an appropriate area, and
the appropriate multi layer repair effected in accordance with the
manual. No big deal. (but quite a lot of effort)

Just saying.

On 2015-08-11 07:40, Bob Kuykendall wrote:
> On Monday, August 10, 2015 at 4:59:42 PM UTC-7, wrote:
>
>> Original poster- contact me off line and I will give
>> you some guidance without the panic mongering.
>
> Seconded. This looks like it'd be a pretty straightforward repair, nothing to get too bent out of shape about. Hank will set you straight.
>
> Thanks, Bob K.
>

--
Bruce Greeff
T59D #1771

[krasw]

Is there a reason this damage cannot be repaired by putting simple multilayer patch (right size, of course) on the inside surface? With proper overlap it gives you original strength without time-consuming surface finish work. Why not take advantage that fuselage shell is not sandwich structure and inside of the shell is easily accessible?

[Eric Munk]

At 08:52 12 August 2015, krasw wrote:
>Is there a reason this damage cannot be repaired by putting simple
>multilay=
>er patch (right size, of course) on the inside surface? With proper
>overlap=
> it gives you original strength without time-consuming surface finish
>work.=
> Why not take advantage that fuselage shell is not sandwich structure and
>i=
>nside of the shell is easily accessible?
>

Yes. The manufacturer's repair manual does not specify this as an approved
method (it is, by the way, quite clear and helpful as a guide for repairs
like this).

[[email protected]]

.....and you would have the choice of either telling a future prospective purchaser that the glider had a non approved repair or else knowingly lying about it.

[Bill T]

You still have the exposed crack on the outside to fill and finish.

[Bob Kuykendall]

On Wednesday, August 12, 2015 at 1:52:27 AM UTC-7, krasw wrote:
> Is there a reason this damage cannot be repaired by putting simple multilayer patch (right size, of course) on the inside surface? With proper overlap it gives you original strength without time-consuming surface finish work. Why not take advantage that fuselage shell is not sandwich structure and inside of the shell is easily accessible?

The conventional reasoning for not going with a simple patch like that is that it results in a steep stiffness gradient at the site of the damage. The more widely accepted scarf repair, when properly done, restores not only the strength, but also the stiffness distribution of the original. That helps ensure that the repaired area will not be prone to delamination or cracking as it ages.

At issue is that gliders tend to be very limber structures--they bend a lot.. As they bend, some parts of them get stretched out, and other parts get pressed together. And where there are abrupt changes in stiffness, for example, where there is a change in sectional thickness, the stretching or shrinking happens unevenly. That uneven stress distribution can cause cracking in the most brittle layer, the gelcoat. Sometimes the cracking can go deeper, into the structure below, but that's pretty rare in a well-designed glider. Typically you'll see this effect in gelcoat cracks that form at the corners of airbrake boxes, along ribs and bulkheads and other internal reinforcements.

Thanks, Bob K.

[Steve Leonard[_2_]]

On Wednesday, August 12, 2015 at 11:25:03 PM UTC-5, Bob Kuykendall wrote:
> On Wednesday, August 12, 2015 at 1:52:27 AM UTC-7, krasw wrote:
> > Is there a reason this damage cannot be repaired by putting simple multilayer patch (right size, of course) on the inside surface? With proper overlap it gives you original strength without time-consuming surface finish work. Why not take advantage that fuselage shell is not sandwich structure and inside of the shell is easily accessible?
>
> The conventional reasoning for not going with a simple patch like that is that it results in a steep stiffness gradient at the site of the damage. The more widely accepted scarf repair, when properly done, restores not only the strength, but also the stiffness distribution of the original. That helps ensure that the repaired area will not be prone to delamination or cracking as it ages.
>
> At issue is that gliders tend to be very limber structures--they bend a lot. As they bend, some parts of them get stretched out, and other parts get pressed together. And where there are abrupt changes in stiffness, for example, where there is a change in sectional thickness, the stretching or shrinking happens unevenly. That uneven stress distribution can cause cracking in the most brittle layer, the gelcoat. Sometimes the cracking can go deeper, into the structure below, but that's pretty rare in a well-designed glider. Typically you'll see this effect in gelcoat cracks that form at the corners of airbrake boxes, along ribs and bulkheads and other internal reinforcements.
>
> Thanks, Bob K.

Think you misunderstood his question, Bob. He was asking "Why scarf from the outside and make a very large area you have to re-finish? Why not scarf the inside, and have a small area that needs the more aesthetically time consuming finish work outside?" Inside is less "optically critical".

Eric says the manufacturer does not approve of such repairs. I have seen several manuals, and all seem to show scarfing to be done from the outside for a glass shell. However, they are also all showing the repair as a hole into something that you do not have access to the other side of as you close it up. In the cockpit, you would have this access. In the tailcone, you would not. And on the inner skin of cored structure, I have seen splices shown in both directions for the inner skin. Honestly, you are putting back the same number of plies, with the same orientation as what was there before the break. Can you tell me the repair will be weaker if the scarf is made from one side than the other?

The bigger thing is that it is MUCH easier to scarf a convex surface (outside of the fuselage) than a concave surface (inside of the fuselage).

Steve Leonard

[Bob Kuykendall]

On Wednesday, August 12, 2015 at 9:48:18 PM UTC-7, Steve Leonard wrote:
> ...Think you misunderstood his question, Bob. He was asking "Why scarf from the outside and make a very large area you have to re-finish? Why not scarf the inside, and have a small area that needs the more aesthetically time consuming finish work outside?" Inside is less "optically critical".

He uses the word "patch," but doesn't mention "scarf" anywhere, hence the general shape of my reply. I suppose that a scarf repair might be considered a patch, but a patch is not necessarily a scarf repair.

Thanks, Bob K.

[JJ Sinclair[_2_]]

A scab batch is just as strong as a scarf repair as long as the scab is as large as the scarf. So, a 1/8" skin with a 40:1 scarf would call for 5" all around the cut, with the same number of layers and orientation of the cloth. Sand the area with 40 grit, clean with acetone and lay up a scab patch on the inside and fill the cut from the outside with white filler.
Much to do about nothing!
JJ

[Darryl Ramm]

Given how serious the damage looks I think the owner should consider pulling a mold off the fuselage and starting over. That is if the fuselage has not already broken in half from ground handling as Brad warned...

(Today's lesson is really more that you cannot delete posts from USNET groups than anything about composite repairs)

[krasw]

torstai 13. elokuuta 2015 16.55.47 UTC+3 JJ Sinclair kirjoitti:
> A scab batch is just as strong as a scarf repair as long as the scab is as large as the scarf. So, a 1/8" skin with a 40:1 scarf would call for 5" all around the cut, with the same number of layers and orientation of the cloth. Sand the area with 40 grit, clean with acetone and lay up a scab patch on the inside and fill the cut from the outside with white filler.
> Much to do about nothing!
> JJ

Yes, this is what was thought to when studying basic fiberglass repairs. Sure, scarf repair is elegant, but not stronger if patch is correct size. We are still talking thin fuselage shell, not main spar.