Grantmac said..

Freeflight said..

FarNorthSurfer said..
I have the same foil and after reading this will try not to leave it on the beach like a old wave board again! That's a bummer.
Also be interested in what AFS come back to you with.
I used to be an aircraft engineer with composite experience and think I might be looking for something like this to do the repair. It would be best using a drill press to get the holes right and I didn't see where in the world you are. These things could be hard to source.
www.tappex.co.uk/product_category/titanium-threaded-inserts?cn-reloaded=1

Those tappex titanium inserts look very very nice, be good if all ali fuses came with those installed,
Does anyone know how it cost each for them ?

Most decent alloy fuselages come with inserts? Only the really poorly built ones like Slingshot thread right into the aluminum from what I've seen.

In the case of this fuselage repair I'd still be inclined to go with Chicago bolts. Much stronger allow you to reinforce the area more completely.

Grantmac, thanks for the feedback, I appreciate it. But drilling 3 holes through the fuselage, with all 3 aligned exactly perpendicular to the fuselage is a little much for my workshop. And I just do not like the idea of weakening the fuselage with the through holes.

But I am now thinking of peeling back the thin partially erupted carbon twill layer covering the top edge of the inserts, and then pull out the now loose inserts, then add epoxy on the outside of the inserts and the inside of the cavity, and then press the inserts back into the fuselage as I described above in step 3. That would insure the inserts were epoxied in about as good as originally. Then use epoxy to seal the carbon twill back down over the top edges of the inserts. But that is for mostly cosmetic reasons, the outside wall of the insert contacting the fuselage is what is going to keep the insert in place, much greater surface area than the 1/8" top edge of the insert.

so I decided to pull out one threaded insert from the fuselage, it is a tappex insert, see pic., has the distinctive tappex cutting edge (see upper left side). So these inserts were not epoxied in, but just screwed in. Not much to hold a big wing. Maybe go to an 8 mm tappex or similar style screw in threaded insert, but then wing holes will have to be drilled out a little. It would have been nice if someone from AFS would have told me beforehand what the insert was and how it was inserted. Last I heard, Julien want to do a video conference to explain how to repair it, and said okay I have Facetime, and then no response. So they screwed it in and then covered the collar with carbon twill. The threads seem shallow for what they have to hold.

McMaster has SS inserts, the 8 mm needs a 12 mm hole that is 16 mm deep, have the depth with the existing hole. 12 mm, or 1/2", diameter seems large but there is room in the fuselage for it.

Any thoughts on going with 8 mm inserts and screws? Lucky I did not try to epoxy the 6 mm insert back in like I said I would, because when the inserts got pulled out that small amount the grooves for the outside threads got degraded, and epoxy would have a hard time coming up from the inside even with a screw trying to force it upward. Probably would have ended up losing a wing in-flight.

thedoor said..

Grantmac said..

Freeflight said..

FarNorthSurfer said..
I have the same foil and after reading this will try not to leave it on the beach like a old wave board again! That's a bummer.
Also be interested in what AFS come back to you with.
I used to be an aircraft engineer with composite experience and think I might be looking for something like this to do the repair. It would be best using a drill press to get the holes right and I didn't see where in the world you are. These things could be hard to source.
www.tappex.co.uk/product_category/titanium-threaded-inserts?cn-reloaded=1

Those tappex titanium inserts look very very nice, be good if all ali fuses came with those installed,
Does anyone know how it cost each for them ?

Most decent alloy fuselages come with inserts? Only the really poorly built ones like Slingshot thread right into the aluminum from what I've seen.

Not sure about that. Pretty certain my moses fuse is taped straight into the aluminium. I don't know why you would put inserts into a aluminium

Hey guys, can we stay on topic, please! Topic is carbon fuselage with tappex inserts that partially stripped the grooves they cut in the carbon fuselage. Go to 8 mm inserts?

thedoor said..

Sandman1221 said..

thedoor said..

Grantmac said..

Freeflight said..

FarNorthSurfer said..
I have the same foil and after reading this will try not to leave it on the beach like a old wave board again! That's a bummer.
Also be interested in what AFS come back to you with.
I used to be an aircraft engineer with composite experience and think I might be looking for something like this to do the repair. It would be best using a drill press to get the holes right and I didn't see where in the world you are. These things could be hard to source.
www.tappex.co.uk/product_category/titanium-threaded-inserts?cn-reloaded=1

Those tappex titanium inserts look very very nice, be good if all ali fuses came with those installed,
Does anyone know how it cost each for them ?

Most decent alloy fuselages come with inserts? Only the really poorly built ones like Slingshot thread right into the aluminum from what I've seen.

Not sure about that. Pretty certain my moses fuse is taped straight into the aluminium. I don't know why you would put inserts into a aluminium

Hey guys, can we stay on topic, please! Topic is carbon fuselage with tappex inserts that partially stripped the grooves they cut in the carbon fuselage. Go to 8 mm inserts?

haha sure. I feel your pain bro...nothing worse than not being able to foil.

Before going to 8mm I would probably mix up some epoxy and filler and reinsert them.

You will need to set up some kind of jig to make sure they stay in the right position as it hardens.

Thanks thedoor, what kind of filler? If I use the 6 mm McMaster hardwood tapping inserts, they will have plenty to cut into, can add epoxy and filler, and just mount wing and use that as an alignment jig since they will already be set from the cutting threads.

And I was looking at 6 mm and 8 mm inserts with deeper cutting threads than the tappex, the 6 mm from McMaster takes a 25/64" hole, while 8 mm takes 32/64" hole. The 6 mm would get a decent bite in the hole left by the tappex 6 mm because the tappex cutting threads are not as deep.

Sandman1221 said..Thanks thedoor, what kind of filler? If I use the 6 mm McMaster hardwood tapping inserts, they will have plenty to cut into, can add epoxy and filler, and just mount wing and use that as an alignment jig since they will already be set from the cutting threads.

And I was looking at 6 mm and 8 mm inserts with deeper cutting threads than the tappex, the 6 mm from McMaster takes a 25/64" hole, while 8 mm takes 32/64" hole. The 6 mm would get a decent bite in the hole left by the tappex 6 mm because the tappex cutting threads are not as deep.

I'd try and just pour in epoxy - if a filler is needed I'd use Cabosil Silica filler - not micro balloons.

Your initial repair ideas seem good and I'd follow Subsonic's advice to epoxy multiple layers of carbon cloth over the insert.

Then I'd give it a go in shallow, clear water and see how it holds up.
Probably be fine - you said it was an only an unusual catastrophic event that broke in the first place

I'd still put cloth over all the inserts - it won't change the angle of the wing on the fuselage.
Check first by adding an equivalent thickness of gaffa-tape, that the wing stills fits the fuse curve properly.

Once the cloth is on drill minimum size holes to fit the screws.

I wouldn't worry if the front wing ends up being 3mm lower than it was - the angle to the rear wing will be the same.

Yes, buy a drill press - I bought one when I installed the Helicoils on my fuses, worth getting it straight.

Maybe get the price for the replacement fuse before spending any money
Cheers
Rod

Freeflight said..
Maybe get the price for the replacement fuse before spending any money
Cheers
Rod

Freeflight, The fuselage is connected to the mast, one piece all carbon, 950 euro for the 85 cm version plus shipping, probably 120 euro, so around 1100 euro and I am stuck with the 85 cm mast/T-bar since my F-series wings will not fit the new 95 cm mast/T-bar. $22 in new inserts seems a bargin!

Sandman1221 said..

Freeflight said..
Maybe get the price for the replacement fuse before spending any money
Cheers
Rod

Freeflight, The fuselage is connected to the mast, one piece all carbon, 950 euro for the 85 cm version plus shipping, probably 120 euro, so around 1100 euro and I am stuck with the 85 cm mast/T-bar since my F-series wings will not fit the new 95 cm mast/T-bar. $22 in new inserts seems a bargin!

Oh that makes sense. If you don't switch front wings. And if this expoxying of the inserts does not work, then I would just epoxy the wing to the fuse and hope I can fit it in my car all connected

One good-news thing about this is that the front wing PUSHES against the fuselage when in flight. This means that the inserts and screws need to mostly just hold the wing against the fuselage, but not carry any lifting force. Not much tension on the screws and inserts. Yes, of course, there will be some left/right rocking tension on the screws, but that is not nearly as forceful as lift. (Unless, of course, a beach flight slams the foil around in all sorts of unplanned ways.)

The stab, on the other hand, PULLS against the fuselage in the AFS and Moses (and some others). The stab screws do indeed carry lifting force, but since it is relatively small, tension on the screws and inserts for the stab is not as critical.

The repair ideas here look really good. Good enough for the front wing. Thanks for the discussion.

segler said..
One good-news thing about this is that the front wing PUSHES against the fuselage when in flight. This means that the inserts and screws need to mostly just hold the wing against the fuselage, but not carry any lifting force. Not much tension on the screws and inserts. Yes, of course, there will be some left/right rocking tension on the screws, but that is not nearly as forceful as lift. (Unless, of course, a beach flight slams the foil around in all sorts of unplanned ways.)

The stab, on the other hand, PULLS against the fuselage in the AFS and Moses (and some others). The stab screws do indeed carry lifting force, but since it is relatively small, tension on the screws and inserts for the stab is not as critical.

The repair ideas here look really good. Good enough for the front wing. Thanks for the discussion.

Thanks Segler, not sure why no one from AFS suggested this approach, i.e., use M6 inserts that are larger in OD and longer too, both will help keep the wing on.

Grantmac said..
Chicago bolts will be stronger in every way because of how they distribute force (pulling the fuselage together instead of relying on a weak mechanical bond to the core material) and they are actually smaller outside diameter than all these inserts which will allow adding material to properly locate them. Any "peeling back" of the fuse skin is a recipe for disaster since that is literally where all the strength is, the core just holds it apart and you'll never get that adhesion back since epoxy doesn't chemically bond to previously cured epoxy.

I think any solution is likely to fail but the Chicago bolts will be the least likely. But it's your foil and you will do what you want. I just build custom fuselages and repair boards for fun so what do I know.

Lack of any inserts is a major shortcoming in foil design. Not going with a cross-bolt in the fuselage/mast connection is another (as Armstrong found out). Manufacturers who spend significantly more money developing their equipment then promoting it seem to have this figured out.

Thanks Grantmac, you could be right about the Chicago bolts, but I just do not want to try installing them, too many things I could screw up! Bigger in OD and longer inserts should be better than the originals, and the original inserts took many hard hits and were fine, just having the board/foil flying in the air and then landing on one wing tip on hard packed sand was just too much for them. With Chicago bolts that same impact could of broken the fuselage, and that would of been the end of it. Looking at the original inserts I am amazed they held up they way they did. I think overall the AFS design is good, and that is why I am sticking with inserts. I mean that was a catastrophic impact, and nothing was broken!, yes the inserts pulled out but the wing, stabilizer, and foil are all good.

If the original inserts have partially pulled out, then the bond between the insert and the fuse is compromised. I would think that they then need to be fully removed and replaced. The Chicago bolts are a sound alternative. Replacing the fuse is another.

Trying to push the insert back into position and reuse is a band-aid fix

Awalkspoiled said..
Understand the reluctance to drill through the fuse, but with a proper jig (you can make one out of clay) and a drill press the process is very simple. I would then install helicoils on the far side of the fuse, to receive the bolts. The advantage of this is that the helicoil is being pulled into rather than out of the fuse as you torque each bolt.

I do suspect you're going to eventually have to acquire a new fuse, expensive though it is. The risk of having the front wing come off four miles out would frighten me to death, I'd ride more cautiously and as we all know - that's when the trouble really starts....

Awaikspoiled, thanks for the information, I will keep that in mind since as you point out it is a very strong attachment, my only concern is the fuselage was not designed with that in mind, like the new ones are. I ordered the A4 SS replacement tapping inserts, since they are larger in OD with deeper cutting threads and longer, they will cut new grooves into the fuselage, just like the originals ones. Installing them with epoxy will make a stronger bond than the original inserts which from what I can tell did not have epoxy put on them during installation, that combined with rather shallow cutting grooves made for a weaker bond.

John340 said..
If the original inserts have partially pulled out, then the bond between the insert and the fuse is compromised. I would think that they then need to be fully removed and replaced. The Chicago bolts are a sound alternative. Replacing the fuse is another.

Trying to push the insert back into position and reuse is a band-aid fix

I agree with this statement

John 340, that's a great seabreeze Avatar image of you blazing on the foil
Love to get a shot of myself looking that good one day