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User avatar
By ascaro
#406479
Hi guys,
has anybody got some experience regarding the inspection or the simply maintenance of a full carbon frame for a flex wing?
How do you do if a nose in occur, or a bad landing happens?
I know that the carbon fiber is way more and more stronger than any aluminum equivalent part, but how do we do with the inspection?
Somebody says that you can test a frame by gently tapping on it with a coin or something that could 'sound' to give you an idea if the part is completely solid and filled, but it seems such an empiric thing that I can't help being doubtful...
What do you say?








User avatar
By red
#406484
ascaro wrote:
Tue Feb 12, 2019 1:11 pm
Hi guys,
has anybody got some experience regarding the inspection or the simply maintenance of a full carbon frame for a flex wing? How do you do if a nose in occur, or a bad landing happens? I know that the carbon fiber is way more and more stronger than any aluminum equivalent part, but how do we do with the inspection? Somebody says that you can test a frame by gently tapping on it with a coin or something that could 'sound' to give you an idea if the part is completely solid and filled, but it seems such an empiric thing that I can't help being doubtful... What do you say?
Ascaro,

You have hit on one of the main issues (beyond original cost) that I have with CF, or any composite structures for HGs. How can you test this stuff, after a few whacks?

I have done some good work in that arena, using an infrared camera where I worked. I was using a lab-grade IR camera, but it is possible that lesser (and far less expensive) gear MAY give you decent results. I used heat lamps (such as the fast-food places use to keep food warm) as a heat source for composites. I aimed the heat at one side of the part, with the camera looking from a 90 degree angle to the heat rays. As the part warms up, the heat should spread smoothly and evenly through the composite material. Any crack or void in the structure would show up as a line with warm material on one side and cooler material on the other side. You would need to repeat the test from fully cold (room temperature) in three axis - rotate the target object 90 degrees (without moving the lamps or camera) to view front, side, and top images of the target. For long structures, such as a main spar or keel, you would need to pass the target through the camera viewpoint at a slow and steady speed. I never had that requirement, so you may need some creativity there. In all cases, I used image capturing software to allow repeated views of any test done. The factory that made our composites told us to tap with a coin and listen; we told them to go take a flying leap at a rolling doughnut. :lol: Any faults found by the camera could only be verified by cutting the part into pieces, but our testing never called a bad part that was not verified by cutting.

If you are still with me, the heat lamps do NOT need to cook the target; usually you could barely feel a warmth in the target object, but the camera showed a rainbow of "false" colors, as any section became "warm." Attached you will see"false colors" of a transmission line tower as an infrared image - one side is the everyday view of normal metal, and the other side shown with heated parts (as "false colors" in infrared). Each part fades from one color to the next, in infrared normally. If any part was cracked or broken, the heat would stop at the crack. I am guessing that the Sun was providing the heat on the tower that you see in the picture. Electrical power was heating the transmission lines.

Image
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#406491
For inspecting the CF parts on a hangglider the coin-tap method is, in my opinion, good enough, assuming that the part was properly manufactured and inspected prior to assembly. The reason being that it's mostly thin-walled tubing where any damage invariably will happen on the outside, impact damage or over-bending will show on the largest diameter as cracks or delamination which both are easily detected by vision and the change in sound when tapped. The damage render the part unserviceable. It takes a lot to damage them though but less than an aluminum le. X-bars have thicker walls, I have yet to see one damaged by normal transport on a car roof or whacking.
#406493
Thank you, I didn't know that technique,SG. It all makes perfect sense, without being destructive, pretty much like xrays.
And cheaper.
Anyway, it's been a long time since carbon frames (or frames with carbon xbars) are on the real world, and it's pretty reassurng that very very few exploded while flying. So... I'd say they are reliable.
I'm currently flying a full carbon frame, and I've had a hard landing the last flight. That's when my concern started to arise.
I've broke the speedbar and bent both uprights,but apparently there are no issues at all for the nose in. Anyway I'll get the glider checked by my dealer, and I'll ask the manufacturer.
It would be interesting to know how they do at A-I-R,for their carbon wings...
Thanks again.
User avatar
By red
#406495
ascaro wrote:
Wed Feb 13, 2019 12:57 pm
Thank you, I didn't know that technique,SG. It all makes perfect sense, without being destructive, pretty much like xrays. And cheaper.
Ascaro,

That infrared technique was my own "invention," which the composites manufacturer soon adopted. Just part of the job, for me. I would hope that it gets used often and everywhere. It floors me that they built airliners with that material, but they had no way to inspect it for cracks or damage. Tapping with a coin does not work when it's a structural block weighing ten pounds (~4,5 kg) and drilled in several directions.

BTW, SG is SpeedGliding, or Jack, who owns this forum. Me, I'm just another regular (crazy) HG pilot, dropping by now and then, and maybe doing some good when I can. Our avatars are somewhat similar, but flying in opposite directions. Happy to help. 8)
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#406501
Tapping with a coin does not work when it's a structural block weighing ten pounds (~4,5 kg) and drilled in several directions.

Read more: viewtopic.php?t=36367#ixzz5fVFrucq6
No, but we're talking about CF tubing used in hanggliders aren't we? Hidden damage is hardly an issue except for delamination which is the condition easiest detected with the coin tap method. CF adds to the maintenance of a hangglider so the ones not up to it should stay clear.

I've had full carbon frames on my glider since 2012 and twice had damage, they were both after severe hits and were hard not to notice even though the tubes didn't break.
#406502
Oh, sorry Red, my mistake.
I owe you a drink... :) Thank you again. Great.

So...Back on topic.
@Tormod: You said you've had some accidents where the wing was compromised,and it was clearly noticeably.
But how do we do when it's subtle,and everything seems ok? Do you trust your frame again?
I've had a crash where I broke the speedbar and bent both my uprights,but I hit the ground at the same time,so the wing was already unloaded when it hit the ground (soft grass) with the nose. The damage seems to be just on the A frame,I've inspected everything.
Visually it seems perfect.
You've replaced the broken parts, but what about the rest?
#406504
After damage I either remove the sail or crawl into it (lay the glider flat on a soft surface) unzipping the shear webs to be able to look and feel every part of the tubes and look at brackets and bolts. Any fibers sticking out or areas looking scratched or hit by something on CF are reasons for concern. Those areas I tap-test and look more closely at but if fibers are found I remove the part to be able to look very closely. Everything that looks OK, are OK.

If you suspect a invisible delamination, which is unlikely to go undetected by visual inspection because of the thin walled tubing, you must remove the sail and tap the length of the tubing every inch at 6 places around the OD. Also look inside, fibers sticking out are never a good sign. The test should sound something like: tik-tik-tik-thump-tik-tik... if you find a fault. Else it's only "tiks"

The basebar is overly strong and there's a cable inside so no need for concern as long as it looks OK and no crunching noises comes from it when handled.

The X-bar is very strong and well protected against any direct hits but can get damaged by transport or if you "landed" upside down but again, the wall thickness is great so it's probable that damage will show at the ends by bent brackets or disfigured holes visible on the inside looking from the ends. Any crush marks or loose fibers are cause for concern.

If you are really concerned maybe you could invest in a cheap boroscope, they come with WIFI and a phone-app now for less than $25.
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