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In flight CA hinge failure...

Old 10-02-2006, 09:59 AM
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tychoc
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Default In flight CA hinge failure...

So, up until now I've sworn by CA hinges. Never had a problem, until yesterday. Granted the conditions where not the best with up to 20-25 mph gusting cross wind, but I've never expected this. Take a look at the pictures. This happened mid-air. The hinges look like someone took a #11 exacto knife and cut them off. Luckily I managed to land safely on the runway (not a pretty landing in the cross wind without a rudder)

What would have caused this?? Now I'm worried about the other hinges. I have already repaired the rudder by using Robart hinge points, but it would be a pain to do that to the rest of the plane.

The hinges were installed per instructions using a GP hinge electric hinge tool to cut the slots and I did drill a hole in the middle.

thanks,

tychoc
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Old 10-02-2006, 10:09 AM
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Dr1Driver
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Default RE: In flight CA hinge failure...

Any flutter? How much and what type of CA did you use? You didn't double the hinges, did you?

Dr.1
Old 10-02-2006, 10:19 AM
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Default RE: In flight CA hinge failure...

That's why I always fly with pinned hinges - never had a failure with them. Klett, DuBro, etc. I like the hinge points, and if installed properly never seen one fail. I seen a couple of planes have flutter with hinge points and they held tight (flutter was caused by to much slop in the linkage and excessive speed in a dive on one plane).

I lost an Astro Hog last year after it went into elevator flutter - one of the CA hinges looked like it failed causing the flutter and blowing one half of the stab off. The other side had a ripped CA hinge also. (I didn't build this hog - it was from an estate sale, that's why it had CA hinges) I'll only use a CA hinge for a slow flying plane like a park flyer or glider that won't get into the speed range to create flutter.

Hogflyer
Old 10-02-2006, 10:57 AM
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Default RE: In flight CA hinge failure...

ORIGINAL: Dr1Driver

Any flutter? How much and what type of CA did you use? You didn't double the hinges, did you?

Dr.1
No flutter that I'm aware of, however this is only the 3rd time I'm flying this plane. No, I'm sure I haven't doubled the hinged. I used Zap CA and applied 5-6 drops of CA to each side as I belive the instructions said.

There's no slop in the linkages, but is it possible that a standard servo is not strong enough for this size rudder?

-tychoc
Old 10-02-2006, 11:16 AM
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Default RE: In flight CA hinge failure...

The servo might be too small. Also, I only use 2-3 drops of thin CA per hinge side. Too much CA will stiffen the hinge and not allow proper flexing. Some people swear at them, some sweat by them. I've used CA hinges for over 20 years on everything from sport to trainers to pylon racers to giant scale. Never had an in-flight failure.

Dr.1
Old 10-02-2006, 11:39 AM
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Default RE: In flight CA hinge failure...

It's possible you may have damaged one or more prior to flight and didn't notice it? I'm not a big fan of CA hinges either but they usually seem to do OK. I prefer the hinge points where I can fit them in. Keep an eye on the remaining hinges.
Old 10-02-2006, 01:15 PM
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tychoc
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Default RE: In flight CA hinge failure...

bruce88123

It's possible you may have damaged one or more prior to flight and didn't notice it? I'm not a big fan of CA hinges either but they usually seem to do OK. I prefer the hinge points where I can fit them in. Keep an eye on the remaining hinges.
I guess that's possible somehow. Not sure what I did wrong. So far CA hinges have worked great for me. I will also watch for flutter next time just to rule that out.

Yes, I will definetly keep an eye on the remaning hinges. I will try to "stress test" them at home to see if they appear brittle.

thanks,

tyychoc
Old 10-02-2006, 01:18 PM
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Default RE: In flight CA hinge failure...

When I get a kit that has CA hinges, I toss them aside and use only the metel pin type. [8D]
Old 10-02-2006, 01:27 PM
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Default RE: In flight CA hinge failure...

A friend brought me a fuselage the other day. He had jammed the rudder into someones back while carrying it. In doing so he managed to destroy 2 of the CA hinges. I know they were OK that morning because I had looked the plane over for him before he flew it. I cut the remaining 2 CA hinges (one partially torn) and installed pinned hinges for him.
Old 10-02-2006, 01:35 PM
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Default RE: In flight CA hinge failure...

I will never use ca hinges,used them once did not like the way they flexed compared to dubro or klett pinned hinges.I have airplanes that are over 30 years old still flying with the original pinned hinges intalled and no failures or loose hinges.I do check them as part of pre flight each time to make sure,just as on full size aircraft
Old 10-02-2006, 01:42 PM
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Default RE: In flight CA hinge failure...

You said you cut the slots with a Slot Machine - That's good

You said you drilled a wicking hole - also good...

The question that comes to my mind is: Did you have the rudder flexed MORE THAN IT WOULD TRAVEL IN FLIGHT before adding the CA?

I find that this type of failure is almost always caused by this. You can't just flex the surface a little (either in hopes of keeping a small gap or any other reason), it MUST be flexed farther than the servo will move it or this type of failure is almost sure to happen.
Old 10-02-2006, 01:42 PM
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Default RE: In flight CA hinge failure...

sorry but what is a pinned hinge?
Old 10-02-2006, 01:56 PM
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Default RE: In flight CA hinge failure...

A hinge with a metal hinge pivot pin in it?

http://www2.towerhobbies.com/cgi-bin...?&I=LXD940&P=7
Old 10-02-2006, 02:19 PM
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Default RE: In flight CA hinge failure...

When you go to epoxy a pinned hinge, make sure you heat a bit a vasaline in a spoon, fold the hinge in half and dip the hinged portion in. You want the liquid vasaline to penetrate around the pin - this keeps exoxy out of it and keeps it from being a pain to free up. Also, make sure you don't mix up the protected (vasalined) hinges from the non-protected or you'll spend an evening with an X-Acto blade cutting out epoxy and flexing the hinges - and don't as how I know that .

Also, some people will drill and put a tooth pick through the plastic flat to secure it in place after they epoxy them in place just for added security so they won't pull out.

Hogflyer.
Old 10-02-2006, 03:00 PM
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Default RE: In flight CA hinge failure...

If you use hinge glue
http://www2.towerhobbies.com/cgi-bin...&I=LXCX67&P=ML
the extra care will not be needed. Or at least that is what darock has promised me. I haven't tried it yet myself. I'm willing to trust him though.
Old 10-02-2006, 03:06 PM
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Default RE: In flight CA hinge failure...

Bruce,

Next time I do hinges I'll try that hinge glue. If it does bind them up I'll expect you to head west a bit and take care of flexing them for the evening until they free up - don't worry, it's only about a 9 hour drive over mostly 2 laners.

Hogflyer
Old 10-02-2006, 03:12 PM
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Default RE: In flight CA hinge failure...

Not me, call Darock! [:@]
Old 10-02-2006, 03:15 PM
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Default RE: In flight CA hinge failure...

Or you can call some friends of mine in Gridley,Ks.
Old 10-02-2006, 03:21 PM
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Default RE: In flight CA hinge failure...


ORIGINAL: MinnFlyer

You said you cut the slots with a Slot Machine - That's good

You said you drilled a wicking hole - also good...

The question that comes to my mind is: Did you have the rudder flexed MORE THAN IT WOULD TRAVEL IN FLIGHT before adding the CA?

I find that this type of failure is almost always caused by this. You can't just flex the surface a little (either in hopes of keeping a small gap or any other reason), it MUST be flexed farther than the servo will move it or this type of failure is almost sure to happen.
At this point I don't know if I did flex it appropriately. This certainly is a possible reason for the failure. Due to the strong cross wind, I had the rudder on high rates while taxing on the runway and several times I had to give full rudder to turn the darn thing around.

I certainly will remember to check for this in the future

-tychoc
Old 10-02-2006, 03:30 PM
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scratchonly
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Default RE: In flight CA hinge failure...

I accidently dropped some thin CA on my pants a while back; when I flexed the spot where the CA was the cloth BROKE like a piece of glass!! What does this tell you?
Old 10-02-2006, 03:37 PM
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Default RE: In flight CA hinge failure...

Cheap pants that shouldn't be used as hinge material?
Old 10-02-2006, 04:17 PM
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Default RE: In flight CA hinge failure...

This tells you that you should:

1. Not use your jeans for hinge material.
2.. Not wear the PLASTIC hinge material as clothing.
3. Wear an apron in the shop.
4. Be less clumsy.

Dr.1
Old 10-02-2006, 07:02 PM
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da Rock
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Default RE: In flight CA hinge failure...

It's really interesting that the hinges failed after only three flights. Never seen any that failed that quickly.

It appears that at least some of the CA hinges that fail were not installed in slots that were straight along the hinge line. If the slot isn't cut in line with the surface the hinge can't easily flex along just a simple fold. It'll stress from each side. I've seen a number of prehinged "you get what you pay for" models that had hinge failure and two things were common in each case. There was at least one hinge that wasn't in line, and the hinge material was the naked or slick plastic. They weren't the layered CA hinges that have wicking material on both sides.

I would hazard a guess that either one of the outboard hinges was not in line or had been nicked. Some plastics will tear easily if given a starting place for the tear.

I also wonder if some of the plastic used might not be weaker in one direction and more likely to tear across than lengthwise (or vice versa).
Old 10-02-2006, 07:14 PM
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da Rock
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Default RE: In flight CA hinge failure...

I almost always use flat "pinned" hinges instead of CA ones, but it's mostly because.... awwww, forget this long winded spin off..... back to the topic:

I do use CA hinges sometimes, and have started flexing them before using them. I flex in both directions to see which way, if any, they bend easier. And I've run into a couple that seemed odd feeling and trashed them. And seen a couple that had ragged edges, although the "ragged" wasn't along the edges that'd be flexing.

When I started out checking them, I thought that they all seemed pretty stiff to be good hinges. I was "brought up" in modeling to understand that any binding or resistance was detrimental. That's not nearly a problem today in RC. But I recently started assembling a SkyBolt and was taken by the obviously greater quality of the hinges in that ARF. They were obviously better than all that I'd seen before.

So it's clear that there is a fairly wide range of quality in CA hinges.

I guess we're just going to have to develop some experience with them that includes learning to spot the ones that are going to fail. Now, if we just knew what to look for.
Old 10-02-2006, 07:25 PM
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da Rock
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Default RE: In flight CA hinge failure...

I CAN'T STAND IT!!! I GOTTA SPIN OFF!!!!!

I have found that for me, it's as quick to use Dubro flat pinned hinges as it is to use CA hinges. I use hinge glue and it's dead easy and quick. And I've yet to assemble a pre-sliced ARF that didn't have a couple of skewed slices or slices that were above or below the hinge line and was going to need correction.

I discovered through autopsies, that CA hinges that're simply slipped into the slices through Monokote don't always wick CA into them. And drilling the wicking holes takes time that isn't needed with flats and hinge glue, so that balances out. So if I do use CA hinges, I spend time slicing away covering, and drilling wicking holes. If I use flats, I spend less time with a piece of hacksaw opening the slits. And can easily correct skewed slices or off line slices, and the covering "closures" are actually a positive. The glue gets into the slots because it's mechanically put there and the covering closing back simply helps fuelproof the area.

OK..... sorry...... had to spin............

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