da Rock

I've become the "coroner" at our field. I do autopsies. Truth is, I've been doing them on model airplanes since my first one and that was back...... sorry...... starting to blabber......

After looking at the three pictures of the failure, I've noticed something. Everyone would certainly agree that from the 1st picture it's clear that the hinges failed from the top one down. Now, if you look at the 2nd picture, look at the top hinge.

Where did that sucker let go? Down inside the slot, right. You can see that the hinge material that really should be in the slot is gone.

I'd hazard a guess that it wasn't a flex failure that defeated that hinge. The sucker shouldn't have been able to flex down inside the wood. And it wouldn't have wanted to anyway. No doubt the model checkout for the maiden and next two flights included working the rudder and the model certainly was taxiied some. So the hinge must have been flexing ok along the hinge line. Yet the failure is obviously away from that line.

My coroner's report would suggest the quality of materials of the hinge material in the top hinge gave under load due to a weakness in the material near the hinge line. We've all seen plastic stuff with bad streaks in them, right.

......... ok, time to quit running my mouth

CafeenMan

As has been said about CA hinges - some people swear by them, some people swear at them. But any hinge that you have to know so many "secrets" to install correctly have too much wrong with them.

CA hinges are the only hinges ever made that have this high of a failure rate. Every other hinge system is better including monokote hinges and sewn hinges. I guess if you know all the secrets then there's nothing wrong with using them.

Add me to the group that only uses "real" hinges. I always trash CA hinges when they come in a kit.

hogflyer

Now I'm disapointed - I was just getting ready to hear some stories of Langley and his Aerodrome.......

Sorry, but I just could resist that open door.......

Hogflyer

Fastsky

Thankx for the info on the hinge glue. I have a bottle of it but haven't used it because as mentioned before, it ljust looks like wood glue. I won't be so leary to use it now. I always pin my hinges after any way with the round tooth picks and wood glue. Then I dremel the outside edges flat and seal them with a drop of CA. [8D]

da Rock

hogflyer,
That whippersnapper Langley? JohnnyComeLatelys ain't worth talking about. Heck, he didn't even build his own motor, did he.

Now Leonardo was a modeler you can get me to talk about. He was over to my hut one day, wantin' ta borry some balsa wood 'cause I'd just discovered it and........

Deadeye

While I've never had a CA hinge fail, I can say that I don't use them unless I have to. Robart hinge points are soooooo much easier to use. They are bullet proof, easy to align, easy to glue in with poly, inexpensive, strong, I could go on and on.

Once you go Robart, you'll never go back.

tychoc

I think I will be joining the "throw away CA hinges" camp after this....

Just the thought that the model could have crashed on it's third "day" out after hours and hours of building the kit is enough. No chain is stronger than the weakest link etc.

Consider me converted, well actually, when I was a kid and built kits (70s and 80s) there were no CA hinges and I used the regular pinned ones, so I guess I'm going back to what I used to do.

-tychoc

da Rock

Fastsky,
Make up a quick and easy test. Cut a slot for a Dubro flat pinned hinge in a couple of pieces of balsa. Drill the holes for robarts too. Use the hinge glue and take only the minimum effort. After the drying time suggested. Try to pull each apart. Then go ahead and cut what's left up to see how well both are glued to the wood.

I think you'll find that both types were very, very solidly glued to the wood. I wound up trying to hold the balsa in a vice without crushing it so I could pull harder. And autopsys of crashed airplanes will have pulled hinges, but the flats are still solidly glued completely to the shredded balsa that was pulled out with the flat.

Robarts are excellent and easier with hinge glue.
Dubros are excellent and easier with hing glue.

I wish I owned the company.

MinnFlyer

My Feedback: (4)

Well, like Deadeye, I too have never had a CA hinge fail. However, with the exception of a few large-scale planes, I have used CA hinges exclusively since the late 80's - that's almost 20 years.

I have even used them on some large-scale gassers.

Two of the planes that I used them in back in the 80's are still flying.

Also keep in mind that I do product reviews for RCU. That means that while most guys build one or two planes a year, I build about one per month - and I have NEVER had a failure.

Are there a lot of "Secrets" to getting them right? No.

I wrote a "How To" about putting in CA hinges that many of you may have read where I say to "Remove the covering around the hinge slot, and drill a wicking hole" - The truth is, I don't even do THAT! I put them in, bend the control surface MORE THAN IT WILL MOVE IN FLIGHT, and add 4 - 5 drops of CA (to each side)

I have used every type of hinge on the market (And some that AREN'T on the market) and NOTHING is easier.

As far as CA cracking the material of your pants, yep, I've got several articles of clothing with one of those dredded CA cracks, but this is FABRIC that the CA wicks into and hardens. CA does not wick into the plastic which stays flexible (AS LONG AS YOU HAVE GIVEN IT ROOM TO FLEX)

THE single most critical thing about installing CA hinges is to hold the control surface in a deflected postion (Once again, more than it will move in flight) as you are applying the glue. If you do that, you should never have a problem.

redskytattoo

I love the CA hinges........I have never had them fail.......Darock...good coroners report, but I need to be devils advocate here...I agree the top hinge was the first to go....But under normal circumstances the others should have held tight....I feel flutter must have torn the hinges for all of them to go like that...My 2 cents...

Also I never drill wick holes or open up the slots anymore than to slip the CA hinges in....I would say one of the most important things that is commonly overlooked is to use Super Thin CA........very important...I think alot of people use the regular CA they got laying around.....Doesnt wick very well at all.....

CGRetired

My Feedback: (1)

One thing I didn't see in any replies (may have missed it) but double applications of CA can and will cause failure. The failure in the picture looks like the CA hinge 'tore' away from the joint, not pulled out from the balsa that it was set into. Double applications of CA can result if you put one side of the hinge in ( let's say you put it in the vertical stab ) and let it set. Then apply CA then attach the other side of the control surface, in this case, the Rudder and let that set too.

This is a double application of CA and is probably going to fail. I saw this myself with my Tiger 60 aileron a while back.

I was not aware of this double application of CA and, for simplicity sake, and because I didn't know better, I put the hinge in the wing TE and applied glue then mounted the ailerons and applied glue again. Not good. After several flights, I noticed that the ailerons were beginning to get 'loose' or flex when pressure was applied. My flight instructor asked me a few questions and it came out that I had applied CA twice to the hinges. We took the ailerons apart, and re-hinged it, this time correctly. The old hinges were loose in their slots and were ready to pull out. One actually broke or tore like the picture above.

That does not mean that this was the cause of the failure, it appears that flutter may have taken it's toll by tearing as mentioned above. But dual glue applications can and will make the hinges brittle and prone to failure.

DS

Fastsky

Wow! It seems that even though there are lots of flyers that swear by the CA hinges, there are lots of rules that have to be followed or the hinge will fail!! From following this post I have concluded that I will stick will my metel pinned hinges and I will try the hinge glue that I have a full bottle of. [8D]

AllTheGoodNamesAreTaken

My Feedback: (180)

For pinned hinges, I've always had an issue with the glue being wiped off the hinge as you insert it into the slot. It always made me leary of the amount of glue that is actually in the slot.
My friend came up with (or at least suggests) using a small syringe (he uses one that came with a tooth whitening kit) filled with glue and flattened on the end to fill the slot with glue.

By the way, he submitted his idea to Tower Hobbies and they gave him a $20 credit for his next order. Something to keep in mind.

drksky1056

Back when I built a PT-40, I used Dubro hinges. Manual suggested using a soda straw with the end flattened to do this. Scoop up some epoxy with the flattened straw, insert it into the hinge slot, blow. Worked pretty well

da Rock

The flat Dubro hinges have holes through the flats. Those holes are the trick.

The hinge glue solves the problem as well. It's simple to place the tip against the hinge slot and squeeze. You can see that glue gets into the slot. Now, take some time to smear glue on the flat of the hinge that's to go into the slot. That time gives the glue in the slot time to start soaking into the balsa. And the slot isn't going to be smooth on the insides anyway. The gouges and cracks in that slot are going to soak some of the hinge glue into themselves. It's also very easy to use the hinge glue bottle tip to spread a thin layer of glue on the hinge flats. The glue coming out of the bottle almost automatically fills each of the holes in the hinge flat.

The hinge glue starts to get tacky almost right away. By the time you've gotten the hinge flat lightly coated with it's holes filled (something that was dead easy to do and actually didn't take any time at all) the glue on the flat is tacky and the glue in the slot has worked into the balsa. When you push the hinge into the slot you'll feel the tackiness. But you'll also see some excess push back out of the slot.

Once the flat is in the slot, the glue that rode into the slot in the holes in the flats will then start to bridge from the balsa on one side of the slot to the other. You'll have glue "pins" from balsa to balsa in 6 places on each flat.

How do I know all this "inside" stuff? I've done some test hinging and torn the test pieces apart. And I've had the opportunity to autopsy some crashed airplanes that had Dubro flat hinges glued in with hinge glue. Do that yourself and you'll find out for yourself just how well the hinge glue holds to flat, pinned hinges. But be prepared for an effort. You WILL have some trouble getting down to the hinge flats themselves. They will be solidly "coated" with balsa that isn't coming loose without a struggle.

da Rock

BTW, the holes in the hinge flats came about in the early days of flat, pinned hinges. They were originally epoxied into the balsa. (And that was a mess and a pain to keep the hinge joint free of epoxy, but that's another story.) And turns out that the hinges would let go after awhile sometimes.

They discovered that the plastic in the hinges was releasing itself over time from the epoxy. So they drilled holes through the flats so the epoxy would "pin" the hinges into the slots. Dubro also changed the plastic they were using.

Hinge glue bonds to the plastic being used today. Bonds good. Plus the holes are still there in the hinge flats.

CafeenMan

You know, everybody says to use vaseline on the hinge pin when using that type hinge to prevent epoxy from fouling the hinge.

I found that because epoxy doesn't really stick to the plastic that the vaseline isn't necessary. I use a needle point oil applicator to put a drop of very thin oil on the end of the pin and it wicks down the hinge.

When the hinge is inserted, I wipe off epoxy that oozes out before I push the hinge all the way in. The keeps most of the epoxy off the hinge line.

Then I put the control surface on a flat surface and push it down so all the hinges go in the exact same amount.

Now, DO NOT MOVE THE HINGES TO SEE IF THEY ARE FREE! That will do nothing but work glue into the hinge. When the epoxy is fully cured... and I do mean fully cured - not just hard, give the hinge a good flick with your finger and it will pop free of the epoxy and move perfectly smoothly. Very simple to do.

Oh, and CA hinges still suck.

PropSpinner

My Feedback: (15)

I've only had CA hinges break once and that was while I was carrying the plane into the house I bumped the rudder into the door. I repaired with Robarts because it was the easiest thing to do. I like them OK and never had a in flight failure. Of course I fly ARF's too and I know that there are some posting here that would never own one.

LT-40

My Feedback: (2)

I have never used pinned hinges, and have always used CA hinges. Now I'm wondering if I should give pinned hinges a try because I recently had two CA hinges fail on my trainer. Pinned hinges look good, but how big of a gap do they leave between the two surfaces being joined? Does that round pinned joint get in the way?

Charlie P.

You all do know it's common practice to drill 3/4 of the way up from the underside surfaces where the CA hinges are and pin the CA hinges in place with a piece of toothpick? If you peg them before you CA they will all be snug and secure, and the CA will secure the peg at the same time. A real belt-and-suspender's solution. If you're fussy a small piece of covering will hide the end of the toothpick.

SoonerAce

My Feedback: (1)

I've used both flats and CA's and I now drill both and push a epoxied toothpick into ALL of them. Lil bit of peace of mind, keep ya from wondering and losing your mind.

Fastsky

I use wood glue for the round tooth pick. No 2 part mixing needed.

bruce88123

Doesn't stop them from tearing though.

Pete1burn

I'm going to be rebuilding a new Avistar to replace mine and using only pinned hinges. Just the thought of some thin fabric keeping my investment in the air is scary.

bruce88123

Pete, the Apollo space capsules landed under thin fabric parachutes, skydivers use thin fabric parachutes daily, the airbags in your car are made of a thin fabric. Are you getting my point?