CA hinges installation - and CA talk

[Keith Black]

Re: CA hinges installationI have some questions regarding the foam friendly CA. 

Is it as thin and as strong as the regular stuff? 
If so why isn't all CA made to be foam friendly? It would seem to me that if the chemistry of the CA is changed such that it didn't damage foam then it is reasonable to assume that other properties may differ as well. In other words, what does one "give up" by using the foam friendly stuff?

Without knowing this I'd be very concerned about using it rather than the regular stuff. 

Personally I'd think with just a few drops on the hinge there wouldn't be enough foam damage to make a difference anyways. Think about it, people honeycomb their wings. What's the big deal if a wee bit of foam is eaten away? One argument may be that the trailing edge and control surfaces aren't honeycombed and foam lost in these areas is more critical. Well I have a hard time buying that. 

BTW, after writing the above paragraph I experimented with this several times using a Radio City 1/4" scale hinge going through 1/4" balsa into foam attached to the back side of the balsa. The CA never did any damage to the foam and seemed to be absorbed completely by the balsa. Of course, I didn't use the "Slot Machine" to make the slots, I used a #11 blade. With wider slots the CA may make it's way to the foam more easily.  

One thing I've noticed that all thin CA's are not created equal. Therefore I would think the quality of the hinge may be effected by type of CA one uses. For example, it's been my observation that the Bob Smith Industries stuff (that every hobby shop puts their own name on) doesn't soak in nearly as well as Zap CA. (If Bob Smith is on this forum my sincere apologies for singling you out :-) ).

And while I'm on a roll here. I've heard the crayon idea many times before, and quite frankly it never made sense to me. My first thought was that hinges are absorbent enough to wick the CA down into the hinge slot, so why would crayon on the "outside" of the hinge prevent the CA from wicking right through the middle of the hinge? Well, I did some tests with the Radio City hinges and found that the hinge itself really isn't absorbent, not without contacting balsa anyways. You can drip CA right on these hinges and it will just puddle in droplets and not soak in. But touch a piece of balsa to it and SLURP, the CA spreads through the wood and across the surface of the hinge and bonds instantly. It appears that the balsa actually absorbs the CA and the surface of the hinge provides a superb bonding surface. Probably due to its texture (the chemist among us could probably explain, Gray, you there?).

So, in trying to prove that CA would soak under the crayon I found that what really happens (on these hinges anyway) is that it doesn't soak in at all, at least not deep into the hinge fabric. As to the crayon I marked a hinge with a heavy crayon line on both sides and applied drops of CA and as stated it pooled not only on the crayoned portion, but on the non-crayoned portion. Therefore, my theory was incorrect, but I still am unsure that the crayon would do any good. If you ended up with excess CA caked on the hinge gap and you had a crayon line there then you'd just have CA caked over the crayon line (I tested this and it does bond to the crayon line).  

I'd be interested in hearing other's experiences with different types of CA and opinions/suggestions about CA hinges.

Keith Black

  ----- Original Message ----- 
  From: Bill Carpenter 
  To: discussion at nsrca.org 
  Sent: Monday, February 10, 2003 11:13 PM
  Subject: Re: CA hinges installation


  Another suggestion FWIW, if you have a foam wing core under the balsa sheeting and glued to the trailing edge, use foam friendly CA.  It will not eat the foam if it gets in that deep.  Also, some people either drill a hole in the center of the slot to allow CA to go deeper into the slot at the center, or some CA hinges come with a slot in the middle of them to allow CA to go in the slot deeper.  

  Bill 3544

  ----------
  From: "Chris Larson" <csmulti at volcano.net>
  To: <discussion at nsrca.org>
  Subject: Re: CA hinges installation
  Date: Mon, Feb 10, 2003, 9:59 PM



    Xavier-
    I have used a crayon from my sons toy box, sharpened, and drawn along the hinge line.  This not only serves as an alignment point, but also as a release agent for the glue.  I guess I should also note I haven't used that method on most of my planes ( just wicked in CA at the hinge line, let dry, and flex vigorously back and forth ) with great results too.  You shouldn't worry too much about making the hinge stiff - just be sure you are using THIN CA!! :-)
    Chris Larson
    NSRCA 3484

      ----- Original Message ----- 
      From: Anne & Xavier <mailto:xavier.mouraux at sympatico.ca>  
      To: discussion at nsrca.org <mailto:discussion at nsrca.org>  
      Sent: Monday, February 10, 2003 7:56 PM
      Subject: CA hinges installation

      Hi guys,
       
      I am about to install the CA hinges (fiberglass) on two of my winter projects and I would appreciate any recommandations on the proper procedure to do it. I have the tight slots done. I am worrying about the glue making the hinge stiff. How do I ensure the glue doesn't go in the flexing area ?
       
      Note that these are 2 sport planes that I am using to improve my building skills before moving on to pattern plane building next year. I have been flying second hand pattern planes.
       
      Thanks
       
      Xavier


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