CA hinges installation - and CA talk

[Gray E Fowler]

Keith

I am here-I just do not always care...........I do not worry about the CA 
hinge foam deal because

1. The hinge only adheres to the balsa (Trim the length of the hinge to 
match the depth of the balsa).
2. The CA will not wick into the foam since the foam is non absorbent.
3. An area of foam that touches the hinge and is damaged will not effect 
the strength of the wing or improve your chances of survivng a mid-air 
collision.

Crayon (wax) will not penetrate below the surface and so yes it will still 
wick-just trim the hinge to the length of the structural bond area.  The 
wicking capability on the same type of hinge vs. different brands of CA 
will be viscosity dependent and humdity dependent. If it is a high 
mumidity day then the CA with the massive CA hinge surface area will react 
more rapidly (hence a viscosity increase). Also consider that all CA's age 
and increase in viscosity-perhaps both brands of CA will wick the same IF 
they start out at the same viscosity. 
>From an ultimate strength and substrate compatibility standpoint foam safe 
CA is not as good as regular CA BUT is it good enough? Probably yes.
CA's rapidly lose ultimate strength as humidity attacks the cured CA. I am 
unaware of how foam safe CA resists moisture in the long term since we as 
modelers are about the only ones using it.
Another fact about different brands of CA. Epoxy resin production volume 
has got to be at least a million times bigger than CA. There are about 4-5 
companies that make epoxy resin. How many companies do you really think 
produce CA? If there are 3 I would be surprized.  Toll manufacturing is 
the reality.



Gray Fowler
Principal Chemical Engineer
Composites Engineering
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