T&T: Blister repai

[LRZeitlin at aol.com]

In a message dated 8/1/07 4:22:30 PM, terry.etapa at gmail.com writes:


>
>  
>
>  I'm not doing any blister repairs, I've just got a question on the scarf
> ratio.
>
>   
>
>  You say:
>
>
>  
>
>  Then get a grinder and grind
> away the surface of each blister with 36 grit paper until you are down to
> intact
> fiberglass. Be carefull, don't grind through the hull.  
>
>  When I specify scarf structural repairs to CFRP, I use a 30:1 taper ratio.
> Is there a reccomended ratio for blister repairs?
>
If you use a 4" disc grinder you probably will get the taper right. If I have
to go 1/4" into the fiberglass I usually like to use a scarfe of 1 1/2"
around the blister.

>
>
>  You say:
>  
>
>  Cut a number of discs out of 10 oz. fiberglass cloth in varying
> sizes ranging from the diameter of the largest blisters, decreasing in size
> by
> half inch increments. Now for the real work.
>
>   
>
>  Are you saying leave a 1/2" overlap per ply?
>
>
>
If each repair patch is 1/2 bigger in diameter than the one underneath, the
one on top overlaps the edge of the one on the bottom by 1/4". The overlap is
not really critical. Just make sure that the replaced thickness of fiberglass
cloth is similar to the amount removed in excavating the blister.

Blister repair is not brain surgery, just a lot of messy work. Each step is
simple and not too critical. Unless the blisters are in a critical stress
area,
structural strength is not needed. Just water tightness.

Larry Z


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