Composite construction T-junctions

[[email protected]]

Hey all,
When laminating several fibreglass tape layers over the fillet in a
T-junction, do you use the widest fibreglass tape on the first or last
layer? I've heard different answers from different sources, so is
anybody here doing this right now for a kit and what do your kit
instructions state?

Omri

[Bob Kuykendall]

Earlier, wrote:

> When laminating several fibreglass tape
> layers over the fillet in a T-junction, do
> you use the widest fibreglass tape on the
> first or last layer? I've heard different
> answers from different sources, so is
> anybody here doing this right now for a
> kit and what do your kit
> instructions state?

This Ron Alexander article suggests putting the narrowest tape on
first, and covering it with successively wider tapes:

http://members.eaa.org/home/homebuilders/authors/alexander/Part%203%20Composite%20Construction%20Bonding.html

That is the practice that I follow. I seem to recall that the rationale
is to reduce the number of exposed tape edges by covering them with the
wider tapes. That practice helps keep the tape edges bonded down for a
good shear connection, reduces the potential for making jagged spikes,
and reduces the number of exposed fiber ends that can wick moisture
into the glass/epoxy interface.

I suspect that the difference in strength and durability between
narrowest-first and narrowest-last is probably pretty small for most
homebuilt aircraft applications, but I have no particular data to back
that position.

The instructions for the HP-18 sailplane, on which I have done bulkhead
taping, are not particular about the width sequence at all. They just
say:

> All bulkheads joining with other bulkheads
> and the fuselage shell must be cleaned with
> MEK or lacquer thinner, sanded, and taped
> with two layers of two-inch fiberglass tape,
> and polyester resin (provided in the kit).

Note that the HP-18 fuselage pod is generally made with polyester
resin, so the tapes are applied with more polyester. For epoxy
composites I'd recommend applying the tapes with epoxy.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24

[Highflyer]

> wrote in message
oups.com...
> Hey all,
> When laminating several fibreglass tape layers over the fillet in a
> T-junction, do you use the widest fibreglass tape on the first or last
> layer? I've heard different answers from different sources, so is
> anybody here doing this right now for a kit and what do your kit
> instructions state?
>
> Omri
>

Each successive lamination should be wider than the one under it. Then
every lamination bonds to the substrate as well as to the previous layers.
The finished surface has a minimum of edges.

Highflyer