LV3 update for 2016-4-14

We're putting the finishing touches on the fin frames and the parts and
tooling for the nose. We will most likely have that ready for Machine
Sciences on Friday. The rail sled has also been designed
is ready to be manufactured. It will be be made out of three 1/4" layers of
laser-cut HDPE with an aluminum base.

Also, all of the updates are now on the LV3 repo
A previous
version of the layup procedure
put up earlier, and there should be a document for our latest procedure up
there later today. A document describing the overall design process is
coming soon. (All the information already exists, it's just scattered.)

Since the last update, we conducted some tests based on LV4's results with
using the 1515 adhesive as a surface finish. We also did a full size layup
based on the results from those tests.

The LV4 team will fill people in on the details, but they noticed in the
datasheet for the 1515 adhesive that it's also useable as a patching
material and a cosmetic finish. So, we can lay that up on the outside of a
module and sand it down to get a really nice aerodynamic surface. It also
fills in any dry cells. They tried a test with a vacuum bag and another one
with a vacuum bag and caul plate. Both turned out with no delaminations,
and none could be induced from hand-sq
eezing. The only real downside is that it makes the rocket green/blue
instead of black.

through LU16.9

The tests consisted of:

   - LU16.6 -- flat coupons using PCC's CF:
      - CF; release film; mold release; aluminum plate (for reference. same
      as LU16.3 and LU16.4)
      - CF; layer of shrink tape; release film; mold release; aluminum plate
      - CF; mold release; aluminum plate flat coupons using
   - LU16.7 -- Boeing's CF:
      - CF; release film; mold release; aluminum plate
      - CF; layer of shrink tape; release film; mold release; aluminum plate
      - CF; mold release; aluminum plate
   - LU16.8 -- mini cylinder with an adhesive coating on half and shrink
   tape on the whole thing (Boeing's CF)
   - LU16.9 -- small rings of CF layed up on a spare bar of aluminum, just
   for fun.

[image: small carbon fiber tests]

The results were as follows:

   - The shrink-taped mini tube was just as hard and smooth as the stuff
   from the last team. None of the people I had handle it could feel any
   delaminations. The adhesive-skinned portion is even better, and, as we saw
   from LV4's layup, may be sanded for an even better finish.
   - The flat coupons are a little quirky. *The tape surfacing didn't turn
   out well. The shrink tape shrunk... go figure. So, it got all wrinkly and
   transferred that to the CF.
      - The release film surfacing was pretty much the same as the previous
      - The raw caul plate surfacing was very smooth where there was
      sufficient pressure. The adhesive leaked through the bottom layer of the
      flat PCC CF, which we'll need to consider for the fins.
      - The Boeing CF is a similar weave as the PCC, but has an even worse
      wetting problem. The adhesive doesn't leak through it though.

[image: closeup of the small scale cylinder, showing the CF surface and the
adhesive surface]

After that test, we added another layer of adhesive to the mini cylinder
and put it through another cure cycle (hot enough for adhesive but cold
enough for cured epoxy). The motivation behind this was because trying to
sand down a single layer would most likely damage the fibers. On a full
sized layup, this would be pretty much guaranteed. So, we now have samples
of (everything shrink-taped):

   - CF outer surface
   - single layer adhesive surface
   - double layer adhesive surface (due to overlap)
   - CF surface with single layer post-cure adhesive surface
   - single layer adhesive surface with single layer post-cure adhesive
   - double layer adhesive surface with single layer post-cure adhesive
   - CF surface with double layer post-cure adhesive surface (due to
   - single layer adhesive surface with double layer post-cure adhesive

Long story short: we were too quick to abandon the tape method as too skill
based / not repeatable enough. The shrink tape reduced a lot of the dry
cell problem, but the adhesive completely eliminated it. We also found that
we can make the tape much easier to remove by using the outside surface of
the tape, rather than the inside surface (as it sits on the spool). The
small scale test was actually able to withstand Andrew's full body weight,
when he stood on it laterally!

We did an 18" layup with a single layer of adhesive surfacing and shrink
tape around the outside. The surface finish turned out extremely well.
Interestingly, the pattern of the nomex is shown by preferential flow of
the adhesive. It's still on the mandrel now. We're going to take it off
once it's cool. If we don't detect any thumb-streng
delaminations, we're going to do another tomorrow. We'll likely add another
layer of release film to the inside of our future layups, since the shrink
tape results in the mandrel curing much tighter of the mandrel.

[image: LU16.10]
close-up of the surface finish for LU16.10]
Of course, now that the modules have this color, there is only one logical
course of action

~Joe Shields
psas-airframe mailing list

Reply via email to