# Corporate Colors

## Motivation

This is the airframe Bdale built for his second attempt at hitting 
Mach 3.  This is a step along a learning path building confidence before 
trying to assemble a minimum-diameter airframe to fly a CTI O3400 someday.

The first attempt was made with a very similar airframe that was assembled 
entirely
using [West System](http://www.westsystem.com) epoxy, including the fin 
can tip to tip laminations that were all done in a single vacuum bagging 
operation.  That airframe flew at Airfest in 2016 on a CTI M2245, and was at 
about Mach 2.91 when the fin can
came apart.  Post-flight analysis suggested the leading edge of the tip to
tip laminations got hot enough for the epoxy to soften allowing the carbon
fiber to be ripped off...  West System is and will continue to be my go-to 
epoxy for normal airframe builds, and worked great on a previous project
that got to Mach 2.21... but with a glass transition temperature of 129-242 F,
it's just not up to the challenge of staying together above Mach 3!

So, for this build, the plan was to use essentially the same design, but 
switch to one of the Cotronics high-temperature epoxies.  Others have talked
about using lesser epoxy for the bulk of the fin build-up laminations and then
just using Cotronics as a top coat, or the thicker version to build up leading 
edges, but it seemed to me that using the lower viscosity type for all of the
fin can laminations might be the easiest way to go.  After studying the
options, I chose [Duralco 4461](https://www.cotronics.com/vo/cotr/pdf/4461.pdf)
which is supposed to be good to 500 F with a suitable post-cure.  A pint kit
with shipping cost me nearly $130, but I used much less than half the kit 
building this airframe.  So, in the grand scheme of things, it's not that
expensive.

## Design Details

This is basically a "2 fins and a nose cone" design, using a single 5 foot
length of filament would fiberglass airframe, a filament would nose cone
with aluminum tip, and plywood fins covered with tip to tip carbon fiber.  

The fins were made using high quality 1/8" Baltic birch plywood cores glued 
into slots milled in the airframe tube, then 3 layers of 5.8 oz 2x2 twill 
carbon fiber were laminated "tip to tip" across the airframe through each 
valley. My normal peel-ply and breather were used, and the entire fin can 
was laminated and vacuum bagged in one operation to yield a full chemical 
bond across all fin edges.

Actually, the inner carbon fiber layer was cut smaller
to not go all the way to the fin edges, the outer two were big enough to go
past the edges slightly to allow for sanding back to the final fin shape after
initial cure.  The middle layer was rotated 45 degrees from the inner and
outer layers, giving us fibers in 4 directions.  

The OpenRocket design file is 
[CorporateCollors.ork](/rockets/airframes/CorporateColors/CorporateColors.ork),
and that design file plus all content on this page are released under the [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/legalcode) license.

### Electronics ###

## Build

## Photos

I've put all the [build photos](http://gallery.gag.com/rockets/CorporateColors/Build/)
I took together in one place.

## Result and Lessons Learned