5 This is the airframe Bdale built for his second attempt at hitting
6 Mach 3. This is a step along a learning path building confidence before
7 trying to assemble a minimum-diameter airframe to fly a CTI O3400 someday.
9 The first attempt was made with a very similar airframe that was assembled
11 using [West System](http://www.westsystem.com) epoxy, including the fin
12 can tip to tip laminations that were all done in a single vacuum bagging
13 operation. That airframe flew at Airfest in 2016 on a CTI M2245, and was at
14 about Mach 2.91 when the fin can
15 came apart. Post-flight analysis suggested the leading edge of the tip to
16 tip laminations got hot enough for the epoxy to soften allowing the carbon
17 fiber to be ripped off... West System is and will continue to be my go-to
18 epoxy for normal airframe builds, and worked great on a previous project
19 that got to Mach 2.21... but with a glass transition temperature of 129-242 F,
20 it's just not up to the challenge of staying together above Mach 3!
22 So, for this build, the plan was to use the same design and build techniques,
23 but switch to one of the Cotronics high-temperature epoxies. Because high
24 temperature epoxy is seen as expensive, others have talked about using lesser
25 epoxy for the bulk of the fin build-up laminations and then just using
26 Cotronics as a top coat, or the thicker version to build up leading
27 edges. But it seemed to me that using the lower viscosity type and staying
28 with the same build approach would both be the easiest way to go, and from
29 a learning perspective the idea of "change only one variable at a time" really
30 appealed to me. After studying the
31 options, I chose [Duralco 4461](https://www.cotronics.com/vo/cotr/pdf/4461.pdf)
32 which is supposed to be good to 500 F with a suitable post-cure. A pint kit
33 with shipping cost me nearly $130, but I used much less than half the kit
34 building this airframe. So, in the grand scheme of things, it's not that
35 expensive. I just need to make another fin can or two with it before the
40 This is basically a "2 fins and a nose cone" design, using a single 5 foot
41 length of filament would fiberglass airframe, a filament would nose cone
42 with aluminum tip, and plywood fins covered with tip to tip carbon fiber.
44 Due to the CTI M2245 reload that was used for the first attempt not being
45 available for a while, the M3464 Loki Blue from Scott Kormeier at
46 [Loki Research](http://lokiresearch.com) was chosen to power this attempt.
48 The fins were made using high quality 1/8" Baltic birch plywood cores glued
49 into slots milled in the airframe tube, then 3 layers of 5.8 oz 2x2 twill
50 carbon fiber were laminated "tip to tip" across the airframe through each
51 valley. My normal peel-ply and breather were used, and the entire fin can
52 was laminated and vacuum bagged in one operation to yield a full chemical
53 bond across all fin edges.
55 Actually, the inner carbon fiber layer was cut smaller
56 to not go all the way to the fin edges, the outer two were big enough to go
57 past the edges slightly to allow for sanding back to the final fin shape after
58 initial cure. The middle layer was rotated 45 degrees from the inner and
59 outer layers, giving us fibers in 4 directions.
61 The OpenRocket design file is
62 [CorporateCollors.ork](/rockets/airframes/CorporateColors/CorporateColors.ork),
63 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.
71 I've put all the [build photos](http://gallery.gag.com/rockets/CorporateColors/Build/)
72 I took together in one place.
74 ## Result and Lessons Learned
projects / web / gag.com / blob