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 129-142 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](http://cotronics.com) high-temperature
25 temperature epoxy is seen as expensive, others have talked about using lesser
26 epoxy for the bulk of the fin build-up laminations and then just using
27 Cotronics as a top coat, or the thicker version to build up leading
28 edges. But it seemed to me that using the lower viscosity type and staying
29 with the same build approach would both be the easiest way to go, and from
30 a learning perspective the idea of "change only one variable at a time" really
31 appealed to me. After studying the
32 options, I chose [Duralco 4461](https://www.cotronics.com/vo/cotr/pdf/4461.pdf)
33 which is supposed to be good to 500 F with a suitable post-cure. A pint kit
34 with shipping cost me nearly $130, but I used much less than half the kit
35 building this airframe. So, in the grand scheme of things, it's not that
36 expensive. I just need to make another fin can or two with it before the
41 This is basically a "3 fins and a nose cone" design, using a single 5 foot
42 length of filament wound fiberglass airframe, a filament wound nose cone
43 with aluminum tip, and plywood fin cores covered with tip to tip carbon fiber.
45 Due to the CTI M2245 reload that was used for the first attempt not being
46 available for a while, the M3464 Loki Blue from Scott Kormeier at
47 [Loki Research](http://lokiresearch.com) was chosen to power this
50 The fins were made using high quality 1/8" Baltic birch plywood cores glued
51 into slots milled in the airframe tube, then 3 layers of 5.8 oz 2x2 twill
52 carbon fiber were laminated "tip to tip" across the airframe through each
53 valley. My normal peel-ply and breather were used, and the entire fin can
54 was laminated and vacuum bagged in one operation to yield a full chemical
55 bond across all fin edges.
57 Actually, the inner carbon fiber layer was cut smaller
58 to not go all the way to the fin edges, the outer two were big enough to go
59 past the edges slightly to allow for sanding back to the final fin shape after
60 initial cure. The middle layer was rotated 45 degrees from the inner and
61 outer layers, giving us fibers in 4 directions.
63 The OpenRocket design file is
64 [CorporateCollors.ork](/rockets/airframes/CorporateColors/CorporateColors.ork),
65 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.
73 I've put all the [build photos](https://thor.gag.com/index.php?/tags/100-corporatecolors)
74 I took together in one place.
76 ## Result and Lessons Learned
78 The airframe flew on 8 July 2017 in Argonia, Kansas, at a Fun Fly hosted by
79 the Kloudbusters at their rocket pasture. The motor was a Loki M3464 Blue,
80 and everything performed perfectly until apogee. The maximum velocity was
81 1047 m/s, or right at Mach 3.1, on the way to an apogee of 32,635 feet above
84 Unfortunately, while telemetry shows the electronics correctly fired the
85 apogee ejection charge, clearly the nose cone did not successfully
86 separate. The resulting ballistic return impacted about 1.1 miles down range
87 to the south-south-west, at 37 9.1739 N, 97 44.8809 West.
89 With the final telemetry frame received from about 200m altitude on the way
90 down, we know impact was at about 2/3 Mach. Not surprisingly, then, what
91 we found in the middle of the wheat stubble was a 3" diameter hole with 3
92 slots radiating outward, and quite a bit of visible purple paint on the sides
93 of the hole. Probing with a shovel handle, we learned the aft end of the
94 airframe was on the order of 18 inches below ground level, and the aft end
95 of the motor nozzle was at least 4 feet down! Curious to know the fate of
96 the fin can that was the focus of this project, we took turns shoveling until
97 the fin can was sufficiently exposed to reveal two perfectly intact fins and
98 the third sheared off by impact with a fist-sized rock several inches below
99 ground level. Given the heat, and lacking either a backhoe or an army with
100 shovels, after taking a bunch of photos and logging GPS coordinates, the
101 decision was made to abandon recovery and just fill in the hole.
103 So, two big lessons learned.
105 Yes, Bdale can build a fin can that can survive Mach 3!
107 Getting so focused on one part of the project that you forget things
108 you know you should do elsewhere to ensure success leads to loss...
110 What I mean by the second is that while this is the first time I've personally
111 put an airframe above 30,000 feet... I've hung around other people who do it
112 successfully, and I've listened to details of what they did. In hindsight, I
113 "coulda, shoulda, woulda" put more attention on the apogee ejection
114 event. More black powder in the charge. More confinement to allow more of
115 the powder to burn before being dispersed in the lower-pressure environment
116 at altitude. Using one of the spare TeleMega channels to fire an up-sized
117 backup charge. Flying a TeleMetrum for full ejection event redundancy instead
118 of just a TeleGPS for redundant tracking. But I didn't do any of those things,
119 and lost the airframe and everything in it as a result. Yep, lesson learned!
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