5 The [V-2](https://en.wikipedia.org/wiki/V-2_rocket) has a significant place
6 in the history of rockets, and Bdale always thought it would be cool to build
7 and fly a model of one. After learning how to make APCP research motors and
8 experimenting with Everclear (which has visible flame characteristics
9 reminiscent of the LOX and ethanol fuel used in the original V-2) the
10 idea became even more appealing.
12 And then, [Composite Warehouse](http://compositewarehouse.com/) put their
13 [8 inch V-2 kit](https://www.compositewarehouse.com/index.php?route=product/product&path=18_70&product_id=158)
14 on sale during their Black Friday sale in 2020... and it was just impossible
19 This 8-inch diameter kit is all filament-wound fiberglass, with an
20 aluminum-tipped nose cone and 98mm motor mount. A short coupler section is
21 provided to attach the pre-slotted tail transition section to the main
22 airframe tube, and a longer coupler section is provided to double as the
23 nose cone attachment and electronics bay. Beautiful, thick, stepped glass
24 bulk plates with central 1/4-inch holes were included to enclose this bay.
26 When the kit finally arrived in mid February 2021, the parts all seemed to be
27 of outstanding quality, and the coupler sections in particular showed up in
28 thick-wall glass that seems really robust. An hour or so of fun involving
29 a bathtub, a couple shop towels, warm water, and dish soap cleaned everything
30 up and eliminated the residual fiberglass dust on all the parts in the kit.
32 Further examination showed that there was one minor problem. The aft
33 centering ring's inside diameter was fine, but the outside diameter was
34 smaller than the opening at the aft end of the fin section. It wasn't a
35 grossly un-usable part, and the gap could have been addressed by using some
36 small balsa shims to center the ring in the opening and sufficient epoxy with
37 fiber filler to close the gap. But, since a CNC router was available, the
38 decision to fabricate a custom replacement aft ring with precisely positioned
40 [Aeropack 98mm retainer](https://aeropack.net/motorretainers.asp)
41 was easy to make. The ring was cut from 1/2-inch birch plywood, stepped with
42 about a 1/8" lip to the outside diameter of the glass, and 12 holes the
43 correct size to directly tap for a #8 screw thread. The point of the lip
44 was to make assembly easy. With the machined lip, the ring could be epoxied
45 in place by itself but still assuring axial alignment. The part was designed
46 in [FreeCAD](https://www.freecadweb.org/) and cut on Bdale's
47 [Probotix](https://www.probotix.com/) Comet CNC router.
49 ## Design / Simulation File
54 Kit ordered during Black Friday kit-buying spree.
57 Kit arrived! Fun in the tub cleaning up all the kit parts. Dry fit various
58 bits to get a feel for how it should all go together. Discovered aft
59 centering ring OD too small, reported to kit seller not asking them to take
60 any action since I want to make a custom replacement anyway.
63 Built up an [OpenRocket](http://openrocket.info/) model of the airframe,
64 except that using the latest released version, 15.03, it's not possible to
65 model the fins correctly. The fundamental issue is that this version of
66 OpenRocket doesn't support fins on transition sections. Several work-arounds
67 were explored, but the net effect is that Bdale needs to package a fresher
68 version of OpenRocket for [Debian](https://debian.org) despite the lack of
69 a new upstream release, since it appears this deficiency got addressed sometime
70 since the 15.03 release.
73 Designed and machined replacement aft ring, located the unused 98mm Aeropack
74 retainer already on hand.
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