8" V-2
Motivation
The V-2 has a significant place in the history of rockets, and Bdale always thought it would be cool to build and fly a model of one. After learning how to make APCP research motors and experimenting with a variant of Everclear (which has visible flame characteristics reminiscent of the LOX and ethanol fuel used in the original V-2) the idea became even more appealing.
And then, Composite Warehouse put their 8 inch V-2 kit on sale during their Black Friday sale in 2020... and it was just impossible to resist buying one!
Design Details
This 8-inch diameter kit is all filament-wound fiberglass, with an aluminum-tipped nose cone and 98mm motor mount. A short coupler section is provided to attach the pre-slotted tail transition section to the main airframe tube, and a longer coupler section is provided to double as the nose cone attachment and electronics bay. Beautiful, thick, stepped glass bulk plates with central 1/4-inch holes were included to enclose this bay.
When the kit finally arrived in mid February 2021, the parts all seemed to be of outstanding quality, and the coupler sections in particular showed up in thick-wall glass that seems really robust. An hour or so of fun involving a bathtub, a couple shop towels, warm water, and dish soap cleaned everything up and eliminated the residual fiberglass dust on all the parts in the kit.
Further examination showed that there was one minor problem. The aft centering ring's inside diameter was fine, but the outside diameter was smaller than the opening at the aft end of the fin section. It wasn't a grossly un-usable part, and the gap could have been addressed by using some small balsa shims to center the ring in the opening and sufficient epoxy with fiber filler to close the gap. But, since a CNC router was available, the decision to fabricate a custom replacement aft ring with precisely positioned mounting holes for an Aeropack 98mm retainer was easy to make. The ring was cut from 1/2-inch birch plywood, stepped with about a 1/8" lip to the outside diameter of the glass, and 12 holes the correct size to directly tap for a #8 screw thread. The point of the lip was to make assembly easy. With the machined lip, the ring could be epoxied in place by itself but still assuring axial alignment. The part was designed in FreeCAD and cut on Bdale's Probotix Comet CNC router.
I originally anticipated this would be another "dual deploy from one airframe break" design, which to be honest I've had mixed results using. But once I saw how the longer coupler in the kit was intended to be assembled, I changed my mind. The kit came with a switch band for the coupler that is meant to be both ebay and nose coupler, and when I realized there's enough volume inside the nose cone to hold my choice of "laundry", a "traditional" dual deploy setup with two pyro initiated separation events became plan A.
The airframe geometry should easily support a 4-grain 98mm motor, which can be a "full M", so this should be a fun airframe to make research motors for!
Design / Simulation File
Construction Log
2020.11.22 Kit ordered during Black Friday kit-buying spree.
2021.02.17 Kit arrived! Fun in the tub cleaning up all the kit parts. Dry fit various bits to get a feel for how it should all go together. Discovered aft centering ring OD too small, reported to kit seller not asking them to take any action since I want to make a custom replacement anyway.
2021.02.19 Built up an OpenRocket model of the airframe, except that using the latest released version, 15.03, it's not possible to model the fins correctly. The fundamental issue is that this version of OpenRocket doesn't support fins on transition sections. Several work-arounds were explored, but the net effect is that Bdale needs to package a fresher version of OpenRocket for Debian despite the lack of a new upstream release, since it appears this deficiency got addressed sometime since the 15.03 release.
2021.02.21 Designed and machined replacement aft ring, located the unused 98mm Aeropack retainer already on hand.
2021.02.23 Installed aft ring with 5-minute epoxy.