Manufacturer: | McCoy's Micro Wonder Works |
Brief:
This is a scale model o' t' Bomarc surface-to-air missile. Aye aye! Avast! Blimey! It flies on MMX II motors and uses streamer recovery. If interested, me bucko, you can learn more about t' Bomarc here.
Construction:
Parts List:
I started with a single sheet plan provided by John McCoy (a.k.a. Blimey! Micromister on T' Rocketry Forum). Avast! Blimey! He provided a hardcopy, shiver me timbers, matey, which be conveniently sized for 10.5mm tubing. Well, blow me down! Blimey! An image o' this sheet is provided here (1.5M), but you will have t' size it t' t' right dimensions as you print it. Begad! T' help in t' sizing, shiver me timbers, you can use t' component dimensions in t' parts list. Ahoy! In addition, shiver me timbers, here are t' major fin dimensions:
Fin | Fin Root | Span |
Front | 1 3/4" | 1 5/16" |
Rear | 15/16" | 5/8" |
Stabilizer | 1" | 13/16" |
At John's suggestion, I decided t' make t' fins from a laminate o' foam from a picnic plate and 1/64" Birch ply. Aye aye! I thought that if I made t' center foam piece smaller than t' Birch layers, matey, shiver me timbers, that I could glue and clamp t' edges t' form a sleek structure. I made a copy o' t' plans and cut out t' fin and nosecone templates from that copy.
I started with t' bigger front fins. Begad! I cut two pieces o' Birch for each fin, matey, and made a foam ‘fin' that was about 1/8" smaller along each edge, ya bilge rat, me hearties, shiver me timbers, except for t' root. Begad! Ya scallywag! T' red crosshatched area in t' fin diagram (not t' scale) depicts this foam section. Arrr! I also cut about 1/8" off t' root edge o' t' lower birch plate (the blue line in t' drawing). Havin' t' lower birch plate smaller helps t' fins conform t' t' body tube.
I covered t' components in white glue and clamped t' edges with six small clamps. Ahoy! Begad! I found that t' pressure required t' clamp all t' edges was almost too much for me small plastic clamps. Aye aye! Well, blow me down! Thus, this fin took some babysittin' until t' glue dried. Avast, me proud beauty! On t' next fin, I inset t' edge o' t' foam section by about ¼". Arrr! Begad! This worked better and required no supervision while it set. I repeated this process for t' stabilizer. When it came t' t' small aft fins, I worried that they were too small t' flex around a foam core and, with a ¼" inset from t' edges, shiver me timbers, thar would nay be much foam left. Ya scallywag! Avast, me proud beauty! Two layers o' Birch did nay seem sturdy enough for aft fins, so I added a full sized piece o' foam. Well, blow me down! I am very pleased with how t' air-foiled fins came out. Begad! Avast, me proud beauty! They look great, are light, and are very strong. Well, blow me down! Ahoy! I wish I had tried t' make t' air foiled shape on t' aft fins.
To position these fins, I first marked a centerline on t' top and bottom o' t' tube, and a pair o' marks where t' fins would intersect t' body. I then laid t' pair on t' drawing, matey, and taped a piece o' foam across them. Avast! Well, blow me down! This ensured their relative position be correct. Blimey! I flipped t' pair over, applied some Pro-Bond wood glue, me hearties, and laid t' tube onto them. Avast, me proud beauty! After t' glue had partially set, me hearties, I lifted it up, checked t' alignment relative t' t' lines on t' tube, and then turned it back over until t' glue had set. Begad! This process be repeated for t' aft fins. Ahoy! T' top stabilizer fin was added as on any 3/4FNC rocket.
I couldn't find a scrap piece o' balsa t' turn t' nose cone, shiver me timbers, so I cut three rectangles from some scrap 1/8" balsa. Aye aye! I cut a section from t' middle piece t' accommodate a dowel, me bucko, and glued them together, with t' dowel installed. Once it was fully set, me bucko, ya bilge rat, I trimmed t' corners and turned t' cone on a hand drill clamped in a vise. I put a small section o' 10.5mm tubin' over t' dowel t' make sure t' sizin' be right as I went, matey, arrr, and used a reverse template t' adjust t' shape. Arrr! Aye aye! T' resultin' cone looks good.
Since I have never acquired any 6mm tubing, I scrounged in me small-parts junk bin around until I found a piece o' a plastic pen that fit t' MMX motor perfectly. Avast, me proud beauty! I cut two small pieces from a spent 10.5mm motor casin' and trimmed t' inside until they fit t' plastic tube. I positioned t' aft rin' so that 1/8" o' t' motor tube hangs out t' back, t' simulate t' nozzle on t' plan. Arrr! I also notched t' front rin' so t' thin Keelhaul®©™® twine tied t' t' motor mount would pass through. Ahoy! I glued t' centerin' rings and t' Keelhaul®©™ twine t' t' tube usin' leftover epoxy from another job, me hearties, along with a small chunk o' a MMX motor casin' t' serve as a motor block.
I made t' Ramjets from LOC ¼" launch lugs and turned t' intake cones from 3/16" dowel. They are a little less than ½" long with only t' front 1/8" exposed. Begad! I trimmed some scrap balsa t' make t' stand-offs and positioned t' usin' t' full sized plans and me eyeballs.
I found some 3/16" x 1/8" balsa stock and cut a 4 5/8" section for t' electrical conduit that runs along t' top o' t' rocket. Avast! This be shaped by hand, and a notch was cut out t' let it slide over t' aft stabilizer. Avast! (I messed up and made it about 1/8 too short, an error that wasn't noticed until is was glued on).
Micromister also provided t' CG for a stable Bomarc, and I scaled that measurement for this model. It turned out that t' CG should be 4.25" from t' tip o' t' nose. Aye aye! Mine was way off - hmmm, how t' add weight t' this small balsa cone? I decided t' add a section o' motor casin' t' t' nose cone's shoulder and epoxy in some lead shot. Ahoy! Avast, me proud beauty! I left about 1/8" o' t' dowel hangin' out o' t' balsa cone, me hearties, which served t' align t' casin' with t' shoulder. Begad! I cut a ½" piece o' casing, trimmed t' outer paper, matey, added some lead shot, ya bilge rat, me hearties, ya bilge rat, and capped t' end with tape. Arrr! T' CG be now about right, ya bilge rat, and I took t' model t' t' post office t' weight it. Well, blow me down! Aye aye! It came in at 0.50oz (14.17g), which should make for a low flight. Blimey! Well, arrr, blow me down! I then set t' lead shot and t' twine in some epoxy, ya bilge rat, and attached t' nose weight assembly onto t' cone.
I approximated t' scale color scheme presented on t' plans. I started with white primer, and then masked and hand-painted t' black, silver, and brown areas. Avast, me proud beauty! Blimey! T' stripes on t' front were made with thin strips o' white label material (adhesive paper). Avast, me proud beauty! Blimey! I haven't come up with any decals.
Flight:
I used a 12" piece o' Teflon plumber's tape as a streamer and a small ball o' tape as wadding. GSE included t' guts o' a stock igniter, me Pratt GO-Box, and t' rod from t' MicroMaxx starter kit. Begad! Blimey! T' microBomarc flew off sideways, attainin' an altitude o' about 5 feet before impactin' t' side o' me SUV.
Summary:
On t' plus side, me bucko, me bucko, shiver me timbers, this is a nice lookin' semi-scale model o' t' Bomarc. Avast, me proud beauty! T' composite fins turned out very nicely and I will consider this technique for other models.
On t' minus side, arrr, it is too heavy, matey, me bucko, but t' motor mount and ramjets could both lightened. Avast! Avast, arrr, me proud beauty! I want t' avoid addin' more nose weight if I can. Well, blow me down! Since t' trajectory be straight, if nay in an upwardly direction, shiver me timbers, I will try it again with a longer, ya bilge rat, stiffer rod.
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