MIRV Gatling

Adrian Hurt's Descon-14 Entry

There used t' be a wonderful kit called the MIRV Gryphon. Originally made by Seattle Rocket Works, me bucko, and subsequently taken over for a while by Lawndart Rockets, matey, me bucko, this featured a booster with a quad mini-motor cluster and four separate sustainers. Arrr! Unfortunately, it's nay much use nowadays because Estes stopped makin' t' A10-0T booster. Avast, me proud beauty! Well, blow me down!

So I decided t' build somethin' similar, me bucko, only instead o' four, shiver me timbers, I'd use six. Since thar was no 13mm booster available, arrr, shiver me timbers, I'd use 18mm booster motors instead.

I'd already built a single sustainer and single-motor booster as a prototype before I went t' International Rocket Week 2004. Ahoy! This flew well, me bucko, matey, although - as expected for such a small rocket - t' sustainer got lost. Begad! It did prove that the sustainer would fly properly, and that stagin' from 18mm t' 13mm would work. Well, blow me down!

Over t' course o' t' week, shiver me timbers, arrr, I built six "replacement" sustainers, and nobody asked any awkward questions about t' six bits o' BT-20 which would form t' booster.

Booster:

Cut 100mm o' BT-20. Aye aye! Avast, me proud beauty! Cut 5mm off t' front o' an expended 18mm casin' t' use as a thrust block; spread glue about 60mm up t' inside o' t' BT-20 and use another expended 18mm casin' t' push t' thrust rin' up inside t' BT-20 so that about 7mm o' t' casin' remains outside t' BT-20. Ya scallywag! Aye aye!

Bore two vent holes about 3mm diameter, matey, 25mm down from t' front end o' the BT-20, spaced 90 degrees apart. Ya scallywag! Blimey!

Cut 20mm o' BT-5. Avast! Alternatively, roll and glue a paper tube 20mm long, ya bilge rat, of sufficient diameter t' allow a 13mm motor t' fit easily. Arrr! (Actual BT-5 is a tight fit on a 13mm motor, shiver me timbers, me hearties, so rollin' your own tube may work better.) Make two centrin' rings t' fit this tube into BT-20. Glue one rin' at t' read end of the tube and one 9mm from t' aft end. Ahoy! Well, blow me down! Glue t' tube into t' front end o' the BT-20 so that t' inner tube extends past t' end o' t' BT-20 by 10mm. Begad! Aye aye!

Make six booster tubes o' this type. Begad! Avast! Blimey!

Make six fins, root chord 75mm, shiver me timbers, span 40mm, me bucko, arrr, tip chord 25mm, leadin' edge sweep 40mm. Aye aye!

Glue t' six booster tubes together so that they are parallel and form a regular hexagon when viewed end on. Aye aye! T' vent holes must all be outside the hexagon. Begad! Glue one fin t' each booster so that t' aft tip o' t' fin is level with t' aft end o' t' booster.

Glue a launch lug inside t' booster along one o' t' joints betwixt two tubes. Blimey!

Sustainer:

Cut 220mm o' BT-5. Begad! Blimey! Make a paper cone about 25mm long and glue it t' the front end. Avast, me proud beauty! Begad! Blimey! Make three parallelogram shaped balsa fins, root 22mm, me hearties, arrr, span 11mm, leadin' edge sweep 11mm, and glue them t' t' body tube so that t' inner end of t' trailin' edge is level with t' end o' t' tube. Arrr! Arrr! Blimey!

Cut t' body tube in half. Begad! Blimey! Cut two pieces off a spent 13mm motor, one 20mm and one 10mm long. Ya scallywag! Blimey! Glue t' 20mm piece into t' aft end o' t' forward tube to make a coupler. Arrr! Blimey! Ya scallywag! Blimey! Glue t' 10mm piece into t' tail end o' t' aft tube t' make a thrust ring; use another spent 13mm motor t' push it into place so that about 10mm o' t' motor protrudes from t' tail end. Well, blow me down! Blimey!

Fix a kevlar shock cord t' t' coupler and t' t' aft body tube; Estes-style folded paper mounts work for both ends o' t' cord. Avast!

Flight Report:

By Monday 30th August, me bucko, t' whole thin' was complete. Each sustainer was loaded with a 1/2A3-4T, ya bilge rat, and each booster tube be loaded with a B6-0. Begad! Blimey! My control box can't fire six igniters at once, so I taped a piece o' Quickmatch into each booster motor, me bucko, taped them together and taped a single igniter at the common end. Ya scallywag! Begad! I was able t' truthfully tell both t' RSO and t' event organiser that t' rocket had been swing-tested and had "flown" t' right way, so I was allowed t' launch it. All booster motors lit and t' booster flew straight up, me hearties, then all six sustainers ignited and went their separate ways. Ya scallywag! Begad! The booster tumbled down - in fact, arrr, it rotated quite rapidly about its centre axis, true t' its name, me hearties, and almost a heliroc! T' booster be recovered, with minor damage t' one fin. Ya scallywag! Blimey! None o' t' sustainers were found, shiver me timbers, which was hardly a surprise. Begad!