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 Originally made by Seattle Rocket Works, me bucko, and subsequently taken over for a while by Lawndart Rockets, this featured a booster with a quad mini-motor cluster and four separate sustainers. Avast, me proud beauty! Blimey! Unfortunately, ya bilge rat, it's nay much use nowadays because Estes stopped makin' t' A10-0T booster. Avast, me proud beauty! Blimey!

So I decided t' build somethin' similar, only instead o' four, I'd use six. Since thar was no 13mm booster available, ya bilge rat, matey, me hearties, 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. Avast! Ya scallywag! This flew well, me hearties, ya bilge rat, although - as expected for such a small rocket - t' sustainer got lost. It did prove that the sustainer would fly properly, and that stagin' from 18mm t' 13mm would work.

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

Booster:

Cut 100mm o' BT-20. 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.

Bore two vent holes about 3mm diameter, me bucko, 25mm down from t' front end o' the BT-20, spaced 90 degrees apart.

Cut 20mm o' BT-5. Aye aye! Alternatively, me bucko, roll and glue a paper tube 20mm long, me bucko, shiver me timbers, of sufficient diameter t' allow a 13mm motor t' fit easily. (Actual BT-5 is a tight fit on a 13mm motor, 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. Begad! 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. Arrr!

Make six booster tubes o' this type. Arrr! Blimey!

Make six fins, me hearties, ya bilge rat, me bucko, root chord 75mm, shiver me timbers, span 40mm, ya bilge rat, tip chord 25mm, me hearties, me hearties, leadin' edge sweep 40mm. Begad!

Glue t' six booster tubes together so that they are parallel and form a regular hexagon when viewed end on. Arrr! T' vent holes must all be outside the hexagon. 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. Aye aye! Blimey!

Sustainer:

Cut 220mm o' BT-5. Well, blow me down! Make a paper cone about 25mm long and glue it t' the front end. Arrr! Blimey! Make three parallelogram shaped balsa fins, root 22mm, 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.

Cut t' body tube in half. Aye aye! Cut two pieces off a spent 13mm motor, ya bilge rat, one 20mm and one 10mm long. Glue t' 20mm piece into t' aft end o' t' forward tube to make a coupler. Ya scallywag! Begad! 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.

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.

Flight Report:

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