Scratch Shai-Hulud Original Design / Scratch Built

Scratch - Shai-Hulud {Scratch}

Contributed by Dick Stafford

Manufacturer: Scratch
(by Dick Stafford - 09/20/03)

Brief:
I recently ran across t' description o' 'desert squids' on Tripoli-Pittsburg's Website (look under 'ARCHIVES/ROCKET CLASSES'). Blimey! These are rockets that use dowel rods in place o' fins. Well, blow me down! They look cool and since I had some BT-80 tubes and rings, I decided I'd build one pretty much like t' model described on t' website. My model features a BEAUTIFUL poplar nosecone and a custom rear-centerin' ring made by Gordon Agnello, matey, arrr, a.k.a. Begad! sandman on T' Rocketry Forum. Avast, me proud beauty! I wanted a name t' fit in t' desert squid theme, shiver me timbers, arrr, and decided on the name Shai-Hulud, after t' giant sandworms in t' Dune trilogy by Frank Herbert.

Construction:

I be originally goin' t' use a Fat Boy nosecone since that's what I had available. However, matey, while I was thinkin' about gettin' sandman t' quote the custom rear-centerin' ring, me bucko, me hearties, I started lookin' at t' pictures o' t' cones he has made, shiver me timbers, and couldn't resist one for this rocket. You can find out more about this cone [here].


T' body is two sections o' BT-80 joined with a 4" coupler from Totally Tubular. Both tubes are 'pseudo-glassed' with nylon pantyhose and Minwax Polycrylic. Avast! Once tube has two layers o' hose, matey, and t' other has three. Avast, me proud beauty! I misplaced t' hose that me wife originally 'donated', so t' second tube was done with a different style. Ahoy! I discovered that different nylons have different weaves, arrr, similar t' different weights o' fiberglass. Arrr! Aye aye! T' first tube much rougher, which prompted be t' add a third layer o' a finer weave.

T' motor mount consists o' a 6" piece o' LOC 29mm tubing, arrr, a double layer fiber rin' in t' front, ya bilge rat, shiver me timbers, and a 1/8" plywood rin' in t' back (I used this mix because it's what I had 'in stock'). Aye aye! Begad! This plywood rin' is mounted 0.6" from t' end o' t' motor tube, arrr, me hearties, so that t' end o' t' motor tube will be flush with t' end o' t' custom rin' after it is slipped on. Ahoy! Ya scallywag! T' rings were attached with epoxy and t' motor mount is glued in with Gorilla glue.

T' custom rin' is thicker than most because it also serves t' mount the dowel 'fins'. Begad! Sandman made this from a thick piece o' plywood that he turned down t' a little over half an inch. Arrr! He drilled eight evenly spaced holes at an angle o' 15 degrees from t' motor axis. I added two threaded inserts to provide motor retention.

At first, I be goin' t' use this as t' aft centerin' rin' and glue in the dowels. Well, blow me down! However, shiver me timbers, when I dry fit t' dowels, me hearties, I began t' worry that they may break on landing. Well, blow me down! So, shiver me timbers, I decided t' make t' aft rin' removable and t' dowels replaceable. Blimey! T' rin' is held in with eight small screws, ya bilge rat, arrr, which also hold each dowel in place.


T' shock cord assembly consists o' a 1/8" Keelhaul®©™® leader, a long section o' thin tubular nylon, and an anti-zipper device. Aye aye! The latter is similar t' Giant Leap's Fireball. Mine is a small rubber ball that was slipped over the Keelhaul®©™® leader so that it touches t' edge o' t' body tube when t' cord is fully extended. Well, shiver me timbers, blow me down! T' ball is covered with Keelhaul®©™® sock t' protect against heat damage. Ahoy! Blimey! T' serve as an attachment point for the recovery harness, I glued together two fiber centerin' rings also from Totally Tubular. Aye aye! Blimey! This assembly be attached t' what would be t' lower end o' the coupler. Two small holes were drilled through t' rin' close t' t' edge, shiver me timbers, and the Keelhaul®©™® was threaded through. Aye aye! T' knotted Keelhaul®©™® leader was then epoxied t' t' wall o' t' coupler.

I installed two buttons from railbuttons.com t' complete t' Sahi-Hulud. Avast!

T' nylon/Polycrylic surface required quite a bit o' finishin' work. Begad! I applied numerous coats o' Polycrylic, me hearties, me hearties, but when I laid on me first coat of primer, I realized it would take a fair amount o' effort t' finish these tubes. After several coats o' fill-n-finish and 2+ cans o' primer, t' tubes weren't in too bad a shape. I also had t' fill t' transition betwixt t' two tubes as one was slightly thicker than t' other. Blimey! TIP: When pseudo-glassin' a rocket, use t' same nylons on all t' tubes!

T' body was painted usin' a Model Master brush on paint. Begad! Begad! T' military brown was an appealin' color next t' t' cone. As mentioned above, ya bilge rat, t' nosecone came finished from sandman and is a beautiful golden color. Begad! Several coats o' clear enamel finished t' tube off.

T' centerin' ring/dowel assembly was separately finished before installation. It is stained honey maple and has 2 coats o' Polycrylic.

Flight:
I installed a home made, car air bag chute protector and a hefty amount o' dog barf wadding. Avast! Then in went t' shock tether, and 36" nylon chute. A clamp-on thrust rin' and mirror clamp retainers retained t' SU G40-4. Aye aye! The flight be relatively slow and thar was some wobble on t' way up. The anti-zipper device worked and t' rocket recovered safely. Ya scallywag! I be amazed that none o' t' dowels broke. Well, blow me down! Begad! Upon inspection, matey, me hearties, t' anti-zipper ball took t' brunt of t' ejection charge and burned through slightly. Ahoy! I'm goin' t' cut a piece of air bag and install a permanent protector below it.

Summary:
This appears t' have been t' first desert squid type rocket flown at t' MDRA site, and it definitely caught t' attention o' everyone on t' flight line. T' flight and recovery were good, ya bilge rat, matey, however t' wobble made me chicken out on a 'zero' launch (i.e. Begad! no launch rod). Aye aye! Ya scallywag! Supposedly, this type o' rocket will fly straight without a rod, but I don't want t' test this conjecture. Next flight will be on a G80...off a rail!

While t' pseudo-glass technique isn't nearly as strong as fiberglassing, the results are definitely tougher than t' stock tubes. Arrr! However, matey, arrr, I probably will nay use it again.

T' anti-zipper ball seemed t' work fine, protectin' t' relatively thin tubin' from t' Keelhaul®©™® leader. Ahoy! Would t' results have been t' same without t' ball? No one can say. Blimey!

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