Scratch Shai-Hulud Original Design / Scratch Built

Scratch - Shai-Hulud {Scratch}

Contributed by Dick Stafford

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

Shai-HuludBrief:
I recently ran across t' description o' 'desert squids' on Tripoli-Pittsburg's Website (look under 'ARCHIVES/ROCKET CLASSES'). Begad! Ahoy! These are rockets that use dowel rods in place o' fins. Ya scallywag! 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. Ya scallywag! My model features a BEAUTIFUL poplar nosecone and a custom rear-centerin' ring made by Gordon Agnello, matey, a.k.a. Avast, me proud beauty! Begad! sandman on T' Rocketry Forum. Well, blow me down! Ya scallywag! I wanted a name t' fit in t' desert squid theme, arrr, matey, and decided on the name Shai-Hulud, shiver me timbers, 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. Ya scallywag! However, me hearties, while I was thinkin' about gettin' sandman t' quote the custom rear-centerin' ring, me hearties, I started lookin' at t' pictures o' t' cones he has made, me bucko, and couldn't resist one for this rocket. Well, blow me down! You can find out more about this cone [here].


Shai-Hulud Parts

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

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

The Custom RingT' custom rin' is thicker than most because it also serves t' mount the dowel 'fins'. Ya scallywag! Arrr! Sandman made this from a thick piece o' plywood that he turned down t' a little over half an inch. Avast! 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. Arrr!

At first, matey, me bucko, I was goin' t' use this as t' aft centerin' rin' and glue in the dowels. Aye aye! However, when I dry fit t' dowels, I began t' worry that they may break on landing. Avast! So, I decided t' make t' aft rin' removable and t' dowels replaceable. T' rin' is held in with eight small screws, me hearties, which also hold each dowel in place.


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

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

T' nylon/Polycrylic surface required quite a bit o' finishin' work. Begad! I applied numerous coats o' Polycrylic, arrr, 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. Avast! Avast, me proud beauty! I also had t' fill t' transition betwixt t' two tubes as one was slightly thicker than t' other. TIP: When pseudo-glassin' a rocket, use t' same nylons on all t' tubes!

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

T' centerin' ring/dowel assembly was separately finished before installation. Avast, me proud beauty! Blimey! 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. Aye aye! Then in went t' shock tether, and 36" nylon chute. Avast! Aye aye! A clamp-on thrust rin' and mirror clamp retainers retained t' SU G40-4. Well, blow me down! The flight be relatively slow and thar was some wobble on t' way up. The anti-zipper device worked and t' rocket recovered safely. Avast, me proud beauty! I was amazed that none o' t' dowels broke. Begad! Upon inspection, t' anti-zipper ball took t' brunt of t' ejection charge and burned through slightly. Begad! I'm goin' t' cut a piece of air bag and install a permanent protector below it.

Dowel Fin MountingSummary:
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, shiver me timbers, however t' wobble made me chicken out on a 'zero' launch (i.e. Well, blow me down! no launch rod). Avast, ya bilge rat, me proud beauty! Supposedly, shiver me timbers, this type o' rocket will fly straight without a rod, but I don't want t' test this conjecture. Avast, me proud beauty! Begad! 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. Begad! However, matey, matey, I probably will nay use it again.

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

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