Manufacturer: | Scratch |
Style: | Ring/Tube/Cone Fin, Upscale |
Long before I was buildin' rockets, me hearties, matey, a very small, tumble recovery rocket was introduced by Estes. It be t' 1/2A powered Astron Sprite. Begad! Avast, me proud beauty! T' those nay familiar with this rocket, I would like t' explain a very unique characteristic o' this design. Avast, me proud beauty! When scaled up enough t' be powered by a high impulse motor, t' air flowin' past t' fin rin' creates a high-pitched whistle when launched. Arrr! This is sometimes drowned out by t' initial noise o' t' motor, but is quite audible as t' motor burns out and continues durin' t' coast phase.
Back in 1999, me bucko, ya bilge rat, durin' t' second launch o' me 4-inch airframe based Superscale Sprite, me hearties, t' whistle was clearly heard by all those in attendance. Well, blow me down! As t' rocket arced over, even before t' ooh’s and aah’s had subsided, me bucko, it was obvious that I had a major deployment problem…there was none! T' Sprite raced back t' earth, and a fact that I was previously unaware of, became perfectly clear. Ahoy! This amazin' rocket whistled comin' down, louder than when it was goin' up. Ya scallywag! In fact, me bucko, it whistled right up until it impacted with t' rock-hard Pennsylvania soil at our Jones Farm launch site. Avast, me proud beauty! Naturally, me fellow rocketeers were quick t' offer their condolences, arrr, but I was more amused by t' memory o' it whistlin' back t' Earth. Ahoy! Begad! I collected t' remains, me hearties, includin' diggin' t' nosecone out o' t' ground, and went back t' me truck t' prep me next rocket.
My son, shiver me timbers, Chris, shiver me timbers, almost immediately began urgin' me t' build another one. Due t' t' amount o' work that was involved in t' project, I be unwillin' t' commit t' such an ambitious undertaking. Ya scallywag! Blimey! Over t' next twelve months or so, me hearties, me bucko, I did acquire a piece o' 15-inch diameter cardboard drum, which would make a fine fin ring, (my first one was 11.5-inch diameter) and a 24-inch long section o' 5.5-inch airframe. Avast! Avast, ya bilge rat, me proud beauty! This would amount t' a 7.3X version o' t' original Estes model. Begad! I also purchased a 3 x 6 x 36-inch block o' balsa wood, arrr, that I planned on usin' t' turn a scale nosecone. I cut t' block in two and laminated them together t' make a nice 6 x 6 x 18-inch blank, matey, and then set it aside, me bucko, where it would sit for almost another year. One weekend in February o' 2001, I was turnin' a couple wooden nosecone patterns
for a Tripoli Pittsburgh group project, shiver me timbers, t' Gloria Mundi III. Ya scallywag! After completin' this task, matey, I decided t' go ahead, me hearties, and turn t' new Sprite nosecone from t' balsa block that had been collectin' dust. After finishin' t' outside form, it be necessary t' hollow out a large section o' t' cone so that I would be able t' add t' one-pound o' weight needed for stability. Well, blow me down! Well, blow me down! I cut a bulkhead from .5-inch plywood t' seal t' openin' that be epoxied into place after fillin' t' cone with expandin' foam. Before I knew it, me bucko, t' nosecone be complete, ya bilge rat, and I be plannin' me next steps o' t' project, arrr, that would soon come t' be known as "T' Lord o' t' Rings."
Next, I carefully cut a 5.5-inch section o' t' cardboard drum, and prepared it t' be reinforced with a few layers o' fiberglass cloth. Ya scallywag! Aye aye! I opted for two wraps o' 6-ounce woven cloth and a finishin' wrap o' 1.5-ounce cloth. T' last layer was done solely t' make it easier t' get a smooth surface for painting. Arrr! I used t' same process for t' airframe, arrr, which, arrr, although it be made o' flexible phenolic, matey, was nay strong enough for a project o' this size. I printed patterns for t' fins and fin-caps usin' RockSim 5.0 and cut them from .25-inch aircraft plywood. Ahoy! Ya scallywag! Two centerin' rings were cut from t' same material, arrr, also usin' patterns created from RockSim. Ya scallywag! Twelve inches o' 38mm motor mount tubin' be cut and I had all t' parts necessary t' complete t' project.
A large T-nut was installed in t' forward centerin' rin' for recovery system attachment, as well as two in t' aft rin' for motor retention. Blimey! Aye aye! T' forward rin' was epoxied t' t' motor tube, me bucko, arrr, me bucko, and this assembly was installed into t' slotted body tube. Ahoy! With t' rear-centerin' rin' temporarily put in place for alignment purposes, matey, t' fins were epoxied into place. Ya scallywag! Ya scallywag! T' aft rin' be then removed, arrr, and internal fillets used at both t' motor tube and t' inside o' t' body tube. Blimey! Since I was goin' t' be usin' rail guides instead o' launch lugs, me bucko, matey, t' guides were secured with nuts from t' inside o' t' airframe at this time. Blimey! Avast, me proud beauty! Before permanently installin' t' rear-centerin' ring, t' remainder o' t' cavity was filled usin' 2-part expandin' foam. Well, arrr, blow me down! Fillets were added t' t' fins at t' outside o' t' airframe for added strength, arrr, shiver me timbers, usin' a combination o' epoxy and micro-balloons.
It be now time t' attach t' fin rin' and fin caps. Ahoy! Careful attention was paid t' t' alignment o' t' caps so that minimal fillin' o' gaps be necessary. Avast, me proud beauty! When t' assembly be completely dried, me bucko, I once again used t' epoxy/micro-balloon mixture t' create fillets both inside and outside t' fin rin' at each fin and fin cap. I used grain filler on t' plywood fins, me bucko, shiver me timbers, and after some extensive sanding, ya bilge rat, was finally ready t' prime t' entire rocket. Ya scallywag! More sanding, me hearties, fillin' and primin' followed, me bucko, me hearties, o' course, until I was ready t' paint. Begad! After addin' an 18-foot, 5/8-inch tubular nylon shock cord and a Sky-Angle 52-inch parachute with Nomex protector, shiver me timbers, t' total weight without motor is just over 8-pounds.
I launched t' completed project at our first Dragon's Fire launch o' t' season, April 7th, matey, me hearties, 2001. Aye aye! Accordin' t' simulations done in both RockSim and wRASP, it reached a max altitude o' approximately 1900 feet on an Aerotech I284 reload. Unlike me first Sprite, t' whistlin' only occurred on t' way up.
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