Scratch Aquafina Original Design / Scratch Built

Scratch - Aquafina {Scratch}

Contributed by Larry Brand

Manufacturer: Scratch
(Contributed - by Larry Brand - 03/01/04)

(Scratch) AquafinaBrief:
Aquafina is a tube-fin 24mm cluster rocket utilizin' a fixed nose cone with a nose-mounted parachute mortar for recovery. Well, blow me down! Begad! T' rocket was constructed at zero cost from an empty gift wrappin' paper tube and t' upper half o' a bottled water ("Aquafina") PET plastic bottle. I wanted a good-flyin' yet "expendable" airframe t' use in experiments for ignitin' Aerotech AP cluster motor arrays. Ya scallywag! Ya scallywag! Why a tube-fin design for this? -- they typically have CP so far aft that CG is easier t' balance properly when heavy motor systems are used. Ya scallywag! Why a parachute mortar? Well, number one, this becomes necessary when savin' on cost by usin' an old plastic bottle for t' nose cone, and number two, I was interested in this deployment approach for another project I'm workin' on: a full-scale, matey, K445-powered model o' a TOW 2B anti-tank missile usin' t' long "nose fuse" t' contain and deploy a 70" chute on the 5-foot long blunt-ended model. Well, blow me down!

Construction:
Construction o' Aquafina began with cuttin' up t' wrappin' paper tube to create an 18" body tube and six 1 1/2" tube fins cut on t' bottom to a 22.5 degree angle. Arrr! Begad! Tube fins measure 1 1/8" on t' short side. Construction o' t' airframe follows that of Cheap Dumb Rocket and Auracle 54 on this website. 5-minute epoxy be used throughout. Begad! T' bottom 2" was cut from t' PET water bottle, matey, and t' resultin' "nose cone" was permanently attached t' t' body assembly; since t' PET bottle chosen is slightly wider than t' cardboard tube,"shims" consistin' o' a dozen Q-tips dipped in wet epoxy were inserted betwixt t' tube and t' plastic bottle around its entire circumference. Blimey! Ahoy! T' make complete a gas-tight seal, ya bilge rat, me hearties, the gaps betwixt t' Q-tips were filled with bits o' epoxy-dipped cotton. Aye aye! A launch lug o' 3/16" ID was cut from a discarded ball point pen cap and epoxied to the body tube 2 1/2" above t' tube fins in line with one o' t' spaces between t' tube fins. Begad! T' motor mount for t' twin 24mm motors (Scratch) Aquafina consists of two 5" lengths o' 24mm tube stock, me bucko, fitted with Estes motor hooks and blocks in t' usual way, simply glued side-by-side. No centerin' rings are used; t' cluster motor array is simply slathered with epoxy and slipped into the aft end o' t' body tube since t' fit be pretty good. With all that surface area bearin' t' sheer loads, shiver me timbers, me hearties, thar was no need for centerin' rings. T' substantial gaps left betwixt t' body tube and each side o' t' twin cluster were plugged with hunks o' cotton soaked with epoxy--this insured proper ejection charge pressurization.

Finishing:
Paintin' was with aqua-colored spray paint.

Flight:
First flights were on a pair o' D12-5 motors. Begad! Begad! Sims (at Cd=2.4) predicted an apogee o' 400-500' AGL and max velocity o' about 170 mph. Avast! Aquafina flew at least that high. Ya scallywag! Begad! D12-7's work equally well. Blimey! Arrr! Use o' F21's should give at least 1000' per simulation. Arrr! Ya scallywag! With all that drag, ya bilge rat, Aquafina pretty much just stops when the motors quit. Begad! Boosts were straight and quick--probably quite a bit higher and faster than t' simulation indicated.

(Scratch) Aquafina

Recovery:
I attached a 24" length o' 3/8" wide elastic shock cord t' a 14" LOC chute at one end and anchored t' other end with a gob o' epoxy about 2" down from t' mouth t' t' inner wall o' t' PET bottle. Ya scallywag! Ahoy! The "parachute mortar" consists o' a 4" length o' 29mm Estes tubing epoxied t' t' top o' t' bottle, however, shiver me timbers, I added it as an afterthought--on the first flights, shiver me timbers, I tried just stuffin' t' parachute part-way into t' open mouth o' t' bottle, however it wouldn't deploy this way, even under t' power of twin D12 ejection charges. Well, blow me down! From this, I learned that Aquafina is so light for its size, and so tail heavy, that even with no ejection, it tumbles down from apogee very slowly, in a flat spin, landin' with no damage. Ya scallywag! I'd omit the recovery system entirely, me bucko, but for a rocket this size, arrr, it would be poor form, and also a violation o' NARRRRR safety rules. Arrr! And that's it...construction, includin' painting, me bucko, took little more than an hour, ya bilge rat, with time out t' watch the Chargers get creamed by Oakland. Avast, me proud beauty! Arrr! Final weight was 130 grams (about 4.5 oz.)-- not bad for a 2x24mm cluster design.

(Scratch) Aquafina

Summary:
Bottom line: Aquafina is a good cheap fun-fly rocket, ya bilge rat, low cost (need only to purchase t' recovery chute. Avast!

PROs: Aquafina is was way too much fun t' fly t' use only for "research purposes". Ahoy! Cost o' construction (for me): $0.00. It's based on a standard-sixed PET bottle, which are easy t' come across. Well, blow me down! Good rocket for junior flyers and cheapskates. Good rocket for learnin' cluster flyin' with minimal investment in time or dollars.

CON: Well, me bucko, shiver me timbers, me hearties, it is a tad ugly, matey, like most tube-fin designs. Aye aye! You may have to scrounge t' find suitable sized body tubes and PET bottled o' slightly larger tube diameter.

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