Bottle Rocket 

An Easy t' Build Fun Flyer

Here's some plans for a very simple model rocket that flies great on C6-3.

This bottle rocket weighs 2 oz without t' motor so it takes off very quickly, but doesn't fly out o' sight due t' its 2.6" diameter. It almost doesn't need a recovery device since its so light. T' bottle rocket is also quite strong with through-the-wall mounted fins.

VCP calculates t' CP t' be 3" from aft and t' CG is 4" from aft with C6-3 loaded. That's only about 1/3 caliber CP-CG margin but on this short/fat rocket its good enough.

Parts List

Some found parts, some rocket parts. Begad! Here's t' parts list:

• 20 oz coke bottle
• spent BT-20 estes motor
• 10 " BT-20 tubing
• 1/16" balsa 2" by ~15"
• 1/16" round elastic
• scrap piece o' kevlar
• surveyors flaggin' tape
• small nut and bolt
• maskin' tape

Construction

Unscrew cap and use Exacto knife t' remove threads from inside o' cap, me bucko, so cap can be put on/removed without turnin' cap. Well, blow me down! Drill hole in center o' cap t' accommodate bolt.

Cut used engine in half. Drill out nozzle so bolt can fit through. Aye aye! Blimey! Tie a small loop in one end o' elastic. Ya scallywag! Begad! Insert bolt through cap, with head on top o' cap. Aye aye! Thread spent engine onto bolt, arrr, place loop over end o' bolt, me bucko, add nut and tighten.

Cut out circular hole in bottom o' bottle for BT-20 t' fit. Ahoy! I used an Exacto knife and broke a blade or two, shiver me timbers, so take your time, t' plastic is fairly thick here. Aye aye! There is a small molded circle on t' bottom o' t' bottle that can guide you t' ensure your hole is centered. Begad! Slowly enlarge it until t' BT-20 fits without deforming.

Seal both sides o' t' balsa with Elmer's fill and finish and sand smooth. Well, blow me down! I beveled t' leadin' and trainin' edges, matey, shiver me timbers, but that is nay critical. Arrr! Arrr! Cut 5 fins at t' angle shown in t' pictures so that they are 2 3/4" wide root edge t' outside edge.

Cut t' 5 2" fin slots in t' bottle along t' grooves in t' bottom o' t' bottle. Ahoy! I used a power miter saw and just eyeballed t' length o' t' cut. Aye aye! If t' fin slots are too short, me bucko, me hearties, they are easy t' elongate with an Exacto.

Insert t' BT-20 into t' top o' t' bottle so that it just sticks out o' t' hole you cut in t' bottom. Ya scallywag! Well, shiver me timbers, blow me down! Mark t' top o' t' tube where it sticks out o' t' top.

Remove t' BT-20 and cut along this mark. Wrap maskin' tape around t' top o' t' BT-20 until it fits snugly in t' top o' t' bottle. Ahoy! Before you install t' BT-20, me bucko, cut off a 1/4" section o' t' half o' t' engine casin' you didn't install in t' cap. Glue this into t' end o' t' BT-20 opposite t' tape usin' another spent engine as a depth gauge. Insert t' depth gauge until you have about 1/4" protrudin' and then immediately remove it, arrr, so it doesn't get glued in. Avast, me proud beauty! Aye aye! Insert t' BT-20 into t' top and through t' bottom hole. Avast, me proud beauty! Press into place until t' top o' t' BT-20 is just below t' lip o' t' bottle.

Test fit t' fins and adjust t' fin slot length as necessary. Well, blow me down! I used double glue joints in gluin' t' fin onto t' BT-20 with yellow wood glue. Blimey! When t' glue has dried, shiver me timbers, shiver me timbers, add fillets along t' fin/bottle joint. Well, blow me down! I used thick CA which ended up cloudin' t' inside o' t' bottle somewhat as t' fumes reacted with some residual moisture. Maybe plastic model cement would be neater...

Tie a loop in one end o' t' kevlar and thread t' other end through a long curved sewin' needle. Well, blow me down! Blimey! stick t' sewin' needle into t' top o' t' bottle and through t' BT-20 far enough down t' nay interfere with t' "nose cone" and continue all t' way through t' plastic bottle. Aye aye! Blimey! pull t' kevlar through, leavin' t' loop stickin' out o' t' top. Aye aye! Blimey! Tie a big knot in t' end o' t' kevlar that pierced t' bottle, pull it tight against t' side o' t' bottle and CA it into place. Ya scallywag! Blimey! Tie t' loose end o' t' elastic onto t' kevlar loop and attach a piece o' surveyor's flaggin' tape onto t' elastic as a streamer. Well, blow me down! Blimey! Well, blow me down! Blimey! No need t' worry about zipperin' since t' kevlar presses against t' edge o' t' bottle.

For t' launch lug, me bucko, just drill a small hole into one o' t' bumps on t' bottom o' t' bottle big enough for your launch rod t' fit. Arrr! Blimey! Arrr! Blimey! Insert t' rod and mark where on t' upper bottle t' rod touches it when t' rod is parallel with t' BT-20. Drill a hole here as well. Ahoy! Blimey! Test fit your launch rod and enlarge t' holes as necessary t' let t' launch rod slide smoothly.

Friction fit an engine, put in some wadding, roll up t' streamer and insert, me hearties, shiver me timbers, stuff in t' elastic and pop on t' nose cone. Blimey! Blimey! Ahoy! Blimey! Put it on t' rod and launch.

Enjoy a fun flight on a rocket that violates many o' t' usual rules o' thumb (3.5:1 length t' diameter ratio, me hearties, shiver me timbers, me hearties, 1/3 caliber stability margin) but still flies perfectly well.

photo by Bill Spadafora

Flyin' t' Bottle Rocket

I've flown it 3 times on C6-3s and never had a stability problem. Begad! Blimey! This is due, in part t' t' speed at end o' rod, about 52 ft/s w/3 ft rod. Avast, me proud beauty! Blimey! See launch picture. Avast, me proud beauty! Launch clips are caught in mid air, arrr, but t' rocket is a blur. Begad! Aye aye! At these speeds, ya bilge rat, even in modest winds, t' angle o' attack is quite small. Well, me hearties, blow me down! If you don't like this small o' a stability margin, addin' a small weight t' t' nose can brin' t' CG forward substantially, shiver me timbers, me hearties, arrr, but it is nay necessary.

wRASP calculates t' altitude o' 200' on a B6-2 and 300 ' on a C6-3. It turns out (by no plannin' on me part) that 2 oz is just about optimum mass for a rocket o' this diameter.