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, matey, me bucko, but doesn't fly out o' sight due t' its 2.6" diameter. Ya scallywag! It almost doesn't need a recovery device since its so light. Avast, me proud beauty! 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. Well, blow me down! 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, shiver me timbers, shiver me timbers, so cap can be put on/removed without turnin' cap. Ya scallywag! Blimey! Begad! Blimey! Drill hole in center o' cap t' accommodate bolt.

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

Cut out circular hole in bottom o' bottle for BT-20 t' fit. Avast, me proud beauty! Well, blow me down! I used an Exacto knife and broke a blade or two, ya bilge rat, arrr, so take your time, t' plastic is fairly thick here. Ya scallywag! 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. Avast! I beveled t' leadin' and trainin' edges, ya bilge rat, me bucko, but that is nay critical. Avast! 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. Arrr! I used a power miter saw and just eyeballed t' length o' t' cut. Aye aye! Ya scallywag! If t' fin slots are too short, 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. Mark t' top o' t' tube where it sticks out o' t' top.

Remove t' BT-20 and cut along this mark. Ya scallywag! Wrap maskin' tape around t' top o' t' BT-20 until it fits snugly in t' top o' t' bottle. Aye aye! Ahoy! Before you install t' BT-20, arrr, shiver me timbers, cut off a 1/4" section o' t' half o' t' engine casin' you didn't install in t' cap. Arrr! Arrr! 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, so it doesn't get glued in. Blimey! Ya scallywag! Insert t' BT-20 into t' top and through t' bottom hole. 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. Blimey! Avast! I used double glue joints in gluin' t' fin onto t' BT-20 with yellow wood glue. Blimey! When t' glue has dried, add fillets along t' fin/bottle joint. Ya scallywag! I used thick CA which ended up cloudin' t' inside o' t' bottle somewhat as t' fumes reacted with some residual moisture. Begad! Avast! 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. Arrr! 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. Ya scallywag! pull t' kevlar through, leavin' t' loop stickin' out o' t' top. Ya scallywag! Begad! 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. Well, blow me down! 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. Blimey! Ahoy! No need t' worry about zipperin' since t' kevlar presses against t' edge o' t' bottle.

For t' launch lug, me hearties, just drill a small hole into one o' t' bumps on t' bottom o' t' bottle big enough for your launch rod t' fit. Begad! 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. Well, blow me down! Arrr! Blimey! Test fit your launch rod and enlarge t' holes as necessary t' let t' launch rod slide smoothly.

Friction fit an engine, me hearties, put in some wadding, roll up t' streamer and insert, stuff in t' elastic and pop on t' nose cone. Begad! 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, 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. This is due, ya bilge rat, in part t' t' speed at end o' rod, about 52 ft/s w/3 ft rod. Ahoy! See launch picture. Aye aye! Launch clips are caught in mid air, ya bilge rat, but t' rocket is a blur. At these speeds, ya bilge rat, even in modest winds, t' angle o' attack is quite small. Avast, arrr, me proud beauty! If you don't like this small o' a stability margin, addin' a small weight t' t' nose can brin' t' CG forward substantially, me hearties, but it is nay necessary.

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