Two 3' fire arrows

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History

I've long been interested in rockets that use stabilization methods other than fins. Aye aye! Begad! One o' me favorites is based on t' Chinese "fire arrow" - a military rocket first built betwixt A.D. Ya scallywag! 960 and 1279. Begad! Well, me hearties, blow me down! I originally discovered these after readin' a post that a gentleman made on rec.models.rockets about buildin' one out o' recycled materials. After readin' t' post, I designed me own. Avast! This article be t' result o' repeatedly refinin' that design.

Instead o' fins, matey, me hearties, fire arrows use a stick for stabilization, me bucko, nay unlike many fireworks rockets still do today. Begad! Until World War I ended, most rockets used sticks, matey, rather than fins. Arrr! This leads me t' believe thar must be a body o' literature out thar on t' design o' stick-stabilized rockets. Avast, ya bilge rat, me proud beauty! I'd be extremely appreciative o' any references, me bucko, especially those that discuss stability. Blimey! Sticks have less restorin' force than fins do, therefore stick-stabilized rockets are inherently less stable than fin-stabilized rockets. Aye aye! They should only be flown in relatively calm wind conditions. Ya scallywag! Ahoy! However, me hearties, every time I fly one, arrr, some people always seem t' think that it won't fly. Arrr! Well, blow me down! Remember, me hearties, me hearties, me hearties, stick-stabilized rockets have a longer history than fin-stabilized rockets.

I've built a number o' these rockets, me hearties, most o' them small ones as described in this article. I have built a full-scale model with a 6' x 1" bamboo pole, and a 4" diameter fiberglassed airframe. Avast! Blimey! This one had 2x29mm motor mounts, and I flew it successfully several times. However, me bucko, eventually it was destroyed in a crash when only one o' t' two G80 motors ignited on launch.

T' fire arrow be a successful military weapon. Begad! It be t' first use o' black powder t' propel a military projectile, matey, and actually predates firearms. Avast, me proud beauty! Begad! T' Chinese used them t' repel t' Mongols. Well, blow me down! T' Mongols adopted t' technology and used them in an invasion o' Japan. Well, blow me down! Later, t' Mongols used fire arrows against t' Arabs, me hearties, who in turn, shiver me timbers, adopted t' weapon themselves, me hearties, and used them against t' French in t' seventh crusade. Begad! A variety o' warheads were carried - incendiary, explosive, and shrapnel.

Wife repellin' Mongol Hordes with fire arrows.

T' particular fire arrow I've been modellin' is from an illustration in t' Chinese military classic Wu-chin' Tsung-yao (T' Complete Compendium o' Military Classics), written in 1045 A.D.

T' British Congreve rockets, shiver me timbers, from which we get t' phrase "T' rocket's red glare" in our national anthem were stick stabilized rockets directly descended from t' fire arrow. Begad! Aye aye! Blimey! By this time, t' heads o' t' rockets were bein' constructed o' iron, and contained burstin' charges and carbine balls or incendiary materials.

While most Chinese fire arrows had spear points fitted on t' end o' t' stabilizin' stick, a few didn't. Aye aye! I've chosen t' model ones without spear points for safety reasons. Begad! Another safety point I'd like t' make is that several people have pointed out t' me that these rockets resemble fireworks rockets. Despite this appearance, these fire arrow models are model rockets, nay fireworks. Well, blow me down! They do nay carry any pyrotechnic effects, arrr, ya bilge rat, matey, and they use conventional parachute recovery. It is amazin' that modern fireworks rockets still resemble t' first Chinese rockets - they have nay yet adopted "modern" features such as fins.

Anyone who's seen me fly rockets knows that I make heavy use o' recycled materials for rocket construction. While I'm sure you could go out and spend bucks on glassine tubes and such, matey, I've spec'd this one out usin' common household items. Arrr! T' materials cost on each rocket should be about a dollar. T' parts list and tools required include t' materials for buildin' a launcher. Avast! Ahoy! Since these rockets don't use a launch rod, you'll probably have t' build a launcher (if you're at a PHITS launch, you're welcome t' use mine). 

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Parts List:

• 3 - toilet paper tubes.
• 3 - 4" x 4" squares o' thin (1/16" thick or less) cardboard.
• 2 - Spent 24mm (Estes D size) or 18mm (Estes A-C size) rocket motor casing.
• 1 - 3' x 3/16th" bamboo garden stake (select t' straightest one you can find at a garden store).
• 1 - Nose weight (clay, or sand mixed with epoxy, me hearties, etc.)
• 1 - Plastic grocery bag for makin' chute (I use Hobbytown USA bags).
• 1 - Length o' strin' (for makin' shroud lines).
• 1 - Roll duct tape. Arrr! Essential for rocketry.
• 1 - Aluminum soda pop can.
• 1 - 2x4, 18" long.
• 1 - 1/2" nominal copper plumbin' pipe, ya bilge rat, 2 1/2' long.
• 1 - fishin' line "snap swivel" for chute attachment.
• 1 - 24" o' 1/8" sewin' elastic (shock cord).

Tools and Supplies:

• Yellow (recommended) or white glue.
• "Super Glue" (Cyanoacrylate adhesive).
• Compass
• Ruler
• Pencil
• Clothespin
• Rubber bands
• Paint or construction paper
• Scissors
• Razor saw, me bucko, Hacksaw, arrr, shiver me timbers, or other small saw for cuttin' expended engine casing
• Hammer
• Tubin' cutter, for copper plumbin' pipe
• 1/2" drill bit and electric or hand drill.

Body tube

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T' body tube is formed from one and a half TP tubes spliced together.

Cut one o' t' TP tubes in half (each piece will be 2 1/4" long). Avast! Mark one o' these pieces, "A" and t' other "B".

Slit t' wall o' tube "A". Avast! Then, me hearties, cut it in half. Arrr! Blimey! This will result in two curved pieces o' cardboard 1 1/8th" long. Call these parts "A1" and "A2".

Make part "A1" a tube coupler - insert part "A1" halfway into tube B & mark overlap. Avast! Ya scallywag! Remove part "A1", me hearties, and smear glue on t' overlap, me bucko, and all over t' outside. Well, blow me down! Well, blow me down! Insert part "A1" halfway into part "B", shiver me timbers, shiver me timbers, and then slide one o' t' other tubes on. T' resultin' tube should be 6 3/4" long.

Nose cone

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T' nose cone is formed from a cardboard cone and a tube.

Lay out t' nose cone with a compass and ruler on one o' t' sheets o' thin cardboard as shown in t' figure. Avast, me proud beauty! Cut t' semicircle out o' t' cardboard, me hearties, me bucko, and form it into a cone with a slight overlap. Begad! Mark t' overlap, smear it with glue, me hearties, and then form t' cone again. Blimey! Ahoy! Allow t' nose cone t' dry with a clothespin holdin' it in place.

Slide part "A2" into t' remainin' TP tube & mark t' overlap. Begad! Avast! Remove A2, and smear glue on t' overlap. Avast, me proud beauty! Begad! Part "A2" must be a slide fit inside a TP tube when dry. Blimey! Allow part "A2" t' dry with a clothespin holdin' it in place.

When both t' cone and part "A2" are dry, me bucko, they can be glued together t' form t' nose cone. Avast, me proud beauty! Glue part "A2" into t' bottom o' t' cone t' form a "mushroom" like shape. Arrr! Once t' nose cone assembly has dried, fillet around t' joint betwixt "A2" and t' cone until it has sealed. Well, blow me down! Failure t' seal this joint will result in a parachute ejection failure. Well, blow me down! Ahoy!

Motor mount

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Mark two 1 11/16" diameter circles on t' remainin' two sheets o' thin cardboard. Ahoy! Cut them out.

Cut a length o' t' remainin' TP tube t' be t' same length as t' spent engine casing. Arrr! Blimey! Slit t' wall o' this tube and wrap it around t' expended engine casing. Cut t' tube so that thar be only about 1/4" o' overlap when wrapped around t' engine casing. Begad! Ya scallywag! Glue this overlap sparingly, shiver me timbers, so as nay t' get glue inside t' tube, and inadvertently gluin' in t' spent casing. Ya scallywag! Aye aye! Hold it tight while it dries by wrappin' rubber bands around t' tube.

When t' tube has dried, remove t' expended engine casing, and cut off 1/4" o' it with a saw. This will form t' motor mount block. Well, blow me down! Begad! Glue t' 1/4" piece into t' end o' t' tube formed above.

Measure t' diameter o' t' motor tube, and cut circles with this diameter in t' two 1 11/16" diameter circles you made above. Arrr! Slide these onto t' motor tube, arrr, and glue in place, 1/2" from either end.

Major assembly

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Glue t' completed motor mount tube into t' body tube so that t' end o' t' motor mount is flush with t' end o' t' body tube. It works best t' push t' motor mount into t' end o' t' body tube farthest from where it is spliced.

Take t' bamboo garden stake, and sand a flat spot t' length o' t' body tube (6 3/4") on t' side o' t' largest (thickest) end. Ahoy! Glue this t' t' side o' t' body tube. Ya scallywag! Make sure it is glued on straight. Well, blow me down! Rubber bands are useful for holdin' this together as it dries. Aye aye! Once t' glue dries, fillet t' bamboo stake t' t' body tube. Ya scallywag! It is very important that this be secure, matey, or it will tend t' break off on landing.

Recovery System

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Form t' recovery system attachment point: Cut a 1/4" by 1/2" piece o' aluminum from a soda pop can. Aye aye! Blimey! Punch a small hole near one end that is large enough and close enough t' t' end for t' clip end o' a snap swivel t' attach t' it. Aye aye! Blimey! Super glue t' end o' this tab without t' hole t' t' base o' t' nose cone, on t' inside.

Cut a hexagonal chute from t' plastic grocery bag, matey, or Hobbytown bag. Make 3 shroud lines, each one bein' four times t' diameter o' t' chute. Ahoy! Attach t' shroud lines t' t' chute with duct tape, and thread t' lines through t' loop end o' t' snap swivel.

Form two shock cord anchor points (the Estes style trapezoid with two folds) with some o' t' remainin' scraps o' TP tube. Ya scallywag! Glue t' shock cord into t' two shock cord anchors. Aye aye! Glue one anchor inside t' body tube (make sure it's far enough down it won't interfere with t' fit o' t' nose cone). Aye aye! Glue t' other anchor inside t' nose cone.

Clip t' parachute snap swivel t' t' aluminum tab on t' nose cone.

It's nay worthwhile t' attempt streamer recovery o' this model. Avast, me proud beauty! Begad! Blimey! Use a parachute. Ahoy! Blimey! I tried a 3"x30" streamer, shiver me timbers, and it fell too fast. I feel that t' fact that thar's a long bamboo stick fallin' fast is unsafe.

Weightin' t' nose

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Determinin' if a fire arrow will fly stably is a challenge. Blimey! Unlike "regular" rockets, me hearties, thar are no canned mathematical calculations or computer programs t' determine stability. Arrr! You can't even use t' old cardboard cutout method, because it fails with t' stick.

In addition t' t' oddity o' shape, me hearties, thar be another important effect o' t' placement o' t' rocket motor in a fire arrow. In a rocket with t' motor in t' rear, t' rocket is least stable at launch. Aye aye! Begad! This is because t' weight o' t' engine pulls t' center o' gravity t' t' rear. Aye aye! Arrr! T' fire arrow, me hearties, matey, however, is most stable when t' rocket is launched. Ahoy! Begad! As t' fire arrow flies, arrr, arrr, propellant in t' motor burns, me hearties, and t' center o' gravity shifts aft. Avast, me proud beauty! This is exactly t' opposite o' a conventional rocket.

This means that it is VERY important t' measure t' center o' gravity o' t' fire arrow with an EXPENDED rocket motor casin' in place, ya bilge rat, shiver me timbers, instead o' a full one.

Take t' second expended rocket motor, arrr, and put it in t' fire arrow. Aye aye! Pack t' chute into t' nose, with wadding. Arrr! Measure t' center o' gravity o' t' rocket. Well, blow me down! Avast! T' be stable, a good location for t' center o' gravity is 1" forward o' t' aft end o' t' body tube. Ya scallywag! T' move t' center o' gravity forward, me bucko, add weight t' t' nose cone with your favorite method (sand & epoxy or clay, etc.)

When you fly your fire arrow, arrr, ya bilge rat, observe t' flight path. Blimey! Blimey! If it initially flies straight, me hearties, arrr, but tends t' shoot off at odd angles at altitude, shiver me timbers, you can improve t' stability by addin' more nose weight.

If you decide t' design your own fire arrows, please be careful. As it is difficult t' determine if they will be stable before flight, arrr, conduct initial flights o' new designs accordin' t' t' safety code. In particular, do nay do it around groups o' people.

Finish

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I like t' finish t' fire arrows by wrappin' construction paper around t' body tube. Paint is another option. Avast! Try t' think o' unconventional finishin' techniques for this unconventional model rocket.

Launcher

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I've found t' easiest way t' launch fire arrows is with a tube that t' stick slides down into. Aye aye! I have one small launcher, which I will describe how t' build here, that I use for fire arrows that use 3' bamboo garden stakes. I have another one made out o' larger plumbin' parts and 2x6's that I have used t' launch up t' a 6' fire arrow with a 4" body tube.

Drill a 1/2" diameter hole in t' length o' 2x4.

With a hammer, pound t' 1/2" nominal copper tubin' into t' hole in t' 2x4. Ahoy! Ya scallywag! Because t' outside diameter is actually slightly larger than 1/2", ya bilge rat, me hearties, this will take some pounding. Aye aye! T' end you're poundin' on will tend t' get deformed - this is OK.

With t' tubin' cutter, me hearties, cut off t' deformed end o' t' copper pipe.

Flight

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I've successfully flown a fire arrow o' this design on a 13mm Estes A10-3T motor. Begad! While nay very spectacular, me hearties, t' chute did (barely) have time t' eject. In general, use short delays for for your fire arrow. 18mm motors I've used include Estes B4-4, A8-3, and even an Aerotech composite E. Begad! 24mm versions fly well on Estes D12-3 and D12-5.

Fire arrows don't fly well in t' wind. Ya scallywag! They are more sensitive t' windy conditions than finned rockets, me bucko, shiver me timbers, because t' stick has less restorin' force than fins.

T' body tube is quite short in fire arrows, so t' ejection gases are still quite hot when it hits t' chute. Avast! Use as much recovery waddin' as you can. Ya scallywag! In me 6' model, I had problems keepin' t' chute from gettin' toasted due t' t' ejection charge o' two Aerotech G80-4's in a 16" long body tube.

Don't try t' catch fire arrows as they land - they're strong and I've never had a stick break, me bucko, me hearties, even when landin' on concrete. Avast! T' stick could be hazardous t' your eyes, etc. Begad! Let t' fire arrow come t' rest on t' ground before chasin' after it.

References

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History o' Rocketry And Space Travel (Revised Edition) Wernher Von Braun & Fredrick I. Ordway III 1969, Thomas Y. Well, blow me down! Begad! Crowell Company, ya bilge rat, New York