Rocketry - Model Technical Manual

8/12/2019 Rocketry - Model Technical Manual

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By William Simon Revised 1993 By Thomas Beach and Joyce Guzik

Model RocketryTechnical Manual

www.estesrockets.com


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TABLE OF CONTENTSTopic Pa ge

Why Estes Model Rocketry 3

A Safe Progra m 3

Your First Model Rocket 3

Construct ion Techn iques 3

Types of Glues 3

Fin ishing 6

Stability 7Swing Test For Stability 8

Prepar ing For Flight 8

Ignite r In sta lla tion 9

Launching 9

Coun tdown Checklist 10

Tracking 10

Trackers 10

Recovery Systems 11

Multi-Staging 11

Cluster ing 13

Model Rocket Engines 14NAR Safe ty Code 15

Publica tions back cover

INTRODUCTION

Welcome t o the exciting world of Estes

mode l rocket ry! This tech nical ma nu al was

writt en to pr ovide both a n e as y-to-follow guide

for the beginner an d a referen ce for the exper i-

enced rocket enth usiast. Here youll find the

answer s to the most frequ ently asked que s-

tions. More complete techn ical informat ion on

all the subjects can be found on t he Estes

website (www.estesrockets.com) and the Estes

Educator website (www.esteseduca tor.com)

2

*Copyright 1970, 1989,1993, 2003 Estes-Cox Corp. All Rights Reser ved.

Estes is a registered t rade mar k of Estes-Cox Corp.


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WHY ESTES MODEL ROCKETRY?The hobby of model rocketry originat ed at the d awn of the

space a ge in the lat e 1950s. Seeing space boosters carry thefirst ar tificial satellites into Ear ths orbit inspired man y enthu-siastic young people to try to emulate the r ocket pioneers bybuilding their own rockets. Unfortun ately, these home maderockets usually involved stuffing flammable chemicals int ometa l pipes, very often with tra gic results. Newspapers told offingers an d eyes lost an d all too freq uen tly of lives lost. Wha twas need ed was a safe alter nat ive tha t would allow young peo-

ple to experience t he thr ill of constru cting and laun ching theirown rockets and pr ovide them with the opp ortun ity to explorethe fascinat ing science of rocketry. Estes model rocketry is theanswer.

A SAFE PROGRAMEstes model rocketry is a sa fe activity because it incorporates

three importa nt feature s. The first is the model rocket engine, aprofessiona lly man ufactu red , low cost, solid-fuel rocket en gine.This frees the rocket b uilder from the inheren tly dangerous pr o-cedures of mixing chemicals and pa cking propellant.

The second feature is the use of safe materials for constructingthe r ockets. All model rockets a re bu ilt using only lightweight

materials such as paper , plastic, and wood. Metal parts ar enever used for the ma in structural components of the model.

The third featur e is the incorpora tion of the Model RocketSafety Code int o all our flying activities. The safety code pr o-vides guidelines for the safe opera tion of model rockets, suchas launch ing the rockets electrically from a safe distance, andusing recovery systems to gently retu rn th e model to Earth.When the sa fety code is followed, model rocketry is an extr eme-ly safe activity, safer than baseba ll, soccer, or swimming. Ourhobbys excellent safety record span s over 45 years and 300million rocket laun ches.

YOUR FIRST MODEL ROCKET

The Estes Alpha is shown here to i llustrate th e par ts of atypical model rocket for the beginning rocket builder . Theconstruction technique s used in this and other model rocketsare explained in greater det ail in this manual.

For your first model rocket we recommen d one of the EstesE2X series. No modeling experience is needed to build anE2X model. Construction involves almost no cutting or sand-ing, and t he models do not need pa inting.

The Skill Level 1 models ar e an excellent choice for your sec-ond or third model. These models are also a good startingpoint if you ha ve previous model building experience.

As your kn owledge of rocketr y and your modeling skillsincrease you can move up to building higher skill level models,and eventua lly to building your own cu stom designs from part savailable in the Estes ca talog.

CONSTRUCTION TECHNIQUESIn the constru ction of your Este s model rockets you will typi-

cally need the following tools and su pplies (see kit inst ructionsfor specific requiremen ts):

Mode ling knife Scissors

Ruler Spray Primer Spray pa in t Tube-type p lastic cemen t

Masking tape Fine and ext ra fine sa ndpaper

White glue or carpen ters glue

Always exercise car e when using a mode ling knife (the y arevery sharp!) and dont leave the knife laying around after youfinish with it. Use some sort of cutting board und er the kn ife.A smooth, flat p iece of board is great; an old phone b ook orthick catalog also works well on a har d surface. Use newspa -per t o protect your work surface from acciden tal glue sp ills.

TYPES OF GLUE

Several types of glues an d adh esives are commonly used inthe constr uction of model rockets; the prope r glue to usedepends on the ap plication.

1. White Glue: This glue works on p orous ma terials such a s

paper and balsa . It is a good choice for engine mounts,

balsa and fiber fins, launch lugs, paper parts , an d for

ap plying fillets t o fin-body joints.

2. Alipha tic Glue: Also known as wood glue or carp en-

ter s glue ; it is usu ally yellow or ta n in color. It is used

ju st lik e wh it e glu e , b ut it is st ron ge r and dr ie s fa st e r .

3. Tube-type Plastic Cemen t: This thick, clear liquid is used

to glue styrene plast ic par ts to porous m ateria ls such as

pap er. It is typically used to glue plastic par ts to bodytube s. Some E2X series kits use th is glue for assembly.

4. Liquid Styrene Ceme nt: This thin, clear liquid is used to

bond styrene parts together. The cement comes in a bot-

t le and is applied with a small brush.

5. Cyan oacrylate: Commonly known a s supe r or instan t

glues, these a dhesives are a vailable in both thin an d

thick formulations. Because th is type of glue can

instantly bond skin, it should never be u sed by unsuper -

vised children. Eye prote ction and gloves are re com-

mended . These adhe sives are u seful for quick assembly

or field rep airs. They work well for gluing plastic part sto balsa or body tubes.

6. Epoxies: These two-par t adhe sives are also recommen d-

ed for the advanced modeler. Epoxy provides extra

stren gth for the engine mou nts an d fins of high-thru st

rocket kits. It also makes excellent fin fillets in one step.

1. ENGINE MOUNTING METHODS

It is importa nt to ha ve a strong engine mount. This secure sthe e ngine, allowing it to push your rocket int o the a ir.

Engine Block InstallationSome models use an en gine block to keep the e ngine from

traveling too far forward in t he rocket body when the r ocket islaunched.

When building a model, use an e ngine casing (or the spe cialspacer tu be supp lied in some kits) to push the en gine block intoposition. First, mark the e ngine casing 1/ 4 inch from the end.Apply glue to the inside of the tube using a cotton swab or smalldowel. Place the engine block just inside the rea r of the bodytube, then push th e block forward into position with the enginecasing in one smooth motion so th e glue will not freeze theblock in the wrong place. When th e mark on t he engine casingis even with th e rear of the body tube the block will then be in

the correct position. Remove the en gine casing immediately.

CenteringRings

ENGINE MOUNTASSEMBLY

EngineHook

EngineHolder Tube

Shock CordMount

Body Tube

Launch Lug

Engine MountAssembly

EngineHook

Fins

Parachute

ShockCord

NoseCone

ShroudLines

3


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4

4

4

520

50

55

60

70

80

4

3

3

3When m ounting the en gine in a mod el with an engine block,wrap th e engine with masking tape u ntil it makes a tight fric-tion fit in the tu be, then slide the en gine into place. If the fit istoo loose, the e ngine will kick out at ejection and may notdeploy the recovery system. If the fit is too tight, you may dam-age the model trying to push the engine in place. Adjust theamount of tape as needed.

If the ar ran gement of the engine mount tu be and fins allowsenough space, a wrap of tape around the tube and engine jointcan help hold the engine in the model.

Engine HoldersIn man y models a quick release e ngine holder (also called an

engine hook) is the best device to use for mounting an engine.The forward end of the engine holder is insert ed throu gh a 1/ 8inch wide slit in the tu be, and preven ts forward movement ofthe en gine. Apply glue fillets where the en gine moun t spacerr ings attach t o the engine mount tube for extra stren gth.

To mount an en gine in a model with an engine holder, springthe en d of the holder up an d slide the engine into place. Checkto make sure the en d of the holder la tches securely over theend of the engine.

2. SHOCK CORD MOUNTS

Attach th e shock cord securely. Both methods shown yieldgood result s. The slit-n-glue meth od is good for body tu bes toosmall for an anchor mount.

The anchor is cut from paper or index card stock. Be sure toglue th e anch or far enough into the tu be or it will inter fere

with the prope r fit of the nose cone.

3. SECURING A SCREW EYE

If your model uses a screw eye to atta ch the shock cord to abalsa nose cone or adapter , make sure the screw eye is secure-ly atta ched. Make a hole by inserting and re moving the eye;then squir t glue into the hole and replace the eye.

4. MARK THE BODY

This Fin Spacing Guide will space eq ually three or four finson all popular body tubes sold by Estes Indu stries. To spacethe f ins, center the end of the tube in the circles, then mark a tthe (4) lines for four fins or on the (3) lines for th ree fins.

Mark the body tube for fin a lignmen t usin g the V notch of adrawer sill or door frame. Match the edge of the notch with aspacing mark; run a p encil along the ed ge to draw your guideline. Gluing the fins to the body on the se lines will insur e thatthey are straight.

Estes also man ufacture s a special Tube Marking Guide formarking fin location lines on body tubes,

5. INSTALL THE ENGINE MOUNT

Be sure the glue on the en gine moun t rings is completely drybefore you install the moun t in the body tube. The fin align-ment lines shou ld be drawn on th e body before insta lling theengine moun t. You will position the moun t so the engine hold-er is midway between t wo fin lines for easier opera tion.

Before gluing, make su re the mount slides easily in the bodytub e. If its tight, san d it until it slides ea sily.

Smear a liberal amoun t of glue aroun d the inside of the bodytube over th e are a where the m ounts ring or coupler will fit.Insert th e mount into position in one smooth motion. DONT

pau se, or the glue willgrab it in th e wrongplace! Support the tubenose-up while the gluedries.

6. BALSA FINS

Fins are used t o aerodynamically guide your rocket. Some modelrockets use fins made from thin sheets of balsa wood. In manykits the fins are pre -cut for you by a pun ch die. In other kits, or tomake custom fins, you must use a pa ttern t o mark and cut a blanksheet of balsa. All balsa fins must be cut so tha t the grain of thewood runs par allel with the leading

edge of the fin for maximumstrength.

Die-Cut Balsa Fins

Before removing the die-cut finsfrom their sheet, use extra fine sand-pap er to sand both surfaces of the sheet of balsa (a san ding blockis helpful here). Use a mode ling knife to carefully cut th rough thepoints where th e fins ar e still atta ched to the d ie-cut shee t, thenremove the fins. Stack the fins together a nd san d all edgessquare.

4

Engine Block

Engine Casing

Glue

Body Tube

B6-4

3

2

1

GLUE

3

GLUE

YES

1"

Spread Glue, Fold - Pinch & Hold

Slit-N-Glue Method

Anchor Method

Cut 2 Slits 1/2 Long1/4 ApartThread InApply Glue

GrainDirec

tionLeadi

ngEdge

Tip

Trailing Edge

RootE

dge

SandpaperSanding Block

Die-CutBalsa Sheet

Fins StackedTogether

Remove UsingModeling Knife

Sandpaper

1/4(6 mm)


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Balsa Fins From Pattern s

To make fins from an u n-cut she et of balsa, start with a full-size fin patt ern cut from stiff pap er or thin cardboard . Whenlaying out the fins on th e shee t of balsa be sure t o position thepattern so that the leading edge of the f in runs par alle l to thegrain direction! Trace aroun d the patte rn with a pencil or ballpoint pen to ma rk the balsa for each f in.

Use a me tal straightedge whenever possible. Hold the knifeblade at a 90 angle to surface being cut, and handle at about45 for clean cut . If blade is dull or held too high, balsa tends totear. A razor saw blade may be required to cut thicker balsa.

Shaping Balsa Fins

The instruction she ets in ma ny kits tell you to sand all edgesof the fins squa re. This is fine, and it is the e asiest met hod, butyou can reduce drag and increase the alt i tude performance of your rocket by proper sha ping of the fin edges.

For gene ral purp oses, sand a ll fin edges round excep t theroot edge (the edge that glues to the body). Make the rootedges straight and squar e, never rounded! The sides of the finsshould be san ded smooth.

On high performan ce models sand the fins to the stream linedshape sh own for minimum dra g. The front (leading) edge of

the fin should be round ed; the back (tra iling) edge should cometo a sharp edge.

7. ATTACHING THE FINSAfter marking the tu be an d sand ing the fins, you are re ady to

atta ch them to the body. The best way to attach ba lsa or fiberfins t o a r ocket with white glue is b y using a double glue joint.Apply a layer of glue to the root edge of a fin an d a t hin layer ofglue to the b ody tube where the fin will be att ached . Do thisfor all fins an d allow this glue to dry. Then app ly a second line

of glue to the r oot edge and pr ess the fin in place onto thebody, holding it in place u ntil the glue begins to set. Before th eglue se ts completely, sight down along the body tube to m akesure th at the fin is aligned p arallel with the tu be, and orientedstraight away from the surface of the tube. Adjust the fin align-ment a s needed . Support the rocket body in a vertical positionwhile the glue on t he fins dries.

Sometime after th e fin joints h ave dried completely, they shouldbe re inforced. Do this by app lying a fillet of glue as shown.Always suppor t the b ody in a horizonta l position while fillets a redrying so that th e glue does notrun. Build up th e fillets in severalthin layers , allowing each layer todry between a pplications (this ismuch faster t han waiting for a sin-gle thick fillet layer t o dry).

8. ATTACHING LAUNCH LUGSThe launch lugs are u sed to position the rocket on the laun ch

rod. The lugs and rod help guide t he rocke t in its first few feet offlight. The m odel must be guided unt il it is going fast en ough forthe fins to guide it. Launch lugs are a ttached in m uch the sameway as fins. If a sta nd-off is used to kee p th e rod from hitting alarge diamete r payload section, attach th e lug to the stan d-offpiece first, then at tach the unit to the body. Sight along the tu beto be sure t he lug is par allel to the body tube be fore the gluesets. Apply glue fillets to th e lug after the in itial glue joint h asdried.Rea d LAUNCHERDESIGN starting on

page 9 for launch lugplacement.

9. PARACHUTE

ASSEMBLY

The most common model rocket recovery system is the pa ra-chute. On page 11 you will find a lterna te re covery systems.Estes pa rachu tes are now fully assembled. To assemble anunassembled parachute , cut out the plastic parachute alongthe dott ed lines. Apply the six vinyl tape rings to the corne rs ofthe parachute a nd pun ch holes through the para chute mater ia lin the center of the tape r ings using a sharp p encil. Cut threeequal length shroud l ines that ar e twice as long as the pa ra-chute diame ter. Tie both ends of the shroud lines through theholes in the tap e rings, as shown.

To atta ch the para chute to the nose cone or adap ter eyelet,threa d the shroud lines through the eyelet, pass the parachut ethrough the loop of shroud lines as shown, then p ull the lines tight.

In addition to regular, pre-printe d model rocket para chute s,you can a ssemble custom pa rachu tes using a wide variety ofthin plastic sheeting. When ma king a chute from scratch, cutthe plastic sheet to shape, then a ttach shroud l ines as shownpreviously. Carpet thre ad makes excellent shroud lines.

Parachute Shape

The most common parachute shape s are square, round,

hexagonal and octagonal. While squar e parachu tes are the eas-iest to make, the y are not very efficient and allow a consider-able amount of sway during descent. Round pa rachutes arevery stable in descen t, but are more d ifficult to make.Hexagonal and octagonal parachutes are stable an d reasonablyeasy to make. The accompanying drawings illustrate me thodsfor making these sha pes.

5

TRACING

Rounded Edges Streamlined

Plain

Glue

Stand-Off

GlueFin DryingPosition

Fillets

LAYOUTFINPATTERN R

ootEd

ge

LeadingEdgeGrain


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Snap Swivel Assem bly

Its often worthwhile to attach your para chute t o a snap swiv-el to allow the chute to be ea sily removed. This lets youchan ge parachu te size in respon se to different wind conditions,or swap chutes be tween m odels. A snap swivel has an eyeleton one end a nd a wire snap hook on the othe r. The swivel con-nection in between helps keep your parachute l ines from tan-gling up if the chute r otates on d escent . Snap swivels areavailable where fishing supplies are sold.

10. CONNECT IT TOGETHERThe first illustrat ion shows how nose cone, para chute a nd

rocket are conne cted on most models. If the rocket has aheavy payload se ction, its a good idea t o use two chu tes asshown in the second picture .

11. CUTTING TUBES

When b uilding custom design rockets or replacing dam agedtubes on your models, you will often ne ed t o cut a specificlength body tube. Heres how to get a ne at cut e very time.

(1) Mark the tube at t he point where the cut is to be made.Wrap a stra ight str ip of paper around the tube and a lign theedge with the mark. Draw a line completely aroun d the tube.You can also use the pencil holder on the Estes Tube MarkingGuide to draw the line.

(2) Slide a stage coupler or expended en gine casing into thetube center i t un der the cut posit ion to support the tube.

(3) Using a sharp blade, cut lightly along the line, rotatingthe tu be as you cut. Dont try to cut all the way through on thefirst tur n. Use a light pre ssure on the kn ife for several turn sunt il you cut th rough.

(4) Slide the stage coupler into the cut end of the tube. Holdthe tube near the cut en d and work it over a f la t sheet of veryfine san dpap er, with a circular motion, to remove burrs an drough edges.

12. CLEAR PAYLOAD SECTIONS

Models that ha ve a clear plastic payload section pre sent aspecial problem: White glue will not bond th e plastic to a ba lsanose block. To overcome this, app ly tap e strips to the inside ofthe pa yload tube , then glue the balsa nose block to the tapestrips usin g white glue.

FINISHINGThe finish of a rocket star ts with the very first ste ps of assem-

bly. Sloppy gluing and other me ssy habits will ruin the a ppea r-ance of a rocket so that nothing can be d one to get the perfectappeara nce which is desired. On the other hand, careful con-struct ion will make a m odel look good even before th e pain t isapp lied. A model with a smooth finish not only looks more pro-fessional, it expe riences less dra g in flight, so it flies h igher.

The degree of difficulty in finishing a model rocket de pen dson the mat erials used in its construction. Models with plasticnose cones an d fins ar e the ea siest to finish. Some come withall pre-colored pa rts an d requ ire no finishing at all. Modelsbuilt with balsa par ts require extra steps to produce a smooth,shiny finish.

1. SANDING AND SEALING BALSA PARTS

To get a smooth finish, the wood grain of the ba lsa must befilled. Many suitable types of spray primer s and wood fillersare available at hobby shops and hard ware stores. Sprayprimers a re widely available and work great. Water -basedwood fillers ha ve no noxious fumes; you ma y need t o add waterto thin them to a brush able consistency.

Paint cannot replace sandpaper . I f a balsa surface is notsand ed a nd se aled car efully, it will be impossible to get asmooth paint job. Begin by sanding all balsa surfaces withextra-fine san dpa per un til smooth.

Next, app ly a coat of spray primer to the ba lsa. Let this drycompletely, then sand with 320 grit (or finer) sa ndp ape r, untilthe surface is smooth again. Apply more primer, repeating theprocedu re un til all the pores in the ba lsa are filled.

Pract ically all of the spray primer should be san ded off aftereach coat. This is because the p urp ose of the pr imer is to fill inthe holes, not the smooth areas of the balsa.

2. SPRAY PAINTING THE MODEL

Using a good ename l spray paint is the easiest way for anovice to get a smooth, un iform finish on a model rocket.Other types of paint s can be use d, but be wary of mixing differ-ent types of paint on th e same m odel; paint comp atibility prob-lems may cause the m odels finish to wrinkle or craze. If indoubt, test t he compa tibility of different p aints on a piece ofscrap mat erial. Paint fumes can be harmful; only paint out-doors or in a well-ventilated a rea.

To hold the model dur ing painting, make a painting wandby rolling a sheet of newspape r into a very long, narrow coneand inser ting it into the rockets engine mount. An expend ed

engine casing glued on to a wooden dowel also makes a great6

Balsa SandedBut Untreated

1st, Coat Sanded Surface

Note Grain Depression

3rd, Coat Sanded'Till Surface Is Smooth

Depressions Are Filled

2nd, Coat Again Sanded

Slight DepressionRemains

Draw Line

4 or 5 Turns OfTube Will Cut Clean

Apply LightEven Pressure

Tape Strips OnInside Of Payload

Section

GlueAdapter

Wrap tape aroundnose cone shoulder

for friction fit


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paint ing wand , especially for heavier models. Before pa inting,wipe the mode l with a clean , slightly dam p cloth to remove an ydust from its surface.

3. PRIMER COAT (Option al)

While not necessa ry, a coat of sand able primer provides auniform base color and a bette r bonding surface for the p aintlayers; it also helps fill any rema ining minor surface imp erfec-tions. Spray on the primer in thin coats unt il the mode l is auniform color. When the p rimer is completely dry, lightly sand

the sur face with 400 grit (or finer) sa ndp ape r.

4. BASE COLOR

The base color is the lightest of the colors to be use d on themodel. Usually this will be white. If the mode l is to be painte dwith fluorescen t colors, the base coat m ust be white.

Always spra y on the paint in light, even coa ts, allowing themodel to dry between e ach coat. Trying to cover the modelwith one thick coat of paint will only result in paint r uns.Several thin coats will also dry faster than a single thick coat.When the first coat has d ried complete ly, sand lightly withextreme ly fine sandpa per. Wipe off any dust and ap ply anoth -er coat. Let this dry, then follow with add itional light coats

unt il the mode l has a clear, pure color.Let the ba se coat dr y completely in a warm , dust-free are a.

Allow the model to dr y a full day if it is to be ma sked for a ddi-tional colors.

5. THE SECOND COLOR

When t he base color has d ried completely, cover all areas onthe model which are to remain th is color. Cover small areaswith masking tap e. Large area s should be covered with typingpap er, held down at the edges with masking tape . Its impor-tan t to seal the tape down tightly along the edge. Masking tapethat is too sticky may pull up the base color paint whe nremoved; if you have this problem, you can stick the ta pe toyou skin before app lying it to the m odel to remove some of itstackiness.

With the model maske d, apply an additional thin coat of thefirst color to finish sealing the ed ges of the ta pe. When t his isdry, app ly the secon d color in several thin coats. Use justenough pa int to get good color. After the last coat is dry,remove the masking carefully to avoid peeling the paint. Athird color would be app lied in the sa me way as the second .

6. FINAL TOUCHES

For best resu lts, let the pa int dry overnight before app lyingdecals. Some models have self adh esive decals; these mu st bepositioned very carefully before pre ssing into place, since theycan not be moved once they are stuck d own.

To apply a water-tran sferable deca l, first cut it out of thedecal sheet , then soak it in lukewarm water for 60 seconds orunt il it begins to slide on the backing sheet. Slide the de cal sothat on e edge is off the backing. Position this edge on themodel and hold it in place while pulling the ba cking out fromund er. Smooth the decal down with a damp finger, then blotaway any excess water with a rag or pape r towel.

After the d ecals have dried completely, spra y the model withclear acrylic coating to protect t he finish. Apply the clearspray in severa l thin coats, allowing time for each coat to d ry.If the model was finished with fluorescent paint, ap ply a lightcoat of clear spra y before a pplying decals.

STABILITYOne of the first things a model rocket designer learn s is that a

vehicle will not fly un less it is aerod ynam ically sta ble. By sta -ble we mean that i t will tend t o keep i ts nose pointed in thesame direction throu ghout its upward flight. Good aerodynam-ic stability will keep the rocket on a tr ue flight pa th even

though some force (such a s an off-cente r en gine) tr ies to turnthe m odel off course.

If a model is not stable, it will constan tly turn its nose awayfrom the inten ded flight pa th. As a resu lt it will try to go allover the sky, but en d up going nowhere . An un stable rocketwill usually tumble to ear th after t he engine bur ns out, dama g-ing the model.

When a fre e-flying objectrotate s, it always rotatesaroun d its balance point. Theproper term for the balancepoint is the cente r of gravity,abbre viated as CG. Thus thebalance point (CG) is the pivot

for all forces trying to turn therocket.

The most significant forces acting on a model rocket in flightare cau sed by the thru st of the engine, the action of air on thenose and t he action of air on the fins. Off-cente r thru st andforces on the nose try to bring the nose of the rocket aroun d tothe rea r. They are oppose d by the forces acting on the fins. Allthese forces are a mplified by the distan ce from the location ofthe force to the cente r of gravity.

As long as the forces on the fins of the rocket a re greatenough to counte ract th e forces on the nose an d any off-cente rthru st, the rocket will fly straight. If the fins are too smalland / or too close to the cente r of gravity, there will not beenough force to countera ct the force on the nose. As a result,the n ose will swing out to the side and the m odel will try tochase itself around th e sky.

The side forces on th e nose a nd fins of a rocket tha t is flyingstraight are very small. When somet hing disturbs the rocketand it sta rts to rotat e sideways, the side forces on both noseand fins increase. (There is some aerodynam ic force on thebody; however, it is small and can usua lly be ignored.)Depending on the size and shape of the nose an d f ins an d theirdistance s to the cen ter of gravity, one will overpower the oth erand force the rocket to turn its way. If the nose overpowers thefins, its too bad. However, if the fins overpower the n ose, therocket will swing back into line a nd cont inue on its way.7

2

oz2oz

1

oz

Areas To ReceiveSecond Color

Areas To RemainOriginal Color

Move CanParallel To

Work8 To 10

From Body

DontForget TheEnds And

Edges

Sag Or RunResults From

Holding Can TooClose To Work

Slide Decal FromThe Backing Sheet

Dip DecalIn Water

Blot Away

Excess Water

Force On Left Side Can Be

Balanced By Large Force Close By, Or

Small Force Far Away


8/16

Although determinin g the exact re lationships between vari-ous forces on a model rocket requires higher mat hema tics, cer-tain pra ctical rules can be used by even the be ginning rocketmodeler to design stable rockets. The first rule is to use a longbody. Until you have considera ble experience in de signingmodels, the length of the body tube u sed should be at lea st 10times its diamet er. This makes it easier to get enough distancebetween the cen ter of gravity and t he fins.

The second rule is to make the fins large. The larger the fins,the more force they will produ ce when the rocket sta rts to turn .For the first few designs, use a fin which is at least a s large asthe examp le in the illustration.

The third rule is to place the fins as far back on the rocket a spossible. Generally, this means th at the r ear edge of the finwill meet th e rea r end of the body and the fin will be swept

back. Do not place any fins ahea d of the center of gravity!Finally, the rocket should balance a t least 1/ 8 its length

ahea d of the front of the fins. This gives the fins th e leveragethey will need t o countera ct the force on the nose.

Remember that the se rules are general; they are based onexperien ce rather than pr ecise mathema tical ana lysis. Alwaysremem ber to te st your model for stability before you launch it.

SWING TESTING FOR STABILITYThe easiest way to te st the stability of a model is to fly it

without launching it. Do this by atta ching a string to the modeland swinging it through the air. If the string is attached a t therockets CG, its beha vior as it is swung thr ough the air will indi-

cate wha t it will do in powere d flight.Test your m odel by forming a loop in the end of a six to ten

foot long string. Install an engine in the r ocket; use the hea vi-est en gine you expect t o fly in the model. (The center of gravi-ty is always determ ined with an engine in place.) Slide theloop to the prope r position around th e rocket so the model bal-ances horizontally. Apply a small piece of tap e to hold thestring in place.

With the r ocket suspe nde d at its cen ter of gravity, swing itoverhead in a circular p ath. If the rocket is very stable, it willpoint forward into the wind created by its own motion. Somerockets which are stable will not point forward of their own

accord unless the y are sta rted str aight. This is done by holdingthe rocket in one hand with the arm extended and then pivot-ing the entire body as the rocket is star ted in the circular path.It may take several atte mpts before a good start is achieved.

If it is necessary to hold the rocket to start it, an ad ditionaltest should be made to d etermine when the model is stableenough to fly. Move the loop back on th e body until the tubepoints down at a 10 angle below the horizontal . Repeat theswing test. If the mode l will keep its nose pointed a head on cestart ed, it should be stable enough to launch.

Be careful when swinging a rocket overhead: A collision witha nea rby object or person could be serious. Always do yourtesting in an open, uncluttered a rea.

Dont try to fly a rocket tha t has not p assed t he test . Mostunst able rockets loop aroun d in the air harm lessly. However, afew marginally unst able mode ls will make a coup le of loopsand th en become stable due t o a CG shift as the propellantburns. When this happen s, the model can crash into theground at high speed.

If your rocket d oes not pa ss the st ability test, it can u suallybe made stable. Two meth ods can be used: The balance pointcan be moved forward, or the fin area can be en larged. Tomove the balance p oint forward, add weight to the n ose cone.For models with hollow plastic nose con es, pack some clay intothe tip of the nose. To add weight to balsa nose cones, atta chwashers to th e base of the cone. The CG can also be moved for-ward by adding a payload section to the model. Fins can eitherbe replaced with larger ones or extra tabs can be glued to therear or tip edges of the fins. Additional fins could also beadded to the m odel. Some scale models use supplementaryclear plastic fins. After making your changes, swing test themodel again to be sur e it is now stable.

PREPARING FOR FLIGHTParachutes an d streamers must be protected from the heat of

the e jection charge by using flame-resistan t recovery wadding.NEVER use re gular tissue pa per in place of flame-resistan twadding! Ordinary tissue paper will continue to smolder afterejection and can cause da ngerous grass fires.

Loosely pack en ough flame-resistan t re covery waddin g intothe tu be to fill it for a dep th of at least twice the body diameter.The wadding should fit against th e side of the tub e all the wayaroun d to give a good sea l.

To fold the para chute , hold it between two fingers at its cen-ter an d pass the other hand down it to form a spike shape.Fold this spike into several sections as shown. Pack shr oudlines and sh ock cord in on top of the wad ding. Push the foldedchute d own into the tube on top of the shroud lines an d shockcord, then slide the nose cone into place.8

Add A Nose Cone Weight

Or Add A Tab To Each Fin

Here Here Or Both

Clay

Double Check A Rocket WithQuestionable Stability AsFollows:

Rocket Should Still "Fly"Nose Forward

Move String Back UntilNose Of Rocket Points

Ten Degrees Down -Repeat TheSwing Test0

-5-10-15

Example:Rocket 12" Long

10dd

Minimum Fin Size

Rocket Should Balance Here

1.5" Ahead Of Finsd= Body TubeDiameter

1-1/2dd

2d

Starting A Rocket


9/16

If the par achute h as been pa cked in the model for an extend-ed per iod, re-pack the chute just p rior to launch. Dusting thepara chute with ta lcum powder before packing will also increasethe cha nces of a successful deployment . It is especially impor-tant to follow these preca utions on cold days because th e lowtemper atur e makes the plastic para chute mat erial less flexible.

Check the fit of the n ose cone on th e model: If it is too tight,see if the shock cord or shroud lines were trapped between the

nose cone shoulder an d the body tube. If the nose is still tootight, sand t he shoulder of the nose cone or th e inside of the bodytube with fine sandp ape r. If the n ose cone fit is too loose, wraptape on the shoulder to adjust the fit. The nose cone should sepa-rate easily, but should n ot fall off if the rocket is inverted .

To deploy the stream er or par achut e recovery gear corre ctly,the en gine MUST be h eld in p lace SECURELY. This may bedone by wrapping the en gine with tap e unt il it makes a sn ug fitin the body tube or engine mount.

On models using engine holders, make su re the e nd of theholder latches secur ely over the end of the en gine.

IGNITER INSTALLATIONFor safety reasons, do not insta ll igniters in model rocket

engines unt il you are r eady to fly the rocket. Never conn ect alaunch cont rol system to an igniter insta lled in a rocket en gineunless the mode l is on a launch pad . Never ignite a rocketengine indoors.

Use scissors to separ ate th e igniters; leave the pap er stripatta ched to the igniter wires. Hold the engine nozzle end up,then insert th e igniter into the nozzle as far as it will go. Tooperat e pr operly, the t ip of the igniter MUST touch t he pr opel-

lant. Insert the igniter plug into the n ozzle and firmly push itall the way in. Be sure to use the corre ct color-coded igniterplug for the engine to insure prop er fit. Bend the en ds of theigniter wires back; this provides a larger area for atta ching themicro-clips.

If an igniter p lug is not available, roll a 1 square of flame-proof recovery wadding into a ba ll and insert it into th e nozzlealongside the igniter wires using the point of a pe n or pe ncil.Press t he wad ding ball firmly in p lace.

LAUNCHINGModel rockets, like professional rockets, are laun ched e lectri-

cally. This provides both safety and r ealism. Each engine soldby Estes Industr ies is supplied with an igniter, igniter p lug,and complete instr uctions; still more information is suppliedwith laun cher kits. However, the basic information neede d tolaunch m odels successfully is included in th ese pa ges.

1 LAUNCH CONTROL SYSTEMS

The electrical launch system controls the flow of electricalcurre nt to the igniter. Safety feature s built into the controllerinsure that curr ent does not reach the igniter unti l i t is t ime tolaunch. An Estes laun ch controller is shown below:

All laun ch contr ol systems work b y passing electrical curren tthrough th e high-resistan ce wire in th e tip of the igniter; thiscurre nt hea ts the wire, which ignites the coating on the igniter,which in turn ignites the en gine. The laun ch system is attache dto the igniter with micro-clips, one clip on each igniter wire.When connectin g the micro-clips to the igniter, make sure t heclips do not touch each othe r or the rod or blast deflector. Ifthey do touch, the cu rren t from the ba ttery will short throughthe clips, rod, or deflector and not r each th e igniter. Micro-clips become corroded with use; use san dpaper to c lean theinside of the clip jaws to insure good electrical conta ct.

All launch cont rol systems mu st have a sprin g return laun chbutton so the current turns off automatically when the but ton isreleased . In add ition, a rem ovable safety interlock (safety key)must b e pr ovided; this could be a n electr ical key-switch or aninserta ble metal pin. Estes launch cont rollers have a re movablespring-retu rn safety key also. Both the key and laun ch buttonmust be pr essed down for laun ch. When th e safety key isremoved or not held down, the laun ch controller cannot completethe electrical circuit to send cur rent t o the igniter. ALWAYSremove the sa fety key and car ry it with you when you go hookup t he igniter! This insures tha t no one could activate th elaunch contr oller while your han ds are ne ar the rocket n ozzle.

Any homemad e electrical launch control system must includeall the safety featu res outlined above. See the Estes publica-tion Model Rocket Launc h Syste ms for more de tails. A typi-cal launch controller circuit is shown below:

This circuit includes a continuity check light. This is a small bulb (nomore tha n 1/ 4 amp for safety) that lights when a complete circuit existsbetween ba ttery and igniter; this indicates that the r ocket can belaunched. If the continuity check bulb does not light when the safetyinter lock is closed, remove safety key and check to see if the micro-clipsare properly connected to the igniter. ALWAYS re move sa fety keybefore approaching the rocket.

2. LAUNCHER DESIGN

A model rocket cann ot be simply set on its fins an d launche dsince the rocket re quires a fast airflow over its fins for sta bili-ty. The model must be guided u ntil it is moving fast en ough for

the fins to operate ; the launcher p rovides this initial guidan ce.9

B6-4

Launch Wires

Micro

Clips

Launch Button

Safety Key

ContinuityCheck Light

Safety KeySwitch

Micro ClipsContinuity CheckLight

LaunchSwitch

6V or 12VDCPower Source


10/16

Most model rockets are guided during launch by an 1/ 8diamete r, 32 long laun ch rod (hea vier models require thickerrods for extra stren gth). A short tu be, called the lau nch lug, isglued t o the side of the rocket. This tube slips ea sily over therod and keeps the rocket pointed in the r ight direction dur inglaunch. A single launch lug should be mounted ne ar the bal-ance point of the rocket; two lugs located either side of the CGprovide better su pport for longer models.

The blast deflector is a meta l plate th at pre vents the en gineexhaust f rom hitt ing the launch pad or ground, preventingfires. Heavier rockets will requ ire thicker launch rods an d alaunche r with a heavier base. Bricks or rocks can be used toweight the b ase when e xtra-large models are being launched .

When building a launch pa d be sure to use a base that is bigenough and he avy enough to provide a secure foundat ion. Apiece of 3/ 4 plywood a foot squa re works well for most r ock-ets; a larger base made from two-by-fours easily handles on epound models.

3. LAUNCH SAFETY

Only launch mode l rockets from a large open ar ea. Makesure the ground around t he launcher is c lear an d has no dryweeds or highly flamma ble mater ials. Always cover the laun chrod with the launch rod caps! After sliding the rocket onto thelaunch rod, replace the cap on the rod before hooking up theigniter. The cap protects you from accidental eye injury from

the rod. If the cap is not available, put your han d on the end ofthe r od before leaning over. Remove cap for launching.

Immediately before launching a rocket, check for low-flyingaircraft . I f there are other people in the launch area,ann ounce th e launch loudly to get the ir atten tion, followed byan audible five-second coun tdown.

After a successful launch, remember to remove the safety keyfrom the controller and r eplace the cap on the launch rod. If therocket becomes entan gled in a power line or other dangerousplace, to avoid injury DO NOT attemp t to re trieve th e mode l!

4. LAUNCH AREAS

Choose a large field awa y from power lines, tall trees, andlow-flying aircr aft. It shou ld be free of easy-to-bur n ma ter ials.The length of the sma llest side of the field should be at leastone fourth of the rockets expected ma ximum altitude. TheModel Rocket Safety Code cont ains a table of minimum fielddimensions for each en gine size.

COUNTDOWN CHECKLISTUse a countdown che ck list when you laun ch your models.

Youll find it makes your rocket flights more successful an denjoyable. The following procedu re is recommen ded for mostpara chute or streame r models. For other types of rockets, tryto develop your own complete ch eck list.

12) Pack flame-resistan t recovery wadding into the body tube .Inser t the parachute or streamer.

11) Install the nose cone or pa yload section, checking for prop-er fit. Check condition of the p ayload (if any).

10) Apply enough masking tape to the e ngine(s) for a tight fric-tion fit in the body tube (if required for this model). Whenlaunching a multi-stage rocket be sure tha t the en gines arein their prope r relative positions and tha t a layer of cello-phane tape is wrapped t ightly around each engine joint .Mount the en gine(s) in the rocket. If the rocket usesengine holders, check that the holder proper hooks therear en d of the engine.

9) Install an igniter in each engine.

8) Be certa in the safety key is not in the launch controller!Place the rocket on the launcher . Clean an d attach themicro-clips.

7) Clear the area , check for low flying aircraft, alert therecovery crew, tracke rs, and spectat ors.

6) Insert the safety key into the laun ch controller and holddown. Give an aud ible count down: 5) 4) 3) 2) 1)

5) Push laun ch button while safety key is held down.LAUNCH!

TRACKINGThe easiest way to me asure how high a rocket flies is to visu-

ally track the model using a tracking instrumen t, then trian-gulation is used to determine the altitud e. The trackinginstrument is used to measure the angle between the groundand the line of sight to therocket a t i ts peak alt i tude.

This angle is called t heelevation angle. When theelevation angle and the dis-tance from tracker to launcherare known, it is very easy todetermine the alt i tude.

TRACKERSThe Estes Altitrak is one of the best a ll-aroun d basic tra ck-

ing devices. However, it is easy to construct a simple tra cker:A plastic protractor is atta ched to a ruler as shown. Tie aweighted string through the small hole at the cente r of theprotra ctor. When sighting along the edge of the ru ler towardthe horizon, the string should hang by the 0 mark on the p ro-tract or; when sighting at a p oint in the sky, the position of thestring will indicate th e elevation an gle.

The distance from the launch area to the t racking sta tionshould be appr oximately equa l to the altitude e xpected for anaverage rocket flight to be tracked . This distance is called thebaseline and its length should be carefully measu red. Thetracke r should have a clear view of the laun ch area a nd shouldnot be looking into the sun .

Before launch, alert the person at th e tracking station. Whenthe tracker signals readiness, the rocket can be launched. Thetracke r sights along the tra cking instru ment and follows the

rocket as it rises. When the rocket re aches its peak altitude,the tra cker locks the tra cking instrum ent. An Altitrak islocked by releasing the trigger. To lock the home made tr acker,the oper ator use s a finger to clamp the st ring in place beforemoving the instrume nt (this takes pract ice!). The elevationangle is then re ad from the tracker .

Find the tan gent of the elevation angle from the ta ble at the en dof this section, or using a scientific calculator (ente r th e an gle,then press th e TAN key). Multiply this tangent by the baselinelength (the distance from the tra cker to launcher) to find the rock-ets altitude. The Altitrak gives a direct rea dout of the altitude,assuming the tracker is located 150 meters from the launch pad .

A single tra cker gives best r esults on calm da ys. Wind inter -

feres with accuracy since models tend to tilt over into the wind a sthey fly. The result is that t he rocket will not be stra ight over thelaunch site at peak altitude,but inste ad will be somedistance over in the direc-tion of the wind. To keeperror du e to wind drift to aminimum, locate the track-er at a 90 angle to thewind direction as shown.

For better accu racy, usetwo tracking stations onopposite sides of thelaunch pad, or place more than one tracker a t ea ch sta tion.

The easiest way of calculating rocket height using multiple

Steel RodLaunch Lug

Blast Deflector

Baseline

ElevationAngle

TrackingStation

LaunchSite

MODEL

MOD

ELRROC

KET

OCKET

ALALTITUDEFINDER

TITUDEFINDER

IIIIIIIIIIIIII

IIII

2200 3300

4400

90

WIND

Tape

Protractor

WeightedString

Ruler EstesAltitrak

10

WIND


11/16

TABLE OF TANGENTS

Angle Tan Angle Tan Angle Tan Angle Tan Angle Tan

1 .02 17 .31 33 .65 49 1.15 65 2.14

2 .03 18 .32 34 .67 50 1.19 66 2.25

3 .05 19 .34 35 .70 51 1.23 67 2.36

4 .07 20 .36 36 .73 52 1.28 68 2.48

5 .09 21 .38 37 .75 53 1.33 69 2.61

6 .11 22 .40 38 .78 54 1.38 70 2.75

7 .12 23 .42 39 .81 55 1.43 71 2.908 .14 24 .45 40 .84 56 1.48 72 3.08

9 .16 25 .47 41 .87 57 1.54 73 3.27

10 .18 26 .49 42 .90 58 1.60 74 3.49

11 .19 27 .51 43 .93 59 1.66 75 3.73

12 .21 28 .53 44 .97 60 1.73 76 4.01

13 .23 29 .55 45 1.00 61 1.80 77 4.33

14 .25 30 .58 46 1.04 62 1.88 78 4.70

15 .27 31 .60 47 1.07 63 1.96 79 5.14

16 .29 32 .62 48 1.11 64 2.05 80 5.67

trackers is to f ind the alt itude for each tracker a nd then takethe avera ge of these a ltitude figures. More complete informa-tion on basic altitude t racking is containe d in Estes IndustriesTechnica l Report TR-3.

RECOVERY SYSTEMSThe recovery system is one of the most importan t par ts of a

model rocket. It is designed to provide a safe means of retu rn-ing the rocket and its payload to ear th without da maging it orprese nting a hazard to persons on the ground. Also, the recov-ery system provides an ar ea for competition when rocket flyershold contests to see whose rocket can rema in aloft the longest.In addition, rocket recovery is an ar ea for valuable exper imen-

tation and research a s modelers develop new and better meth-ods of retu rning their rockets to earth .

Most recovery systems in u se today dep end on drag (or windresistan ce) to slow the rocket. Each chan ges the model from astrea mlined object to one which the air can catch against andreta rd its descen t. Six main recovery method s are used bymodel rocketeers today:

1. Featherweight Recovery, 2. Streamer Recovery, 3. TumbleRecovery, 4. Parachute Recovery, 5. Helicopter Recovery, 6.Glide Recovery.

Some of the m ost common err ors causing recovery systemfailures are listed below with th eir solution.

PROBLEM (1) Engine not held secur ely and ejects, instea d ofrecovery device being dep loyed.

SOLUTION: On m odels with engin e holder hooks, m akesure hook latches properly over end of engin e. If engin e isheld by fr iction fit, wrap enough maskin g tape aroun dengin e to hold it tightly.

PROBLEM (2) Para chute or stre amer is melted or scorchedby hot ejection gases.

SOLUTION: Be sure you hav e used suffi cient r ecoverywaddin g to fill a len gth of two body d iam eters.

PROBLEM (3) Nose cone fails to sepa rate from body tube.

SOLUTION: Check fi t of nose cone in t he body tube; be sureno shroud lin es are trapped by n ose shoulder. Parts shouldseparate easily, but not be loose. If fit is too tight, sand in sideof body tu be or n ose cone shoulder wi th fin e sandp aper.

PROBLEM (4) Nose cone falls off before e jection.

SOLUTION: Fit is too loose. Wrap m asking tape on shoul-der of nose cone for a snu g but not tight fit .

PROBLEM(5) Para chute d eploys, but wind car ries rocketaway.

SOLUTION: In win dy con dit ions replace the parachu tewith sm aller chu te or stream er. Or, reef the chute byapplyin g a wrap of tape aroun d the parachute shroud lines,half-way up; this prevent s the chute from openi n g fully so them odel falls faster. Or, cut a spi ll hole in the cen ter of the

pa ra chu te.

PROBLEM (6) Hole or cra ck in rocket allowing ejection gases

to leak through.SOLUTION: Constr uction at rear of rocket m ust be air t ight

when engin e is in place.

PROBLEM (7) Failur e to dep loy recover y device beca usebody tube is too large for proper pre ssurization.

SOLUTION: Add a stu ffer tu be, usu ally m ade from BT-20 orBT-50. Center stu ffer tube in side rocket w ith pap er r in gs an dglue securely in place. Stuff er tube reduces area to be pres-surized.

MULTI-STAGING

1. IGNITIONThe first stage of a mu lti-stage rocket is always ignited by

stan dard electrical means. Second stage ignition occurs auto-matically upon bu rnout of the first stage. Figure 1A shows thatthe first stage engine has n o delay or ejection charge. Thisgives instant ignition of the n ext stage at bu rnout .

1

2

3

4

5

6

11


12/16

In figure 1B the propellant is part ially burned , leaving a largecombustion chamber . As the prope llant continu es to burn , thewall of prope llant be comes thinne r unt il it cannot withstan dthe high pressure inside the chamber. At this point the remain-ing propellant wall rup ture s, and the h igh pressu re blows for-ward towar d the nozzle of the next st age, carrying hot gasesand small pieces of burning propellant int o the n ozzle of thesecond sta ge engine. This action is illustra ted in figure 1C.

For this system to work, the stages must be h eld togetheruntil the upper stage engine has ignited. When this happen s,the stages must then se par ate in a straight line. This is accom-plished by wrapp ing one layer of cellopha ne tap e aroun d the

join t betwe en engin es and then rece ss in g t h is join t 1/ 2 r ea r-ward in the b ooster body tube, as in figure 2. Recessing the

join t for ce s the st a ges to s epara te in a st ra igh t lin e.

Figure 2 shows the engine inst allation in a typical two-stagemodel. Always tape th e engines together before inserting theminto the rocke t. IMPORTANT: Che ck carefully before an d aftertaping to be sure the engines are in the in pr oper posit ions(nozzle of upper sta ge engine against top end of boosterengine). Failure to check carefully can be highly embar rassingas well as dam aging to the rocket .

After taping the engines together, wrap maskin g tap e aroun dthe upper stage engine at the front and near the rear as in f ig-ure 3 to give it a tight fit in the b ody. Push it into place. Wrapthe booster engine and pu sh it into position. Failure to get theupp er sta ge engine in place tightly enough will result in th erecovery system m alfunctioning; failure t o secure t he boosterstage tightly can r esult in its dropp ing off under accelerat ion.

Rockets using large diameter tubes (BT-50 and BT-60) requiresomewhat d ifferent me thods, but the sa me prin ciples of tightcoupling and st raight line sepa ration must be followed. The

recommen ded coupling method for large diamete r tubes isillustra ted in figure 4A. The stage coupler is glued t o the boost-er body tube, with the motor adapt er for the upper stageengine moun t positioned forward to allow the sta ge coupler tofit into the up per sta ge, while the motor a dapt er of the boosterengine moun t is posit ioned to the rear .

The up per stage en gine h older tube projects 1/ 4 rearwardfrom the end of the upper body tube. The engine is held inplace by wrap ping a layer of ma sking tape TIGHTLY aroun d th eend of the tube an d the end of the engine as in figure 4B. Theengine mount in the booster mu st be built to leave space forthis system (see figure 4C). The booster engine is held in placewith a wrap of masking tape in the sam e mann er as the u pperstage engine.

In some multi-stage models the en gines can not be coupleddirectly together with cellophan e tape , such as the case wherea D12 is staged to a stan dard size engine. In this case, usemasking tape on the stage couplers as needed to achieve atight fit between stages, to prevent sepa ration before upp erstage ignition.

2. STABILITYSince two or more engines are mounted near the rear of a

multi-stage rocket, it ha s a t ende ncy to be ta il-heavy. To com-pen sate for this, larger fins are often used on t he lower stage.Each additional stage requires even great er fin area s. Thiseffect can be minimized if the u pper stage is fairly long,increasing the stability of the mode l.

When ch ecking for stab ility, test first the upp er sta ge alone,then add the next lower stage and test , and so on. In this wayyou can b e sure th at th e rocket will be stable in ea ch step of itsflight, and you can locate any stage which does not ha ve suffi-cient fin area . Always check for stability with the he aviestengines to be used in p lace.

3. BOOSTER RECOVERY

Most lower stages are de signed to be un stable after sepa ra-tion. The booster should be built so that the cente r of the are aof the fin (its balance point) ma tches or is up to 1/ 4 ahea d of

the boosters balance p oint with an exp ende d engine casing inplace. Thus, boosters will requ ire no par achut e or strea mer,but will norma lly tumble, flutter, or glide back t o the ground . Abooster sta ge should be paint ed an especially bright colorbecause i t does not have parachute or streamer to a id in spot-ting it once it is on the ground.

4. TYPES OF ENGINES

Lower and int erme diate stages always use engines whichhave no delay element , and no para chute ejection charge. Nodelay is used so tha t the n ext stage will receive the ma ximumvelocity from its booster. Suitable engines have designationswith a 0 de lay, su ch a s th e B6-0, C6-0, D12-0, an d A10-0T.

In the upper stage an engine with a delay and a p arachuteejection charge is used. As a genera l rule the longest possibledelay should be used. Engines suitable for upper sta ge use areth ose wit h long de lays su ch a s th e A8-5, B4-6, C6-7, D12-7, etc.12

Masking Tape

Cellophane Tape

Masking Tape

EngineMount Tube

Engine Block

Adapter RingAdapter Ring

FIG. 4C

CellophaneTape

CellophaneTape

Booster

Masking Tape

Masking Tape

EngineJoint

Body TubeJoint

1/2


13/16

CLUSTERINGWhen large models an d heavy payloads have to be laun ched,

one engine often cann ot supply enough power. A cluster of sev-eral engines can be used in t his case.

ENGINE ARRANGEMENTS

In designing a cluster ed model the first rule to reme mber isthat thru st must be balanced around the center line of the rock-et. Figure 1 shows several engine arran gements that sat isfy

this requirem ent. All engines should be located close togetherto keep un balance d thru st from forcing the model off course.

CLUSTER IGNITION METHODSReliable ignition is the most imp ortan t pa rt of successful clus-

tering. All engines mu st be ignited simultan eously; thisrequ ires a hea vy-duty launch con troller that ca n sup ply highcurre nt levels. The Estes Comman d Control launch controller

is designed specifically for cluster ignition. A custom d esignedcontroller using a 12 volt car batt ery for the power sup ply anda h eavy gauge wiring is also suitable.

Carefully install igniters in th e cluster engines using igniterplugs in the norm al way, making sure t he tips of the ignitersare touch ing the propellant and a re held firmly in place.Igniters mu st be connecte d in parallel not in series! The eas-iest way to do this is using clip whips. Meticulously clean allclips with sandpa per before hooking up the igniters. Everyigniter m ust be connect ed to on e micro-clip from ea ch clipwhip. Double-check tha t one an d only one clip from each whipis connect ed to every engine. At the launcher , check that non eof the igniter lead s or micro-clips ar e shorted to each oth er, to

the blast deflector, or to the launch rod. Check one last timethat a ll clips are in p lace.

GENERAL INFORMATION

Use a heavy-duty launch pad su ch as th e Estes Por ta-Pad Elaunch pa d with cluster models. When he avy rockets are beingflown, the laun ch pad should be an chored to the ground withstakes or weights.

The Safety Code requ ires that you stan d at least 30 feet awaywhen igniting an engine or cluster of engines tota lling morethan 30 Newton-seconds of total impulse.

To legally fly rockets weighing more t han one p ound or usingengines contain ing more than four ounce s of propellant, youmay nee d to n otify the Fede ral Aviation Administration, orobtain an FAA waiver, depending on th e type of airspace con-trol over your launch ar ea.

Before insta lling the engines in your cluster r ocket, pack thefront of each en gine above the ejection end cap with flame-resistan t wadding. This eliminates the p ossibility of oneengines ejection char ge igniting the ejection cha rge of anunignited engine and dama ging the rocket. For more complete

information on clustering, see Est es Technical Report TR-6 inThe Classic Collection .

PAYLOADS

Flying payloads on model rockets is a n exciting and challeng-ing activity for both n ovice an d exper ienced r ocket hobbyists.A wide variety of payloads have be en flown succes sfully onmodel rockets.

Cameras: The Estes Snap Shot Camer a rocket allows evennovice rocket flyers to t ake a erial photos from 500 feet high.Depend ing on the en gine delay used, the photo can be a verti-cal shot of the laun ch area or an oblique view of the n earb ylandscape. Advanced modelers have adapt ed and f lown auto-sequen ce 35 mm camer as, movie cameras, and even video cam-eras an d digita l cameras on rockets.

Electronic payloads: These payloads ra nge from simple sonicbeacons that a id in recovering rockets that lan d in tall grass,a ll the way to radio transmitters and miniature computers thatmake temp erature or a lt i tude measurement s during f light.

Eggs: Launching a raw egg and r ecovering it unbroken ca nchallenge the p ayload h and ling skills of any rocket flyer. Theegg must be p roperly padd ed to su rvive the flight; you ma ywant to en close it in a plastic bag just in case!

Biological payloads: Excep t for insects , you should NEVERlaunch a live anima l in your rocket. The high launch accelera -tion or a recovery failure could seriously injure or kill the ani-mal. For a similar cha llenge, try flying a raw egg.

BOOST-GLIDERS

Boost-gliders a re m odels which fly straight into t he air like

any other rocket. However, they glide back to eart h instead ofcoming down suspended from a pa rachute .

There are severa l types ofboost-glider s, includ ing: 1. Rearen gine, 2. Fron t en gine, 3. Pop-pod, 4. Varia ble geomet ry, and5. Para site. Some boost gliders u se radio control to allow the

modeler to pilot the glider. Although these types appe ar verydifferen t, many of the same p rinciples app ly to all.

A boost-glider, as a ny other rocket, must be sta ble to flyupwar d. During glide a model must still be stable, but not bynea rly so great a ma rgin. Boost-gliders can accomplish thetran sition from boost to glide configura tion in severa l ways.Some use a cha nge in balance point, often by ejecting enginepods; others u se a shifting of aerodynamic sur faces; still othersuse c ombin ation s of both me thod s. See TR-4 and TR-7 in TheClassic Collection for further discussion on gliders.

GLIDE TESTING

A boost-glider mus t be trimm ed to glide cor rect ly beforelaunching. Some models are trimme d by adjusting the posi-tions of elevons or other ae rodynamic control surfaces. Othermodels are t rimmed by add ing or removing weight, such asclay, to the nose or t ail of the glider.

When trimming a model, give it a straight, smooth, level tossinto the wind an d note how it glides. If it stalls, add weight tothe nose. If it dives, remove weight from the nose. If it turnstoo much, place a very small weight on the wing tip which is onthe outside as i t turns.

13

Glide Paths Observed AsGlider Is Tossed Lightly

Into The Wind FromShoulder Height

Stall

NormalDive

FIG. 1


14/16

Few models are as spe ctacular in flight an d as en joyable towatc h as a good boost-glider. The modeler looking for a chal-lenge will find that developing improved boost-glide designs isone of the most reward ing areas of research in mode l rocketry.

MODEL ROCKET ENGINESTodays rocket flyers can choose from a large variety of

engines to power t heir models, with a n en gine a vailable foralmost every purp ose. NOTE: The rocket engine design andperforman ce information given here is for educat ional purpos-

es only. We believe that knowing how rocket engines work willincrease your und ersta nding of science and h elp you designbette r rockets for specific purp oses. Manu facturing rocketengines is an inher ently dangerous act ivity that should only beattempted by professionals!

OPERATION

The figures below show the inte rna l structure a nd thr ustcurve of a typical model rocket en gine.

The combustion of the solid propellant produ ces high temper-ature , high pressure gases that are e jected thr ough the nozzle .The reaction to forcing the exhau st out th e nozzle is a forwardthru st (an example of Newtons Third Law of Motion). Duringthe thrust phase the model rocket accelerates upward, gainingvelocity and altitud e.

After propellant bur nout, the delay element is ignited. Thedelay mate rial is slow-burn ing; it p roduces tracking smoke, bu tnegligible thrust. The delay allows the rocket to coast t o peakaltitude be fore igniting the ejection char ge.

The rapidly-burn ing ejection cha rge produ ces a bu rst of gasto pressur ize the body tube a nd activate the r ecovery system of

the model.

ENGINE CODES

Model rocket en gines a re labeled with a t hree-part classifica-tion code (B6-4, for examp le) that describes th e per formancepara meter s of the engine. You must under stan d this code inorder to choose the p roper en gine for your model.

The first part of the en gine code is a letter de signat ing themot ors TOTAL IMPULSE class (t he B in B6-4). You ca n th inkof total impulse as the total power the en gine prod uces.Technically, total impulse is a mea sure of the m omentu mchange the engine can impart to the rocket, measured inNewton-seconds. In practical terms, an engine with greater

total impulse can lift a rocket higher a nd faster , and can liftheavier rockets, than an engine with lower total impulse. Thetable below gives the tota l impulse ranges an d typical rocketperforman ce for each class.

TYPE TOTAL ALTITUDE RANGE APPROX. ALTITUDE OFCODE IMPULSE OF TYPICAL MODELS 60 gram, BT-50 ROCKET

Newton -Sec mete rs mete rs

1/ 4 A 0 - 0.625 10 to 75 3 (not rec.)

1/ 2 A 0.626 - 1.25 20 to 120 10

A 1.26 - 2.50 40 to 250 40

B 2.51 - 5.00 60 to 400 110

C 5.01 - 10.00 80 to 600 260

D 10.01 - 20.00 100 to 700 440

E 20.01 - 40.00 130 to 800 760

F 40.01 - 80.00 160 to 1000 N/ A

The second par t of the engine code (the 6 in B6-4) gives theAVERAGE THRUST of the en gine, mea sur ed in Newt ons. TheNewton is a mea sure of force; 1 pound equ als 4.45 Newtons.The greater the thrust of an engine, the harder i t pushes on therocket and t he faster the rocket will accelerat e. The B8 and B4are both B engines (so they have the sam e total impulse) butthe great er thr ust of the B8 will cause a rocket to leap into th eair much faster .

The third p art of the engine code follows the dash (the 4 inB6-4); this nu mbe r is th e TIME DELAY, in secon ds, bet weenburn out of the pr opellant and a ctivation of the ejection charge.This delay allows the rocket to coast to pea k altitude b eforedeployment of the recovery system. The proper choice of delaytime depends on how long it takes a rocket to reach peak alt i-tude with a particular en gine. Engines with codes ending in-0 are booster e ngines; they do not conta in delay and ejectioncharges. There is also a spe cial type of plugged engine withcodes en ding in -P; these a re useful in r adio-control gliderswhere n o ejection or booster blow-through is de sired.

THRUST CURVES

Estes en gines come in d ifferent t ypes including end-burn ingand sem i-core-burn ing. The different thr ust curve shap es ofthese t wo types ar e primar ily the re sult of the de pth of theport formed in the the propellant.

The most common model rocket engine is the end -burn er,which has a shallow port. This design is used in many Estesengines a nd is especially effective with lightweight high perfor-man ce rockets. The high initial thru st boosts the rocket to asuitable flying speed almost immediate ly; thrust the n drops toa lower sustaining level to maintain spe ed an d gain the mostdistance with the least fuel consump tion.

For hea vy rockets, espe cially those car rying large pa yloads,semi-core-burn ing engines are a vailable. These engines have

deep er ports, produ cing a very high initial thrust pe ak due t o alarger surface area for propellant bur ning.

SELECTING THE CORRECT ENGINE

Always use an ap propr iate engine to fly your rocket. Justbecause an engine f i ts in the model does not mean i t is a suit-able engine! When flying an Estes rocket, consult the Este scatalog or the kit instru ctions for a list of engines recommen d-ed for that model.

If the launch field is small, or if the weath er conditions a rewindy, use a lower tota l impulse engine to increa se yourchan ces of recovering the rocket. If you are launching a heavypayload in a model, it may be necessar y to use an engine with ashorter time de lay than is recommende d for the rocket withouta payload.

ENGINE ERING AND QUALITY CONTROL

Today the Estes en gine re presen ts the re sult of ever 45 yearseffort in engineering, craftsman ship and qu ality control. Thetotal impu lse of Estes e ngines is closely controlled, whichallows us to make our engines very nea r the maximum p ermis-sible size in a given class.

Three out of every hun dred en gines ma de by Estes Indu striesare sta tic tested on a recordin g type of test sta nd which graphi-cally records the ma ximum thrust , thrust variations, minimum

thru st, overall thrust d ura tion, length of time delay, and t he14

ThrustinNewtons

14.0

12.0

4.0

2.0

0 0.20 0.40 0.60 0.80

1/2A6

Time in Seconds

ThrustinNewtons

0.00.50 1.00 1.50 2.00 2.50 3.00

Time in Seconds

5.0

10.0

15.0

20.0

25.0

30.0

0.00

D12

C11

1.00 1.20

0.0

6.0

8.0

10.0

D11

C6

E9

B6

B4

A10

A8

A3 1/2A3

1/4A3

ComparativeThrust Curves OfAll Estes Engines

1/4A3-B6

C6-E9

Cross-Section ViewOf B6-4 Engine

Thrustinnewtons

20

18

16

14

12

10

8

6

4

2

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Time in Seconds

Typical Thrust Curve B6-4 Engine

Total Impulse = Average Thrust x Thrust Duration

AverageThrust

Delay Period NoMeasurable Thrust

Ejection ChargeActivities

4.0 5.0

(Pounds)

1

2

3


15/16

stren gth of the ejection char ge. Any batch of engines whichdoes not meet rigid stand ards is discarded. All tolerances ar ekept as sma ll as possible so that t hese en gines mak e excellentpropu lsion un its for contests, exhibitions and science st udies.

SAFETY

Rocket engines are not toys, but scientific devices. With com-mon sense a nd close adhere nce to safety rules, model rocketryis as safe as any other sport, hobby, or scientific stud y.Carelessness can ma ke it dangerous, as with model airplanes ,

baseba ll or swimming. If you are hit by a model rocket tr avel-ing 300 or more miles per hou r, you will be hurt. Use commonsense and follow the safety code. Dont spoil model rocketrysexcellent record of safety.

MODEL ROCKET PE RFORMANCE

Several factors affect the alt i tude pe rformance of modelrockets.

ENGINE SIZE

The greater th e total impulse of an en gine, the h igher it willboost a model. The approximate altitud es achieved by typical

single stage rockets a re listed in the table on p age 12; high per-formance models can exceed these values. The kits, compo-nents, and engines produced by Estes Industr ies have beendesigned to cover the ent ire performan ce ran ge from low alti-tude sport a nd demon strat ion models to high altitude, high per-formance payload and competition rockets.

WEIGHT

In most cases, the hea vier a rocket, the lower the a ltitude itwill reach. A baseba ll can be tossed higher tha n an 8 poundbowling ball; the same holds true for model rockets. In addi-t ion heavier rockets are more a pt to t i l t a t an angle as theyleave the laun cher, reducing altitude even more.

Weights listed for rocket kits in the cata log do not includeengines. To determine the lift-off weight of a mode l, add theengine weight, shown in th e engine selection cha rt, to the kitweight. Remember t o also add th e weight of any payload car-r ied in the rocket.

Use high-thru st en gines with he avy rockets to insure ad e-qua te lift-off spe ed. The lift-off weight of the rocket m ust n otexceed t he Maximum Liftoff Weight for the e ngine being u sed(see the engine tables in your Estes catalog).

DRAG

Drag, or wind resistan ce, is the third item which affects per -formance. The more drag on a rocket, the lower the altitude it

will reach . A num ber of factors determine th e amount of dragon a rocket. The more frontal area the rocket has, the greaterits drag will be. As a resu lt, large diamet er model rockets willgenerally not reach a s great an alt itude a s smaller diameterrockets with the same engine power. Rough surfaces createturbu lence in the air as it flows past the r ocket, increa singdrag. Smooth finishes will increase the ca pability of the model.The sta bility of the rocke t also affects dr ag if it wobbles inflight, it will have greater drag. Careful atten tion to red ucingdrag can sometimes doub le a rockets altitude performan ce.

NAR SAFETY CODE1. MATERIALS. I will use only lightwe ight, non -met al pa rts

for the nose, body, and fins of my rocket.

2. MOTORS. I will use on ly certified, comm ercia lly-ma demodel rocket motors, and will not tam per with the se motors oruse them for any purposes except those recommended by themanufacturer .

3. IGNITION SYSTEM. I will lau nch my rocke ts with an elec-trical laun ch system and electrical motor igniters. My launch

system will have a safety interlock in series with the lau nchswitch, and will use a launch switch that retu rns to the "off"position when released.

4. MISFIRES. If my rocket does not launch when I press thebutton of my electrical launch system, I will remove thelaunche r's safety inte rlock or disconnect its ba ttery, and willwait 60 seconds after t he last launch a ttemp t before allowinganyone to approach the rocket.

5. LAUNCH SAFETY. I will use a cou nt down before laun ch,and will ensure tha t everyone is paying atten tion and is a safedistance of at least 15 feet (4.6 m) away when I launch rocketswith D motors or smaller, and 30 feet (9 m) when I launch larg-er rockets. If I am uncert ain about th e safety or stability of anunt ested rocket, I will check the stability before flight and will

fly it only after warning specta tors an d clearing them a way to asafe distance.

6. LAUNCHER. I will lau nch m y rocket from a lau nch r od,tower, or rail that is pointed to within 30 degrees of the vert icalto ensur e tha t the rocket flies nearly straight up, and I will usea blast deflector to preven t the motor's exhau st from hittingthe ground . To prevent acciden tal eye injury, I will placelaunche rs so that th e end of the laun ch rod is above eye levelor will cap the en d of the rod when it is not in use.

7. SIZE. My mode l rocket will not weigh more t ha n 53 ounces(1500 grams) at liftoff and will not contain more th an 4.4ounces (125 grams) of propellant or 71.9 pound-seconds (320 N-sec) of total impulse. If my model rocket weighs more th an one

pound (453 grams) at liftoff or has more th an 4 oun ces (113grams) of propellant, I will check an d comply with Federa lAviation Administrat ion r egulations before flying.

8. FLIGHT SAFETY. I will not lau nch m y rocket a t ta rgets ,into clouds, or near airplane s, and will not put an y flammableor explosive pa yload in my rocket.

9. LAUNCH SITE. I will launc h my rocke t out doors, in a nopen area at least as large as shown in the a ccompanying table ,and in safe weather conditions with wind speeds n o greaterthan 20 miles per hour (32 km/ h). I will ensu re that the re isno dry grass c lose to the launch pad , and that the launch sitedoes not pr esent r isk of grass fires.

10. RECOVERY SYSTEM. I will us e a re cover y system s uch asa streamer or parachute in my rocket so that i t re t urns safelyand u nda maged an d can be flown again, and I will use onlyflame-resistan t or firepr oof recovery system wadd ing in myrocket.

11. RECOVERY SAFETY. I will not a tt em pt t o recove r myrocket from power lines, tall trees, or other dan gerous places.

15

LAUNCH SITE DIMENSIONS

Installed Total Equivalent Minimum Site

Impulse Motor Type Dimensions

Feet Meters

.00 - 1.25 1/4A, 1/2A 50 15

1.26 - 2.50 A 100 30

2.51 - 5.00 B 200 60

5.01 - 10.00 C 400 120

10.01 - 20.00 D 500 150

20.01 - 40.00 E 1,000 300

40.01 - 80.00 F 1,000 300

80.01 - 160.00 G 1,000 300160.01 -320.00 Two Gs 1,500 450ROCKET

TIP:

ROCKETTIP:

In most cases, baseball,

soccer or football fields

are great launch areas!

In most cases, baseball,

soccer or football fields

are great launch areas!


16/16

Electron ic Model Rocket NewsProvides articles of inte rest, techn ical tips, information about

new pr oducts, special offers, and much m ore. Available at

www.estesrocket.com

Newtons Laws of Motion and Model Rocketry - 2821The three laws of motion are explaine d in easily und erstood

terms. Simple examples and experiments are included.

Este s Guide for Aerosp ace Clubs - 2817The perfect source book for organizing and opera ting a suc-

cessful model rocket club or ESP chapter .

Model Rocket Contest Guide - 2815Use to p lan mode l rocket contest s for clubs or schools. Details

on compet itive events a nd su ggestions on a ll facets of contest

organization.

Projects in Model Rocket ry - 2831Suggestions on how to plan, prepa re, and present research pro-

je ct s, id eas for abou t on e hundred proje ct s.

Model Rocket Laun ch System s - 2811Contains a wea lth of information. Photographs a nd clearly-

drawn sche matics make it easily und erstood.

The Clas sic Collection - 2845A compreh ensive collection of techn ical reports an d notes th at

make a valuab le referen ce t ool. Includes TR-1 throu gh TR-7 an d

TN-1, TN-3, TN-4, a nd TN-6.

Model Rocketry Study Guide - 2841A logical program for an yone who wants t he most from model

rocketry. Guides a beginne r on the pat h to becoming an expe rt

rocketeer .

Altitude P red iction Chart s - 2842A simple system by which aerod ynamic drag and other e ffects

can be t aken into account in pred icting rocket peak alt i tudes.

Technica l Repor t TR-10.

Aerodynamic Drag of Model Rockets - 2843Gives practical exam ples of ways to minimize ae rodynamicdrag a nd improve per formance. Technical Report TR-11.

Elemen tar y Math em atics of Model Rocket Flight - 2844Information on how to make your own altitude tracker a nd cal-

culate sp eeds and accelerat ions. Technical Note TN-5.

Model Rocke try Techn ical Manu al - 2819Handy guide for constru ction an d flight of mode l rockets. Tips

on scratch building, launch systems, tracking, staging, boost-

gliders, and m ore.

Estes Educator NewsInteresting technical articles, new product information, plus

activities and resources on space and model rocketry subjects

suitab le for classroom use . Available at www.estes educa tor.com.

Guide for Tea che rs a nd Youth Group Lea der s - 2814Introduce s you to Estes model rocket tech nology and the com-

plete services offered in our edu cational program.

Camp Leade rs Model Rocketry Manu al - 2822Proven guide for intr oducing model rocketr y successfully into

camp p rograms.

Find all these informative publications at

www.estesr ockets.com or www.estesed ucator .com.

Est es Indust r ies

1 2 9 5 H St reet

Pr inted in China

www.estesrockets.com

EST 2819

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Rocketry - Model Technical Manual