wmci-estes rocket manual

8/13/2019 Wmci-estes Rocket Manual

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Model RocketryTechnical Manual


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TABLE OF CONTENTSTopic Pa ge

Why Estes Model Rocketry 1

A Safe Progra m 1

Your First Model Rocket 1

Construct ion Techn iques 1

Types of Glues 1

Fin ishing 4

Stability 5Swing Test For Stability 6

Prepar ing For Flight 6

Ignite r In sta lla tion 7

Launching 7

Coun tdown Checklist 8

Tracking 8

Trackers 8

Recovery Systems 9

Multi-Staging 9

Cluster ing 11

Model Rocket Engines 12NAR Safe ty Code 13

Publica tions back cover

INTRODUCTION

Welcome to th e exciting world of Estes mode l

rocketry! This technical man ual was written t o

pr ovide both an ea sy-to-follow guide for the

beginner an d a reference for the experienced

rocket enth usiast. Here youll find the answer s

to the que stions most common ly aske d. More

complete techn ical informa tion on all the sub-

je cts can be found in the many p ublica t ions

listed in your Este s cat alog.


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W HY ESTES M ODEL 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 safe activity because it incorporat es

three importa nt feature s. The first is the model rocket engine,a professionally manufactur ed, low cost, solid-fuel rocketengine. This frees the rocket builder from the inheren tly dan -gerous procedur es of mixing chemicals and p acking propellant.

The second feature is the u se of safe mate rials for construct -ing the rockets. All model rockets are built using only light-

weight mate rials such as paper, plastic, and wood. Metal part sare ne ver used for the main structural components of themodel.

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 35 years and 300million rocket laun ches.

YOUR FIRST M ODEL ROCKETThe Estes Alpha is shown here t o i llustrate t he pa r ts of a

typical 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 neede d to build an E2Xmodel. Constr uction involves almost no cutting or sanding,and the models do not need painting.

The Beta series of models is an excellent choice for your sec-ond or third model. The Beta mode ls are also a good start ingpoint if you ha ve previous model building experience.

As your kn owledge of rocketr y and your modeling skillsincrease you can move up to th e Explorer, Challenge, Master ,and Pro series mode ls, and eventu ally to building your own cutom designs from parts available in the Estes cat alog.

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

cally need the following tools and supp lies (see kit instruct ionfor specific requiremen ts):

Mode ling knife Scissors Ruler

Spray pa in t Ba lsa sea ler or filler Maskin g tape Tube-type p last ic cemen t

White glue Fine a nd ext ra fine sandpaper

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 GLUESeveral types of glues an d adh esives are commonly used in

the constr uction of model rockets; the prope r glue to use

depends on the ap plication.

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

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 use

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 body

tube 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 bo

tle and is applied with a small brush.

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

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 s

to balsa or body tubes.6. Epoxies: These two-par t adhe sives are also recomme nd

ed for the advanced mode ler. Epoxy provides extra

stren gth for the en gine mou nts an d fins of high-thr ust

Pro Series 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 pushyour rocket into t he 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 i

Shock CordMount

Body Tube

Launch Lug

Engine HolderAssembly

EngineHook

Fins

Parachute

ShockCord

NoseCone

ShroudLines


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4 4

4

4

3

3 3

520

50

55

60

70

80

When 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 en gine 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 inser ted th rough 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 too

small for an anchor mount.The anchor is cut from paper or index card stock. Be sure to

glue the a nchor far en ough into the tube or it will interferewith the prope r fit of the nose cone.

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 athe (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 drawer sill or door frame. Match the edge of the notch with aspacing mark; run a p encil along the ed ge to draw your guide

line. 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, and a Fin AlignmentGuide that holds fins in p roper alignme nt while gluing.

5. INSTALL THE ENGINE MOUNT

Be sure the glue on the en gine moun t rings is completely dry

before 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 holder 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 bodyover the area where th e mount s ring or coupler will fit. Inserthe moun t into position in one smooth motion. DONT pau se,or the glue will grab it in the wrong place! Support th e tubenose-up while the glue dries.

6. BALSA FINS

Fins are u sed to ae rodynamically guide your rocket . Somemodel rockets use fins mad e from thin sheets of balsa wood. man y kits the fins are pr e-cut for you by a punch die. In otherkits, or to ma ke customfins, you must u se a pat -

tern to mark and cut ablank sheet of balsa. Allbalsa fins must be cut sothat the grain of thewood runs p arallel withthe lead ing edge of thefin for ma ximumstrength.

Die-Cut Balsa Fins

Before re moving the die-cut fins from the ir sheet, use extraf ine san dpaper to sand both surfaces of the sheet of balsa (asand ing block is helpful here). Use a modeling knife to care fu

ly cut thr ough the points where the fins are still attached t o thdie-cut sheet , then remove the fins. Stack the fins togethe r ansand a ll edges square.

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 Apart

Thread InApply Glue

LeadingEdg

e

Tip

Trailing Edge

RootE

dg eGrain

Direction


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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 pa ralle l to thegrain direction! Trace arou nd the patt ern 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 sh aping of the fin ed ges.

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 linedshap e shown 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 ake

Sometime after th e fin joints have dr ied completely, theyshou ld be rein forced. Do this by ap plying a fillet of glue asshown. Always suppor t the b ody in a h orizontal position whilfillets a re dr ying so that the gluedoes not run. Build up the filletsin several t hin layers, allowingeach layer to dry between a ppli-cations (this is much faster th anwaitin g for a sin gle thick filletlayer to dry).

8. ATTACHING LAUNCH LUGS

The laun ch lugs are use d to position the rocket on th e launcrod. The lugs and r od help guide the r ocket in its first few feetof flight. The model mu st be guided un til it is going fast enou gfor the fins to guide it. Launch lugs are att ached in mu ch thesame way as fins. If a stand-off is used to keep the r od from hting a large diameter pa yload section, attach t he lug to thestan d-off piece first, then atta ch the un it to the body. Sightalong the tube to besure th e lug is para l-lel to the body tubebefore the glue sets.

Apply glue fillets t othe lug after the ini-tial glue joint h asdried.

9. PARACHUTE ASSEMBLY

The most common model rocket recovery system is the pa rachute. On page 9 you will find a lterna te re covery systems. Toassemble an Estes parachute , cut out the plastic parachutealong the dotted lines. Apply the six vinyl tape rings to the coners of the parachute and pun ch holes through the parachutemater ia l in the center of the tape r ings using a sharp pencil .Cut three equ al length shroud lines tha t are twice as long as

the para chute diameter . Tie both ends of the shroud l inesthrough the holes in the tap e rings, as shown.

To attach the parachute to the nose cone or adapter eyelet ,thread th e shroud l ines through the eyelet , pass the pa rachutethrough the loop of shroud lines as sh own, then pull the linestight.

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 eaiest to make, the y are not very efficient and allow a consider-able amount of sway during descent Round pa rachutes are

LAYOUT

FINPATTERN

Grain

LeadEdge

RootEd

ge

TRACING

Layout

FinPattern

Tracing

Rounded Edges Streamlined

Plain

G

W/Stand-Off

Fillets


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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 chut e to be eas ily rem oved. 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 from Estes or where fishing supplies ar e 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 section, 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 mar k. 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 veryfi d i h i l i h

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 appe arance 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 be fore the pa int isapp lied. A model with a smooth finish not only looks more professional, it expe iences less drag in flight, so it flies higher.

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 p arts a nd r equire n o 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 sandin g sealers and wood fillersare available at hobby shops and har dware stores. Many sanding sealers give off harmful fumes an d mu st be u sed only inwell-vent ilated ar ea s. Wate r-bas ed wood fillers have no nox-ious fumes; you may need to ad d water to thin them to a brushable consisten cy.

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 sanding sealer to the ba lsa. Let this drcompletely, then sand with 320 grit (or finer) sa ndp ape r, untithe surface is smooth again. Apply more sealer, repe ating theprocedu re un til all the pores in the ba lsa are filled.

Pract ically all of the sealer should be sand ed off after e achcoat. This is because the purp ose of the sea ler is to fill in theholes, not the sm ooth area s of the ba lsa.

2. SPRAY PAINTING THE MODEL

Using a good ename l spray paint is the easiest way for a

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

GlueGlue

Tape Strips OrTape Inside Of

Payload Section


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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 additional 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 area swith 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 lying

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

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 upwar d flight. Good aerodynamic stability will keep the rocket on a tr ue flight pa th eventhough 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 ging 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 flighare 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 thrust a ndforces on the nose try to bring the nose of the rocket aroun d tthe rea r. They are opp osed by the forces acting on the fins. Athese forces are a mplified by the distan ce from the location othe 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-centethru 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.

2oz

2

oz1

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 DecIn Wat

Blot Aw

Excess W

Force On Left Side Can Be

Balanced By Large Force Close By, Or

Small Force Far Away


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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 mean s that 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 to fly in the m odel. (The center of gravi-ty is always determ ined with an engine in place.) Slide theloop to the prop er position around th e rocket so the model bal-ance s 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 it

accord unless the y are sta rted str aight. This is done by holdinthe rocket in one hand with the arm extended and then pivot-ing the entire body as the rocket is star ted in the circular pathIt 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 wita 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,few 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 poincan 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 intthe 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 foward by adding a payload section to the model. Fins can eithebe 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

the e jection charge by using flame-resistan t recovery waddingNEVER 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 diameteThe wadding should fit against th e side of the tub e all the way

d t i d l

Add A Nose Cone Weight

Or Add A Tab To Each Fin

Here Here Or Bot

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


9/34

If the para chute has been packed in the model for an extend-ed per iod, re-pack th e chute just p rior to laun ch. Dusting thepara chute with ta lcum powder before packing will alsoincrease th e chances of a successful deployment . It is especial-ly importan t to follow these preca utions on cold days becau sethe low temperature ma kes the plastic parachute ma ter ia l lessflexible.

Check the fit of the n ose cone on th e model: If it is too tight,

see if the shock cord or shroud l ines were trapped between thenose 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 thebody tube with fine san dpa per. If the n ose cone fit is too loose,wrap tap e on the shoulder to adjust the fit. The nose coneshould sepa rate easily, but should n ot fall off if the rocket isinverted.

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.

LAUNCHINGModel rockets, like professional rockets, are laun ched e lectr

cally. This provides both safety and r ealism. Each engine solby 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 currenthrough 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 ignitewhich in turn ignites the en gine. The laun ch system is attacheto 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 througthe 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 spr ing return lau nchbutton so the current t urns off automatically when the bu ttonis released. In addition, a removable safety inter lock (safetykey) must be pr ovided; this could be a n e lectrical key-switchor an inserta ble metal pin. When th e safety key is removed,the laun ch controller cannot complete the e lectrical circuit tosend curren t to the igniter . ALWAYS rem ove th e sa fet y keyand ca rr y it with you when you go hook up the igniter ! Thinsures th at no one could activate the launch cont roller whileyour ha nds are near t he rocket nozzle .

Any homemad e electrical launch control system must includall 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 cont inuity check light. This is a smalbulb (no more than 1/ 4 amp for safety) that l ights when a complete circuit exists between batt ery and igniter; this indicatesthat the rocket can be launched If the continuity check bulb

B6-4

Safety Cap

Batteries

Launch Wires

MicClip

Launch Button

Safety Key

ContinuityCheck Light

Safety KeySwitch

Micro ClipContinuity CheckLight

LauncSwitch

6 or 12 V.D.C.Power Source


10/34

Most model rockets are guided during launch by an 1/ 8diamete r, 32 long laun ch rod (heavier models requ ire 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. A

piece 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 materials. For maximum safety, tiethe laun ch controller safety key to the plastic launch r od capsupp lied with the launch er. Always carry the cap an d key withyou to the laun ch pad! After sliding the rocket onto the launchrod, place the cap on t he rod before hooking up the igniter.The cap prote cts you from accidental eye injury from the rod.

If the cap is not available, put your ha nd on th e end of the rodbefore leaning over.

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, rememb er to remove the sa fety keyfrom the controller. If the rocket becomes en tan gled in apower line or other d angerous p lace, DO NOT attempt toretrieve the model!

4. LAUNCH AREAS

Choose a large field awa y from power lines, tall trees, and

low-flying aircra ft. The length of the sma llest side of the fieldshould be at least on e fourth of the rockets expected m axi-mum a ltitude. The Model Rocket Safety Code contains a ta bleof minimum field dimen sions for each en gine size.

COUNTDOW N 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)

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, trackers, and spectat ors.

6) Insert the safety key into the laun ch controller. Give anaudible count down:

5) 4) 3) 2) 1) LAUNCH!

TRACKING

The easiest way to me asure how high a rocket flies is to visually track the model using a tracking instrumen t, then triangulation 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 all-aroun d basic tr ackin

devices. However, it is easy to construct a simple tra cker: Aplastic protractor is attache d to a ruler as shown. Tie a weighed string through the small hole at the center of the p rotractor. When sighting along the ed ge of the ru ler toward the h orizon, the string should hang by the 0 mark on t he protr actor;when sighting at a point in the sky, the position of the stringwill 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. Thetracker should have a c lear view of the launch are a an d shoulnot be looking into the sun .

Before launch, alert the person at th e tracking station. Whethe tracker signals readiness, the rocket can be launched. Thtracke r sights along the tra cking instru men t and follows therocket as it rises. When the rocket re aches its peak altitude,

the tra cker locks the tra cking instru ment . An Altitrak islocked by releasing the trigger. To lock the home made tr ackethe 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 theend of this section, or using a scientific calculator (ent er theangle, then pr ess the TAN key). Multiply this tan gent by thebaseline length ( the distance from the tracker to launcher) tofind th e rockets altitude. The Altitrak gives a direct read out the altitud e, assuming the tra cker is located 150 meters fromthe launch pad.

A single tra cker gives best r esults on calm da ys. Wind interferes with accura cy since mode ls tend t o tilt over into th e winas the y fly. The resu lt isthat t he rocket will not bestraight over the launch

Steel Rod

Launch Lug

last Deflector

Baseline

ElevationAngle

TrackingStation

LaunSite

MOD

EL ROCKET

MODE

LROCK

ETALTITUDEFINDER

ALTITUDEFINDER

IIIIII IIII II

IIII

2200 3300 4400

Tape

Protractor

WeightedString

Ruler EstesAltitrak


11/34

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

t iple trackers is to f ind the alt itude for each tracker a nd the ntake th e average of these a ltitude figures. More complete infor-mation on basic altitude tra cking is conta ined in EstesIndustries Technical 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 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.

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

SOLUTION: Be sure you have 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 suren o shroud lin es are trapped by n ose shoulder. Parts shouldseparate easily, but n ot be loose. If fit is too tight, sand in sidof 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 askin g tape on shoul-der of n ose cone.

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 lineshalf-way up; this preven ts the chute from open in g fully so thm 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 gas

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

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 oBT-50. Center stu ffer tube in side rocket w ith pap er r in gs anglue 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-

1

2

3

4

5

6


12/34

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 ma lfunctioning; failure to secur e the boosterstage tightly can r esult in its dropp ing off under a cceleration.

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. Therecommen ded coupling method for large diamete r tubes is

illustra 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 tofi i h hil h d f h b

The upper 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 maskin g tape TIGHTLY aroun d thend of the tube an d the en d of the en gine as in figure 4B. Theengine moun t in the booster mu st be built to leave space forthis system (see figure 4C). The booster engine is held in placwith a wrap of masking tape in the sa me 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 sta ges, to prevent sep ara tion before upperstage 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 the r ocket will be stable in each step of iflight, and you can locate any stage which does not h ave 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 areof the fin (its balance point) ma tches or is up to 1/ 4 ahea d of

the boosters balance p oint with an e xpende 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 . booster 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.

Masking Tape

Cellophane Tape

Masking Tape

EngineMount Tube

Engine Block

Adapter RingAdapter Ring

FIG. 4C


13/34

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 METHODS

Reliable 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 high

curre nt levels. The Estes Comman d Control launch controlleris designed specifically for cluster ignition. A custom d esignedcontroller using a 12 volt car batt ery for the p ower supp ly 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 Power Plexlaunch 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 tota l impulse

PAYLOADS

Flying payloads on model rockets is a n exciting and challenging activity for both n ovice an d exper ienced r ocket hobbyists.A wide variety of payloads have be en flown succe ssfully onmodel rockets.

Cameras: The Estes Astrocam camer a payload allows evenovice rocket flyers to take a erial photos from a rocket.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 adapted and f lown auto-sequen ce 35 mm camer as, movie cameras, and even video cameras on model rockets.

Electronic payloads: These payloads ra nge from simple sonbeacons (such a s the Estes Transroc II) that a id in recoveringrockets tha t land in ta ll grass, all the way to radio tran smitterand miniature computers that make temp erature or a lt i tudemeasurements during flight.

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 acceleration 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 likeany other rocket. However, they glide back to eart h instead ocoming down suspended from a pa rachute .

There ar e severa l types of boost-gliders, including: 1. Rearen gine, 2. Fron t en gine, 3. Pop-pod, 4. Varia ble geomet ry, and

5. Para site. Some boost gliders u se radio control to allow themodeler 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 m argin. 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 otheruse c ombin ation s of both me thod s. See TR-4 and TR-7 for fur-ther d iscussion 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. Other


14/34

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.

M ODEL 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. Manufacturing 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 pre ssure gases that are e jected through 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 t o coast to 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 formanceparameters of the engine. You must understan 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 rocket

f f h l

The second par t of the engine code (the 6 in B6-4) gives thAVERAGE 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 throcket and t he faster the rocket will accelerat e. The B8 and Bare 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 chargThis delay allows the rocket to coast to pea k altitude b eforedeployment of the recovery system. The proper choice of delatime 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 cont ain de lay and ejectiocharges. There is also a spe cial type of plugged engine withcodes en ding in -P; these a re useful in radio-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 th e 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 perfoman 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 Estes engines ar e available. These engines

have deep er ports, produ cing a very high initial thrust pe akdue to a larger surface area for propellant bur ning. The B8 anC5 engines a re semi-core-burn ers.

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 s caalog or the kit inst ructions for a list of engines recomm ende dfor 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 heavpayload in a model, it may be necessar y to use an engine withshorter t ime delay than is recommended for the rocket withoua payload

Thrust(Newtons)

Thrust(Pounds)

2

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

Time in Seconds

4

6

8

10

12

14

16

18

20

22

24

26

28

30

327

6

5

4

3

2

0.0

B8

D12

A8

1/2A6 E15

C5

B6

B4C6

1

ThrustinNewtons

Pounds

14.0

12.0

8.0

4.0

0 0.2 0.4 0.6

1

A10- (0) (3)

1/2A3- (2) (4)

A3- (4)

2

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

Thrust(Newtons) 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

Comparative Thrust CurvesOf All Estes Engines

Cross-Section ViewOf B6-4 Engine


15/34

Three out of every hundred e ngines made by Estes Industriesare sta tic tested on a recordin g type of test sta nd which graphi-cally records the m aximum thru st, thrust variations, minimumthru st, overall thrust d ura tion, length of time delay, and t hestren 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 airplane s,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 a ltitude pe rformance of model rock-ets.

ENGINE SIZEThe greater th e total impulse of an en gine, the h igher it will

boost a model. The approximate altitud es achieved by typicalsingle 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 it

will 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 itwill reach . A num ber of factors determine th e amount of dragon a rocket. The more fronta l area th e rocket has, the great erits 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 CODE

3. Recovery--I will always use a recover y syste m in my rockethat will return it safely to the groun d so it may be flown againI will use only flame-resistan t r ecovery wadding if required .

4. Weight Limits--My mode l rocket will weigh no more tha n1500 gram s (53 oz.) at lift-off, an d its rock et e ngine s will pro-duce n o more th an 320 Newton-seconds (4.45 Newtons eq ual1.0 poun d) of tota l impu lse. My mode l rocket will weigh nomore than the engine manu facturers recommended ma ximumlift-off weight for the en gines use d, or I will use en gines recommended by the manu facturer for my model rocket.

5. Stability--I will check t he st ability of my mode l rocketbefore its first flight, except whe n laun ching a model rocket oalready pr oven stability.

6. Payload s--Excep t for insects , my mode l rocket will ne vercarry live animals or a payload that is inten ded to be flamma-ble, explosive, or harmful.

7. Laun ch Site--I will laun ch my model rocket s outd oors in acleared a rea, free of tall trees, power lines, buildings, and drybrush a nd grass. My launch site will be at least as lar ge as tharecommen ded in t he following table.

LAUNCH SITE DIMENSIONS

Minimum

Inst a lled Equivalent Sit eTot a l Impulse Engine Dimension

(Newt ons-Seconds) Type (feet ) (met er s)

0.00-- 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 1000 300

40.01-- 80.00 F 1000 300

80.01-- 160.00 G 1000 300

160.01-- 320.00 2Gs 1500 450

8. Laun cher --I will laun ch my model rocket from a stab lelaunching device that pr ovides rigid guidan ce unt il the mode lrocket has reached a speed adequ ate to en sure a safe fl ightpath . To prevent accident al eye injury, I will always place th elaunche r so that the en d of the rod is above eye level or I willcap the end of the laun ch rod when a pproa ching it. I will cap disassemble my launch rod when not in use a nd I will neverstore it in a n u pright position. My laun cher will have a jetdeflector device to preven t the en gine exha ust from hitting thground directly. I will always clear the area aroun d my launchdevice of brown grass, dry weeds, and othe r eas y-to-burn materials.

9. Ignition System--The system I use to laun ch my model rocet will be rem otely controlled and electrically opera ted. It wicontain a launching switch that will return to off whenreleased . The system will conta in a re movable safety interlockin series with th e laun ch switch. All persons will rema in atleast 15 feet (5 mete rs) from the model rocket when I am igniing model rocket engines t otalling 30 Newton-seconds or less ototal impulse or less and at least 30 feet (9 meters) from themodel rocket when I am igniting model rocket enginestotalling more th an 30 Newton-seconds of total impulse. I willuse only electrical igniters recommen ded by the engine man ufacturer that will ignite mode l rocket engine(s) within one second of actuation of the launchin g switch.

10. Launch Safety--I will ensure that people in t he laun charea are aware of the pending model rocket launch and can sethe mode l rocket s liftoff before I begin my au dible five-secon dcountd own. I will not launch a model rocket using it as a


16/34

12. Pre -Laun ch Test--When con duc ting resea rch activitieswith unp roven model rocket de signs or me thods I will, whenpossible, determine the r eliability of my model rocket by pre-launch te sts. I will condu ct the laun ching of an u npr ovendesign in complete isolation from persons n ot part icipating inthe a ctual launching.

13. Laun ch Angle--My laun ch de vice will be pointe d within 30degrees of vertical. I will never u se model rocket engines topropel a ny device horizontally.

14. Recovery Hazar ds--If a model rocket be comes en tan gled

in a power line or other da ngerous place, I will not at temp t toretrieve it.

As a m ember of the Estes Model Rocketry Program, Ipromise t o faithfully follow all rules of safe condu ct as estab-lished in the above code.

Signa tu r e ________________ __________________ __

*This is the official Model Rocket ry Safety Code of theNational Association of Rocketry and the Model RocketManu facturer s Association.

Estes Note: The largest model rocket engine a s defined byCPSC is an F (80 NS). To laun ch r ocket s weighing over on epound including propellant or rockets containing more than 4oz. of propellant (n et weight), you must obtain a waiver from

the FAA. Check your t elephone directory for the FAA officenearest you.

PUBLICATIONS AVAILABLE FROM ESTES

Model Rocket News Magazine

Provides articles of inte rest, techn ical tips, information aboutnew pr oducts, special offers, and much m ore. Available to ESPmembe rs and thr ough local reta ilers.

Alpha Book of Model Rocket ry

An informat ive book for beginne rs in model rocketr y. 32 pages.

EST 2820

The Laws of Motion an d Model Rocketry

The three laws of motion are explaine d in easily und erstoodterms. Simple examples an d experimen ts are included . 12pages.

EST 2821

Estes Guide for Aerospace Clubs

The perfect source book for organizing and opera ting a suc-cessful model rocket club or ESP chapter . 34 pages.

EST 2817

Model Rocket Conte st Guide

Use to p lan mode l rocket contest s for clubs or schools. Detailson compet itive events a nd su ggestions on a ll facets of contestorganization. 18 pages.

EST 2815

Projects in Model Rocketry

Suggestions on how to plan, prepa re, and present research pro-je ct s, id eas for abou t on e hundred proje ct s.

EST 2831

Model Rocket Launch Systems

Contains a wea lth of information. Photographs a nd clearly-drawn sch emat ics make it easily und erstood. 20 pages.

EST 2811

The Classic Collection

A compreh ensive collection of techn ical reports and notes th amake a valuab le referen ce tool. Includes TR-1 throu gh TR-7 anTN-1, TN-3, TN-4, a nd TN-6.

EST 2845

Model Rocket ry Study Guide

A logical program for an yone wh o wants t he most from modelrocketry. Guides a beginne r on the pat h to becoming an expe rrocketeer .

EST 2841

Altitude Pred iction Chart s

A simple system by which aerod ynamic drag and other e ffectscan be t aken into account in pred icting rocket peak alt i tudesTechnica l Repor t TR-10.

EST 2842

Aerod ynam ic Drag of Model Rockets

Gives practical exam ples of ways to minimize aer odynamicdrag a nd improve per formance. Technical Report TR-11.

EST 2843

Elementary Mathematics of Model Rocket FlightInformation on how to make your own altitude tracker a nd caculate sp eeds and accelerat ions. Technical Note TN-5.

EST 2844

Model Rocketry Technical Manual

Handy guide for constru ction an d flight of model r ockets. Tipson scratch building, launch systems, tracking, staging, boosgliders, and m ore.

EST 2819

Estes Educator News

Intere sting technical articles, new produ ct information, plus

activities and re sources on space an d model rocketry subjectssuitable for classroom u se. Available th rough ma ny local retaiers.

Guide for Teachers a nd Youth Group Leade rs

Introduce s you to Estes model rocket tech nology and the complete services offered in our edu cational program.

EST 2814

Industrial Arts Teachers Manu al for Model Rocketry

Very pract ical 52 page guide on model rocketry an d its ap plictions in the st udy of manufactur ing, tran sporta tion, R&D, communications, and construction.

EST 2810

Camp Leaders Model Rocketry Man ual

Proven guide for intr oducing model rocketr y successfully intocamp p rograms. 10 pages.

EST 2822

Video Model Rocket ry - The Last Fron tier*

Capture the excitement of model rocketry in th is full color VHvideo prese nta tion, narrat ed by and featuring William Shatnerof Star Trek** fame! An excellent p rimer t o model rocketrywith drama tic launch footage and grap hic, easy-to-und ersta ndillustra tion. 15 minut es.

EST 2792

*Copyright Estes Industries 1989. All Rights Reserved.

** Copyright Paramount Pictures Corporation 1975. All Rights Reserved.


17/34

ESTES EN GIN E CH A RT

Delays have a tolerance of plus or minus 10% or 1 second, whichever is greater. A ll Estes engines com e comp lete with igniters and patented igniter plugs (Pat. N o. 5,410,966 and 5,509 ,354) . The Estes

Igniter Plug makes engine ignition extremely reliable. D o no t f ly a rocket/ engine com bination w hose maximum l ift-off weight exceeds the recom mended m aximum l ift-off weigh

Prod. N o. Engine Type

Total

ImpulseTimeDelay

Max.

Lift W t.

Max.

Thrust

Thrust

Durat ion

Initial

W eight

Propellant

W eight

N -sec Sec. 0z. N ew tons Lbs.g Sec. 0z. g 0 z. g

SINGLE STAGE ENGINES (GREEN LABEL)

1502 1 / 4A 3 -3T 0 .625 3 1.0 28 4 .9 1.1 0 .25 0 .20 5 .6 0 .03 0 .8

1503 1 / 2A 3 -2T 1.25 2 2 .0 57 8 .3 1.9 0 .3 0 .20 5 .6 0 .06 1.7

1507 A 3 -4 T 2 .50 4 2 .0 57 6 .8 1.5 0 .6 0 .27 7.6 0 .12 3 .5

1511 A 10 -3T 2 .50 3 3 .0 85 13 .0 2 .9 0 .8 0 .28 7.9 0 .13 3 .7

1593 1 / 2A 6 -2 1.25 2 2 .0 57 8 .9 2 .0 0 .3 0 .53 15 .0 0 .06 1.5

1598 A 8 -3 2 .50 3 3 .0 85 10.7 2 .4 0 .5 0 .57 16 .2 0 .11 3 .1

1601 B4 -2 5 .0 0 2 4 .0 113 13 .2 3 .0 1.1 0 .70 19 .8 0 .29 8 .3

1602 B4 -4 5 .0 0 4 3 .5 99 13 .2 3 .0 1.1 0 .74 21.0 0 .29 8 .3

1605 B6 -2 5 .0 0 2 4 .5 127 12 .1 2 .7 0 .8 0 .68 19 .3 0 .22 6.2

1606 B6 -4 5 .0 0 4 4 .0 113 12 .1 2 .7 0 .8 0 .71 20 .1 0 .22 6.2

1613 C6 -3 10 .0 0 3 4 .0 113 15 .3 3 .4 1.6 0 .88 24 .9 0 .44 12 .4

1614 C6 -5 10 .0 0 5 4 .0 113 15 .3 3 .4 1.6 0 .91 25 .8 0 .44 12 .4

1622 C11 -3 10 .0 0 3 6 .0 170 22 .1 4 .9 0 .8 1.14 32 .2 0 .39 11.0

1623 C11 -5 10 .0 0 5 5 .0 142 22 .1 4 .9 0 .8 1.18 33 .3 0 .39 11.0

1666 D 12 -3 20 .0 0 3 14 .0 396 32 .9 7.4 1.6 1.49 42 .2 0 .88 24 .91667 D 12 -5 20 .0 0 5 10 .0 283 32 .9 7.4 1.6 1.52 43 .1 0 .88 24 .9

1673 E9 -4 30 .0 0 4 15 .0 425 25 .0 5 .6 2 .8 2 .00 56 .7 1.27 35 .8

1674 E9 -6 30 .0 0 6 12 .0 3 40 25 .0 5 .6 2 .8 2 .00 56 .7 1.27 35 .8

UPPER STAGE ENGINES (PURPLE LABEL)

150 4 1 / 2A 3 -4T 1.25 4 1.0 28 8 .3 1.9 0 .3 0 .21 6 .0 0 .06 1.7

1599 A 8 -5 2 .50 5 2 .0 57 13 .3 3 .0 0 .5 0 .62 17.6 0 .11 3 .1

1607 B6 -6 5 .0 0 6 2 .5 71 12 .1 2 .7 0 .8 0 .78 22 .1 0 .22 6 .2

1615 C6 -7 10 .0 0 7 2 .5 71 15 .3 3 .4 1.6 0 .95 26 .9 0 .44 12 .4

1624 C11 -7 10 .0 0 7 4 .0 113 22 .1 4 .9 0 .8 1.22 34 .5 0 .39 11.0

1668 D 12 -7 20 .0 0 7 8 .0 226 32 .9 7.4 1.6 1.55 44 .0 0 .88 24 .9

1675 E9 -8 30 .0 0 8 10 .0 2 83 25 .0 5 .6 2 .8 2 .00 56 .7 1.2 35 .8

BOOSTER STAGE ENGINES (RED LABEL)

1608 B6 -0 5 .0 0 N one 4.0 113 12 .1 2 .7 0 .8 0 .58 16 .4 0 .22 6 .2

1616 C6 -0 10 .0 0 N one 4 .0 113 15 .3 3 .4 1.6 0 .80 22 .7 0 .44 12 .4

1621 C11 -0 10 .0 0 N one 6 .0 170 22 .1 4 .9 0 .8 0 .98 27.8 0 .39 11.0

1665 D 12 -0 20 .0 0 N one 14 .0 396 32 .9 7.4 1.6 1.44 40 .9 0 .88 24 .9

PLUGGED ENGINES - FOR USE WITH R/C ROCKET GLIDERS (BLUE LABEL)1669 D 11 -P 20 .0 0 N one 16 .0 453 27.6 6 .2 1.8 1.55 44 .0 0 .88 24 .9

1676 E9 P 30 0 0 N 15 0 425 25 0 5 6 2 8 2 0 56 1 27 35 8


18/34

TIM E/TH RUST CURVES

im e/ thru st cur ves areepresentative of randomro duction samples.raphs are not drawn to

h e sam e scale

EJECTION

LIFT

C O A S T P

H A S E

THRU

STPHASE

LIFT0

C O A S T P

H A S E

THRU

STPHASE

14

13

12

11

10

9

8

7

6

5

43

2

1

0

3

2

1

0Time (Seconds)

Thrust(Newtons

)

(Poun

ds

)

1.0 2.0 5.0.8 4.8

Max. Thrust

Prope l lan t Bu rnou t

.6.4.2

EjectionCharge

Act iva tes

Delay Period - No Measurable Thrust

Tot a l Impu lseAverage Thr ust Du r a t i o n=

0 0.2 0.4 0.6 0.8Time in Seconds

1/4A3 Eng ine(M in i )

1/2A3 Eng ine(M in i )

Thrus

tinNewtons

14

12

8

4


1/2A6 Eng ine

Time in Seconds0.05 0.10 0.15 0.20 0.25 0.30 0.35

A3 Engin e(M in i )

4


6

1

A10 Engine(M in i )

ThrustinNewtons

14

12

8

4


1

A8 Engin e

ThrustinNewtons

2

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Time in Seconds

4

6

8

10

0.0

B4 Engin e

ThrustinNewtons

0.2 0.4 0.6 0.8 Time in Seconds

0.0

3

6

9

12

15

ThrustinNewtons

0.2 0.4 0.6 0.8 1.0

B6 Engine

ThrustinNewtons

0 2 0 4 0 6 0 8 1 00 0

3

6

9

12

15

C6 Engine

1 2 1 4 1 6 1 8 2

ThrustinNewtons

0 2 0 4 0 6 0 80 0

5

10

15

20

25

C11 Engi ne


19/34

by Robert L. CannonUpdated and edited byAnn Grimm and Jim Kranich


20/34

This booklet is designed to help you

understand some principles of rocket

flight. To get the most fromyour

study, follow these instructions:

Whenever ** appear, stop reading

immediat ely and answer the question

or perform the acti on which has just

been suggested. Keep thi nking and

try to reason out why the action was

performed. Try to answer each question

before going on with your reading... .. .

This bit of verse was probably one of

the first things you learned about

space. You now know that stars are

huge bodies of extremely hot gases.

Stars other than Sol, our sun, are extremely

far away. Atomic reactions consume

tremendous quantities of their matter

every second, yet stars masses are so

great that millions of years go by before

their sizes are significantly reduced.

The early astronomers named many of

the stars. Eventually, some noticed

that certain stars did not stay

where they belonged in the sky.

These migrants were named

planets (wanderers).

There are nine of the wanderers or

planets that have been discoveredin our solar system.. Telescopes

(including the Hubble Space Telescope

in Earth orbit) and mathematics have

enabled modern astronomers to also

identify and study numerous moons

accompanying the nine planets.

In addition to these nine planets and

their moons, thousands of asteroids

and a number of comets revolve

in orbits around the sun.

.. . An object in motion will continue

in mot ion at a constant speed in a

straight line as long as no unbalanced

force acts upon it .

An object in space near another object

is influenced by the gravitational field

of the other object.

For example, the moon is attracted

towards Earth by the Earths gravita-

tion. Mathematically, the gravitational

attraction that two objects have for

each other is as follows:

As can be seen fromthe formula, as

the mass of either object increases,

so does the gravitational force

between them. As the distance

between both objects increases,

the gravitational force decreases.

The

force of

the Earths

gravity pulls

the moon toward Earth as the moon

revolves about Earth. In effect, the

moon is falling toward Earth.

The moons motion also causes the

moon to move laterally (sideways) at

the same time. The moons velocity is

just enough to keep it falling toward

Earth at the same rate that the Earths

curvature causes the Earths surface to

become farther fromthe moon.

2

NEWTONSFIRSTLAWOF MOTION:

Twinkle, twinkle, li t t le star.

How I wonder what you are;

Up above the world so high,

Like a diamond in the sky.

d

F

Earth MooF=

G x M x m

d2

Objects at rest will stay at rest and objects in motion will stay in motionin a straight line unless acted upon by an unbalanced force.

ORBITPRODUCINGFORCES

WHYSATELLITESSTAYINORBIT

F= the gravitation force between thetwo objects

M=the mass of one object (Earth)m=the mass of another object (Moon)d= the distance between both objects

center of massG=gravitation at constant

If your Estes rocket werelaunched deep into space whereatmosphere (drag) and gravity(unbalanced forces) could notaffect it after engine burnout,it would travel a straight line at

a constant velocity forever!

Moons actual motion asinfluenced by Earths

gravity.

Earth

Moon

Moons motionif not affected byEarths gravity.


21/34

Due to the distance between the

Earths surface and center of mass, weexperience a gravitational acceleration

of 9.81 meters per second per sec-

ond(9.81 m/s2) or 32.2 feet per

second per second (32.2 ft/ s2).

This means that a free falling object

starting froman initial velocity of

zero, will gain speed at the rate of

32.2 ft/s for each second of travel.

For the first second of free fall,

an object will travel approximately

16 feet. The Earths surface curves

down 16 feet in about 5 miles.

Therefore, an object moving

horizontally at 5 miles per second

will fall at a rate which keeps it at a

constant distance above the Earths

surface. This situation produces an

object which is a satellite of Earth

and has a circular orbit.

Mathematically, the expression which

calculates the velocity needed to

maintain a circular orbit around Earth

is as follows:

V= (u/r)1/2

where, r is the distance between the

satellite and Earths center (center ofmass) and u is the Universal Constant

(Gravitational Constant times

the Earths mass).

The velocity which a satellite must

have to go into a circular orbit near

the Earths surface is about 5 miles

per second. This is about 18,000

miles per hour (5 miles/second x 60

seconds/minute x 60 minutes/hour).

To reach this high speed, artificial(man-made) satellites must be

launched by very powerful rockets.

Should an object receive a greater

velocity than required to maintain

a circular orbit, even if launched

in the proper direction, it will not

stay in a circular path. It will instead

go into an elliptical orbit or escape

entirely if the velocity is great enough.

If the

object does

not reach a

high

enough

velocity to

go into cir-

cular orbit,

it will fall

back to

Earth.

The farther an object is fromEarth,

the weaker is the force with which

the Earths gravitation pulls on the

object (remember the earlier equation

that shows the gravitational force

being inversely proportional to the

square of thedistance?!).

Since this is true, the higher an object is

above the Earths surface, the slower is its

rate of fall due to the Earths gravity. Since

the object tends to fall at a slower rate the

higher it is, it follows that the farther anobject is fromEarth, the slower it will have

to move to stay in orbit.

A satellite which is in orbit far above

Earth has a very long orbital path and

is moving relatively slowly. The satel-

lite has a very long period (the time

required to make one revolution).

A satellite in a lower orbit has a

shorter orbital path. As can be seen

fromthe circular orbit and gravitation-

al attraction equations, the satellite

must be moving faster since the gravi-

tational attraction is greater due to

the closer proximity with the primary.

If the actual velocity of the satellite is

not increased accordingly for the lower

altitude, it will fall out of orbit and

re-enter the Earths atmosphere.

These factors cause the satellite to

have a fairly short period.

3

Trajectory of anobject which

falls too fast.

Circular

Orbit

Orbit set up by

an object whic

does not fallfast enough to

remain incircular orbit

C

The moons velocity is just great enoughto carry it farther away from Earth alongpath AB in a certain time during which itfalls toward Earth a distance BC

Moons Position At a Given Moment

A B

Motion as influencedby Earths gravity

Point onEarthssurfacedirectlybelow A

Point on Earthssurface directlybelow B

Distancemoon fallsbecause ofthe Earthsgravity as itmoves fromA to C

Distance Earthssurface dropsbelow horizon line

Satellite

Primary

Satellite

(an object in spacerevolving about anotherbody in space)

Orbit

(path of thesatellite as itrevolves aboutthe primary)

The Moon(Luna) is asatellite ofEarth (Terra)

Orbit

Low Orbi t: High orbital velocity,small orbital path

High Orbi t: Low orbital velocity,large orbital path


22/34

Man-made satellites are placed in

orbits of varying altitudes depending

upon the purpose of the satellite.

Some are close to the Earth to make

detailed observations and some are

placed in very high orbits which

will remain in orbit for long

periods of time.

Fromthe velocities and periods chart,

you can see that one particular orbit

has a period of 24 hours. It makes

one revolution about the Earth every

24 hours. The Earth also rotates about

its own axis once every 24 hour hours.

This results in the satellite remaining

in a fixed position above the Earth and

is referred to as a Geosynchronous

Orbit. Communication satellites are

placed into this type of orbit to

provide continuous communication

coverage for that section of Earth

below it.

Why would a satellite placed in a very

low orbit close to the Earth, less than

200 miles, not stay in orbit for

many months?

* *

You can answer this question yourself.

Lets pretend that you want to throw a

baseball into orbit. You probably

realize that your chances of success

arent too great!! However, lets go

ahead and try. You can go outside

and try this if you wish, but lets go

through the reasoning together first.

If you throw the ball as high and as

far as you can, you dont have much of

a chance of getting the ball into orbit

even if you are very strong. Why not?

* *

You could

not throw

the ballwith

enough

energy to reach

escape velocity (the

minimumvelocity that

a moving object must

have to leave the

vicinity of Earth

and not return).

The ball was pulled toward the center

of the Earth by the force of gravi

wmci-estes rocket manual

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