Introduction to rockets and model rocketry
3……2……1……Blastoff
This session with cover…
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Uses of rockets
Principles behind rockets
What is a model rocket
Motors
Construction tips/why do we need to sand ?
Kits verses scratch build
Sourcing materials
Video examples
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Uses …
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Military – Blowing stuff up…No…no…no not
allowed here.
Space – Yes…yes…yes dreams are made of this,
however not possible for us …YET.
Scientific Research – Science is awesome. Why
would we not propel awesome to Mach 5.
Hobby/Entertainment – Who would not be
entertained ?
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Principles of rocket
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An object at rest or in
constant motion will
stay at rest or in
motion unless acted
upon by a force
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F = ma
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Every action has an
opposite and equal
reaction
A resultant force must be exerted
on a rocket for it to lift off from a
launch pad (first law). The amount
of thrust produced by a rocket
engine will be determined by the
mass of rocket fuel burnt and how
fast the gas escapes the rocket
(second law). The reaction, or
motion, of the rocket is equal to
and in the opposite direction of
the action, or thrust, from the
engine (third law).
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What is a model rocket
http://www.youtube.com/watch?v=86tTsPi0FPc
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Parts
Fins
• Fins are crucial to a rocket as they provide a restoring force when a
rocket moves off course, therefore keeping it stable and flying straight up.
• This is done by providing a moment around the CG which counteracts the
moment from the aerodynamic forces which act at the CP
• Fins can be bought from rocket website however geometries are limited.
• Buying balsa sheets then cutting them out is the best way to make custom
fins.
• You will need a fin template (http://www.robhouse.co.uk/rocksim/ ) to cut
accurately around and you want all your fins to be identical
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Parts
Fins
• Alignment – it is important your fins are all aligned and at the right
distance from each other.
• For scratching building I recommend making a alignment guide e.g.
rolling paper round your body tube, printing one out etc
• Also when your fins are glued on it is recommended to add fin
fillets, this again increase strength, aerodynamics and aesthetics
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Parts
Motor mount
• Motor mount hold your motor in place
• Centering ring and engine block are the most crucial parts
• Motors mount can be made removable, therefore interchangeable
• Cluster motors can be made canted
• Centering rings are best bought with their corresponding body
tube. However it is possible to make your own
• Model rockets come with an engine hook to stop the motor falling
out and in high powered rocketry a retention system is used instead
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Parts
Shock cord
• These attach your parachute and nose cone to the body plus
absorb a lot of the energy when the nose pops off a avoid the
nose cone or parachute detaching from the rocket.
• For model rockets this is normally Kevlar cord attached to an
elastic cord.
• Pretty easy to get from a shop.
• Make sure you attach them properly and glue all knots so they
cannot come undone.
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Parts
Glue
• Your model rocket is solely held together by this magical substance
• Most material in model rocketry are paper based or wood so craft
glue and wood glue are sufficient
• However always use as directed, allowing for proper gluing time,
so do not rush.
• Be careful with application, too much glue adds weight and makes
a rocket messy
• Use the right glue at the right time. Super glue sometime is not that
super
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Parts
Parachute
• This amazing device returns your hard work back to earth in a
relatively safe manor, the alternative is not desirable.
• Size depends on weight and descent rate but 12-15 inches in
diameter should do.
• When attaching your parachute ensure the strings are not tangled
and attachments are strong.
• Always use wadding when launching, to avoid your parachute
being burnt
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Parts
Launch lug
• Crucial item, this is what connects your rocket to the launch pad
• Do not forget it which a lot of people do. If you are using a D
motor your launch lug should be a 5mm(1/4”) launch lug and
below can use 3mm(1/8)” launch lugs.
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Parts
• Any magical parts of a model or high powered rocket that have
mystified you before ?
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Motors
http://www.estesrockets.com/media//catalogs/Estes_2013_Catalog2.pdf
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Motors
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Class Total Impulse Total Impulse
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Class
Total Impulse
Total Impulse
(Metric Standard) (Imperial Standard)
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A
1.26-2.50 N·s 0.29-0.56 lbf·s
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B
2.51-5.0 N·s
0.57-1.12 lbf·s
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C
5.01-10 N·s
1.13-2.24 lbf·s
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D
10.01-20 N·s
2.25-4.48 lbf·s
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E
20.01-40 N·s
4.49-8.96 lbf·s
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F
40.01-80 N·s
8.97-17.92 lbf·s
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G
80.01-160 N·s 17.93-35.96 lbf·s
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H
160.01-320 N·s35.97-71.92 lbf·s
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I
320.01-640 N·s
71.93-143.83 lbf·s
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J
640.01-1280 N·s
143.84-287.65 lbf·s
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K
1,280.01-2,560 N·s
287.66-575.3 lbf·s
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L
2,560.01-5,120 N·s
575.31-1150.6 lbf·s
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M
5,120.01-10,240 N·s
1150.61-2301.2 lbf·s
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N
10,240.01-20,480 N·s
2301.21-4602.4 lbf·s
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O
20,480.01-40,960 N·s
4602.41-9204.8 lbf·s
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Types…
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Sports rockets – Just for fun
Cluster rockets – Two or more engines at once
Multistage – Two or more rockets used one after the other in flight
High performance/ Competition
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Types…
• Cluster - Rockets that have more than one motor burning simultaneously.
• The benefit of this is having smaller, cheaper and more easier to develop
thrusters, which can the provide a larger take off thrust of a bigger engine.
Clustering is suitable for when you need more thrust at liftoff to launch larger or
heavier rockets.
• This total liftoff thrust/impulse is equal to the sum of the thrust/impulse of your
constituent motors,
• Example: If you used two engines in cluster this would be equivalent to a motor
that is twice as powerful but burns just as long.
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Types…
• Example: Two B6 in cluster vs Single C6
• So this would produce the same power as a C6 but in half the time therefore this
would actually be equivalent to a C12 engine which does not exist. Which add a
level of versatility. Consequently you could also lift double the maximum weight
of a B6 or C6 with this configuration.
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Types…
• Important things when designing a cluster rockets is building you rocket strong to
handle this extra power as you can effectively get the thrust of a high-powered
engine with the right configuration.
• Also how you design your motor mount to hold all these
engines.http://www.rocketshoppe.com/info/Engine_Clusters.pdf
• It is important that the thrust must be evenly balanced around the centerline of
the rocket. If there is more thrust on one side your rocket will veer off course and
become unstable. Additionally making the engines as close to the centerline as
possible, therefore if one motor fails the rocket will not loop dangerously near
the ground.
• https://www.youtube.com/watch?v=-ZzpPY4gMkQ
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Types…
• Cluster
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Types…
• Multistage – Rockets that use more than one engine which in succession.
• The benefit of this is to achieve a high altitude because each stage is jettison so
the last stage is very light and can coast for a long time.
• There are two ways to stage a rocket, direct and indirect staging.
• Direct staging is used for black powered motors, the lower stage engines ignites
the upper stage. This is relatively simple process and design once you understand
how the staging works and ensure your rocket is stable
http://www.apogeerockets.com/Tech/How_2-Stage_Rockets_Work
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Types…
• Composite motors (High powered motors) require indirect staging, where there is
a device onboard the rocket that will ignite the upper stage at a chosen time. This
is because composite motor ignite from the top of the stack and not the bottom
like a black powered motor.
• Therefore additional electronics are required on board, this will consist generally
consist of a timer and battery, these can fortunately be bought, then if you are
feeling brave you could design one yourself.
• What starts the timer ? Typically two simple methods are used, pull pin and gswitch.
• Pull pin is simpler and cheaper however g-switch is safer and more reliable.
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Types…
• However there are altimeters that can also do this, plus flight computer packages
which can fire the rocket only once if meets certain requirement (tilt) for added
redundancies and safety.
• I recommend someone adventurous or decent at programming could make an
Arduino or Raspberry Pie based system which could do this.
• http://youtu.be/PLS8sFNJOz4?t=2m40s
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Types…
• Performance/Competition rockets- Rockets that are designed to a specific
high performance target.
• Most commonly these are optimized for speed or altitude, also more speed does
not necessarily mean more altitude so there are different aspects to optimise for
both
• These rockets normally take careful consideration when being designed and built
to perform to their best to achieve a target.
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What else do you need….
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Launch Pad (this guides you rocket)
Launch controller
Building equipment e.g. sand paper, glues, hobby knives etc
Location, ideally a rocketry club
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Construction Tips
• I cannot go through the whole of how to construct a rocket in such a
short time, but apogee rockets, an American rocket supplier has a
YouTube channel with many videos on construction.
• http://www.youtube.com/user/apogeerockets
• http://www.youtube.com/watch?v=5w0LJ7Hw72w
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Construction Tips
Sand till you have no fingers
• Drag of a rocket is a big factor which will affect the performance
of any rocket.
• Drag compromises of two components, skin friction drag and
pressure drag. Pressure drag is to do with how air moves around
the rocket.
• Skin friction drag comes from the boundary layer which is attached
to the rockets surface, so a smoother rocket means less skin friction
• Also it makes your rocket look better
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Construction Tips
Sand till you have no fingers
• Sanding should be done in stages using a coarse grit progressively
using finer grits.
• A good range of grits to use are 240, 360, 600, 1200. However
this will depend on the material you sand.
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Construction Tips
Before applying glue
• Model rockets are held together by glue. So insuring the best
possible strength of you bonds it crucial.
• So one glue might not be best for everything, this will depend on
what your are gluing to what.
• Before gluing it is recommended to lightly sand the contact areas,
this reveals clean untouched material plus give materials a larger
surface area.
• The grater the surface are for a given area the stronger your bond
will be.
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Construction Tips
Built in Fins
• Mainly for Mid/High powered rockets fins are built in.
• What this means is that the fins actually go through the body tube,
this increases the strength of the bond to the body tube.
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Construction Tips
Fin fillets
• These are used to increase the strength of your fins
• They also provide better aerodynamic behavior at the root edge
of your fins.
• Normally made from glue or putty which is then sanded or covered
by filler then sanded
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Construction Tips
Finish
• You are not finished till you have a finish
• Finishing your rocket again is not just for making it look nice but if
you do it right, your rocket will be smooth the sail through the air.
• Before finishing sand your rocket thoroughly by using filler and
sanding it down repeatedly.
• Once this is done choose a colour scheme and paint, glossy has a
decent finish.
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Kits verses scratch build
• A model rocket kit comes with all the parts you need to construct a
certain rocket
• Example: Magnum Hornet
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Kits verses scratch build
• Scratch built rockets are designed and built from scratch, normally
with an aim or some sort of design challenge. This is your starting
point.
• Producing a design on a rocketry CAD software helps with
analyzing stability and simulation, plus visualisation.
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Kits verses scratch build
Scratch build considerations
• Is my design stable and safe
• Does it meet my specification
• Can I get all the materials I need
• Construction
• Cost
• Recovery
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Kits verses scratch build
Pros of Kits
• All the parts are provided
• Model have been tested and
proved to work well
• Normally cheaper than
buying individual parts
• Shorter time scale
• CAD files readily available
• Easiest and recommended for
beginners
Pros of scratch build
• Design to a certain
specification
• Designs are only limited by
your resources, so they can
be as crazy as you want.
• Your own creation and unique
• Greater understanding of
rocketry
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Materials
Common materials.
• Cardboard – Body tube
• Glassine – Body tube
• Quantum tubing - Body tube
• Fiber glass - Fins, Body tubes, nosecones
• Carbon Fiber, Body tubes, fins
• Plywood, Internal structures
• Plastic – Nose cones
• Metal – Nose cone tip (dangerous), bolts and hooks etc
• Other – Light, strong and suitable for their use
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Sourcing Materials
• Sourcing materials can be quite problematic as places to get rocket
specific items are few and far apart in the UK.
• First you need to know what you want to buy, this can be from your
design. It is also a good idea to split what you need into rocket specific
items and items readily available:
• Rocket specific
• Fins (Balsa, Plywood)
• Body tube ( Strengthen Cardboard)
• Nose cone
• Motor mount
• Parachute
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Sourcing Materials
• Readily Available items
• Fins (Balsa, Plywood)
• Body tube ( Strengthen Cardboard)
• Shock cords/Nylon/Kevlar
• Hooks
Once you have that we need to go shopping.
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Sourcing Materials
• There are two main places to go.
www.rocketandthings.com
www.modelrockets.co.uk
• However they do have a limited amount of stock and order items
from America etc only a few times a year.
• So you may find you need to order from both to get al your parts
or neither has them.
• In this case send an email to make sure, the try finding alternative
sources, there are a few in Europe e.g.
http://www.rebelrocketry.com/shop/index.php
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Videos
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http://www.youtube.com/watch?v=_e-sevUOpec
http://www.youtube.com/watch?v=z7fLpKt56Jk
http://www.youtube.com/watch?v=rfnDEryI3Dk
http://www.youtube.com/watch?v=5LL_W2FdEFA&feature=plcp
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Research, Links and information
• Shops
http://www.modelrockets.co.uk/shop/index.php
http://www.rocketsandthings.com/
http://www.estesrockets.com/
http://www.rebelrocketry.com/shop/index.php
• Websites
http://www.ukra.org.uk/
http://www.apogeerockets.com/
http://howtobuildmodelrockets.20m.com/index.html
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References
• http://web.mit.edu/16.00/www/aec/rocket.html
• http://blog.siriusrocketry.com/2013/07/chris-michielssons-modelrocket.html
• http://www.stormthecastle.com/model-rockets/the-estes-hi-flyerrocket-part-2.htm
• http://blog.siriusrocketry.com/2013/07/chris-michielssons-modelrocket.html
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