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rec.models.rockets FAQ Part 12 - Ignition and Launch Systems


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Archive-name: model-rockets/ignition-tips
Rec-models-rockets-archive-name: rockets-faq/part12
Posting-Frequency: monthly
Last-modified: 1996 January 9
URL: http://dtm-corp.com/~sven/rockets/rmrfaq.toc.html

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Rec.Models.Rockets Frequently Asked Questions: PART 12 of 14

IGNITION AND LAUNCH SYSTEM TIPS

[Note:  This portion of the FAQ is maintained by Jerry Irvine
(jjirvine@cyberg8t.com).
 All comments and suggestions should be sent to him.]
------------------------------------------------------------------
12.1   Copperhead, squib, electric match, thermalite, flash bulb.
       What are all these types of igniters, how much current do they require,
       and when are they used?

    Copperhead              used to ignite single composite motors; not
                            good for clustering.  They will light most
                            black powder motors.  Requires strong 12V
                            current source.

    Electric Match          a type of electric igniter requiring
                            little current to ignite.  As little as 200ma
                            of current will set them off.  Used for
                            igniting high power motors and motor clusters.

    Thermalite              a type of "igniter cord" used in pyrotechnic
                            applications.  May be ignited by removing all of
                            the external bridge wired except one and using
                            wire wrap wire leads 1/4" apart 12v, or with an
                            igniter.  Used in longer lengths and sheathed near
                            propellant cores it is used for clustering.  Also
                            used in flashbulb ignition systems.

    Firestar                Igniter kit which has proven popular in general
                            use and is easily shippable.  Uses low or high
                            current (6-12v) depending on which bridge wire
                            you dip in the parially pre-mixed solution you buy.

    Flashbulb/thermalite    some types of camera flashbulbs ignite
                            with very little current (typically as
                            little as 50ma) and burn very hot.  These
                            are used to ignite a piece of thermalite fuse
                            running into the motor.  Used for igniting
                            high power motors and all forms of clusters.

    Magnelite               medium to high current requirements.  Sold
                            by Rocketflite to ignite Silver Streak
                            motors.  Work well to ignite single high
                            power motors.  These are magnesium tipped
                            igniters that burn at a very high temperature.

   In general, almost any current source from a 1.5V 'C' battery up might
   ignite a flash bulb or electric match.  For the other igniters, a 12V
   system capable of delivering several amps of current to the igniter is
   required.
------------------------------------------------------------------
12.2   How do those 'Copperhead' igniters work?  They only have one wire?

    Copperhead igniters are actually two strips of copper wire with a
    thin mylar insulating layer between them.  To use these with regular
    alligator clips you need to use masking tape to insulate opposite sides
    of the igniter from each clip.

           'Thin' (side) view of copperhead igniter:
                      |      |
                      |______| < Motor with Copperhead inserted
                         ||
             Masking   > ||
             tape      > ||
                         ||
                         ||<  Masking
                         ||<  tape
                         ||

    Attach one alligator clip at each masking tape point, so that each clip
    only makes contact with one (opposite) side of the igniter.

    The Quest 'Tiger Tail' igniters are the same type of igniters as
    Copperheads.  They come with a special 'wrapper' with openings for
    alligator clips.

    NOTE: Copperhead igniters require a 12 volt ignition system.
------------------------------------------------------------------
12.3   I've heard that Copperhead igniters are 'unreliable' for igniting HPR
           motors. Is that true?

    Many HPR flyers do not like the Copperhead igniter, preferring alternatives
    when they can be found. It is certain that Copperhead igniters are not
    a good choice for igniting clusters. However, some have found the
    Copperhead to be a reliable igniter for single-motor HPR rockets.

    From: dcrcep@mizzou1.missouri.edu (Elmer M. Price)
      Hi Folks:  I have a comment on the reliability of Copperhead igniters.
      Our small group has had no problems with these, once we figured out the
      best way to use them.  So, in spite of all the negative comments, we
      actually really like these things.  We have launched composites up to
and
      including I-sized motors with great reliability.  For example, two weeks
      ago, two of us (at the excellent St. Louis launch), launched two I284
      birds, one I161, one I211, two H123 and a few F's and G's.  We had 100%
      igniter success.

      O.K. So what do we do to achieve such reliability?  First, open the
      reload pack and assemble the motor in the usual manner.  Second, find
the
      Copperhead that came with the reload kit and THROW IT AWAY.  What we use
      are Copperheads which we purchase separately.  These arrive from the
      dealer (like Magnum) in a nice package and the igniters are not all beat
      up and crimped and bent to heck like the ones which are provided in the
      reload kit. We feel this is an important point.  Second, since the H and
      I (and larger) motors are a bit more difficult to light, we modify the
      new Copperhead as follows (this idea came from RMR):  take a slug of
      white lightning propellant (we use the slug from a D9) and cut a very
      small sliver (and I mean small, about 1/16 inch square and about 1/2
inch
      long).  Tape this sliver (Fred from our group optimized this point) to
      the Copperhead by overlapping the bottom half of the pyrogen on the
      Copperhead with the top half of the sliver.  Use a small strip of
masking
      tape to attach the sliver to the copper below the pyrogen.  The point
      here is to ensure the tape is below the area where the pyrogen and the
      sliver overlap.  This is important because if the tape is higher up the
      igniter, the sliver may fall off of the Copperhead and lead to a chuff
      (ignition too far aft).

      This modification is not necessary for G and smaller motors, since the
      pyrogen is in close proximity (or touching) the propellant.

    And this was added by: bday@fly.HiWAAY.net (Brian Day)
      I've also gotten *MUCH* better reliability from Copperheads by not using
      the red plastic cap over the nozzle, and just using a small piece of
      masking tape to hold the igniter in place.  This technique doesn't crimp
      the Copperhead like the plastic cap does.  Since doing this, I've gone
      from roughly 50% reliability to darned near 100%.

      Oh yeah, someone else on rmr recently suggested clipping off the pyrogen
      part of an old, crummy Copperhead and using it to augment another
one, like
      you do with your sliver of propellant.  Beats throwing it away...

    Finally, regarding the red caps provided with Aerotech motors for holding
    in the igniters,

    From: Bob Kunz <bkunz@boi.hp.com>
      You do know that one is supposed to provide a vent in the red cap? I
would
      presume this is to allow some leakage of pressure but enough to get the
      white/blue/black propellant to ignite. Typically, I find that the red
cap
      is blown through when I recover the rocket. Only once was it blown
off at
      the launch pad. So far in about a dozen launches on RMS 24/80, I've
had no
      failures. But sure those are small grains compared to some of the 54mm
      stuff.

    From: curcio@telerama.lm.com (Larry Curcio)
      Copper Head igniters have acquired reputations for unreliability. I'm
      wondering if the problem is in the igniters or in the red nozzle
      caps, which blow off during most Copper Head failures. IMHO, it's the
      sudden release in pressure that makes ignition fail - by disrupting the
      newly forming flame. When I use a piece of masking tape instead of a cap,
      I don't seem to have the problem.

    Editor's note (jjirvine@cyberg8t.com):
      As of 11-96 Aerotech has made some efforts to eliminate the microshort
      problem which is an artifact of the Coppercrap manufacturing process.
      They have tried making versions with thicker insulator layers.
      While they are more fragile and subject to peeling, they are more
      reliable than before.  Time will tell.

------------------------------------------------------------------
12.4   Do you have any specific suggestions or tips for an ignition power
       sources? Can I use my old Estes ignition system with composite models?

    The Estes, Quest and other model rocket launch systems are fine for most
    model rockets.  If you do a lot of flying there have been some suggestions
    posted to the net.  If you are trying to launch cluster models with solar
    igniters you will need more 'juice' than 4 AA batteries can provide.  This
    is also true of clustered Copperhead type igniters.

    From: cdt@sw.stratus.com (C. D. Tavares)
      A motorcycle gel cell, however, will last a long, long time.
      Our club uses a gel-cell the size of three VHS tapes to launch 120
      rockets over six hours, and it comes home at about 80% charge.

    From: billn@hpcvaac.cv.hp.com (Bill Nelson)
      I bought a 12 volt motorcycle battery for about $20. I only need to
      recharge it 3 or 4 times a year. I have adapted all my launch
      controllers to allow usage of the battery.
------------------------------------------------------------------
12.5  WARNING:  Be very careful using any ignition system with 'flashbulb' or
              electric match type igniters.

    Many (most?) launch ignition systems are not 'flashbulb safe'.  Just
    arming the circuit (i.e., doing a continuity check) will fire the
    flashbulbs and ignite the motor.  If you plan to use flashbulb ignition
    often, you might consider investing in a 'flashbulb safe' ignition system.

    From J.COOK@ens.prime.com (Jim Cook):
      A lot of launch systems use a light bulb to do a continuity check.
      The current through the light bulb is enough to set off flash bulbs
      (They require only milliamps to fire).

    Remember that electric matches may ignite on any amount of current above
    200 milliamps. Flashbulbs may ignite with as little as 50 milliamps of
    current.
------------------------------------------------------------------
12.6  The ignition of rockets by other than electrical means is banned by both
             the NAR and Tripoli safety codes and should not be used.

    There was a fairly lengthy discussion in r.m.r about the use of hand-lit
    fuse to launch rockets.  Although there was an advocate of this method the
    consensus opinion of the net was that the NAR and Tripoli safety codes
    made good sense, hand-lit fuse igniters were unsafe, and electrical
    ignition (even if igniting fuse by electrical means) should be used for
    all activities.  Hand-lit fuses are also against most state laws.

    While it is theoretically safe and practical, it goes against the
    principal of self regulation which has made model rocketry legal and
    available natonwide and worldwide.  Just don't do it.
------------------------------------------------------------------
12.7  What is thermalite fuse and how is it involved in igniting rocket motors?

    Thermalite is is a brand name for igniter cord from CXA Ltd of Canada.
    It comes in three burn rates, identiflyable by the color of the fuse
    wrapping:

      Color      Type     Burn Rate       Usage
      Pink       Slow     20 sec/foot     Flashbulb ignition
      Green      Medium   10/sec/foot     Ignition enhancement
      White      Fast      5 sec/foot     Not used much in rocketry

     The burn rates are approximate and vary with humidity, temperature, age
     of fuse, etc.  The numbers also correspond to burn rates of exposed
     thermalite.  When enclosed in heat-shrink or Teflon tubing, all three
     types burn at an equally fast rate.  A typical usage for thermalite is
     in a flash bulb igniter:

                         |    <  1/2 to 3/4 inch of thermalite exposed out
                         |    <  end of sheathing
                        |||
                        |||   <  thermalite fuse in Teflon or heat-shrink
                        |||   <  tubing (fuse should *just* fit into tubing)
                        |||
                        |||
                       + |
                      + +|    <  1/2 to 3/4 inch thermalite exposed out end
        flash bulb >  + +|    <  of sheathing and taped to flash bulb using
                      + +     <  CELLOPHANE tape (NOT masking tape).
                       +
                      / \
                     /   \    <  electrical leads to ignition system

     The fuse is sheathed except for about 3/4" at each end.  The sheathed fuse
     is inserted into the motor and must be long enough for the exposed end to
     go all the way up through the core and out the bottom of the motor.
     Composite motors are ignited at the top of the core (nearest the delay
     charge).  The sheathing on the fuse is to keep from igniting the motor
     anywhere but the correct location.  The other end of the fuse is tape to
     a hot-burning flash bulb.  The flash is then attached to the ignition
     system and ignited in the normal fashion.  This lights the thermalite
     fuse, which then ignites the motor.

     This is the ignition method of choice for clustered composite motors (in
     any number above 1) and large clusters of black powder motors.

     WARNING:  Flash bulbs require VERY LITTLE current to set them off.  Read
               the warnings above.

     NOTE: Thermalite is classified by the BATF as a 'Class B Low Explosive'.
           Out of state purchase, interstate transport, and personal storage
           of *any* amount of thermalite fuse requires a Federal Low Explosives
           User Permit. Refer to the section on 'High Power Rocketry' for
           more details on LEUPs.

           This is a change of prior enforcement practice and this material
           was widely available as a Class C item for decades.  We will see how
           long this will last.  Several advocates of easy access have
suggested
           that short lengths of under 12" should be exempt from LEUP and
           shipping restrictions, especially those pieces included as stock
           igniters with MR and HPR motors from the factory.

           Thermalite is one of those magic and critical substances to
rocketry.

------------------------------------------------------------------
12.8   How do you ignite second stage composite motors?
       Can I use a black powder booster for the first stage to ignite the
       second (as I do with multi-state A-D rockets)?

    Upper stages of composite powered models may be ignited by
    electrical means or thermalite fuse.  North Coast Rocketry (NCTRA2) and
    California Rocketry (AIR-3) have technical reports covering this subject.
    Excellent articles have also appeared in Sport Rocketry/AmSpam and
    HPRM magazines.

    You cannot use a black powder booster to ignite a composite upper
    stage.  The gasses from a BP booster will not properly ignite a
    composite.  There are composite boosters on the market.  These boosters
    are all 'plugged' and so cannot ignite any type of upper stage motor.
    Composite motors are mostly 'core burners' with the core running the
    entire length of the fuel grain. A composite core burner set up like a
    BP booster would ignite a BP upper stage too soon.

    There are several issues involved in igniting upper stage composite
    motors.  (1) A timing method must be provided to delay ignition until
    the appropriate time, (2) power source for the igniter is required and (3)
    the igniter itself must be provided and be capable of igniting high power
    motors.  Whatever method of ignition is chosen, all 3 criteria must be
    met.

    Timing Methods ....

    Several methods of timing have been developed and used.  The earliest and
    cheapest timing method is to use a length of unsheathed thermalite fuse.
    The fuse is typically ignited by the exhaust from the first stage motor.
    The fuse is long enough to allow for the first stage motor burn time and
    any desired post-burnout coast.  The last portion of the fuse is sheathed
    and inserted into the upper stage motor to act as the igniter.  The problem
    with this method is that not all thermalite burns at the same rate.  Also,
    the same batch of thermalite will burn at different rates depending on the
    altitude, temperature and humidity at the time and place of launch.

    Mercury switches were another early method of 'timing' upper stage
    ignition.  A mercury switch is a small glass bulb with an enclosed drop
    of mercury.  Two wires run out the top of the bulb.  When the switch
    is tilted or decelerated the mercury rolls forward to make contact with
    the two wires and close the circuit.  This results in a closed circuit when
    the booster motor stops firing and the rocket begins to decelerate. The
    ignition circuit would be set up so that power is provided to the igniter
    when the mercury switch closes.    EXTREME care must be exercised when
using
    mercury switches.  Titling the rocket closes the switch, so provisions for
    disarming the circuit must be included.  After the rocket is placed on the
    pad and the circuit armed, any sudden movement of the rocket could set of
    the second stage.

    Bob Weisbe uploaded plans for a mercury switch-based staging system that he
    used in a converted Estes Terrier-Sandhawk kit.  The URL for these plans
    is:

http://sunsite.unc.edu/pub/archives/rec.models.rockets/PLANS/terrier_sandhawk.ps

    The next generation of upper stage ignition systems were based on
    electronic timers of various types, both analog and digital.  The timer
    was set for the appropriate time (first stage burn time + inter-stage
    delay, if any).  A contact switch, usually kept open by the launch rod,
    would often be used to initiate the timer.  As the rocket leaves the
    launch rod the timer is started.  After the preset time interval the timer
    closes the circuit allowing power to the igniter.  Again, great care must
    be taken with these devices.  If the contact switch is allowed to close
    prior to the rocket lifting off the 2nd stage could ignite while the
    rocket is still on the pad and there are people around.

    Another form of early timing device was based on photo-electric sensors.
    A sensor would be placed in a position such that light could get through
    the booster motor tube after all of the fuel was spent.  When the sensor
    detects light the power circuit is closed.

    Remote control has been used to initiate firing sequence in multi-stage
    rockets.  This method has the advantage that the 2nd stage isn't ignited
    unless a human being takes positive action, while the rocket is in the air.
    It also requires an R/C transmitter, receiver, etc.

    Some newer devices are out based on acceleration detection.  These are
    sometimes combined with timers.  Liftoff acceleration is detected.  This
    either starts a timer or enables a deceleration sensor.  At the specified
    time interval, or when deceleration is detected, the power circuit is
    closed.

    Power Sources ...

    Two forms of electric power are commonly used, capacitors and batteries.
    A capacitor is typically charged from an external source just before
    liftoff.  The timing device then closes the circuit at the proper time
    and the capacitor discharges, firing the igniter.  One disadvantage of
    this method is that the capacitor charge slowly bleeds off, meaning that
    the rocket may not sit on the pad a long time after prepping and still
    reliably ignite the upper stage(s).

    All forms of small batteries have been used, depending on the power
    requirements.  Common batteries for igniting a single, low power igniter
    are 9V transistor and 12V alkaline lighter batteries.

    Timed thermalite fuse ignited by exhaust from the booster requires no
    power.

    Igniters ...

    Multi-stage rockets generally have a limited current source for igniting
    upper stages, so very low power igniters are used.  Two common igniters
    are electric matches and flash bulb/thermalite fuse.  Both of these
    igniters are described elsewhere in this document.

    Readers are encouraged to review the NCR technical reports and rocketry
    magazine articles on composite multi-staging.

    A document describing igniters, and how one can make ignitors using
    thermalite and nichrome wire is available on the sunsite archive at:

http://sunsite.unc.edu/pub/archives/rec.models.rockets/ARTICLES/igniter_talk.txt

    Illustrations for this document are also available for downloading:

http://sunsite.unc.edu/pub/archives/rec.models.rockets/ARTICLES/igniter_talk_fig
ures.ps

------------------------------------------------------------------
12.9   What is 'flash in the pan' ignition and for what is it useful in
rocketry?

    From: jjirvine@cyberg8t.com (Jerry Irvine)
    [Editor's note: This is paraphrased from Jerry's postings]
    Flash in the pan ignition is used to ignite clusters of small black powder
    rocket motors. It consists of a thin layer of black powder on a paper
plate
    under the motor nozzles. The powder is ignited via a regular model rocket
    igniter, such as an Estes Solar igniter. When the power ignites, the
    burning particles and hot gasses from the 'flash' ignite the motors.

    It is used to ignite clusters of 7-469 motors and reduces the number of
    igniters needed to one.

------------------------------------------------------------------
12.10   I would like to perfect a method for reliable ignition of clustered
multi-
         stage rockets. Any suggestions or tips?

    From: Leviathan@nighthawk.medtechnet.com (Leviathan)
      So would everyone else... but there's always that chance that something
      may fail when staging and/or clustering... and probably double the
chance
      when staging & clustering. Therefore, my best advice to anyone
attempting
      (large?) projects requiring staging/clustering is to invest in some sort
      of recovery system such as the Adept altimeters with deployment. In the
      case of staging... if the upper motor fails to ignite the altimeter will
      still deploy the upper stage chute(s) SAFELY with NO damage to the
rocket.
      In a case were you're clustering and a motor (or 2, or 3....) fails to
      ignite in the cluster, and the rocket WILL fail to reach a safe
altitude -
      or more precisely  now WILL have a delay time that is TOO LONG -
again the
      altimeter will SAFELY deploy the chute(s). IMO it's a small price to
pay to
      protect a much larger investment of the rocket itself. As a matter of
fact
      in my current project - a 1/4 scale 3 stage Argo D4/Javelin - each stage
      will carry it's own altimeter with the 3rd stage carrying the Adept OBC2
      recording altimeter. Not only will this provide for dual deployment of
      each stage's recovery system, it should provide protection against
failure
      of the 2nd and/or 3rd stage ignition. I also plan on carrying a Pratt
      system aboard to provide redundant back up.

    From: John Dunbar <jdunbar@csd.sgi.com>
      I really recommend the Teflon sheathing method of thermalite.

      Now you can try using a flash pan to get that first stage bohemian
going.
      Its just a nice circular pan, with fine black powder in it. Just order a
      can from your local gun shop, they can ship US postal to your front door
      without a single eyelash batting on the face of a BATF agent.  You stick
      those engine down into the power with a thermalite wick protruding from
      the engine, and WHOOSH...

      The more parts you have to worry about, the  greater the likelihood that
      something is going go terribly wrong.  Now if you don't care, and just
      want to do it for fun, GO FOR IT, otherwise think of ONE BIG MOTOR
for the
      first stage and one smaller, yet BIG MOTOR, for the second.  Do not rely
      on mercury switches for high power ... that's a NO NO.  Instead, use
timers
      in a way that causes the second stage to start its ignition while the
      first is still under power.  Now you can drag separate, and that's
fine to,
      but make sure your bird is flying straight and true, or it will be
doodoo!

      Technical reports on this subject are available from NARTS and California
      Rocketry (see part02 of this FAQ):

      California Rocketry report AIR-3

      North Coast report NCTRA1 (from NARTS)

------------------------------------------------------------------
12.11  How do I cluster rocket motors?  When igniting a cluster of rocket
       motors, should the igniters be wired in parallel or in series? Why?

    The advent of composite model rocket motors in 'standard' black power
    sizes (18 and 24mm) has led to an increase in the use of composite motors
    in cluster rockets.  Mixed black powder/composite clusters are also
    becoming popular.  In particular, clusters of 3 or 4 composite
    motors, or a composite core motor with outboard black powder motors,
    are being seen more.  These offer special ignition challenges.  The old
    black powder techniques don't work when composite motors are
    involved.  The most common method for clustering Estes type black
    powder motors is to use multiple Solar igniters and clip whips.  Flash
    bulb to sheathed thermalite is the most common composite ignition
    method.  Although flash bulb ignition has been used for years, there
    have been safety concerns over its use.  Here are some suggestions from
    rmr posters:

    From PeteAlway@aol.com (Peter Alway):
      I cluster black powder motors with Solar igniters wired
      in parallel and a car battery for power.  I stuff igniters
      with little balls of tissue paper wadding to insure they
      stay in place.  My general rule is only to cluster with
      a technique I use regularly for single-engine models,
      as reliability has more to do with experience and my
      current state of skill than with the particular technique.
      [Editor's note: Estes plastic plugs work well in place of tissue
      wads. The igniter plugs can be reused several times, as well.]

    From: glenn@lightning.nsc.com (Glenn Newell)
      My technique for clustering composite motors is to use equal length
      pieces of thermalite with 1/16" heat shrink tubing as a sleeve. I
      leave about a 1/2" unsheathed in the motor and about one inch unsheathed
      on the other end (I don't shrink the heat shrink, it just happened to be
      around and the right size). I tape all the ends together around a single
      solar igniter. No flashbulb problems here!

    From: billn@hpcvaac.cv.hp.com (Bill Nelson)
      I prefer to use a short section of Thermalite, with igniter wires,
      inserted into each motor - the wires are taped to the motor for security.
      There is no need for an igniter for the Thermalite.  Simply remove the
      cloth wrap, and all but one of the spiral metal wires.  Wrap the end of
      one wire to one end of the thermalite and the end of the other wire to
      the other end.  You can use anything from about 22 gauge wire (if it will
      fit in the grain slot) to about 28 gauge.  The free ends connect to the
      controller ignition wires. When the relay closes, the Thermalite wire
      wrap is essentially vaporized instantly.  I have never seen the
      Thermalite fail to ignite.

    From: burkefj@kodiak.ee.washington.edu (Frank J. Burke)
      The main reason for using parallel igniters is that as one ignites, the
      others are still in the circuit.  As one igniter breaks in a series
circuit
      the circuit is broken and the others will not get any more current.
It may
      be that with a 12V system, and low impedance wire, that the current
      provided is high enough that they flash so fast that it doesn't
matter....
      I have never had a failure with parallel circuits.  I ... prefer using a
      parallel system, knowing the limitations, using a meter to verify
that the
      igniters are "good" before using them, and using good connections when
      wiring them up.

    From: buzzman@netcom.com (Buzz McDermott)
      The biggest concern with wiring cluster igniters in series is that one
      igniter might burn through and break the circuit before all of the
      igniters have fired. Once the circuit is broken, no more igniters will
      fire.

      On the other hand, it was mentioned by several posters that series wiring
      is extensively used in the explosives and pyrotechnics industries
      because of the added reliability you get. With series wiring you can
      verify the complete igniter circuit and you will know if *any* igniter
      is improperly wired. Also, you would be able to ignite many more (fast
      igniting) igniters with series wiring, especially if the resistance
in the
      igniter is high.

    From: kaplow_r@eisner.decus.org (Bob Kaplow)
      For a 4 engine cluster I like to wire the ignitors in a "bridge":

                        X======B
                       / \
                      /   \
                     /     \
                    /       \
                   /         \
                  /           \
                 /             \
        A ======X               X======A'
                 \             /
                  \           /
                   \         /
                    \       /
                     \     /
                      \   /
                       \ /
                        X======B'

        Clips A and A' come from one clip whip. B and B' are from the other
whip.
        I use a manual wire wrap tool for twisting the Solar ignitors together
        AFTER installing the "earplug" (tm). Be sure your wraps are nice
and tight
        so they all touch where they are supposed to. Having a clip on each
joint
        certainly helps. For multiple wire clipping, I've found that the
clips with
        teeth hold better than the standard micro-clips.

        I've used this several times now on 4xD12 in a BT-80 rocket with
100% success.


      Editors Note:
      The bottom-line-consensus of the 'net' seems to favor parallel wiring for
      most clusters of 7 or fewer motors, using a 12V (or more) launch system
      capable of dumping plenty of amps to the igniters. This generally means
      a relay based system with the primary ignition power source close to the
      launch pad.

      Readers are also directed to check out the NCR Technical Reports #1 &
      #2, on black powder and composite clustering, respectively.  Although
      they are a few years old, they still contain valuable information.

------------------------------------------------------------------
12.12   I am new to rocketry.  I was wondering whether anyone has tried
        using waterproof wicks instead of igniters to ignite a rocket engine.

    The main application for Green fuse in rocketry is as an auxuliary delay
    when a timer is not available and Thermalite is too fast burning.  Green
    Visco fuse burns about 30 seconds per foot.

    From: Robert_Kaplow@hccompare.com
      "Green" fuse isn't reliable, and unless electrically ignited via remote
      control (difficult) isn't legal. To use fuse and a match is a
violation of
      the safety code, and most state local regulations.

    buzzman@netcom.com (Buzz McDermott) adds to the above:
      The most common way to use 'green' fuse or Jetex wick to ignite a model
      rocket motor is to cut a fair length, insert it in the motor, light it
      with a match, and RUN!. As Bob stated, it's against EVERYONE's safety
      code to do that. The answer to 'why' is simple. Once you light the fuse
      you've lost all control over launching the rocket. If a breeze kicks it
      over just before ignition you end up launching a land shark. You can't
      stop the launch if you notice a plane come out of nowhere and fly right
      overhead. You can't stop the launch if a little kid comes out of nowhere
      and runs up to your rocket. ...on top of all this, the stuff just
      doesn't really work all that well for rocket ignition...
------------------------------------------------------------------
12.13   The alligator clips on my launch system have worn out. What should
I use to
               What should I use to replace them?

    From: msjohnso@KS.Symbios.COM (Mark Johnson)
      RatShack is fine for clips...and they have a wide collection of
sizes. My
      suggestion, having been-there-done-that and replaced clips on several
      controllers almost annually, is NOT to buy the little 3/4 inch copper
clips.
      They're too delicate for my tastes. Instead, I get the chrome plated
ones
      about 1 1/4 inches long, preferably with the little plastic grips on the
      "handles." These are bigger and thus easier to manipulate while wearing
      gloves, or when your hands are cold and unsteady.

      If you use your launch system frequently, I recommend at least annual
      replacement of the clips. This is more true of a club system than an
      individual one, but remember that you take your choice of corrosives
with
      model rocket motors -- black powder leaves just a bit of sulfuric
acid in
      its wake, and composites drop hydrochloric. The clip bodies of copper
      micro-clips will hold up OK, but the spring that holds the jaws shut is
      steel and will eventually corrode away, as you've seen.
------------------------------------------------------------------
12.14  Other Ignition Tips:

    From: dwade@jarthur.claremont.edu (Doug Wade)
      [concerning adapting launch controllers to 12V car batteries ...]
      Speaking of which, I took my Aerotech launch setup, lopped off the
      igniter attachment, and the place where it attaches to the battery, put
      amp plugs on either end, put a plug on the battery, and made some
      alligator clips in various configurations for launching Estes stuff.
      This means that I can switch batteries and igniter style in basically
      no time at all.  It's not a lot of work, and it makes life easier.  If
      you have the urge to do this kind of thing, make sure that you get
      plugs that can handle it.  A 12V motorcycle battery (Mine was about
      $40 but it's pretty nice) can put out something like 15A for a short
      period of time...

    From: cdt@rocket.sw.stratus.com C.D. Tavares
      [concerning an ongoing discussion about blast deflectors]
      I've had first hand experiences with several types of metals.  I've never
      found a piece of aluminum that was worth dog-doo as a deflector.  In the
      higher engine ranges, even steel will give you problems, especially with
      maintenance.  Stainless isn't much help, since it still cruds up.

      What we use are discarded grinding wheels.  Fireproof, non-conductive,
      free, plentiful, large, and pre-drilled.  The only negative on these is
      that when an engine catos they tend to lose large chunks or crack in
      half.  This happens to us maybe three times per year, but as I say,
      they're free and they're plentiful.

    From: kaplowro@hccompare.com (Bob Kaplow)
      Use clay flower pots for blast deflectors. Get Stainless steel for
      launch rods from welding or metal supply houses.

---------------------------------------
Copyright (c) 1996 Wolfram von Kiparski, editor.
Refer to Part 00 for the full copyright notice.


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