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From:
[email protected] (Wolfram v.Kiparski)
Newsgroups: rec.models.rockets,rec.answers,news.answers
Subject: rec.models.rockets FAQ Part 12 - Ignition and Launch Systems
Followup-To: rec.models.rockets
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Summary: This posting contains a list of Frequently Asked Questions
(and their answers) about Model and High Power Consumer Rocketry
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Date: 07 May 2002 12:02:28 GMT
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Archive-name: model-rockets/ignition-tips
Rec-models-rockets-archive-name: rockets-faq/part12
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Last-modified: 1996 January 9
URL:
http://dtm-corp.com/~sven/rockets/rmrfaq.toc.html
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
(
[email protected]).
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:
[email protected] (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:
[email protected] (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 <
[email protected]>
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:
[email protected] (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 (
[email protected]):
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:
[email protected] (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:
[email protected] (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
[email protected] (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:
[email protected] (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:
[email protected] (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 <
[email protected]>
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
[email protected] (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:
[email protected] (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:
[email protected] (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:
[email protected] (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:
[email protected] (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:
[email protected] (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:
[email protected]
"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.
[email protected] (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:
[email protected] (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:
[email protected] (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:
[email protected] 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:
[email protected] (Bob Kaplow)
Use clay flower pots for blast deflectors. Get Stainless steel for
launch rods from welding or metal supply houses.
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Copyright (c) 1996 Wolfram von Kiparski, editor.
Refer to Part 00 for the full copyright notice.
