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Wildfire was built during
the summer of 2002. It is a scratch built rocket that was designed
to carry my video
transmitter module. (This task was originally performed by Vulcan,
but Vulcan was damaged in May 2002 and can no longer carry the video
payload.) Wildfire is very much like Vulcan in that it is a 5.5-inch
diameter airframe and it can accommodate up to an M1315 motor.
However, Wildfire is slightly longer than Vulcan at just over 9 feet.
This gives more room for the parachutes. Wildfire has a number of
other minor improvements over Vulcan. One such is a 1/2-inch wide steel
band embedded into the fiberglass at one end of the airframe tubing.
This steel band prevents any possibility of zipper damage.
Wildfire has three fins.
The fins are made of 0.125-inch thick G10 material. The airframe has
three wraps of 6 oz fiberglass on it. The centering rings are cut from
0.5-inch aircraft plywood.
Wildfire deploys both the transmitter payload
module and its own recovery parachute at apogee. The transmitter and
the rocket come down separately.
In 2008 a camera module was designed to be flown
in Wildfire in place of the transmitter module.
Details on the camera module
are available here.
Click here to
view launch photos of Wildfire. |
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Length: |
9 feet, 3
inches |
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Diameter: |
5.5 inches |
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Weight: |
45 pounds with
M1315 motor and video payload |
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Motor: |
75mm mount
accommodates up to M1315 motor |
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Altimeters: |
2 each,
Missile Works RRC2 |
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Locator: |
Walston radio
transmitter |
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Payload: |
CCD video
camera, 1.3 GHz transmitter, GPS info overlay |
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Parachute: |
Rocketman R14
on rocket, Rocketman R12 on payload module |
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Built: |
Aug. 2002 |
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First Flight: |
Sept. 28, 2002
on M1315 at XPRS-1 launch at Black Rock desert in Nevada. |
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Construction: |
Body tube:
flexible phenolic + 3 layers fiberglass
Fins: G10 fiberglass
Nose cone: plastic (PNC-5.38L
available from
Magnum.)
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Results are for M1315 motor plus video transmitter payload.
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Simulation Results |
| Motor: M1315W |
| Maximum altitude: 10379 feet |
| Maximum velocity: 600 MPH |
| Maximum acceleration: 7.73 g |
| Time to burnout: 5.95 sec. |
| Time to apogee: 25.4 sec.
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| Time to landing: 366 sec.
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| Velocity at landing: -19.3 MPH
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| Launch guide length: 96 in.
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| Velocity at launch guide departure:
43.5 MPH |
| The launch guide was cleared at:
0.32 sec |
| Liftoff weight: 44.85 lbs |
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 A single fin is cut from a 1 foot by 2
foot piece of G10 fiberglass that is 0.125 inches thick. The photo of
a single fin also shows the right angle brackets that are added to the top
and bottom of it to mount it to the centering rings. |
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This is the 75mm diameter motor tube
with centering rings and threaded rods all installed. The top bulk
head also has the U-bolt installed that serves as the attachment point for
the parachute. |
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This is my fin alignment jig.
It is a 2 foot diameter base of 3/4 inch plywood that has three blocks
mounted to it at exactly 120 degrees. The blocks have a tall vertical
tab that makes it easier for clamping fins in place. The center of the
base has a 3-inch centering ring fixed to it for this particular application
since the motor tube is 3-inch. This jig can be used on all three
finned rockets up to 7.5 inches in diameter. For doing four finned
rockets the blocks are simply moved to 90 degree intervals and a fourth one
is added. |
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These four photos show the
sequence to fixture the fins. First the motor tube assembly with all
the centering rings is added. It is properly positioned by fitting
it over the 3-inch centering ring in the middle of the fin alignment jig.
Next the first fin is positioned and held in place by C-clamping it to the
vertical tab on the fin alignment block. While the fin is held in
place by this C-clamp I can drive wood screws through the right angle
brackets at each end of the fin. This firmly attaches the fin to the
motor tube assembly. Once a fin is complete, another can be added in
a similar manner. Once all three fins are attached with screws, the whole
fin/motor tube assembly can be removed from the alignment jig. Epoxy
and fiberglass strips are then used to do the final attachment of the fin
root to the motor tube. Additional epoxy at each end of the fin to
reinforce the screw connections is also a good idea. For rockets
that do not use screws to pre-attach the fins, the fins are simply glued
in place with epoxy while everything is being held rigidly by the fin
alignment jig. It's simple, it's cheap and it's accurate! In
fact the blocks can even be offset slightly to account for the thickness
of the fins. This ensures the fins protrude exactly perpendicular to
the airframe. |
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These three photos show a
jig for cutting fin slots in the airframe tubing. This particular
jig can only be used on 5.5-inch tubing. The tube is clamped in
place and a router is used to cut a slot the length of the fin root. |
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Once the tube has been slotted, I simply
add some epoxy to it and slid it over the fin assembly. The coupler
tubing is also added at this point. Once the epoxy cures we have a
completed motor section. |
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Motor section after
painting and adding rail guide buttons. These buttons screw into the
internal centering rings at the forward and aft end of each fin.
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An aluminum plate (this one
has obviously been flown before) mounts to the aft end of Wildfire to keep
the motor inside the rocket. (Motor not shown.) There are three
tee-nuts embedded into the aft centering ring so that machine screws can
be used to secure the plate in place. Click on the photos to get a closer
look. |
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"Look Down" Mirror for On-board Video |
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Wildfire was specifically
built to carry my video transmitter
payload package. Consequently it has a hole in the side of the
airframe up near the base of the nose cone for the video camera to see out
during launch. I also added a mirror to the outside of the airframe
so that the camera can look down the length of the rocket during launch
for a good view of the motor burn and a good view of the ground below
during lift off. However, I did not want the mirror to be a
permanent fixture. I wanted the flexibility to either use the mirror
or not so that I have the option of having the camera look straight-out,
or straight-down. I also wanted the option of flying without the
transmitter and mirror and I wanted the option of putting the transmitter
and mirror on another rocket. All this lead me to design a mirror
holder that can be easily removed.
The mirror holder is cut
from a sheet of stainless steel and then formed into the proper shape and
spot welded to some standard steel hose clamps. The hose
clamps make it very easy to attach the mirror to the outside of a rocket.
And the mirror is just as easy to remove! A design drawing of
the stainless steel hood that holds the mirror is shown below. The
mirror is simply glued to the underside of the top surface using the same
type of glue that is used for mounting mirrors to the inside of the
windshield of a car. (It's a special type of glue that sticks to
glass and is available at auto parts stores.) |
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This is a view looking down
on the mirror holder after it was mounted onto Wildfire. There are
two hose clamps that hold it in place. A hose clamp adjustment screw
can be seen on each side of the rocket. The spot welds to the upper
hose clamp can be seen in the tab at the top of the hood. Not the
most aerodynamic structure ever built, but it is very convenient. |
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This view is a little more
straight-on look at the mirror holder. The tab at the top of the
hood is spot welded to the upper hose clamp. There are two small
tabs on each side of the bottom of the hood that are spot welded to the
lower hose clamp. The top of the airframe is at the top of the
picture. The nose cone is not in place in this photo. |
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Here we looking up into the
bottom of the mirror holder. We can see the hole in the airframe for
the camera to look out. If you look closely you can also see the
edge of the mirror glass itself. It is glued onto the underside of
the top of the holder. (Click on the photo to see a larger version of it.)
The camera system that uses
this mirror can be seen by clicking right
here. |
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Assembly Process for
Wildfire Ejection Charges and Altimeter Bay |
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This is the altimeter bay
bulkhead. It has two PVC end plugs mounted on it to serve as
ejection charge holders. (They are slightly discolored here because they
have already been used on two flights before this photo was taken.) Four
Daveyfire ejection charge igniters pass through a small threaded PVC fitting.
A cap for that fitting is about to be installed. |
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This is a close up of the
threaded PVC fitting and cap that the four igniter wires pass through. The
fitting is filled with modeling clay to seal the igniter wires as they
pass through the bulkhead. Once the cap is screwed in place, the cap and
the clay prevent any hot ejection charge gasses from entering the
altimeter bay. The metal U-bolt that attaches to the parachute
harness can also be seen here. |
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This is the altimeter
electronics assembly. It has two
Missile Works RRC2
altimeters, two 9V batteries, and two on-off switches. The two
systems are completely independent and serve as mutually redundant
back-ups for each other. The parts are all mounted to a small wood
block. The block has a hole drilled down the middle of it so that
it can mounted directly onto the central threaded rod inside the
altimeter bay. There is an aluminum bracket that helps hold the batteries
in place. |
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Here is
another view of the altimeter electronics assembly. The yellow
igniter wires have now been connected. The two on-off switches are the
black cylindrical parts mounted in aluminum brackets. The brackets present
the face of the switch to the outer edge of the altimeter bay. This
makes it very convenient to activate the two switches by passing a small screw
driver through two of the altimeter static port holes. |
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Another view of the
altimeter electronics. We see a close-up view of one of the on-off
switches. The switch is really just a 110-220V selector switch, but it is
very useful here because it has high detent forces that ensure the
internal contacts will stay mated against each other during rocket flight.
It can also be wired in a dual pole configuration that provides two
parallel circuits through it. This provides redundancy to ensure
continuity during the high vibration environment of a launch. This
switch is available from
Missile Works. |
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Here we see the altimeter
electronics, the metal altimeter bay lid, and the bottom of the altimeter
bay bulkhead. Everything is now ready to be placed inside the
altimeter bay coupler in the rocket body tube. |
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This is a view looking
straight into the altimeter bay coupler. Inside the coupler is a
5/16" threaded rod. At the base of the threaded rod is a washer with
a small hole drilled in it. This hole serves as an alignment guide
for a small metal stud that is on the end of the wood block that holds the
altimeter electronics. This alignment ensures the altimeter switches
will be aligned with the altimeter static port holes so that the switches
can be easily accessed. |
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Here we see the altimeter
electronics unit sliding onto the threaded rod inside the altimeter bay
coupler. |
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Once the electronics unit
is in place, it is ready to be secured with a wing nut on that same
threaded rod. The altimeter electronics are actually inside a metal
can that is itself inside the altimeter bay coupler. This
metal can has air vent holes near the bottom of it. The metal can is
used to electrically shield the altimeters from the strong signals being
transmitted by the TV transmitter in the payload bay. |
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The altimeter electronics
is now locked in place with a wing nut on the threaded rod. The lid
to the internal metal can is now ready to be installed. |
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The lid to the internal
shield is now in place and ready to be secured with a washer and wing nut.
The igniter leads pass through the lid via a small insulating bushing. |
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The altimeter
bay shielding lid is now locked in place with the wing nut. |
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The altimeter bay bulkhead
is now ready to be installed on to the threaded rod. An O-ring is
used to seal the interface between the bulk head and the coupler tubing.
This prevents ejection charge gasses from entering the altimeter bay. |
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A steel nut (nylon locking
type) is used to secure the bulkhead to the threaded rod. This nut
must always remain tight since it keeps the bulkhead (and therefore the
parachute) attached to the rest of the rocket! |
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Here we see the igniters
being put into position over the ejection charge cups. These igniters are
the HiRMI (sensitive) igniters available from
Blacksky.
The "drogue" or primary igniter from each altimeter must go to the same
ejection change! The "main" or secondary igniter from each altimeter
goes to the other ejection charge. This prevents both altimeters
from firing both charges at once. (Actually it is still physically
possible that both charges could go off at exactly the same time, but for
that to happen, an igniter would have had to have failed. In which case
one altimeter would be firing its secondary igniter at the same time the
other altimeter was firing its primary igniter. This scenario requires a
specific failure and perfect timing, so it is extremely unlikely.)
Here the igniters have been
taped in place and black powder has been added to the ejection charge
cups. Wildfire uses 4.5 grams of BP in each cup. |
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One of the ejection charge
cups has now been completed and is fully taped shut. |
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Fireproof "wadding tissue"
is added to the ejection charge cup to take up any excess space and to
keep the black powder properly packed in place. |
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After the wadding was
added, the second ejection charge cup is sealed with tape. Both ejection
charges are now completed. |
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Just for extra security, I
also tape the top of the igniter wire fitting. Although it is not
really necessary, I like the added assurance that the seal is a good one.
The tape also helps protect the threads on that fitting. |
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We are now ready to mate the
altimeter section to the rest of the body tube. A steel "quick link" is
used as part of the parachute attachment system. |
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The parachute harness
anchor has now been attached to the U-bolt using the quick link.
This harness employs two tubular Kevlar straps for redundancy. The
Kevlar straps can withstand the ejection charge temperatures. These
straps pass through a Kevlar "flame shield" that protects the
tubular nylon harness and the nylon parachute. |
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Aligning the body tube
sections for proper mating. If you look closely you can see one of
the threaded brass inserts that are in the edge of the altimeter bulkhead
plywood. These inserts accept machine screws that will be used to
secure the two body tube sections together. |
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The body tube sections have
now been joined and the screws put in place. |
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