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High Power Rocketry ||
Experimental Rocketry
ENDEVOUR REBUILD
The Endeavour is my first high power
rocket, the one I got my Tripoli level I and level II with and has become
my test bed for various projects now. The Endeavour is a kit from
Public Missles, is 4" in diameter and 71" long. It features their
54/38/29mm Kwik-Switch motor mounts, piston ejection system, and their
particular design screw together altimeter bay designed to give (fairly)
quick access to the altimeter and ejection charges.
I chose this particular rocket for some good reason.
1. It was my first high power rocket so choosing
a kit was the easy way to learn about the differences between these birds
and the small model rockets. The four inch body tube made it easier to
work on because I could get my hand and arm down inside it. With the
dual deployment add-on kit, it included all the parts including the shock
cords and two parachutes.
2. It featured a preslotted body tube for the
fins so I didn't have to cut my own slots.
3. It featured their Kwik-Switch motor mounts so
I could fly three different diameter motors in it.
4. The Quantum tube also made it a quicker and easier
build because there was no fiberglassing and no filling spiral groves on
phenolic tube.
5. The dual deployment kit required no designing or
finding and ordering parts, it was just a matter of following the
directions.
6. Especially I chose this rocket overall because
it was the right size to be used for both my Tripoli level 1 and level 2
certifications.
If you are considering this rocket, I recommend it but I recommend NOT
getting Public Missiles' dual deployment kit with it. If you want to
use dual deployment, plan ahead and do something like I am doing. Most
of my problems were related to the dual deployment kit rather than the basic
rocket kit. This same dual deployment kit is used with several of
their rockets so keep this in mind if considering other rocket kits from
them as well.
The body of the rocket is composed of four pieces, the fin can, the nose
cone, and between them are two parts that screw together using Public
Missiles' own aluminum couplers. These parts hold the altimeter bay,
both the drogue and main parachutes and the ejection charges.
The way it is built, the two center sections that
contain the altimeter bay are screwed together with an aluminum female
coupler on the top half (not shown) and an aluminum male coupler on the
bottom half as shown below and these have a very vulnerable Achilles heal.
 Because the female half screws all the way down on the
male half, you cannot make an epoxy fillet where it contacts the plywood
centering ring. This means that the male half is only epoxied to the
1.65" phenolic tube that is part of the altimeter bay. The entire two
halves of the center part of the rocket are held together by the couplers
and as shown in the picture that stress is concentrated right at the point
where the male coupler contacts the centering ring. Mine broke there
while assembling because it is so weak and after repairing it and adding a
small epoxy fillet there, it still broke twice more. The female half
of the coupler is not a problem because you can put a healthy epoxy
fillet where it contacts its centering ring.
 The piston system is actually a good idea but I also
had a failure with it. On one launch, (it happened to be my first
level 2 attempt), I had a drag separation and the main chute came out
prematurely. The shock cord pulled right through the plywood end on
the piston and the nosecone came down with the main chute separate from the
rest of the rocket which came down with only the drogue. Fortunately,
it landed in soft, fresh plowed dirt and had very little damage. It
was
 repaired on site and launched again with a single deployment and was
successful. Another problem with the piston system is that in this
case at least, the piston is phenolic and the body tube is Quantum tube.
The two have a very large difference in the coefficient of expansion so when
it is cold, the piston is tight, when hot, it is loose. Also, you have
to clean out the inside of the tube where the piston travels really well
between launches so that it moves freely. Even though I am not opposed
to the piston system, personally I prefer a conventional system using
wadding and Nomex chute protectors (and shock cord protectors which are
needed even with the piston system).
Other than for my first rocket I didn't have to do any
design work, there is no redeeming aspects to this feature.
1. The altimeter bay comes with plastic ends that
are attached to each end of their altimeter with screws. These adapter ends
also hold the ejection charges, one on each end. It is only designed
to work with their own altimeter. I didn't use theirs so had to modify
my altimeter to work with this system.
2. The lower end of the altimeter adapter has an
o-ring that seals it against the inside of the 1.65"
 tube shown
above. The top adapter also has an o-ring but sits on the top of the
male coupler and is sealed between it and the female coupler. I found
that it was difficult to push the altimeter down into the tube even with
some grease on the o-ring. The fit was too tight and the o-ring had a
tendency to roll out of the groove. I didn't like having to push hard
on the altimeter to get it down into the tube for fear of breaking it or
damaging it.
3. The system is design to only hold the
altimeter. There is no room for other things you might want to add
such as a backup altimeter, timer, audible beacon, etc.
4. You don't have a choice for a backup main
ejection charge instead of a drogue and main. I changed my altimeter
to use an apogee ejection with the second charge being a backup for my
second level 2 attempt. I taped the bottom section together that came
apart prematurely (that's another story) and moved the wires for the
Explained above.
The kit came with 1/2" brass tubes for a 1/2" round launch rod. Most
everyone nowadays is using launch rails with launch lugs or buttons.
To use a club launch pad, the rocket needs to be equipped with launch lugs,
not launch tubes. Also, a 1/2" round rod is much more flexible and a
launch could experience rod whip throwing the trajectory off and away from
the recovery area.
I will be eliminating (saving for pieces for some future project) the two
center sections entirely with the two pistons and the altimeter bay. I
will be keeping the tail section with the Kwik-switch motor mounts, nose
cone, shock cords, and parachutes. The new center section will be
three parts instead of the two original. They will consist of a new
altimeter bay and two tube sections that will screw on to the center
altimeter bay. The launch tubes will be replaced with launch lugs.
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Two Public Missiles CT-3.9 phenolic couplers.
These are 7" long. The choice from Public Missiles was either 7" or
36" so I opted for two 7" and cut each to 5" long.
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A piece of my 3.9" diameter Quantum body tube,
Public Missiles QT-3.9-48 cut to 3" long.
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The two pieces of the couplers from #1 that I
had cut. They were about 3-7/8" long (1/8" for the saw blade width). I
cut a slot in them so they would fit inside the couplers.
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A piece of 1/8" craft plywood, probably birch,
originally 8" X 12" but cut to 3-1/4" X 9-5/8". This is to mount the
electronics -- altimeter, audio beacon, etc.
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Two pieces of 7/32" OD X .014" wall brass
tubing from the hobby store cut to 9-5/8" lengths.
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Two pieces of 10-24 all-thread from the
hardware store cut to 10-5/8" lengths.
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Two Public Missiles CBP-3.9 "bulkplate for coupler".
These are 3/16" thick plywood plates that are made to fit inside the 3.9"
couplers.
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Two 3/32" thick X 3/4" wide steel strap cut to 3-5/8" long
and with a radius ground on the ends. These straps are for extra
security because they will connect the two ends together through the
all-thread to the U-bolts so there is no way anything can rip thorugh the
plywood bulkplates like they did through the pistons in my first level 2
cert attempt.
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Four 10-32 wing nuts.
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Two 1/4" U-bolt, 1-3/8" on centers.
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Eight 1/4" nuts to fit the U-bolts
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Four pieces of 1/16" thick, 1/2" wide brass
bar cut 1/2" square.
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I used my table saw with a plywood blade to cut the two
couplers down to 5" using the rip fence to set the length. I used the
miter to hold the coupler square, moved it up to the blade that was set only
about a half inch above the table and then holding the miter in one place,
rotated the coupler until it was cut all the way around. I cut the 3"
piece of Quantum tube the same way. Had just a little deburring with
sandpaper after cutting.
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I reset the rip fence to about 2" and cut the slots in the 2" pieces of
coupler. I cut a single cut, tried it in the coupler, cut a little
more, and tried it again until they each just fit snuggly inside the coupler
tubes with the slot closed up.
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Next the 1/8" plywood was cut to size.
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Putting a metal cutting disk in the table saw, I cut off the
two pieces of steel strap to 3-5/8" long, the brass tube to 9-5/8", and the
brass bar to 1/2" lengths. I used the same disk as a bench grinder and radiused the two pieces of steel strap.
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I used a propane torch to solder the four brass tabs (#12) onto the brass
tubes (#6). The tabs and tube were laid on a piece of steel so one
side of the tube and one side of the tabs were flush. It took very
little heat to solder these on but the joints were strong. I might
just try a soldering gun or my miniature butane torch next time because
the propane flame was too big, too hot, too long and hard to control
without getting too much heat on it. When it was done, I used a
Dremel with a small cylindrical cutter to clean it up. Then I
drilled a 13/64" hole in each tab for 10-32 screws.
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Epoxy was spread on the inside of each of the split couplers (#3) and they
were pushed down inside each of the 5" long pieces of coupler until they
were 3/16" from the ends. The 3/16" clearance was for the coupler
bulkplates (#7) so the bulkplates would be flush with the inside of the
tubes. I cleaned off the excess epoxy in the space between the
inside coupler and the end of the 5" couplers. When the epoxy was
dry, I had to sand off the rest of the epoxy in that gap so the bulkplates
would go in. The inside coupler pieces were to provide a stop for
the bulkplates.
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Similarly, epoxy was spread on the inside of the 3" piece of Quantum body
tube and then the two 5" pieces of coupler were slid in from each side.
They were centered by insuring that 3" of each coupler protruded out from
the Quantum tube.
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Next,
matching holes were drilled in the #7 bulkplates and the #8 steel straps.
Two 13/64" holes were drilled 3" apart and centered. These are for
the two lengths of all-thread. Two 17/64" holes were drilled 1-3/8" inches
apart and centered. These were to match the U-bolts. I marked
the holes on one of the steel straps with a steel scribe, center punched
them, clamped the other steel strap to it with vicegrips, then drilled all
the holes using smaller drill sizes and working up in three steps to full
size holes. The straps were deburred, then both bulkplates were
clamped together with one of the steel straps and the bulkheads were
drilled out.
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The
all thread was then threaded through the brass tubes with the tabs and a
steel strap on each end and secured with nuts. This was to get the
right spacing for attaching the plywood to the brass tubes. With the
plywood centered between the brass tubes, I back drilled the plywood using
the holes in the tabs as guides. 1/2" long 10-24 round head machine
screws were put through the tabs, through the plywood, and secured with
washers and nuts. These were tightened so the tubes wouldn't move.
Since I am a belt and suspenders kind of guy (backups on backups) I spread
epoxy all along each tube on both sides to make sure it was secure and
wouldn't move so it would always fit properly.
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The all thread and steel straps were removed from the above assembly.
Next nuts were threaded all the way down the the threads on both sides
of the U-bolts, they U-bolts were inserted into the center holes on the
steel straps and centering rings, flat washers added, and finally, the
nuts were tightened. The U-bolts were way too long so since the
metal cutting blade was still on my table saw, I used that to cut off
the legs of the U-bolts flush with the bottom nuts. |
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The last step was to notch the plywood (#4) to clear the nuts of the
U-bolts. This was done with a cutter on my Dremel. The new
altimeter bay was now ready complete and ready for paint.
Actually, there is one more step. Depending on the configuration, one
or both ends of the altimeter bay may be screwed onto the adjacent body
tubes, the lower end might be epoxied if single deployment is to be used or
the upper end may be a slip fit and separate there instead of at the nose
cone. I will be using dual deployment and separation will occur at the
lower body tube and fin can for the drogue and between the upper body tube
and nose cone for the main chute. I will be screwing both sections of
the body tube to the altimeter bay so I can take the screws out and access
the ejection charges and set up the electric matches.
To do this, I will use blind nuts (T-nuts). I will put the two body
tubes in place on the altimeter bay and drill through the body tube and
through the wall of the altimeter bay just below the bulk plates so I have a
double layer of phenolic tube. Then I 'll take them apart, epoxy the
nuts in place and grind of the excess so it is flush with the outside of the
coupler. I'll run a screw or tab through to make sure a screw will
work easily. I'll put in two #8 steel screws 180°
apart on each end.
The altimeter will be mounted with standoffs and a
switch will go in the center section for outside access for arming the
altimeter and whatever else I put in it. I plan on putting
terminals on both ends and an ejection canister for the black powder on each
end. I'll get more explanations of these and pictures when that is
done.
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