Endeavour Rebuild

 

 

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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.

 

What I Like About the Rocket

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.

 

What I Had a Problem With

 

Center Connection System

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.

 

Piston System

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).

 

What I Don't Like

Altimeter Bay

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

Piston System

Explained above.

 

Launch Lugs

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.

 

What Will Be New?

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.

 

The New Altimeter Bay

 

 

  1. 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.

  2. A piece of my 3.9" diameter Quantum body tube, Public Missiles QT-3.9-48 cut to 3" long.

  3. 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.

  4. 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.

  5. Two pieces of 7/32" OD X .014" wall brass tubing from the hobby store cut to 9-5/8" lengths.

  6. Two pieces of 10-24 all-thread from the hardware store cut to 10-5/8" lengths.

  7. 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.

  8. 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.

  9. Four 10-32 wing nuts.

  10. Two 1/4" U-bolt, 1-3/8" on centers.

  11. Eight 1/4" nuts to fit the U-bolts

  12. Four pieces of 1/16" thick, 1/2" wide brass bar cut 1/2" square.

 

Building the Altimeter Bay

  1. 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.

  2. 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.

  3. Next the 1/8" plywood was cut to size.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

 
  1. 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.
     

 
 
  1. 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.
 
 

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.

 
  1. 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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