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REV 2.4 - Tue Aug 17 04:03:43 2010

DesCon 14
Mercury Transport 29mm
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SPECS: MISSING
ROCKSIM FILE: MISSING - please submit here
SpaceCAD FILE: MISSING - please submit here
REC'D MOTORS: MISSING - please submit here

Mercury Transport

By Nick Esselman

Rocket PicFeeling a little bit like Rocky (you know, "I did it Adrian, I did it!"), I completed my 29mm Mercury Transport. I originally planned on building this rocket, but built an 18mm version first just to test out the design. It worked and so did this 29mm version.

I actually built this almost two years ago, but there hasn't been an appropriate Descon to enter it into, so ta-da....

The Mercury Transport's main purpose is to transport 4 passengers the 91.8 Million Kilometers to the planet Mercury for observation, study and experimentation in a high temperature, zero gravity, high sun-radiation environment. The Mercury Transport has fins that are suspended over the inner Fusion Proton Rod Reactor Core. The fins are in a test configuration for future interstellar travel and to assist in cooling the core as the ship passes close to stars (such as our Sun). The ship is primarily designed for long distance travel. In fact, 95% of the entire ship is a reactor to allow the ship to travel the distance needed.

The 29mm (should be 38mm) Mercury Transport is made from components of the Fat Cat Rockets' Centaurus rocket. I purchased the following from Fat Cat Rockets (now OOP):

  • (2) Lower 4" Body Tubes (7.5" long)
  • (2) Balsa Transitions
  • (1) 2.6" Body Tube


Motor Mount

The motor mount was a custom build with 4" centering rings for a central 29mm and (3) 24mm motors. The 29mm motor tube was 12" long and extended into the 2.6" tubing and had a 2.6" centering ring. This effectively focused the 29mm ejection charge up the 2.6" tubing. (picture is after last flight, even grass from the landing)

The recovery system consisted of an eye-bolt on the upper motor mount (2.6") centering ring. Tied to that was 15 feet of 1/2" Kevlar.

The nose cone was one of RGM's 4" Rounded Nose Cones.

I hand cut the fins from 3/8" Plywood. The long strakes are Walmart Yard sticks with an angle cut from the corner to the 3" mark on each side. Hey, these were a lot cheaper than buying wood and ripping it.

For recovery, I used a 50" rip-stop nylon parachute.

CONSTRUCTION:

The build on this rocket is fairly straight forward. The transitions are glued onto the 2.6" tubing until the tube is flush with the large end. I used TiteBond Original Wood Glue for this. I then used the TiteBond glue and spread it all over the outside of the balsa transitions to seal and strengthen them.

I then glued the two 4" tubes on each end using TiteBond. The shoulder on the Fat Cat transitions is really short, but for both their Centaurus and my Mercury Transport it is strengthened with external structures. In my case, the 29mm motor tube extends into the 2.6" tube from the bottom and the strakes attach to the outside of both sections of the 4" tubing.

Next, I built the motor mount and installed it using ProBond Polyurethane Glue. (additional comments about ProBond Polyurethane glue)

I marked the body tube using an old BSD guide that came with my Thor, after extending the lines to convert from three fins to six. I marked the lines on both 4" tube sections using a door jam.

At this point, I covered the 4" tubes and then used Plastic-Kote primer to prepare the inner tube (2.6") for finishing. After the transitions and inner tube were smooth, I painted them with Florescent Orange by Krylon. To my disappointment, it did not come out as "bright" as my 18mm version. The reason? I painted the 18mm right over the white body tube, whereas, on this one it was over the gray primer. Lesson learned.

After a couple days for thorough drying, I taped and covered the inner tube with paper to protect it.

Next was to prepare the strakes. After cutting the Walmart yardsticks from the corner to the 3" mark on each end, I attached them to the body tubes. I scuffed up the tube and then used TiteBond for this attachment.

I cut my six fins with through-the-wall tabs. Three had to be longer to reach the 29mm motor tube, while three where shorter to attach to the 24mm tube. I also had to ensure that the upper root section was cut at an angle to match up with the yardsticks (strakes). After complete, I attached the fins to with TiteBond and used a clamp on the fin to yardstick interface to keep them straight.

I next used Fix-It Epoxy Putty sold by Apogee Components for the fin fillets. All I can say is Wow! I like it! This stuff was good to work with. I used water to dip my finger in for smoothing out the epoxy fillets. I didn't think this would bond terribly well to the body tube or wood as I didn't think it would penetrate, but after suffering flight damage on the rocket, NONE of the breaks were on the epoxy bonds. Nice stuff.

Unfinished

After everything was dry, I used Plasti-Kote primer and Dark Navy Blue by Krylon to finish it.

Lastly, I checked the center of gravity in proportion to my 18mm rocket and determined that I needs some nose weight. I added nose weight based on my RockSim file (which did not calculate the CP correctly as expected). I did this by drilling two fill holes in the shoulder base and put in BB's. Then I poured epoxy into the holes, shook it, and poured more, until I couldn't hear any BB movement. I then capped it with another pouring of epoxy.

FLIGHT/RECOVERY:

At 2002 NYPowerThe final empty weight of my Mercury Transport was 70 ounces (4 lbs, 6 ounces)

For the first flight I decided to use an H165 plus three (3) F24's. I set it up without any ejection charge in the F24's and was ready to go. A lot of nice comments from others at the 2002 NYPower (see the picture someone took of me?) so that was fun. I had trouble getting it onto the rail as I was the first one to use this particular rail. I ran the rocket up and down multiple times, which "cleaned" the rail. Then, I waited for the LCO to count down. And waited, and waited. Finally it came time and the button was pushed and nothing happened! I had to recycle it. There goes 1 hour. The next rocket on the same pad (#30) failed to ignite too and therefore that pad was taken out of the loop.

I went back the next day and tried again. This time something happened at the "launch" command. The H165 lit and off she went. Ejection on the "Short" delay was very early. The nose cone went a flying one way while the rocket under 'chute descended nicely. The nose cone landed within 50 feet of the pad with no damage. The rocket landed a few hundred feet away with no damage.

That night I discovered that indeed (1) of the F24's lit too.

Lift-Off H238The next day, I loaded it up with an H238 plus the remaining two (2) F24's and threw an E18 into the empty slot. After another hour and a failed ignition. The Head Range Officer recognized that I needed a booster-battery to light this combination, he "guaranteed" me an ignition and we recycled.

On the next cycle, I was loaded with a booster-battery and upon "launch" my "guarantee" was satisfied. The rocket leapt off the pad under the power of the H238 and at least one of the 24mm motors (as seen in the picture) and at about 100 feet I heard/saw the remaining one or two 24mm motors ignite. I used Quick Burst Ignitors. I used a Fat Boy in the H238 and Twiggys in the 24mm motors. The Twiggys had to be built into the motor as they did not fit through the F24 or E18 nozzles. So, my guess, the H238 and E18 lit, while the two F24's delayed a bit. The nice thing is that those ignitors stayed in the motors after the H238 pushed the rocket off!

Well, again the ejection on the "Short" delay was very early. This time the nose cone seems to explode. Several parts floated down. I never found the nose weight. Don't really know what happen, but I have a guess. My guess is that the BB-epoxy nose weight fell upon ignition and then upon ejection, at the limit of the shock cord (non-elastic), slammed into the top the nose cone and shattered it.


DamageThe rest of the rocket descended and hit hard, hard ground. It broke one fin and strake off. But notice that it did not break the epoxy, so again, I am very pleased with the Fix-It Epoxy Putty. I have decided to R.I.P. this rocket and move on to my next project. This was fun!

SUMMARY:

In hindsight, I would recommend that this be built with a 38mm motor mount and forget about the cluster. And that is it, really!

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[Enter Flight Log]
Date Name Motor Ejection/
Altitude
Wind Notes
07-04-2002 EMRR 1x AT RMS H165/1x AT RMS E18 Very Early 5-10 mph winds - This was supposed to be 1 29mm and 3x 24mm, but only one 24mm lit. The ejection was early and the nose cone took off on its own. The rest of the rocket recovered fine. Re-attached the nose cone.
07-06-2002 EMRR 1x AT RMS H238/3x AT RMS F24 Very Early 10+ mph winds RIP - All motors lit, even though 1 of the 24's wasn't until it was 100 feet in the air. The ejection was early (again). Nose cone broke all into pieces at ejection. Lost a fin and a strake upon landing. Status: Not Repairable
   

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