Saturday, May 31, 2008

The foam finally arrived!!

Despite reasonable packing the cans arrived pretty beaten up.  In any event progress can now resume.  Here are two shots of the foamed fin spaces and nose cone tip, respectively:
I'll need to grind down one fin cell since it rose above the bottom of the fin plane, add a bit more foam to these regions, and finish filling the nose cone in batches but you get the idea.

Monday, May 26, 2008

The Nose Cone

While the nose cone appears to be completely assembled this is not the case.  The seams/gaps formed by the two-part mold cavity are pronounced and must be filled for aesthetic and strength reasons.  I propped up the nose cone on my sander for support and, using a spirit level, I ensured that the seam was horizontal.  I then mixed up a batch of epoxy and filled it with some colloidal silica.  I applied this gel to the length of the seam verifying that the gap was filled and that I'd left a ridge so I can later sand it flat forming a smooth cone.  It's a bit difficult to see but this is the best I could do with garage lighting and a flash:

Next I had to add 70 ounces (~4.5 pounds!) of lead to the inner tip of cone to ensure stability with the heaviest motor.  I weighed out the lead shot into two 35 oz batches, mixed up two cups of epoxy ~1/3 full each, combined the two batches, and poured them into the inverted nose cone:

Finally I drilled and mounted a U-bolt into the final bulkhead and sanded it to fit inside the uneven shoulder of the nose cone:

Again the fixing of this bulkhead is on hold until the expanding foam arrives.  I plan to fill the nose cone with foam to improve its rigidity and resilience.  It seems fragile and likely to crack/break upon ground impact without inner foam.

The Payload Section

In parallel with the sustainer I built the payload section.  Here's where those fixed bulkheads came into play.  I epoxied one smaller diameter bulkhead onto the larger diameter bulkhead to tack them in place for subsequent drilling.  I placed the coupler tube over the smaller bulkhead to ensure it was centered correctly on the lower bulkhead and allowed the two to cure.  Since I don't have a drill press and straight holes are important here I took the bulkhead pair and the single bulkhead to work and used the press there.  My employer rocks.  Here's the drilled and assembled electronics bay:

There's a washer and nut on each side of the bulkhead holding each of the four 14"x20 threaded rods securely in place.  Note the two outward facing U-bolts the lower of which (in my hand) will connect the payload section to the sustainer section.  The upper of which will tether to the nose cone bulkhead.   I also used a hacksaw to cut the tops of the threaded rods off.  Next I sanded the inner circumference of the coupler tube and applied a ring of epoxy in this sanded area.  I twisted the above assembly into place and poured more epoxy into this coupler to fillet/strengthen the assembly:

After this shot I poured more epoxy into this cavity to improve strength.  Note that only this top bulkhead will end up epoxied into place.  The lower plate pair must remain removable to assemble/disassemble the electronics package. Uh huh huh... I said package... uh huh huh huh.

Securing the fins in the Sustainer

Ideally all 24 fin/tube interfaces would be covered with a fiberglass/epoxy layer to maximize strength.  I pondered how to best achieve this since the 4" diameter motor tube leaves only about 1.75" of working radius inside the 7.5" sustainer tube.  Luckily I'd previously bought a 25 foot roll of 1" wide fiberglass cloth at a local composites store and realized this would fit the need perfectly.  I cut strips into 11" lengths (just short of the fin root length) and capped one end (and later both ends) with narrow strips of gaffer's tape.  These caps both prevented fraying of the cloth on the short ends and also allowed me to poke the sharpened tip of a dowel into them so I could extend the strip inside the narrow working radius by holding the back end of the cloth strip then laying it into place (this was impossible to photograph while I was doing the procedure):
By tilting the fin/sustainer assembly so each fin pair pointed up at 45˚ I was able to apply the epoxied strips into all four bottom interior interfaces as well as the two fin fillet areas since gravity would force the resin right where I wanted it:

I should note that I also loaded the exterior two fin fillets with colloidal silica as it increases strength and eliminates resin drip during curing.  I've had this batch of West Systems epoxy and both colloidal silica and microfibers for years but never appreciated the power of the additives until this build.

I then repeated this procedure for the other 18 interfaces (in three batches of six, of course).  

Now the sustainer's on hold until my 2-part expanding foam arrives from Giant Leap rocketry.  I had previously purchased a similar foam, Foam-It, for <$40 at Home Depot but this type failed me because part A had cured in the can.  Better living through chemistry?  Please?  I went to purchase more Foam-It to find it had increased in cost to $96 at three different places!! Inflation rocks.  I decided to purchase the same volume of foam from Giant Leap for $41.  Quite a price difference no?

The Booster

I then sanded the inside of sustainer tube about 30" up from its bottom, applied a ring of West System epoxy along this ring, and slid the partially assembled motor tube up into the sustainer from the bottom.  I stopped just before the lower centering ring passed the fin slots, poured more epoxy up into this space, and twisted the assembly the rest of the way pushing the bottoms of both tubes down on the floor to ensure they were flush. Next I threaded two screw eyes into one of the two remaining centering rings and slid this into the base of the sustainer to ensure that the motor tube cured parallel to the sustainer body. :

I then stood the assembly upright and poured in a layer of epoxy into the sustainer/upper centering ring/motor tube interface and allowed all to cure:
Next I ensured that the sustainer tube was horizontal and one fin slot was pointing 90˚ up using a spirit level.  I test fit a fin into this slot, applied epoxy to the fin root, inserted the fin, and taped it in place.  I also verified the fin was normal to the sustainer tube using a spirit level and allowed this fin to cure:

I then repeated this procedure three more times constantly checking fin angle using a spirit level.  After the fourth and final fin had cured I placed the assembly upright, mixed up a batch of epoxy, mixed in colloidal silica until I achieved a thin paste, and filled in the gaps at the tops of the fins and allowed them to cure:

The Motor Tube Assembly

Before I realized the video camera wouldn't fit in the sustainer I did a bunch of work to integrate a mounting plate system onto the top-most centering ring surrounding the motor tube:

Basically the bottom plate would have mounted to the centering ring, the 1/4"x20 bolt would have threaded up through the upper plate into the camera's tripod mount, and this plate would then be screwed down into the lower plate.  It would have worked very well but I wanted credit for trying even though I abandoned this feature.  :)  After sanding the exterior of 4" motor tube and assembling this upper ring and I epoxied it 1/2" below the top of the upper end of the motor tube, applied masking tape below to hold it up and allowed it to cure:

I then marked the motor tube at 15.5" up from the bottom and epoxied a second centering ring above this line (just above the fin slot as seen in this next shot), secured it with masking tape, and allowed it to cure:

Quick build overview

I've been building for awhile now and there are way too many details to share in a few blog posts.  If you've perused the lengthy documentation packet below you'll understand that I threw away the instructions included with the kit and totally rewrote the build plan from scratch.  I'm going to summarize my work thus far in roughly four posts above: 
  • the motor tube - the 4" motor tube and upper two centering rings
  • the sustainer - the lower body tube containing the motor tube and fins
  • the payload section - the upper body tube housing both the electronics bay and huge main parachute
  • the nose cone - contains nose weight, expanding foam, and a bulkhead to connect it to the payload section
There will be some future entries above those including finishing touches, fiberglassing, and painting as well.  

It's not my intent to document every step and every picture here but rather to spot verify that I followed the rigorously detailed build plan in the doc packet.  If you have questions or need clarifications on any of the steps please read the documentation packet or post comments and I can respond to them in this blog. 

Sunday, May 18, 2008


I just spent almost an entire sunny Sunday working on version 1 of my documentation packet [updated on 8/8/08]. I sent it to my TAP members and now I'm off to do something else for awhile.  Expect a flood of blog entries covering the build very soon.  Thanks for reading.

Friday, May 16, 2008

Three things...

  • It turns out that my parents can't make it out to my level 3 attempt on June 7th.  As a result I'm going to push to the June 14th Lucerne Valley launch instead.  This coincides with RocStock XXVII so it should be a good scene.  This will also eliminate the lengthy drive my TAP members would have had down to Plaster City.
  • After piecing together the area where I'd planned to add a video camera I realized that there's no room!  Unfortunately I'm going to have to abandon on-board video for this vessel. There's much to be said for custom designs...
  • I am making progress on my level 3 design, component honing, and documentation and I'm still on track for the June 14 event.  I plan to spend the weekend updating this blog, sending documentation packages to my TAP members, and building.  Stay tuned.

Sunday, May 4, 2008

Great success!! I liiiiiiike!

I've had a bad streak of luck in the last few months:
  • In February I made a mistake setting the timer on a two-stage project (how sweet is the dude in that picture!) and crashed my AltACC 2A altimeter.  That little device served me perfectly for five years and now it's gone.  To make things worse they're now out of production!  Grrrr.  I did some homework on a replacement and decided to buy the Ozark Aerospace ARTS2 altimeter.  It's bigger than the AltACC and lacks a convenient built-in 9V battery mount but it's FAR more capable.
  • At the Lucerne launch last month I launched a new, sturdy little rocket on the new Aerotech Mojave Green 350I245, it flew and landed perfectly, then was dragged along the lake bed by the parachute for several minutes and was really beaten up.  It's functionally intact and I was able to repaint it but... stupid wind.
  • At that same launch I flew my Public Missiles Sudden Rush (those dudes rock too!) on the new ARTS2 altimeter but I was rushing to make the last flight of the day.  As a result the up part of the flight was beautiful but we lost site of it and nobody saw it after that.  I drove around the lake bed as best I could but, shocker, the IS300 doesn't deal with ruts very well.  I never found the rocket [crash site] and that was a $550 mistake.  Learning's expensive in this hobby.
Well that streak is done.  Ever tenacious, and convinced that I'd made some sort of mistake on that last failure, I bought yet another ARTS2.  The Plaster City launch was yesterday, 5/3/08, and I had three totally successful flights of three attempts.  Yay! One of those flights used this second ARTS2 in my V2 scale missile.  After reading the altimeter manual several times I figured out my mistake on that last failed attempt... there's a jumper that needs to be enabled when you're using only one 9V battery.  The default configuration disables this jumper as they recommend you use one battery to run the altimeter and another to fire the electric match(es)/ejection charge(s).  I never noticed this, used a single battery, so power was never sent to either of the two e-matches; hence the pile of expensive rubble in the Mojave Desert.
I'm very pleased that I figured this out before my level 3 attempt!  Despite the ambiguous and somewhat confusing documentation/ configuration the ARTS2 is impressive.  It has a feature I just discovered that allows one to analyze the performance of the motor(s) flown.  All you need to enter is the liftoff weight (rocket + motor), the propellant weight, temperature and pressure at the launch site and the program twirls those up with the flight data to give a damned accurate estimate of total impulse and average thrust.  In this case I flew the new Aerotech 1762K805 Mojave Green motor and the program calculated it to be a K820.  Now that's close!