Scratch High Priority Original Design / Scratch Built

Scratch - High Priority {Scratch}

Contributed by Mitch Marchi

Manufacturer: Scratch
(Contributed - by Mitch Marchi II - 12/09/07) (Scratch) High Priority

Brief:
Built for the "Recycle" portion of the EMRR 2007 Challenge contest, this rocket is scratch built entirely from recycled trash. With squared-off fins and a blunt nose cone, it has an air-to-air missile look to it. It derives its name from the priority mail shipping tube which comprised its airframe. It is a single stage, 24mm powered, chute recovered, 4 fin rocket.

Construction:
The list of components and the material that they are made of:

  • BODY TUBE - recycled heavy walled cardboard shipping tube, 2.1" diameter
  • NOSE CONE - the top half of a body lotion bottle and its cap. The bottle fit perfectly on the outside of the body tube!
  • FINS - Actually a fin can, made out of a discarded plastic MIG welding wire spool.
  • LAUNCH ROD GUIDE - A BIC pen barrel.
  • PARACHUTE - Black trash bag, chute lines and shock cord made of used construction string.
  • MOTOR MOUNT TUBE - Hand rolled, made of some heavy paper stock from an eBay mail ad and lined with tin foil.
  • 2 CENTERING RINGS - cut from heavy cardboard from a paper tablet.
(Scratch) High Priority

I started with a mailing tube that I had laying around. It's an obvious choice, but this one had a really heavy wall, so right off the bat I knew it would be a D/E engine bird.

So now I had a body tube and had to fit an engine into it. I took some heavy paper out of the trash from a mailing ad. I then sprayed 3M artists spray mount on it and covered it in aluminum foil. I rolled this around 3 D engines and glued and taped it. Instant motor tube! I was going to go the masking tape thrust ring and motor retention route with this one, so no type of hook or block was needed.

(Scratch) High Priority (Scratch) High Priority
(Scratch) High Priority (Scratch) High Priority

Then I hand cut the centering rings out of some very heavy, dense cardboard that was the backing to a pad of paper that I had. With a little sanding and some epoxy, it fit together perfectly!

(Scratch) High Priority So now I had a bare booster section. I was going to use the same cardboard that the centering rings were made of for the fins, and in fact had cut some out. But I was changing the wire spool in my MIG welder when it hit me - the empty spool was plastic, about 10" in OD, 2" in ID, and had 8 ribs. Perfect! I cut the outside of it off, cut it down to 4 ribs (fins) and did some sanding to the inside diameter to make it fit the mailing tube. Voila! An indestructible fin can! While this may not be "household" trash, you can go to any welding or fabrication shop and they will probably give you as many as you like!

(Scratch) High Priority (Scratch) High Priority

I glued a section of BIC pen barrel to the fin can to serve as a launch rod guide.

The parachute I cut out of a black plastic garbage bag and used some construction string for the chute lines and shock cord. I attached the shock cord with some heavy paper stock, using the Estes "tri-fold" method.

(Scratch) High Priority (Scratch) High Priority

So it was complete, except for a nose cone. This one had me stumped. The "balsa shipping block nose cone" seemed like a stretch to me, and I really wanted to keep it something recycled, not fabricated. The idea hit me while I was in the shower, looking at the shampoo. I could use some type of bottle! I tried a 20oz pop bottle, and was working with that when I came across my girlfriend's hand lotion bottle while cleaning up one day. Yes, it was kinda blunt on top, but it fit OVER the body tube perfectly! I epoxied the end of the shock cord into it. The top still screwed on and off!

It was complete! It ended up pretty heavy (11.8oz RTF), but the CG was good (about 3x in front of the fins) and I knew that an E would get it off the ground.

Finishing:
The only finishing work I did was to paint the fin can and nose cone in orange. This offset the white body tube nicely with the USPS "priority mail" sticker still stuck to it. "High Priority" had come to fruition!

(Scratch) High Priority

Flight and Recovery:
They always say start out with a low-impulse engine on an untested design. Nonsense. I had D12-5s and E9-6s in my box. This was a heavy rocket, and I needed to make sure it made a flight. Add to this that my "racer" rocket, which was more than an ounce heavier, had to fly today so I needed some research info! In goes the E9-6. The motor was friction fit with a 1/2" masking tape thrust ring on it. Retention was tape also.

It lit up and launch was nice. In the 5-10mph winds, it took a slight weathercock and looked to hit about 800 feet or so. Nice and visible, it arced over and was headed down when the chute popped. The 18" chute opened and descent was a little fast, but that's good in my book. Touch down was about 100' past the pad. I'll take it! No damage, I packed it again, but this time with a D12-5. Hindsight being 20-20, what was I thinking?! However, I wanted to try it on 2 different impulses and only had 3 E engines with another rocket waiting to fly.

The second flight was identical on launch and initial thrust nice off the pad, slight weathercock, and it started to arc over. I doubt that it was even 500' off the deck. Ballistic, straight down, and waiting...Whack! Bounce. Pop! It hit the parking lot about 100' from the pad, and as it bounced the ejection charge went off!

(Scratch) High Priority The damage report: Nose cone "cap" shattered, but the nose cone "base" was still intact. The body tube split open like a can of Pillsbury biscuits for about the top 9"! Keep in mind that the body tube is high density cardboard that is 0.06" thick! I wish I could have recorded the "whack!"

The body tube will be cut down and spliced. This rocket can easily be rebuilt and will fly again!

Summary:
I think that my rocket truly exemplifies the spirit of the "recycle" contest. All of the materials are genuine recycled products. I don't have a simulation program so I just followed some "rules of thumb" and it flew great! The only reason it is a wounded soldier at the moment is that I only had 3 E engines and I knew that I had to use 2 of them for another rocket.

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