Scratch Pushing the Envelope Original Design / Scratch Built

Scratch - Pushing the Envelope {Scratch}

Contributed by Brian Kain

Manufacturer: Scratch
Pushing The Envelope 38
(Contributed - by Brian Kain)

Download RockSim file here!

Brief:
A down scale of my level 2 rocket. TTW to a 29mm MMT. Can fly the I-200 load. If you were crazy you could cert 1 on this rocket with a 29mm H motor. 9400' on the H-90.

Rocket Pic

Construction:

  • 3 38mm body tubes Phenolic
  • 3 1/16" G-10 fins
  • 5 1/8" birch CR's
  • 12" of 29mm motor tube Phenolic
  • LOC 38mm nose cone
  • 15' of tubular Kevlar® shock cord

A super sturdy TTW rocket, all phenolic tubes with G-10 makes it almost indestructible. I cut the slots with a Dremel tool and a cutting wheel. I glued 4 CR's to the front of the MMT to center the motor tube for TTW construction. I did not hold back on the epoxy since there is a very small amount of room between the BT and the MMT. I filled the whole inside of the MMT area with 30 min epoxy lightened with fine micro-balloon fillers to keep weight down. I applied outside fillets with aerospace grade 120 cure epoxy...great stuff. I didn't glass the airframe cause it would add too much diameter. I painted it with a purple automotive lacquer that has a ton of blue and red pearl in it. Clear coated with automotive paint as well. Very nice finish and durable as well.

Flight:
I designed it to fly all these F52-11 loads I had laying around. I used cellulose wadding and a 18" chute, with 15' of Kevlar® with quick links sewn to the ends. The rocket flew very nice on the F52, and the 18" chute brought it home softly to the desert floor.

Summary:
Pro's..... can fly E through I motors, from 24mm up to 29mm with the proper weight added to the nose. Very strong with the TTW.... Con's....NONE

Other:
Very hard to do TTW with 1/8" of space between the BT and the MMT. I used tape to keep epoxy out of the motor tube as well as the outside of the airframe.

Other Reviews
  • Scratch Pushing the Envelope By Brian Kain

    ( Contributed - by Brian Kain) Download RockSim file here ! Brief: My scratch built level 2 rocket. Made for the J-350 but can fly on small 29mm H motors also. Used old phenolic but glassed with 6oz fiberglass and 30 min epoxy. ACME 3/8" lugs, LOC nose cone, G-10 FR4 (fire and heat resistant fiberglass). Radio shack personal body alarm for corn field recoveries. Custom aluminum ...

  • Scratch Pushing the Envelope By Brian Kain

      I wanted to build a rocket with the smallest fins I could get away with.....So I came up with this. I used Rocsim, VCP and WRASP to get my optimal size fin. Oddly enough, most of the programs agreed with my rocket. This is a single stage rocket, with an interchangeable MMT. Anything from 54mm down to 24mm motors will push this little guy. It uses a PML 30" chute with the shroud ...

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