Scratch - Dos Kraken {Scratch} Original Design / Scratch Built

Contributed by Andrew Hansom

Manufacturer: Scratch
Style: Cluster, Multi-Stage, Upscale

Brief:
Dos Kraken is a combination and upscale of two unique rockets. The design is from Pemtech's Kraken with the sculpted tube fins and the canted twin motor tubes design was borrowed from FlisKit's Deuce's Wild. Dos Kraken will fly on a pair of 38mm x 480 AT motors with the total output of a J sized motor. Dual deployment will be handled by a Perfect Flight MAWD and a Missile Works RRC2. Recovery will be dual deployment with a 24" drouge at apogee and a 72" SkyAngle at an altitude of 500'.

scratch_dos-kraken

 

Construction:
The Booster section used 5 pieces of 3.9 LOC airframe tubes. One tube for each sculpted tube fin and the other for the center of the booster. A LOC electronics bay with a 20" payload section completes the rocket body. All tubes were fiberglassed using fiberglass sleeves from Sollar Composits and West System epoxy. The two centering rings and gussets were cut from 1/4" birch plywood. Motor tubes are LOC 38mm x 10" long and canted at 10 deg. from the centerline. The fiberglass nosecone and 1/4" Kevlar shock cords are from What's Up Hobbies.

scratch_dos-kraken_businessend

After buying and building a Kraken from Pemtech, it was fairly easy to use the same destruction techniques for the upscale. The layout of the sculpted fins is explained very well when building the smaller version. I drew the layout lines on the tubes before fiberglassing. After putting the sleeve over the tubing and the resin is applied the fiberglass will be transperant and very easy to see the markings for cutting and fin attachment. A saber saw with a fine tooth blade was used to cut the fiberglassed tubes leaving a fairly clean edge.

scratch_dos-kraken_tubefins

Finishing:
I made a thick paste of epoxy and collidal silica. I rubbed it on the fiberglassed tubes to fill the exposed weave. This leaves a smooth finish that makes final finishing less work. Painting is a little tricky but again the Pemtech destructions give a couple of tips on making painting fairly easy. I used Rust-olium Metallic paints for a very nice metal flake finish. I had the name and flames made by Mark Hayes of Sticker Shock. He made some very nice vinyl decals that were scaled to fit the rocket.

scratch_dos-kraken_allenginesgoFlight:
For the maiden flight I used a pair of Aerotech I-285 Redline's. On the second flight, lift off was on a pair of Aerotech I-284 White Lightnings air starting to a pair of Aerotech H-112 Black Jacks. Recovery electronics are handled by a Perfect Flight MAWD and a Missile Works RC22 as back up. A Perfect Flight MTG3 is used for ignition of the sustainer motors. For motor retention I used some extended Kaplow type clips. The rocket flies straight with very little rotation.

Recovery:
The Drouge parachute is attached to the booster section by 5' of 1/4" Kevlar rope and the booster is conected to the payload section by 25' of 1/4" Kevlar rope.

The main parachute recovery harness consists of 25' of 1/4" Kevlar rope between the nosecone and electronics bay. with the paracute attached 8' from the nosecone.

Summary:

PROs: Dos Kraken has a very unique look and draws alot of attention with the sculpted fin tubes. Using the Deuce's Wild motor mount and the ability to airstart sustainer motors really adds to the overall fun of the rocket.

CONs: This is not really a con but the rocket takes alot more time to prep and is more complex than a single motor rocket.
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