Scratch The Demon Original Design / Scratch Built

Scratch - The Demon {Scratch}

Contributed by Kyle James Yawn

Manufacturer: Scratch
(Contributed - by Kyle James Yawn - 03/18/06) (Scratch) The Demon

Brief:
This is a three 24mm motor cluster rocket with large payload section. It is made for E9-4s but may be flown on D12s or some 24mm Fs. Avast, me proud beauty! T' payload bay is 12 inches long after t' coupler and nose cone shoulder are accounted for. Avast! It has through t' wall fin configuration and gives it a rock solid fin can. Aye aye! It's a real solid mid power cluster rocket.

Construction:
T' parts used in constructin' this rocket were:

  • 1 30" long BT-80 tube
  • 1 18" long BT-80 tube for payload bay
  • 1 9" long BT-80 nose cone
  • 1 sheet o' aircraft plywood t' construct t' fins from
  • 3 24mm motor mount tubes
  • 3 24mm engine blocks
  • 3 Estes "E" sized motor hooks
  • 2 centerin' rings t' center 3 24mm tubes in a BT-80 tube with an 1/8" gap betwixt each motor tube
  • 2 1/4" diameter launch lugs, 1.5" long
  • 1 6" long tube coupler
  • 2 BT-80 bulkheads
  • 1 screw eye
  • 12' long x 1/2" thick elastic shock cord
  • 1 30" X-form parachute
  • 1 9" x 9" Nomex® blanket
(Scratch) The Demon

T' most of t' major airframe parts such as t' body tubes, nose cone, coupler, bulkheads, ya bilge rat, and shock cord were from LOC/Precision. Avast, me proud beauty! T' body tubes were just thick cardboard tubes and t' nose cone is plastic.

There are 3 fins on this design and they have fin tabs for through t' wall fin construction. Blimey! I designed clipped delta fins that were 6 inches on the bottom and 3 inches high. Well, blow me down! T' centerin' rings were made from 1/8" plywood. T' motor mount tubes were cut 6 inches long, me bucko, matey, and t' shock cord was kept at its original length o' 12 feet. T' nose cone was placed on top o' t' payload compartment so an eye screw be placed in t' bottom bulkhead o' t' tube coupler t' attach t' shock cord t' t' main airframe. Aye aye! T' Nomex® just takes t' place o' normal waddin' t' protect t' recovery system.

First I built t' fin can and motor mount. Ya scallywag! Blimey! Blimey! Blimey! I began by cuttin' three 6 inch long motor tubes, arrr, cut slots, and epoxied t' engine blocks just past t' slots. I then inserted t' motor hooks. Usin' epoxy, shiver me timbers, I bonded them t' one o' the centerin' rings 1/8" from one end o' t' tubes. Avast! Blimey! Ahoy! Blimey! Blimey! Blimey! I used 30 min epoxy and applied it t' both sides o' t' ring. Begad! Blimey! T' other centerin' rin' be epoxied on after t' fins and I was sure t' make slots in t' aft rin' for t' engine hooks t' fit through.

(Scratch) The Demon Next, me bucko, I cut out three fins from a template I made. Well, blow me down! Blimey! They were a clipped delta style that measured 6" long and 3" tall with t' back 3" o' t' top flat. They also had fin tabs measurin' 1.25" deep and 4.5" long. Avast, matey, me proud beauty!

Epoxy was then applied t' t' inside o' t' tube past t' fin slots and the motor mount was slid into t' tube with t' bottom o' t' motor tubes flush with t' bottom o' t' airframe. Avast! Arrr! After t' epoxy set, t' fins were fit into the slots and more epoxy was applied betwixt every joint o' where t' fins met the motor tubes, matey, where t' fins met t' airframe tube, me bucko, ya bilge rat, t' aft centerin' ring and t' airframe tube, me hearties, and in t' gap betwixt t' three fins where they meet in the middle o' t' tube. Avast! Epoxy be then applied t' t' bottom edges o' t' fin tabs and around t' bottom edge o' t' airframe and t' other centerin' ring was slid onto t' rocket over t' three engine tubes. Avast! Finally, matey, another epoxy fillet is applied t' t' centerin' rin' and t' inside o' t' airframe from the bottom end o' t' rocket. This provides a rock solid fin can!

Then I drilled a pilot hole in t' middle o' one o' t' bulkheads and inserted a screw eye into t' hole. I placed epoxy on both sides o' the bulkhead on t' screw eye, then epoxied a bulkhead t' each end o' t' coupler tube, with t' screw eye facin' out. Blimey! After t' epoxy on t' bulkheads set, me bucko, I epoxied t' three inches o' t' coupler tube with t' flat bulkhead without the screw eye into t' bottom o' t' payload tube. Well, blow me down! Arrr!

T' shock cord mount was constructed by usin' 200lb test Keelhaul®©™® cord and tyin' knots at each end and coverin' t' knots in a pool o' epoxy inside t' main airframe. Ahoy! This was done deeper into t' tube than t' coupler shoulder will reach so that t' coupler will slide all t' way down.

Tie t' shock cord onto this mount and place t' Nomex® cloth onto t' shock cord. Ya scallywag! Ahoy! Then I tied a loop in t' shock cord about 2 feet from t' other end. Blimey! Begad! I use this loop so I am able t' change out t' parachute used in this kit based on if it has a fragile payload or if t' wind is blowing very hard, although I like t' 30" X-form chute. Well, blow me down! Next, arrr, me hearties, me hearties, I tied t' other end o' t' shock cord t' t' screw eye on t' coupler tube.

I drew a line betwixt two fins and epoxied one launch lug 1.5" from the base o' t' rocket on t' line and t' other one 14" from t' base of the rocket. Ya scallywag! Avast, me proud beauty! You could also apply rail buttons or another type o' guidance as you please.

T' nose cone needed a few layers o' maskin' tape wrapped around the shoulder t' ensure a tight fit into t' top o' t' payload bay so that t' nose cone does nay come off durin' ejection.

Flight:
If t' payload compartment is empty, shiver me timbers, shiver me timbers, me hearties, this rocket could fly on three D11s or D12s with an adapter for them, arrr, but I used 2 E9-4s for its maiden flight. Well, blow me down! The prep was easy since no waddin' is needed due t' t' Nomex® cloth attached t' t' shock cord. Blimey! Arrr! I just installed igniters and plugs in the three motors, me bucko, me bucko, placed them in t' rocket and be ready t' go. Ahoy! T' engine hooks provide motor retention.

I used a clip whip on t' pad t' ensure t' ignition o' all three engines. (I need t' be careful with this rocket when it has a heavy payload while flying it with E9s because if only 2 engines light, ya bilge rat, it won't have a stable flight.) T' ignition o' this rocket be magnificent. I had an altimeter and some other payloads in it. All 3 E9-4s ignited and it rocketed off t' pad. Blimey! You could clearly see all three individual flames which made for a great show at t' club launch. Begad! It flew straight up until t' ejection charge deployed just slightly before apogee at 840'.

Recovery:
T' parachute pulled out and fully opened and t' shock cord held everything together with that strong Keelhaul®©™® mount in t' main airframe and t' screw eye in t' payload bay.

T' recovery speed was perfect and brought t' rocket gently back t' the ground and landin' with a soft thud. Ahoy! Begad! T' 36" X-form works well on this rocket. Begad! With t' Nomex® cloth in there, matey, neither t' parachute nor t' shock cord were even harmed at all by t' hot ejection gases.

Summary:
This is a very well built 3 engine cluster rocket with a large payload capability. Avast, me proud beauty! It is rock solid upon completion and has incredible flights with three beautiful flames. Aye aye! Begad! I have wanted t' build a large, me hearties, high performance cluster and payload kit for a while so I combined t' ideas and it works wonderfully. I can't find any cons in it at all.

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