Scratch Pushing the Envelope Original Design / Scratch Built

Scratch - Pushing the Envelope {Scratch}

Contributed by Brian Kain

Manufacturer: Scratch
(Contributed - by Brian Kain)

Download RockSim file here!

Brief:
My scratch built level 2 rocket. Made for t' J-350 but can fly on small 29mm H motors also. Ahoy! Used old phenolic but glassed with 6oz fiberglass and 30 min epoxy. ACME 3/8" lugs, shiver me timbers, LOC nose cone, ya bilge rat, G-10 FR4 (fire and heat resistant fiberglass). Ya scallywag! Radio shack personal body alarm for corn field recoveries. Custom aluminum motor retainer bracket usin' all-thread for mounting. Blimey! Avast, me proud beauty! I used the 30" chute that came with me level 1 V.B. Arrr! 54mm Extreme.

Filling in the finConstruction:
Components: T' sustainer uses 2 body tubes, shiver me timbers, joined with a phenolic coupler. T' 9/16" tubular nylon shock cord attaches through t' coupler. I cut slits in t' coupler and weaved t' shock cord through, shiver me timbers, looped it around onto itself, and sewed it together with 100lb Keelhaul®©™® thread then epoxied over that. I made an altimeter bay for future use, but was nay plannin' on using electronics for me cert 2. Aye aye! Ahoy! T' rocket has 3 fins made from t' heat resistant G-10 FR4 fiberglass. Avast! Avast! I cut all me 1/8" and 3/16" centerin' rings and bulkheads usin' a drill press and an adjustable hole cutter. Ya scallywag! Aye aye! T' motor mount is 13" long by 38mm with 6 centerin' rings. T' first 4 rings were epoxied to the front o' t' MMT t' keep it centered for TTW construction. Ahoy! Well, arrr, blow me down! I glassed between each o' t' front centerin' rings with 6oz. Some o' t' epoxy I used was aerospace grade 120 min setup. Aye aye! Avast! Great stuff, me bucko, but big $$$. Avast, me proud beauty! Aye aye! I used the aerospace epoxy for external fillets and layed Keelhaul®©™® yarn into t' epoxy runnin' lengthwise along t' fin root. I only use stainless steel hardware for attachment points since I have seen pot metal break. I used SS eye-loops and 3/16" SS quick links. I only added 1.5oz o' lead fishin' weight t' the nose, and secured with 120 min epoxy.

Unfinished

Construction: T' rocket was fairly easy t' build, shiver me timbers, shiver me timbers, me hearties, but thar are a couple hard parts. Blimey! Begad! Blimey! One concern was gettin' t' epoxy t' me TTW attachment points without gettin' it all over t' back where t' final centerin' rings go. Ya scallywag! Blimey! I wrapped self releasin' maskin' tape around t' outside o' t' MMT. Avast! Aye aye! Blimey! Then blue automotive maskin' tape around t' inside o' t' airframe. Well, blow me down! This allowed me to just pour epoxy right onto t' tape and have it flow down inside t' airframe to me fin mountin' points. Just remove t' tape before it cures, ya bilge rat, then re-apply tape for t' next set o' fillets. Arrr! Arrr! Blimey!

Back EndA dremel tool with an extension is a good item t' have when cuttin' fins. Avast, me proud beauty! Use a carbon cuttin' wheel and you can lay the extension flat and so t' dremel tool itself doesn't get in t' way o' the line you are cutting. Ya scallywag! Without an extension, matey, it is hard t' get a flat straight line because t' tool gets in t' way and will end up cuttin' crooked.

I got me components at various launches over t' period o' 6 months. Ahoy!

Flight:
I made t' rocket for t' J-350, for me cert 2 flight. Avast, me proud beauty! Blimey! T' rocket is very straight forward, and basic t' prep. Avast! Blimey! Begad! Blimey! I used cellulose insulation for wadding, about 1 handful. Arrr! Blimey! Motor retention be a 1/16" piece o' aluminum cut t' fit the back o' t' rocket. Blimey! Blimey! Avast! Blimey! I drilled about 1" deep into t' aft centering rings in three points, then epoxied all-thread into t' holes. Begad! Blimey! Aye aye! Blimey! T' AT J-350 was simple t' prep. Blimey! Blimey! Don't mind t' rattlin' o' t' grains, ya bilge rat, as long as you have no left over parts they are supposed t' move inside t' case. Arrr! Blimey! Begad! Blimey! I used 4oz o' red line chalk for tracking. 20' o' 9/16" tubular nylon for t' shock cord. Well, blow me down! Blimey!

Look at that flame!T' rocket flew awesome. Arrr! Avast! Dead straight in 15mph winds. Well, blow me down! Ya scallywag! That means it was perfectly stable, not over stable. Arrr! In t' first 4 seconds o' its 20 second flight, matey, t' rocket was completely out o' site, even though I have perfect vision, ya bilge rat, ya bilge rat, I could nay see the red line chalk when it deployed but someone with binoculars said they may have seen a red chute or chalk. Ya scallywag! Well, me bucko, blow me down! I have no idea if t' recovery was late or early, but drove with t' wind at me back for about 2 miles before I found it. Aye aye! There was no damage at all so it must have deployed around apogee. Begad! Ya scallywag! This rocket simmed out at 9100' goin' about mach 1.1 In t' video footage you can see t' time of each frame in t' corner o' t' screen. Ya scallywag! T' time read 12:46:00 pm for as long as you can see t' rocket in t' picture. Begad! You can see snap shots o' t' video here.

Summary:

  1. This rocket is so strong I swear I can chop down a small tree with it. Arrr! Well, arrr, blow me down!
  2. It is perfectly stable with a J-350 and only 1.5 oz o' weight in t' nose, yet it still has very small fins.
  3. I can still fly it on big G motors, all t' way up t' t' J-570. Begad! Ahoy!
  4. Every time I have flown this rocket t' flight be exactly t' same each time. Recovery was about t' same distance from pad. About 1.7 t' 2 miles away.

Con's I can't really think o' any. Ahoy! :)

Other:
One thin' this rocket taught me is this........ Begad! It is hard t' do through-the-wall on a 54mm rocket with a 38mm motor mount. Especially when you are usin' thick walled phenolic, me hearties, thar be even less room t' work with. Well, blow me down! Well, blow me down!

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