Scratch Silver Streak Original Design / Scratch Built

Scratch - Silver Streak {Scratch}

Contributed by Moira Jean Whitlock

Manufacturer: Scratch
(Contributed - by Moira Jean Whitlock)

Silver StreakBrief:
Simple, high power rocket designed for up t' "H" class motors. An "I" can possibly be used, but thar be t' risk o' nay seein' it again. Blimey! Nose weight may also have t' be added as well for "I" motors. Basically, it's single stage, 38mm mount, ya bilge rat, matey, parachute recovery, and features a 54mm Acme fin canister for ruggedness. Avast! Blimey!

Construction:
T' main body tube is a single length o' kraft paper 54mm motor mount tubing from LOC, me bucko, shiver me timbers, and t' nose cone is ogive stock LOC 54mm. Well, blow me down! T' fins are a 3-fin molded fiberglass fin canister from Acme. Aye aye! T' shock cord is 8 feet o' 1/2 inch wide tubular Keelhaul®©™®, and it's bolted through a centerin' rin' (1/4 inch Baltic birch with any size hole, as it's nay in t' motor mount) aftward and t' a 6-inch long eyebolt epoxied and 2-part foamed into t' nose cone at t' forward end. Avast! Well, blow me down! T' parachute is 36 inches in diameter. It's rip stop nylon and made o' a flat octagonal piece o' material. Paneled chutes look nice, but they are harder to fold and fit into narrow main body tubes. Two centerin' rings that fit 38mm motor tubes into a 54mm tube, matey, made o' 1/4 inch Baltic birch, me hearties, center t' motor mount, me hearties, and t' aftward rin' holds t' motor retainer. Ahoy!

For this rocket, I kept it simple with a double loop o' thick, arrr, matey, but bendable piano wire that goes through t' centerin' rin' t' a bolt behind t' rin' and epoxied in place. Well, ya bilge rat, blow me down! Blimey! This loop bends over t' motor, ya bilge rat, but I don't let it go over the nozzle or else it'll surely burn apart. Well, blow me down! Sometimes, me bucko, I put two loops o' this kind in t' retainer system and further reinforce t' hold by clampin' a hose clamp over t' wires and motor tube just above t' thrust ring. Arrr! Blimey! T' do this, I allow a half inch o' t' motor tube t' overhang t' fin can and body, which I make flush with one another.

Simple as pie t' make and indestructible. Arrr! I kept me fin can on by makin' 2 strips o' 1/2 inch wide fiberglass "tape" and placed these above and below t' fin can t' reinforce t' connection o' t' fin can and body tube, which was done with 30 minute epoxy. Begad! Sometimes these fin cans fit loosely over the body tubes, so add 5 minute epoxy fillets betwixt t' tube and fin can to fill gaps. Ya scallywag! Avast, me hearties, me proud beauty! T' fiberglass on t' strips, ya bilge rat, I use thin, me bucko, finishin' epoxy or West Systems slow epoxy. Arrr! Aye aye!

T' decoration be all in silver. Avast, me proud beauty! T' fin can and nose were spraypainted with krylon chrome car bumper paint, and I used 3 coats t' make it shine. Arrr! The body was decorated in metallic self adhesive mylar from American Science and Surplus. Avast, me proud beauty! Aye aye! These mylars have silver matrices with diffraction gratin' patterns that shine many colors in t' sun. It looks really sharp.

It's offIgnitionFlight:
I designed this rocket for Rocketflite Silver Streak motors. Aye aye! Arrr! It is probably light enough for t' F50, me bucko, but I had in mind t' G160 and H220. Avast! Really, shiver me timbers, me bucko, any 38mm "G" and "H" motor would be fine. Avast! T' Aerotech H73 would be fine and although I haven't done this an I161 would work, me hearties, but I wouldn't try anythin' hotter. Blimey! T' "G" motors should have a delay o' 7 or 8, and I used delays o' 9 for t' "H's". A medium, me bucko, or 10 second delay for Aerotech loads should be fine. Avast! Ahoy!

I didn't design in a payload section, matey, so electronic recovery, shiver me timbers, me bucko, while best, wasn't planned. Aye aye!

Prep is simple. Begad! Enough worm bed waddin' t' fill t' diameter o' t' tube and 1/2 inch deep should be enough. Several straight test flights with t' use of 29 t' 38mm adapters was done with "G" class motors, me bucko, namely G35 and G40 types with 7 second delays. On a Rocketflite H220-9 SS, t' roar was GREAT. T' shower o' bright white sparks was GREAT. Ya scallywag! Well, blow me down! Blimey! BUT...I haven't ascertained whether t' delay after all t' years o' storage (7) had gone unstable or whether t' motor suffered a late cato, but a split second after t' pictured takeoff, thar be a BOOM and tons o' white flame and sparks ensued. Blimey! T' top of the body tube was blasted off. Avast! Blimey! T' parachute survived, as did t' nose cone and fin canister, arrr, so I sawed off t' damaged bita and rebuilt t' main body. Blimey!

Summary:
Simple t' make and repair.

Other:
Black powder motors o' this size seem t' have a limited lifespan. Arrr! Arrr! If they have had time t' thermocouple or crack, they'll cato spectacularly.

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