Scratch One Shot Original Design / Scratch Built

Scratch - One Shot {Scratch}

Contributed by Dick Stafford

Manufacturer: Scratch

Rocket PicBrief:
After losin' me RocketVision Machbuster on a G55, I decided that I wanted t' build a similar rocket that would fly on 29mm motors. Aye aye! I scrounged through me parts bin and, bein' a 'glass-half-full' type, ya bilge rat, shiver me timbers, arrr, named t' result 'One Shot'.

Construction:
Parts List:

  1. 29mm phenolic tube, ya bilge rat, matey, 9.25" (Giant Leap)
  2. 0.047" G-10 stock for t' 3 fins (Giant leap)
  3. 1/8" aluminum tubin' for launch lug
  4. one NC, me bucko, BT-55 (Estes)
  5. one spent 29mm casin' for nose cone shoulder and motor block.
  6. one eyebolt
  7. 5' o' 1000 lb Keelhaul®©™ cord (Pratt)
  8. 3/4" x 25' plastic tape (Home Depot)
  9. lead shot

I started with a leftover section o' 29mm phenolic tubing. I decided t' add a motor block so I cut a 1/2" section out o' a spent 29mm casin' with a razor saw. This be epoxied into t' tube so that a G80 would protrude by 1/2". After playin' around with Rocksim, shiver me timbers, I decided on a fin design that I found appealing. Begad! Blimey! Since I wanted t' fins t' sit flush with t' end o' t' rocket and I wanted t' be able t' wrap a layer o' tape around t' end o' t' rocket and t' engine, matey, t' last 3/4" o' t' root edge o' t' fin was recessed by ~ 1/4" (see pic or Rocksim file).

Usin' a dremel cuttin' wheel, ya bilge rat, I slotted t' tube so t' fins would slip in. Avast! Begad! Blimey! T' install t' fins, I inserted a 29mm casing, arrr, applied a small amount o' epoxy t' t' slot, and pushed t' fin in until it touched t' motor casing. After all 3 fins were installed, t' casin' be removed. Blimey! This was easily accomplished before t' epoxy began t' set. This method o' through-the-wall construction really works well for small fins, especially with relatively thick tube (0.062"). Arrr! Blimey! T' fins were straight and weren't goin' anywhere. Arrr! Begad! Blimey! When t' epoxy dried, I applied fillets.

Since t' NC that I had wouldn't fit in t' body tube, ya bilge rat, I cut t' shoulder-end off so it sat flush with t' tube's OD. Aye aye! Avast! Another section o' 29mm casin' be cut t' use as a shoulder. This fit snugly into t' NC and was held in place with 2 small screws. Aye aye! Arrr! I added nose weight (lead shot, epoxy and t' eyebolt) so t' rocket would be stable. Ya scallywag! Well, me bucko, blow me down! Because t' end o' this little missile was now largely lead, I was conservative on settin' t' CG (see Rocksim file).

T' recovery harness consisted o' 5' o' 1000 lb test Keelhaul®©™ line. Begad! Avast! One end be epoxied into t' body tube and t' other was tied t' t' eyebolt. Avast! In t' end, me bucko, I built a rocket that be probably heavier than it had t' be and had a non-optimal fin design. Oh well, me hearties, won't be able t' see t' difference at ~5000ft anyway! I didn't bother fillin' t' grooves in t' tube since I wasn't optimistic about gettin' this rocket back. I did, however, ya bilge rat, give it a layer o' Krylon chrome paint. Avast, me proud beauty! Ahoy! Maybe a shiny surface would be easy t' spot???

Flight:
Because o' t' predicted altitude and weight, me bucko, this is nay a rocket I would want t' fly at a model rocket field, arrr, so I waited for a HPR launch. Ahoy! Aye aye! T' streamer was a 25' section o' 3/4" bright orange plastic tape. Blimey! When rolled tightly, matey, this fit nicely into t' 29mm tube. Aye aye! Estes-type waddin' be used t' protect t' streamer. Well, blow me down! Begad! I was torn betwixt usin' a G125-15 and a G80-10FWL. Begad! T' 15 sec delay on t' G125 be about right and t' 10 sec delay was too short. Anyway, I ended up usin' t' G125 in another rocket and hoped t' 1000 lb Keelhaul®©™® would hold up. Begad! Begad! Well, One Shot exploded off t' pad and, arrr, shiver me timbers, ya bilge rat, like me Machbuster, me bucko, was never seen or heard from again.

Summary:
PRO's 1. Blimey! High performance rocket built from leftovers in t' parts bin. Ya scallywag! Avast, me proud beauty! CON's 1. Aye aye! Another non-recoverable rocket (when flown on big engines)

Other:
When surface mountin' small fins on minimum diameter rockets, me hearties, you can get added strength by slottin' t' tube and gluin' t' fins into t' slots. An engine casin' is inserted t' keep t' fin flush with t' inside o' t' tube. Aye aye! You must make sure you work fast and don't glue t' casin' in. Well, blow me down! Avast, me proud beauty! In me case I used epoxy and a phenolic motor casin' (AT SU). Well, blow me down! Ahoy! T' thicker t' tube, t' better this will work. Avast! Begad! (Idea 'borrowed' from t' RocketVision Machbuster.)

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