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, ya bilge rat, I decided that I wanted t' build a similar rocket that would fly on 29mm motors. Ya scallywag! I scrounged through me parts bin and, bein' a 'glass-half-full' type, me hearties, me hearties, named t' result 'One Shot'.

Construction:
Parts List:

  1. 29mm phenolic tube, 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, 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. Well, blow me down! I decided t' add a motor block so I cut a 1/2" section out o' a spent 29mm casin' with a razor saw. Avast! Avast! This be epoxied into t' tube so that a G80 would protrude by 1/2". After playin' around with Rocksim, I decided on a fin design that I found appealing. Avast! Arrr! 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, 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, I slotted t' tube so t' fins would slip in. Ahoy! Ahoy! T' install t' fins, I inserted a 29mm casing, arrr, applied a small amount o' epoxy t' t' slot, me hearties, and pushed t' fin in until it touched t' motor casing. After all 3 fins were installed, ya bilge rat, ya bilge rat, t' casin' was removed. Begad! Begad! This be easily accomplished before t' epoxy began t' set. Ya scallywag! This method o' through-the-wall construction really works well for small fins, me hearties, especially with relatively thick tube (0.062"). Ahoy! Arrr! T' fins were straight and weren't goin' anywhere. Arrr! When t' epoxy dried, ya bilge rat, I applied fillets.

Since t' NC that I had wouldn't fit in t' body tube, arrr, I cut t' shoulder-end off so it sat flush with t' tube's OD. Ya scallywag! Another section o' 29mm casin' was cut t' use as a shoulder. Avast, me proud beauty! Blimey! This fit snugly into t' NC and was held in place with 2 small screws. Well, blow me down! I added nose weight (lead shot, me hearties, shiver me timbers, epoxy and t' eyebolt) so t' rocket would be stable. 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. One end was epoxied into t' body tube and t' other was tied t' t' eyebolt. In t' end, I built a rocket that was probably heavier than it had t' be and had a non-optimal fin design. Oh well, me hearties, arrr, shiver me timbers, won't be able t' see t' difference at ~5000ft anyway! Blimey! I didn't bother fillin' t' grooves in t' tube since I wasn't optimistic about gettin' this rocket back. Arrr! Blimey! Avast, me proud beauty! Blimey! I did, however, give it a layer o' Krylon chrome paint. Blimey! Blimey! Arrr! Blimey! Maybe a shiny surface would be easy t' spot???

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

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

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

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